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Swedish Soil Fertility ExperimentsKäll Carlgren & Lennart MattssonPublished online: 05 Nov 2010.

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ACTA AGRICULTURÆActa Agric. Scand., Sect. B, Soil and Plant Sci. 2001: 51, 49–76SCANDINAVICAPrinted in Ireland. All rights reser×edISSN 0906 –4710

Swedish Soil Fertility Experiments

Carlgren, K. and Mattsson, L. (Department of Soil Sciences, Divisionof Soil Fertility and Plant Nutrition, Swedish University of AgriculturalSciences, P.O. Box 7014, SE-750 07 Uppsala, Sweden). Swedish soilfertility experiments. Received September 1, 1999. Accepted September6, 2001. Acta Agric. Scand., Sect. B, Soil and Plant Sci. 51: 49–76,2001. © 2002 Taylor & Francis.

Twelve long-term soil fertility � eld experiments in south, central andnorth Sweden were started in the period 1957–1969. Five of theexperiments, two in south and three in central Sweden, were situatedat favourable sites, the other seven were placed at sites with lessfavourable climatic conditions and natural soil properties. Two croprotations, one with and one without livestock and 16 combinations ofinorganic NPK (nitrogen phosphorus potassium) fertilizers were com-pared in the south and central Swedish experiments. In north Sweden,there was one rotation with livestock and 30 NPK combinations.There was a four-course rotation in the south, a six-course in centralSweden and a seven-course rotation in north Sweden. The ordinaryfertilizer treatments in the rotations without livestock almost doubledthe yields of cereals compared with the unfertilized plots; with morefertilizer yields were even larger. In the livestock rotations the mineralfertilizer effects were smaller owing to positive effects of the manure.N responses were always considerably greater than PK responses. Innorth Sweden yield responses were of the same magnitude as in southand central Sweden. With no fertilizers, in the livestock rotations theuptakes of N, P and K were 50–90, 10–15 and 30–100 kg ha¼ 1,respectively, depending on the crop. In the non-livestock rotationscorresponding values were 25–40, 7–10 and 10–25 kg. In north Swe-den the N removal was even higher owing to the large proportion ofley in the rotation. In zero N treatments in south Sweden, over a 24year period, losses of organic matter were nearly 10 t ha¼ 1 in thenon-livestock rotation and about half as much in the livestock rota-tion. With 100 kg N ha¼ 1 losses were negligible. Levels of AL-ex-tractable P were not maintained where P additions equalled offtakesin the crops, but decreased by about 1 unit during the period. Pdynamics differed between sites; on some, P fertilizer had no effect oneither yields or soil P, whereas in other cases P fertilization increasedyields and kept soil P in plant-available forms. The cadmium contentin sugar beet roots increased with increased NPK fertilization, but theincreases were smaller than differences between sites. The cadmiumcontent varied from 128 to 288 ppb.

Kall Carlgren* andLennart MattssonDepartment of Soil Sciences, Divisionof Soil Fertility and Plant Nutrition,Swedish University of AgriculturalSciences, P.O. Box 7014, SE-750 07Uppsala, Sweden

* Corresponding author.

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Swedish Soil Fertility Experiments

Contents

Preface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51Material and methods. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52

Site descriptions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52A. South region . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52B. Central region . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52C. North region . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53

Experimental design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53Experiments in south and central Sweden . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53Experiments in north Sweden . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55

Climate. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55Statistical analyses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56

Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56A. Yields in south Sweden . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56

Rotation effects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56Fertilizer effects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56Changes in yield during 1957–1996 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56Nutrients in harvest products and NPK removal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57

B. Yields in central Sweden . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58Rotation effects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58Fertilizer effects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59Changes in yield during 1963–1996 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59Nutrients in harvest products and NPK removal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60

C. Yields in north Sweden . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61Fertilizer effects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61Changes in yield during 1969–1996 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62Nutrients in harvest products . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62Levels of replacements and NPK removal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63

Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63Effects on yields . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63

Rotation effects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63Fertilizer effects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63Sustainability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65

Soil organic matter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65Soil carbon . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65

Soil phosphorus and potassium status . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67Aspects on phosphorus dynamics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69

Cadmium in crops and soil . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73Appendices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74

Preface

Field trial experimentation is intrinsically diversi� ed.It has played a very important role in short-termcultivation guidance. Effects on the yield as beingdependent on certain measures were determined in anempirical way. The importance of � eld trials wasrecognized early in Sweden, and the county agricul-tural societies had already started � eld experimenta-tion at the end of the nineteenth century. However,there was an obvious need to co-ordinate these vari-ous activities and to increase the theoretical knowl-edge on how to apply the results. Consequently, anoverall organization, the ‘‘Centralanstalten forhushaÊ llningssallskapens lokala faltforsok’’, was estab-lished, and in 1907 this was incorporated into the‘‘Centralanstalten for forsoksvasendet paÊ jordbruk-somraÊ det’’ at Experimentalfaltet in Stockholm. The

� eld experimentation was managed by the agricul-tural division of the latter organization and later bythe ‘‘Statens Jordbruksforsok’’ which became incor-porated into the former Agricultural College of Swe-den in 1962. Practically all the activities at the variousorganizations were based on � eld trials. The resultswere published in various journals and report series,which show an impressive amount and multiplicity ofexperiments.

The � eld trials are also of great interest in follow-ing long-term changes, e.g. in soil characteristics.Often such changes take place very slowly and can berecorded only after many years. To accomplish this,long-term trials are needed, often combined withdetailed experimentation in the laboratory. From thebeginning most � eld experiments were � nanced bythe state, and still this applies to the long-term exper-

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iments. The short-term trials are no longer state� nanced.

A number of long-term � eld experiments is beingconducted in various countries. Many of these eluci-date the signi� cance of plant nutrients and soil condi-tioners on soil fertility. The oldest and mostwell-known are the trials at Rothamsted in England,which date back to the 1840s. Tests of mineral fertil-izers and farmyard manure began in 1895 at Askov inDenmark. Long-term � eld trials are found being car-ried out in Norway, Finland, Germany and France,among other countries.

In Sweden it was not until the 1930s that severalliming trials were started at Lanna in Vastergotland,a few of which are still continuing. The � agship of theSwedish long-term � eld trials is the fertility trials.They were initiated in 1956 by the Swedish Founda-tion for Plant Nutrition Research, which also� nanced the trials during several years. In 1962 thelate professor Sven L. Jansson took over the respon-sibility of the trials and he also slightly modi� ed theexperimental layout. In the range of trials there wereoriginally six trials, all located in SkaÊ ne in southSweden. In the early 1960s a further six trials wereestablished in central Sweden, and in 1969 a series oftrials was added in north Sweden. The layout of thesenorthern trials was slightly modi� ed with respect tocrop rotation and measurement of the interactionbetween plant nutrients. The � eld trials were laid outwith great care and competence, considering, forinstance, the selection of representative soil types. Asa consequence of complicated ice movements duringthe last glacial period there are many soil types inSkaÊ ne, including different kinds of moraines andwater sedimental clay. These various soil types arerepresented in the soil fertility trials. The trials havebeen followed up carefully with sampling of soil andyield products.

An important aim of these � eld trials is to illustratethe interactions between the conditions given by na-ture and the cultural measures with respect to in� u-ences on the yield. Can these measures build up, oralternatively deteriorate, soil fertility, which is a basicprerequisite in our food supply? History can point toseveral cases where food production was demolishedbecause of soil destruction. It is of utmost importanceto know the soil factors, such as the humus content,the status and balance of plant nutrients and the limestatus, that in� uence and control the quality of foodproducts.

Results from the soil fertility trials have been usedand discussed in a large number of scienti� c papersand doctoral and student theses, as well as duringnumerous � eld excursions. A comprehensive synthesisof the results was accomplished in 1974. Consideringthe time elapsed since then it is of great value that the

present treatise has been compiled, and thanks aredue to the authors, Kall Carlgren and LennartMattsson.

Jan PerssonProfessor Emeritus

Introduction

Factors in� uencing soil fertility can be divided intotwo groups: those related to nature, e.g. climate, soilparent material, topographic and hydrological condi-tions, and those that can be affected by humanactivity, e.g. soil organic matter, soil fertility status,crop rotation and soil management (Persson & Otab-bong, 1994).

Long-term soil fertility studies have been carriedout since the middle of the nineteenth century. Origi-nally initiated in Great Britain, long-term soil fertilitystudies expanded to many countries with signi� cantagricultural research (Cooke, 1976; Steineck & Ruck-enbauer, 1976; Uhlen, 1976; Welch, 1976; Johnston &Powlson, 1994; Korschens, 1994; Leigh & Johnston,1994; Garz et al., 1996; Johnston, 1997).

After World War II, cropping systems withoutlivestock increased in Swedish agriculture. Instead ofcirculating plant nutrients in manure, mineral fertiliz-ers became a more important source of nutrients.This change raised the issue of whether this wasjusti� able in terms of long-term productivity.

Agricultural research and development authoritiesrealized the importance of this problem, and in 1957the � rst � eld experiments started in south Sweden(Jansson, 1975, 1978, 1981, 1983a,b, 1987; Ivarsson &Bjarnason, 1988). The series was extended to centralSweden in 1963 and again in 1966 (Persson, 1983;Nilsson, 1986). Finally, four experiments were startedin 1969 in north Sweden (Mattsson, 1987).

Collectively, these experiments are known as theSwedish Soil Fertility Experiments. There were origi-nally 16 experiments and 12 are still running. Theirlocations are shown in Fig. 1.

The experiments provide data on the long-termin� uence of cultivation measures and natural factorson crop yields and quality and soil productivity.Basic data from the period 1957–1996 are used todescribe this situation.

Principally, the same experimental plan is used inthe 10 south and central experiments. The experimen-tal treatments are at three levels. First, two croprotations are compared. One is intended for milkproduction and includes leys, use of harvest residuesfor fodder and manure application. In the otherrotation only arable crops without manure aregrown. The crop rotations are those typical of theregions where the experiments are situated.

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Fig. 1. Experimental locations. 1: Fjardingslov; 2: S. Ugglarp; 3:Orup; 4: OÈ rja; 5; Ekebo; 6: Bjertorp; 7: HogaÊ sa; 8: Vreta Kloster;9: Kungsangen; 10: Fors; 11: Offer; 12: Robacksdalen.

soils, partly of calcareous origin, were characterizedas follows at the start of the experiment:

1. Fjardingslov (54°24Æ N, 13°14Æ E, altitude 30 m).Classi� ed as a coarse–loamy, mixed, mesicOxyaquic Hapludoll (Soil Taxonomy) and as aHaplic Phaeozem (FAO). Old arable land of highagricultural quality. The soil texture is a sandyloam with increasing clay and calcium carbonatecontent down to 100 cm depth.

2. S. Ugglarp (55°38Æ N, 13°25Æ E, altitude 65 m).Classi� ed as a coarse–loamy, mixed, mesic TypicHapludoll (Soil Taxonomy) and as a HaplicPhaeozem (FAO). A site with less favourable landand climatic characteristics than that of Fjard-ingslov and OÈ rja. The soil texture of the pro� le isa silty loam with the larger clay content in theupper layers. The subsoil is very stony and thegravel content increases in the lower parts of thepro� le.

3. Orup (55°49Æ N, 13°30Æ E, altitude 75 m).Classi� ed as a coarse–loamy, mixed, frigid AquicHaploboroll (Soil Taxonomy) and as a HaplicPhaeozem (FAO). A less favourable site thanFjardingslov and OÈ rja concerning land qualityand climate. The soil texture is a sandy loamthroughout the pro� le 0–100 cm. The Orup soil isnon-calcareous and compacted in the subsoilwhich limits root penetration and crop wateruptake.

4. OÈ rja (55°53Æ N, 12°52Æ E, altitude 10 m). Classi� edas a clayey, illitic, mesic Typic Eutrochrept (SoilTaxonomy) and as a Eutric Cambisol (FAO). Afavourable site with respect to soil and climate. Asandy clay loam with a small calcium carbonatecontent throughout the pro� le.

5. Ekebo (55°59Æ N, 12°52Æ E, altitude 59 m).Classi� ed as a coarse–loamy, mixed, mesicOxyaquic Eutrocrept (Soil Taxonomy) and as aEutric Cambisol (FAO). Originally a heath, theorganic matter content was one of the largest atthe start. Despite that, Ekebo is one of the lessfavourable sites without any calcium carbonate inthe pro� le at start.

B. Central region. There are � ve experiments in cen-tral Sweden, the Kungsangen and Fors experiments,started in 1963, and Bjertorp, Vreta Kloster andHogaÊ sa, started in 1966.

The soils at Kungsangen and Fors sites wereclassi� ed according to the Soil Taxonomy and theFAO guidelines (Kirchmann, 1991). The remainingthree sites have not yet been classi� ed.

6. Bjertorp (58°14Æ N, 13°08Æ E, altitude 90 m). Asilty clay both in the topsoil and subsoil situated

The second level is the phosphorus potassium (PK)application, which is based on the principle of re-placement. There are four PK treatments: none, re-placement of removal in the crop and two levels ofextra P and K intended to achieve slow and rapidimprovement of the soil PK status. The third level oftest is four nitrogen (N) fertilizer levels, ranging fromnone to a high application.

The experimental sites were chosen so that halfwere situated on sites with favourable natural condi-tions while the other half were on less fertile sites.

The two north Swedish experiments were some-what different. There is a single crop rotation includ-ing leys and regular manuring. P and K are variedindependently of each other with three P and two Klevels and � ve N levels. Both sites are similar con-cerning the natural conditions.

Material and methods

Site descriptions

A. South region. Currently � ve sites, all in the countyof SkaÊ ne, are in use. They had been under cultivationfor at least 100 years before the start of the experi-ment, the site at OÈ rja for more than 200 years. Thesoils were classi� ed according to the Soil Taxonomy(Soil Survey Staff, 1990) and the FAO Guidelines forSoil Description (FAO, 1990) by Kirchmann &Eriksson (1993), Kirchmann et al. (1996, 1999). The

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on a former meadow which was � rst ploughed inthe 1850s.

7. HogaÊ sa (58°30Æ N, 15°27Æ E, altitude 80 m). Alight textured soil classi� ed as a silty sand in thetopsoil and a loamy sand in the subsoil.

8. Vreta Kloster (58°29Æ N, 13°08Æ E, altitude 47 m).Situated on old arable land of high quality. Thetopsoil is a silty clay and the subsoil a clay whichcontains free calcium carbonate.

9. Kungsangen (59°50Æ N, 17°40Æ E, altitude 4 m).Classi� ed as a � ne, illitic, frigid Typic Haplaquept(Soil Taxonomy) and as a Gleyic Cambisol(FAO). It is an acid sulphate clay soil (gyttja clay)with a very low pH value in the lower part of thepro� le.

10. Fors (60°20Æ N, 17°29Æ E, altitude 25 m). Al-though situated near a river, this site consisted notof � uvial material but of glacial deposits togetherwith calcium carbonate. It is classi� ed as an illitic,calcareous, frigid Udic Haploboroll (Soil Taxon-omy) and as a Calcaric Phaeozem (FAO). A siltysoil with a small calcium carbonate content in thetopsoil but more calcareous in the subsoil.

C. North region. Descriptions of the soils for thenorth Swedish experiments have been published else-where (Mattsson, 1979). The soils are not classi� edaccording to the Soil Taxonomy System or the FAOguidelines.

11. Offer (63°8Æ N, 17°46Æ E, altitude 27 m). A siltyloam in the topsoil with decreasing clay content insubsoil.

12. Robacksdalen (63°49Æ N, 20°14Æ E, altitude 10 m).A silty soil, typical for the north Swedish coastalregion and river valleys. Textural properties areidentical down to 100 cm.

See Table 1 for further initial soil characteristics.

Experimental design

Experiments in south and central Sweden. The experi-mental design in south and central Sweden includedtwo crop rotations, with livestock and without live-stock, to be tested together with all combinations offour levels of fertilizer PK (A, B, C, D) and four offertilizer N (0, 1, 2, 3), giving 32 treatments (Table 2).At the two northernmost sites of the central experi-

Table 1. Initial soil characteristics for the experimental sites in south, central and north Sweden

ClayOrg. CPhaq(%) P-ALLayer K-HClSite P-HCl(%) K-AL

South sites17 7.5 3.3 26 4.2Fjardingslov 620–20 1.417 7.7 2.5 25 3.6 6020–50

855.2494.98.01350–100Orup 2.4 13 6.2 2.4 53 3.8 470–20

714.4461.66.61520–504.36410.97.1 811250–100

OÈ rja 1.1 15 7.2 5.9 36 8.0 1150–2020–50 19 7.3 2.9 27 5.9 10950–100 32 7.7 2.1 31 11.0 220

364.1384.16.681.50–20S. Ugglarp20–50 8 6.6 2.5 26 2.1 3150–100 301.2231.76.75

14 6.8 6.7Ekebo 37 5.4 560–20 3.11920–50 15 3.6 680.75.4

50–100 17 5.7 0.5 28 5.0 95

Central sites12.4384.66.4302.20–20Bjertorp 242

50 6.7 6.7 41 19.40–20Vreta Kl. 2.1 3682.40–20 43HogaÊ sa 10.7334.45.910

0–20 2.1 56Kungsangen 7.1 44014.0563.77.7 10.6 73 9.0 252Fors 0–20 2.2 18

North sites2.5Offer 20 6.5 7.9 96 10.0 2800–20

0–20 5.2 10 5.8 7.0 82 7.2 114Robacksdalen

P and K � gures in mg 100 g¼1 air-dry soil; organic carbon in per cent of dry matter. After Jansson (1975),Mattsson (1987), Nilsson (1997).

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Table 2. Crop rotations, P, K and N treatments in south, central and north Sweden

Without livestockCrop rotations with livestock

Central South CentralSouth North

Barley Barley Barley BarleyBarleyLey 1 (2 cuts) Oil seedLey 1 (1 cut) Oats Ley 1 (1 cut)

Winter wheat Ley 2 (1 cut) Winter wheat Oil seed Ley 2 (2 cuts)Sugar beet Winter wheat Sugar beet Winter wheat Ley 3 (2 cuts)

Oats Oats Green rapeWinter wheat Winter wheat Barley

Potatoes

PK levels at the south and central sites (kg ha¼1 year¼1)No PK in mineral fertilizerA.Replacement of PK removed with cropsB.

C. Replacement »15 P and 40 K (south)»20 P and 50 K (central)

ReplacementD. »30 P and 80 K (south and central)

PK levels at the north sites (kg ha¼1 year¼1)P KReplacementA. ReplacementReplacement »20 ReplacementB.Replacement »40C. Replacement

D. Replacement Replacement »80E. Replacement »20 Replacement »80

Replacement »40 ReplacementF. »80

Mean N levels (kg ha¼1 year¼1) (actual amount depends on the crop)South Central North

0. 0 0 1. 01. 50 41 2. 36

100 822. 3. 733. 150 125 4. 124

5. 206

In rotations with livestock, 20 t ha¼1 manure is applied every 4th year after winter wheat to all plots (south), 30t ha¼1 every 6th year after ley 2 (central), and 20 and 15 t ha¼1 manure to all plots after ley 3 and potatoes,respectively (north). P and K in manure is accounted for when applying fertilizer PK in the livestock rotations.Leys were always grass clover leys. At Kungsangen and Fors, the PK level D was performed only for the highestN level (3), i.e. the number of fertilizer treatments was reduced to 13 from 16.

ments, Kungsangen and Fors, only the largest PKtreatment was tested for the highest N-level, giving atotal of 26 treatments (Table 2). The treatments werearranged in two randomized blocks in a split–splitplot design with rotations on main plots, PK onsubplots and N on sub-subplots. Only one crop in therotation is grown each year. At Kungsangen andFors the split–split plot design was incomplete.

The central Swedish experiments followed identicalcrop rotations. However, since they were started indifferent years they are not synchronized. TheKungsangen and Fors experiments were initiated in1963 and the others in 1966.

The rotations shown in Table 2 were slightly differ-ent before 1984 at Bjertorp, Vreta Kloster andHogaÊ sa, and before 1988 at Kungsangen and Fors. Inthe livestock rotation, crops 4, 5 and 6 were oil seeds,

winter wheat and oats. In the rotation without live-stock, crops 2, 3 and 4 were spring wheat, fallow andoil seeds (Table 2).

Crop residues are removed in the rotation withlivestock but incorporated in the rotation without. Inthe rotations with livestock 20 and 30 t ha¼ 1 (freshweight) of cattle manure, respectively, are applied toall plots, after winter wheat in the south experimentsand after ley 2 in the central experiments. All plotsreceived manure, including those without NPK fertil-izer addition.

The three rates of P and K are based on theprinciple of replacement and two levels of additionalP and K to achieve slow and rapid improvement inthe PK status of the soil. When manure is applied therates of fertilizer P and K are adjusted for amountsapplied in the manure. This is not the case for N.

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Because the P and K are applied together, theirindividual effects cannot be separated (Table 2).

The calculated amount of PK fertilizer for onerotation is divided into two equally, large applica-tions applied in the south Swedish experiments beforesowing of spring barley and after harvesting winterwheat. In the central Swedish experiments PK isapplied to spring barley and to the � rst winter wheatcrop in the rotation.

Fertilizer N as Nitro Chalk (28% N) was suppliedyearly in spring to each crop. The P fertilizer wasmono superphosphate (9% P) until 1991 and 1994 inthe south and central experiments, respectively.Thereafter, triple superphosphate (20% P) was used.Potassium chloride (50% K) has been used through-out. Other plant nutrients are added if required.

The south Swedish experiments have been limedtwice during the experimental period. In 1981, atFjardingslov and OÈ rja 2 t ha¼ 1 CaO was applied and1 t ha¼ 1 at Orup, S. Ugglarp and Ekebo. In theautumn 1996, Orup, S. Ugglarp and Ekebo werelimed with 2 t ha¼ 1 CaO.

Experiments in north Sweden. Although the mainobjectives are similar for all the soil fertility experi-ments, the north Swedish experiments tested only onecrop rotation (Table 2). Another difference is that Pand K are applied independently but the smallestamount is still based on the principle of replacement.

Initially, the ley was established by undersowing inthe � rst barley crop, but from the third rotationcycle, started in 1990, the ley has been sown without

a cover crop. Thus, there is only one cut the � rstyear, while there are two cuts in the following years.Manure is applied twice in the rotation, in the au-tumn after the third year of ley and after the secondbarley crop. The amounts are 20 and 15 t ha¼ 1 (freshweight), respectively. All plots receive manure, in-cluding those without fertilizer addition.

Mineral fertilizers are applied as shown in Table 2.All combinations of PK and N are tested, giving 30treatments. These are arranged in two randomizedblocks in a split-plot design with PK on main plotsand N on subplots. One crop in the rotation is growneach year.

Fertilizer N, today given as Nitro Chalk (28% N),was applied as ammonium nitrate until 1989. N isapplied annually in spring (Table 2). Mono super-phosphate (9% P) was used until 1993, since whentriple superphosphate (20% P) has been used. The Kfertilizer is potassium chloride (50% K). Both experi-ments have been limed once, in 1979 at Robacksdalenand 1983 at Offer. The average pH at present is 6.6,with only minor differences between the sites.

Climate

The climate is cold–temperate and humid at all sites(Table 3). Winter temperatures decrease from southto north, as do the annual means. However, summertemperatures at the central sites are as high as, orslightly higher than those in the south. At the northsites, summer and winter temperatures are consider-ably lower.

Table 3. Temperature and precipitation: means for 1961–1990 registered at the nearest meteorological station(Alexandersson et al., 1991)

Mean temperature (°C) Precipitation (mm)

Site Oct–Mar Apr–Sept Annual mean Oct–Mar Apr–Sept Annual sum

South sites5903072838.112.73.3Fjardingslov

Orup 1.7 11.5 7.1 378 399 777OÈ rja 3.0 12.9 8.0 259 310 569S. Ugglarp 2.0 12.4 7.2 325 332 657

683348338Ekebo 7.813.02.4

Central sites5713162556.212.10.3Bjertorp

3222466.8 56913.00.6Vreta Kloster0.6 13.0 6.8 246 322HogaÊ sa 569

Kungsangen ¼0.9 11.9 5.5 225 304 528Fors ¼1.4 11.4 5.0 297 340 635

North sitesOffer ¼5.2 10.1 2.8 206 283 490Robacksdalen ¼4.3 9.9 2.4 278 307 582

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Statistical analyses

Plot yields were determined annually and soil analy-ses were done on samples taken plotwise. However,the data are presented treatmentwise here. Observa-tions from years are used as replicates. This meansthat the interactions between treatments and sites,and between treatments and years, which undoubt-edly exist, are not statistically tested. Both of thesecomponents are included in the error variance which,consequently, is overestimated. Duncan’s multiplerange tests have been used and, in cases of signi� -cance, means are marked with different superscriptletters. All statistical calculations were carried outusing SAS Release 6.12 TS level 0060 (SAS Institute,1989).

Results

A. Yields in south Sweden

Rotation effects. Averaged over all fertilizer treat-ments, mean yields of winter wheat and sugar beetwere signi� cantly larger in the livestock rotation thanin the other rotation (Table 4a). Spring barley yieldswere similar in both rotations.

Fertilizer effects. N had the strongest in� uence onyields (Table 4b). When comparing treatments A0and A2, the application of 100 kg N increased yieldsof spring barley and winter wheat in the livestockrotation by about 1400 kg ha¼ 1, and even more, by1600 kg ha¼ 1 for spring barley and 2400 kg ha¼ 1 forwinter wheat in the rotation without livestock.

Where PK was replaced, omitting N (compare A0and C0) the cereal yields increased by some hundredkg ha¼ 1 in both rotations; for sugar beet the increasewas approximately 2000 kg ha¼ 1 dry matter (DM).

Increasing the amount of N applied from 100 to150 kg ha¼ 1 (compare C2 and C3) raised the yieldsby about 300 kg ha¼ 1 for cereals, and sugar beet rootyields by about 1000 kg ha¼ 1. These differences were

statistically signi� cant. However, increasing the PKfertilization by 15 kg P and 40 kg K (from level C tolevel D) had no signi� cant effect except for the leycrop, where the forage yield decreased by about 300kg ha¼ 1 DM (Table 4b).

For all crops in both rotations there were positiveinteractions between N and PK fertilization. In thelivestock rotation the mineral fertilizer effects weregenerally smaller than in the rotation without live-stock (Table 4b).

Changes in yield during 1957–1996. Long-termchanges in yield which can be related to sustainabilityare shown in Figs 2–5 for leys, winter wheat in bothrotations and oil seeds in the rotation without live-stock. The yields varied, partly because of climaticvariations and partly because of fertilization, butwithout obvious interaction between climate and fer-tilizer treatment.

Overall forage yields increased from 3000–4000 kgha¼ 1 in 1958 to 6000–9000 kg ha¼ 1 in 1994 (Fig. 2).Yields increased in the � rst 4 years, decreased duringthe next 8 years (1962–1970) and then generallyincreased. At the end of the experimental period therewere no large yield differences between the treatmentsgiven fertilizers (B1, C2 and D3). The application ofmanure once in the rotation (treatment A0) gave asmall increase in yield but additional NPK fertilizerswere required to give maximum yield.

For winter wheat in the livestock rotation, thetrend was towards slowly increasing yields with alltreatments except for the last years, when yieldsincreased markedly in the fertilized treatments butdecreased without additional NPK (A0, Fig. 3).

Winter wheat yields in the rotation without live-stock were smaller than in the rotation with livestock(compare Figs. 3 and 4). As in the livestock rotation,yields increased markedly during the last years in thefertilized treatments but decreased without NPK. Inthe A0 treatment, yields were about 2000 kg ha¼ 1

throughout the period.

Table 4a. Mean yields for crop rotations 1957–1996, with and without livestock: � ve experiments in southSweden

Rotation Spring barley 1 year ley Oil seed rape1 Winter wheat Sugar beet2

8840aWith livestock 4390a–54903620a

7770b3570a –Without livestock 1290 4000b

236147LSD 515n 101010 1010

Cereal and oil seed grain (kg ha¼1, 15% moisture), forage and sugar beet roots (kg ha¼1, dry matter). Meansfollowed by the same superscript letter within a column are not signi� cantly different (P\0.05).1 Before 1986 white mustard.2 Orup and S. Ugglarp not harvested in 1984 and 1996.

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Table 4b. Mean yields in seven NPK treatments 1957–1996: � ve experiments in south Sweden

Spring barley Ley 11 Oil seed rape2Rotation treatment Winter wheat Sugar beet3

With livestock20 t ha¼1 manure plus4

N P K0 0 0 2530f 4280fA0 – 3190d 5970e

100 0 0 3920cA2 5860c – 4570b 7260d

50 R R 3500d 5450d – 4390b 8250cB10 R»15 R»40 2730eC0 4940e – 3520c 7910c

100 R»15 R»40 4250b 5980bcC2 – 5030a 10 490b

150 R»15 R»40 4560aC3 6370a – 5220a 11 360a

150 R»30 R»80 4510aD3 6070b – 5160a 11 540a

131LSD 191 193 415505n 506 506 467

Without livestockN P K

0 0 0 2220fA0 – 600e 2320e 4450e

100 0 0 3850c –A2 1440c 4770c 6260d

50 R R 3470dB1 – 1150d 3810d 7190c

0 R»15 R»40 2590e –C0 700e 2320e 6410d

100 R»15 R»40 4260bC2 – 1670b 4870bc 9920b

150 R»15 R»40 4600a –C3 2030a 5230a 11 220a

150 R»30 R»80 4450abD3 – 1990a 5130ab 10 980a

LSD 235 123 257 717505 506 506 467n

Cereal and oil seed grain (kg ha¼1, 15% moisture), forage and sugar beet roots (kg ha¼1, dry matter). Meansfollowed by the same superscript letter within a column are not signi� cantly different (P\0.05).1 One cut.2 Before 1986 white mustard.3 Orup and S. Ugglarp not harvested in 1984 and 1996.4 R: replacement of P and K removed in harvested crops. Uptake and hence replacement varies with the Napplied and is approximately 15 P and 40 K (kg ha¼1 year¼1) in C2. Replaced PK in livestock rotation adjustedfor P and K in manure. Manure added once per rotation.5 In A2, C0 and D3 40 observations.6 In A2, C0 and D3 45 observations.7 In A2, C0 and D3 41 observations.

For oil seeds in the rotation without livestock,there were considerable yield differences between thefour treatments (Fig. 5). There were increases inyield until the late 1970s but these increases werenot maintained. The overall trend was towardssmall yields at the beginning and at the end of theperiod.

Nutrients in har×est products and NPK remo×al. Plantnutrient concentrations are given in Appendix 1. Inmany cases the treatments resulted in statisticallysigni� cant (PB0.05) differences. For example, insugar beet roots, as in most harvested products, therewere statistically signi� cant differences for N, P andK. Oil seed grain had higher concentrations of N andP than other products, while N and P concentrationsin sugar beet roots were the smallest. The K concen-tration was larger in beet roots than in grain and waseven greater in ley forage.

The concentrations of N, P and K in sugar beetroots were larger in the rotation with livestock thanin the other rotation, although the differences werenot tested statistically. The manure was applied be-fore growing sugar beet in the livestock rotation andalthough P and K in manure was accounted for, theextra P and K in beets grown with both manure andfertilizer PK suggests that there was more plant-avail -able P and K in the livestock rotation.

For each complete rotation cycle of 4 years, theaverage nutrient removals in grain, forage and sugarbeet roots were calculated and plotted (Fig. 6). With-out external nutrient supply except for manure in thelivestock rotation, N removal decreased initially.Later on, the situation stabilized in the non-livestockrotation, but in the livestock rotation a recovery tookplace.

P removal remained essentially at the same levelthroughout the period, while K in the livestock rota-

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Fig. 2. Forage yields (kg ha¼1 dry matter) in south Sweden.Rotation with livestock. Means of � ve experiments. A0: controlwithout mineral NPK; B1: low N, replacement of PK; C2: ordi-nary N, slow improvement in soil PK status; D3: high N, rapidimprovement in soil PK status.

Fig. 4. Winter wheat yields (kg ha¼1 15% moisture) in southSweden. Rotation without livestock. Means of � ve experiments.For legend see Fig. 2.

Fig. 5. Oil seed yields (kg ha¼1 15% moisture) in south Sweden.Rotation without livestock. Means of � ve experiments. For legendsee Fig. 2.Fig. 3. Winter wheat yields (kg ha¼1 15% moisture) in south

Sweden. Rotation with livestock. Means of � ve experiments. Forlegend see Fig. 2.

more N and K were removed than in the non-live-stock ones. The differences were around 20 kg N andnearly 40 kg K ha¼ 1 (Fig. 6).

B. Yields in central Sweden

Rotation effects. The largest yields were observed inthe rotation with livestock, in which ley cropping andmanure positively in� uenced the yields (Table 5a).Differences were statistically signi� cant.

tion, like N, decreased during the � rst rotation cyclesand later increased again.

There was a gap in the removal of nutrients be-tween the rotations, which seemed to increase withtime. In the non-livestock rotation the long-termnutrient removal of N, P and K averaged 22, 8 and21 kg ha¼ 1 each year. In the livestock rotations,

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Fig. 6. N, P and K removal (kg ha¼1 year¼ 1) at sites in southSweden. Means of 4 year cycles in rotations with (solid line) andwithout (dotted line) livestock. Treatment C0, replacement plusslow improvement in soil PK status and no mineral N, was used tocalculate N removal. For P and K removal the highest N levelwithout mineral PK was used, treatment A3.

both rotations was for spring barley, where yields werealmost doubled in C3 and D3, and in the non-livestockrotation more than doubled, compared with the unfer-tilized treatment A0.

The application of 82 kg N ha¼ 1 (compare A0 andA2) in the non-livestock rotation increased the yieldsof spring barley by 1400 kg ha¼ 1, of oats by 1500–1800kg ha¼ 1 and of winter wheat by about 1600–2500 kgha¼ 1. For oil seed rape the yield increase for 82 kg Nwas about 400 kg ha¼ 1.

Where PK was replaced omitting N (compare A0and C0) for cereals and oil seeds the yields increasedby less than 100 kg ha¼ 1 in both rotations. For ley 1and ley 2 the yield increases were about 200 kg ha¼ 1.

In the livestock rotation the mineral fertilizer effectswere generally smaller than in the rotation withoutlivestock (Table 5b). For ley 1 there was no yieldincrease for 82 kg N, depending on the presence ofN-� xing clover, but for ley 2, where the clover haddisappeared, the yield increase for 82 kg N was about800 kg ha¼ 1 DM.

There were positive interactions between N and PKfertilization for all crops. The span between A0 and D3was less in the rotation with livestock than in therotation without. The positive effects of manure andley in the livestock rotation partly levelled out thedifference between the unfertilized and fertilized treat-ments.

Changes in yield during 1963–1996. The changes inyield with time for some of the crops in both rotationsare presented in Figs. 7–10 for leys, winter wheat inboth rotations and oil seed rape in the rotation withoutlivestock.

Because the experiments in central Sweden startedin different years, their rotations are not synchronized.In Figs. 7–10, each observation represents means foreither Bjertorp, HogaÊ sa and Vreta Kloster orKungsangen and Fors, never for all � ve sites simulta-neously.

Forage yields were larger in ley 1 than in ley 2. Ley1 was harvested twice and ley 2 once, because winterwheat should be sown after the � rst harvest in ley 2.

Fertilizer effects. Fertilizer effects on the yields were insome cases large (Table 5b). The effect of N on yieldswas more pronounced than that of PK. This was validfor both crop rotations. The largest yield increase in

Table 5a. Mean yields for crop rotations, 1963–1996, with and without livestock: � ve experiments in centralSweden

Oil seedSpringRotation WinterWinterwheat3barley Oatslivestock Oats1 wheat4Ley 2 rape2Ley 1

– 5240a 3960a 4990aWith 3380a 7190 4500 –– 3820 910 4530b 3190b 3920b2950b –Without

– 327 254 432LSD 279 – – –1044111112 39n

Cereal and oil seed grain (kg ha¼1, 15% moisture), forage (kg ha¼1, dry matter). Means followed by the samesuperscript letter within a column are not signi� cantly different (P\0.05).1 Oats after spring barley since 1984.2 Oil seed rape after oats since 1984.3 Winter wheat after ley 2, 3 observations.4 Winter wheat after oats since 1984.

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Table 5b. Mean yields in seven treatments, 1963–1996: � ve experiments in central Sweden

Spring WinterWinterOil seedbarley Ley 11 Ley 22 OatsRotation treatment wheatOats wheatrape

With livestock20 t ha¼1 manure plus3

N P K0 0 0 2320d 7090b 3660c –A0 – 5000c 2940d 3030d

82 0 0 3820b 7090b 4450bA2 – – 5310b 4110ab 5530b

41B1 R R 3050c 7430ab 4270b – – 5440b 3830c 4510c

0 R»20 R»50 2330d 7280ab 3850cC0 – – 5350b 3080d 3050d

82 R»20 R»50 3960b 7560ab 4850a –C2 – 6040a 4450a 5840b

125 R»20 R»50 4410a 7470ab 4900aC3 – – 5900a 4370ab 6490a

D3 125 R»30 R»80 4410a 7620a 5090a – – 6120a 4480a 6500a

199 434 279LSD 299 242 396n 30 27 27 8 23 8

Without livestock0 0 0 1810e – –A0 2300d 740c 2920e 1830e 1750e

82 0 0 3230c – – 4120bA2 1170b 4590c 3380c 4300c

41 R R 2610d – –B1 3550c 1140b 4170d 2830d 3380d

C0 0 R»20 R»50 1670e – – 2460d 750c 2830e 1840e 1910e

82 R»20 R»50 3530b – –C2 4690a 1540a 5370b 3710b 4920b

C3 125 R»20 R»50 4090a – – 5020a 1600a 5720a 4100a 5690a

125 R»30 R»80 4130a – – 5040aD3 1690a 5810a 4230a 5880a

184LSD 401 175 205 232 41730 10n 27 24 23 8

Cereal and oil seed grain (kg ha¼1, 15% moisture), forage (kg ha¼1, dry matter). Means followed by the samesuperscript letter within a column are not signi� cantly different (P\0.05).1 Two cuts.2 One cut.3 R: replacement of P and K removed in harvested crops. Uptake and hence replacement varies with the Napplied and is approximately 15 P and 40 K (kg ha¼1 year¼1) in C2. Replaced PK in livestock rotation adjustedfor P and K in manure. Manure added once per rotation.

The overall trend for the clover grass � rst harvestyields from ley 1 was towards increasing yield variation(Fig. 7). Yields with only manure (A0 treatment) weregenerally the smallest but additional fertilizer had onlyweak effects.

For winter wheat, the grain yields between rotationscould be compared (Figs. 8, 9). There was a clearnegative trend without fertilizer in the rotation withoutlivestock (Fig. 9) The fertilizer effects were also thelargest in this rotation.

Yield of oil seeds in the rotation without livestockgenerally declined even when NPK fertilizers wereapplied. The yields without fertilizers (treatment A0)were the smallest and from 1975 were less than 1000kg ha¼ 1. The yields in treatment D3 were mostly thelargest (Fig. 10).

Nutrients in har×est products and NPK remo×al.Full details of nutrient concentrations in differentcrops are given in Appendix 2. The effects of Kfertilizer on K concentrations in the � rst cut of the leywere larger than those in the oil seeds. N concentration

in oil seed grain was high and increased with fertilizerlevel.

The effects of N fertilizer on % N in the ley crop werepartly masked by changes in the botanical composi-tion. With little fertilizer N, the proportion of cloveris larger than with ample fertilizer N supply. Since %N in clover is normally greater than in grasses, thein� uence on % N content in the forage is small whenthe N fertilization level is increased.

For each complete rotation cycle (6 years), theaverage removal of macronutrients N, P and K in har-vested products was calculated and plotted (Fig. 11).Long-term N, P and K removal in non-livestock ro-tations was 30, 7 and 10 kg ha¼1 annually, respectively.In livestock rotations, the values were larger, 60–70 kgN, 10–15 kg P and 40–60 kg K ha¼1 each year.

Only minor differences between the favourable andless favourable sites were observed, being applicableboth to the south and to the central Swedish experi-ments. At favourable sites, the P removal was some-what higher, around 5 kg ha¼ 1 year¼ 1, than at theunfavourable sites, depending on differences in yield.

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Fig. 7. Forage yields (kg ha¼1 dry matter) in central Sweden. Firstharvest in ley 1, rotation with livestock. Observations are means oftwo or three experiments depending on year. For legend see Fig. 2.

Fig. 9. Winter wheat yields (kg ha¼1 15% moisture) in centralSweden. Rotation without livestock. Observations are means oftwo or three experiments depending on year. For legend see Fig. 2.

Fig. 8. Winter wheat yields (kg ha¼1 15% moisture) in centralSweden. Rotation with livestock. Observations are means of two orthree experiments depending on year. For legend see Fig. 2.

Fig. 10. Oil seed yields (kg ha¼1 15% moisture) in central Sweden.Rotation without livestock. Observations are means of two orthree experiments depending on year. For legend see Fig. 2.

C. Yields in north Sweden

Fertilizer effects. The best average yields over fourrotation cycles were approximately 4500 kg barley,9000 kg DM of forage, 6500 kg DM of green rapeand nearly 30 t ha¼ 1 fresh weight of potato tubers(Table 6).

In treatment B an additional 20 kg ha¼ 1 year¼ 1 Pwas applied compared with the replacement level inA. In treatment D 80 kg ha¼ 1 year¼ 1 K was added

In the control plots of the livestock rotations therewas a supply of N with the manure and also frombiological � xation which was not accounted for.

A common characteristic for the N, P and Kremoval at all sites was that the differences be-tween the rotations increased with time. Against thebackground of manure application, this is not unex-pected.

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Fig. 11. N, P and K removal (kg ha¼ 1 year¼ 1) at sites in centralSweden. Means of 6 year cycles in rotations with (solid line) andwithout (dotted line) livestock. Treatment C0, replacement plusslow improvement of soil PK status and no mineral N, was used tocalculate N removal. For P and K removal the highest N levelwithout mineral PK was used, treatment A3.

P and K fertilization did not affect crop yieldssigni� cantly (Table 6). P application seemed to have anegative effect on the ley yields at the lower K level.Where the K level was high, the P effects were positive.Similar results were also observed in green rape. Inpotato, P applications were positive.

N responses were mostly statistically signi� cant(Table 6). Average effects in barley were 500–1000 kgha¼ 1. In leys and green rape, N responses were 4000and 2000 –2500 kg ha¼ 1, respectively. Tuber yields ofpotatoes increased on average by 7–8 t ha¼ 1 for thehighest N rate.

Changes in yield during 1969–1996. A comparison ofrelative yields in A1 and A3 (no mineral N and 73 Nkg ha¼ 1, respectively, replacement of PK) over theyears showed that relative changes were small (Fig. 12).Some years deviated considerably. No mineral Napplication resulted in reduced yields in the order of20–40%.

Nutrients in har×est products. There were evident andoften statistically signi� cant differences between treat-ments in % N in the harvest products (Table 7). Withthe leys, % N was clearly in� uenced by the botanicalcomposition of the forage. In treatments without N,contents were relatively larger than in treatments withmoderate N supply, which is attributed to the largerclover proportion in these treatments.

Effects of P fertilizer on % P are illustrated bytreatments A1 (no mineral N and replacement of P andK) and B3 (73 N, replacement plus 20 P, kg ha¼ 1 andreplacement of K). Observed differences in harvestproducts were small and insigni� cant. Treat-

in addition to the replacement and in E both extra Pand K were supplied.

Table 6. Mean yields over � ve rotations, 1969–1996: two experiments in north Sweden

(kg ha¼1 year¼1)

Green rape PotatoesN P K Barley grain LeyTreatment

5560 23.8– R1 R1 4160A 749026.8558073304260RR»20–B

5180 23.2D – R R»80 3970 723026.5546074004170R»80R»40–E

nsnsns nsLSD45 4070 105n

1 0 – – 3670a 5550a 4110a 21.1c

3 73 – – 4450b 7260b 5830b 26.6a

9320c4290b––206 28.8b6520c5LSD 274 380 579 2.1

84n 4854126

Barley grain (kg ha¼1, 15% moisture), forage of ley and green rape (kg ha¼1, dry matter) and potato tubers (tha¼1, fresh weight). Means followed by the same superscript letter within a column are not signi� cantlydifferent (P\0.05).1 R: replacement of P and K removed in harvested crops. Uptake and hence replacement varies with the Napplied and is approximately 15 P and 135 K (kg ha¼1 year¼1) in treatment A3.

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Fig. 12. Relative yields and development over the years in northSweden in treatments with replacement of PK. No mineral N(dotted line) and moderate N rates, average 73 kg ha¼ 1 year¼ 1 N(solid line). Average of two experiments.

Discussion

Effects on yields

Rotation effects. The results in Tables 4a and 5a showthat the largest crop yields were produced in therotation with livestock. Korschens (1994), Garz et al.(1996) obtained similar results, but both Steineck &Ruckenbauer (1976), Uhlen (1976) found that min-eral fertilizers produced larger cereal yields than or-ganic manure. However, in their experiments, mineralfertilizers and farmyard manure were treated sepa-rately, not in combination, as was the case for thelivestock rotation in the Swedish experiments. In theSwedish experiments P and K in manure were supple-mented with fertilizer PK to equal the amounts offertilizer PK added in the non-livestock rotation.

Garz et al. (1996) found that the effects of mineralfertilizers and manure were additive when there wasno soil PK depletion. This was not the case in theSwedish experiments, where cereal yield differencesbetween livestock rotations and non-livestock rota-tions generally were the largest in treatments with lowmineral N input but levelled out at higher fertiliza-tion rates.

When the sites in south Sweden were grouped withrespect to favourable and less favourable naturalconditions, Fjardingslov and OÈ rja formed the fa-vourable group and Orup, S. Ugglarp and Ekebo theless favourable group. A question asked by Jansson(1975) was whether heavy fertilization at less fa-vourable sites could improve their yields to the levelsof ordinary fertilized favourable sites. His impressionwas that there was no consistent difference in theirbehaviour regarding fertilizer effects. Natural siteconditions in� uenced yields as much as did croprotation and fertilization (Jansson, 1975). The presentstudy found for the � ve latest crop rotations that theanswer depended on the crop. Yields of forage andoil seeds did not differ between heavily fertilized, lessfavourable sites and ordinarily fertilized, favourablesites, but winter wheat and sugar beet yields werealways signi� cantly lower at less favourable sites(Carlgren, 2001).

There was no interaction between rotations andfavourable and less favourable sites.

Fertilizer effects. It was clearly demonstrated that Nwas the nutrient that most strongly in� uenced yields.This was also observed by Jansson (1975, 1983a),Nilsson (1986). At adequate soil PK status N standsfor the largest yield gains, but in two out of threeNorwegian long-term experiments Uhlen (1976)found that P was the most limiting nutrient and thatfertilizer P affected yields more than did N or K.

ments B3 and E5 (206 N, kg ha¼ 1, replacement ofP and replacement plus 80 K, kg ha¼ 1) are equalwith respect to P level, but E5 means high N andK levels, and this causes increased production. Thisis also the reason for the lower % P in barley andpotatoes observed in E5 than in B3.

The effects of K fertilization on % K in the for-age, green rape and potato tubers were large andincreased with applied K. The K application in Aand B is replacement, but in E it is an additional80 kg higher (Table 7).

Le×els of replacements and NPK remo×al. For eachrotation cycle, P and K replacement is determinedbased on the removal with harvest products. Aver-age replacement also depends on N rates (Tables 8,9). Over the four rotation cycles, the removal of Pwas about 50–75 kg ha¼ 1, which is equal to anannual removal of 12–20 kg ha¼ 1 depending on Nrate.

Amounts of K removed were large. There was atendency for the amount to increase until the thirdcycle, followed by a decline. Over the rotationssome 500–1500 kg K ha¼ 1 were removed, which isequal to 100–170 kg K ha¼ 1 annually.

The N removal averaged 87–96 kg ha¼ 1 year¼ 1

(not shown in the tables). Compared with the southand central Swedish experiments, the long-term Nuptake was larger in the north. This was related tothe larger proportion of ley in the rotation and thebiological N � xation by the clover.

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Table 7. Plant nutrient concentrations (% of dry matter), in barley grain, forage and potato tubers in northSweden: average of two experiments

Treatment (kg ha¼1 year¼1) Concentration (%)

N N P KPK N P K

BarleyA 1 0 R R 1.86b 0.40 0.50

3 73 R»20 RB 2.04b 0.40 0.505 206 R R»80E 2.33a 0.36 0.49

LSD 0.20 ns ns14n 10 10

Ley, 1st cutA 1 0 R R 2.02a 0.24b 2.40b

B 3 73 R»20 R 1.64b 0.24ba 2.48b

5 206 R R»80E 2.48c 0.27a 3.11a

LSD 0.29 0.03 0.3321n 21 21

Ley, 2nd cutA 1 0 R R 2.78a 0.27 2.52b

B 3 73 R»20 R 2.19b 0.28 2.57ab

5 206 R R»80E 2.65a 0.27 2.95a

LSD 0.29 ns 0.42n 21 21 21

Green rapeA 1 0 R R 2.13b 0.33 2.92b

3 73 R»20 RB 2.46b 0.37 3.20ba

E 5 206 R R»80 3.30a 0.38 3.72a

0.77LSD ns 0.70n 9 9 9

Potatoes1 0A R R 1.26 0.22 2.14b

3 73 R»20 RB 1.38 0.23 2.27ba

E 5 206 R R»80 1.50 0.18 2.59a

LSD ns ns 0.348 8n 8

Means followed by the same superscript letter within a column are not signi� cantly different (P\0.05).

Table 8. Average removal of P (kg ha¼1 year¼1), rotationwise for different N rates

Rotation cycle

N (kg ha¼1)Treatment 421 Mean, 28 years3

0 8.8d 14.6d 13.4d1 12.2d 12.2a

2 36 10.3cd 16.4cd 15.1cd 15.0c 14.2b

73 11.5bc 17.4cb 16.8bc3 16.5bc 15.6c

124 13.2ab 18.8ab4 18.4ab 17.8ab 17.0d

5 206 14.7a 20.0a 19.8a 19.3a 18.4e

2.2 1.8 2.2 2.1LSD 1.184 84 84n 84 336

Calculations comprise cereal grain, ley forage and green rape and potato tubers in north Sweden. Treatmentswith replacement of P. Means followed by the same superscript letter within a column are not signi� cantlydifferent (P\0.05).

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Table 9. Average removal of K (kg ha¼1 year¼1) rotationwise for different N rates (kg ha¼1)

Rotation cycle

N (kg ha¼1) 1 2 3Treatment 4 Mean, 28 years

1 0 80.0c 110.0d 124.7d 79.4c 98.5a

36 99.7bc2 128.1cd 148.1cd 99.1bc 118.8b

73 113.9b 145.5bc3 167.3bc 121.1b 136.9c

4 124 134.8a 168.2ab 194.8ab 147.1a 161.2d

5 206 143.2a 177.7a 208.7a 169.1a 174.7e

20.3 25.2LSD 28.0 25.9 12.884 84 84n 84 336

Calculations comprise cereal grain, ley forage and green rape and potato tubers in north Sweden. Treatmentswith replacement of K. Means followed by the same superscript letter within a column are not signi� cantlydifferent (P\0.05).

In almost every comparison in the south Swedishexperiments, yields in the most heavily fertilized treat-ment were only the second largest. The only exceptionwas sugar beets in the non-livestock rotation (Table4b).

Sustainability . The 10 experimental sites chosen in thesouth and central regions of Sweden offered possibil-ities to demonstrate whether application of fertilizerscould improve and maintain yields at sites consideredto have either favourable or less favourable naturalconditions.

For most crops there were insigni� cant yield differ-ences between favourable and less favourable siteswith respect to development with time. In treatmentA0 (no fertilizers), the yields dropped and stayed at alow but rather constant level. Apparently, nutrientstores in the soil are not yet completely exhausted. Aslow nutrient release, improved cultivars and the useof ef� cient pesticides contribute to maintain the yieldlevels in treatments with low NPK inputs. Similarresults were found at Askov (Dam Kofoed, 1987),especially for a clay soil.

The forage yields did not decline with time. This wasalso reported by Jenkinson et al. (1994) for thepermanent greenland of the Rothamsted long-termexperiments. Plots unfertilized from 1891 to 1958 orfrom 1959 to 1992 did not decrease in yield.

Sugar beet yields at two of the less favourable sites(Orup and S. Ugglarp) declined in treatments withoutNPK or low NPK input (not shown). Sugar beet is ahighly nutrient-demanding crop. With ample NPKaddition yield levels were maintained.

Short-term trends also occurred. For example, oilseed yields in all treatments dropped in the south andcentral Swedish experiments during the later part ofthe period, partly because the use of new loweryielding erucic acid-free cultivars, and partly becauseof sulphur de� ciency caused by a diminished sulphur

fallout in Sweden. Since 1998 this crop has received adressing with the Mg fertilizer Kieserit to preventde� ciencies of magnesium and sulphur.

For the oil seed crop in the non-livestock rotationsin central Sweden there was an overall negative trend.The reason for this is not known (Fig. 10).

In the north region yield depressions with time dueto soil P and K changes were not expected to occur.Without fertilizer N the yields declined to a level of80% from the � rst experimental year.

Negative yield effects of K fertilization were ob-served, but were more likely to be an indirect effect ofsoil Mg status. At Robacksdalen, where negative Keffects were most common, easily soluble Mg values ofthe soil were 2–5 mg 100 g¼ 1 soil. The balancebetween K and Mg, re� ected in the K Mg ratio,indicates that Mg rather than K is needed here forsuf� cient crop growth.

Soil organic matter

Soil carbon. As an average for all 10 experiments insouth and central Sweden, soil % C decreased duringthe 30 year experimental period by 0.2 percentageunits in the livestock rotation and 0.3 units withoutleys (Table 10). It is notable that % C contentsdecreased in the livestock rotations with 1 or 2 yearsof ley and manure application.

Mineral fertilization is expected to affect % C byincreased production of crop residues and soil organicmatter. This was most evident in the rotation withoutlivestock where NPK increased C from 1.58 to 1.80%at the most recent sampling.

Levels of C were larger at Ekebo and Orup than atOÈ rja, Fjardinglov and S. Ugglarp (Fig. 13). In centralSweden, the site differences were small. All � ve siteshave soil C contents around 2%, with slightly smallervalues in the rotation without livestock (Fig. 14).

At Robacksdalen in north Sweden, soil C contentsdecreased during the experimental period (Fig. 15). In

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Table 10. Effect of crop rotation on the carbon content (% of air-dry soil) of the topsoil in the south and centralSwedish experiments

With livestock Without livestock

N2 P3 K3 1962–1966Treatment1 1993–1995 1962–1966 1993–1995

0 0 0 2.05 1.74 1.96A0 1.58100 0 0 2.02A2 1.83 2.00 1.72

B1 50 R R 2.03 1.86 2.01 1.71C0 0 R»15 R»40 2.10 1.83 1.97 1.61

100 R»15 R»40 2.09C2 1.89 2.01 1.73150 R»15C3 R»40 2.07 1.88 2.02 1.76150 R»30 R»80 2.11D3 1.95 2.08 1.80

Mean 2.07 1.85 2.01 1.70LSD ns ns ns ns

10 10n 10 10

1 R: replacement of P and K removed in harvested crops. Uptake and hence replacement varies with the Napplied and is approximately 15 P and 40 K (kg ha¼1 year¼1) in C2. Replaced PK in livestock rotation adjustedfor P and K in manure. Manure added once per rotation.2 In central experiments N additions were 0, 41, 82 and 125 kg N ha¼1

.3 In central experiments, treatments C0–C3, P and K additions were R»20 P and R»50 K (kg ha¼1 year¼1).

Fig. 13. Soil C contents (%) in topsoils over time at � ve sites in south Sweden with (left) and without livestock (right). Upper row: withoutmineral NPK (A0); lower row: with NPK (C3). 1: Fjardingslov; 2: Orup; 3: OÈ rja; 4: S. Ugglarp; 5: Ekebo.

1969, the % C was 3.4 and in 1996 it had declined toapproximately 2.5. A similar trend was not observedat Offer. The former site is an old meadow, recentlybrought into cultivation, whereas the latter is oldarable land. For both of the north Swedish sites therewas a tendency (statistically insigni� cant) for N fertil-ization to increase % C.

It is an open question whether % C at each site hasattained its equilibrium value for the cropping systemand climatic conditions. Figures 13, 14 and 15 indi-cate that this may be the case, but in any circum-stance the changes are now taking place only slowly.The differences between sites in south Sweden could

be attributed to textural differences between the soils,and or to different starting % C contents. It seemslikely, judging from the results, that soil organicmatter in this temperature region of Sweden, with thetype of cropping systems that are used there, willreach a value equal to 1–1.5% C.

A special investigation has been conducted on thedynamics of soil organic matter in the south Swedishexperiments (Nilsson, 1997). Because methods fordetermining soil C have varied during the years,archived topsoil samples from 1957 to 1988 wereanalysed using the LECO CNS-2000 method (LECO,1996). To calculate organic matter, % C is multiplied

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Fig. 14. Soil C contents (%) in topsoils over time in rotation with(solid line) and without livestock (dotted line). No mineral NPKinput, treatment A0 (above); NPK input, treatment C3 (below).Means of � ve experiments in central Sweden.

Fig. 15. Soil C contents (%) in topsoils at Robacksdalen (above)and Offer in north Sweden (below) with no mineral N applied(solid line) and average 206 N kg ha¼ 1 year¼ 1 (below)

y¾62.1x¼9855, n¾24 (without livestock)

where x¾average N (kg ha¼ 1 year¼ 1) and y¾ totalorganic matter change over 26 years (kg ha¼ 1).

There are estimates that 20½106 t of C have beenlost from Swedish agricultural soils from 1950 to1990, which means approximately 7 t ha¼ 1 (Jernelov,1992). When adjusted to the time span for theSwedish soil fertility experiments and converted toorganic matter, it equals 8 t ha¼ 1.

Losses of this magnitude were observed in thenon-livestock rotation at zero or low N rates. Withyearly inputs of 100 kg N ha¼ 1, organic matter lossescorresponded to 0.5% of the total amount in thelivestock rotation and 3% in the other rotation. It isunlikely that 0.5% losses will in� uence productivitysigni� cantly. In addition, 3% is a small change,hardly detectable in productivity terms.

In absolute values the decrease per year is around100 kg ha¼ 1 organic matter. For comparison, a strawyield of 4000 kg gives approximately 500 kg of stabi-lized soil organic matter per hectare (Persson, 1981).

Soil phosphorus and potassium status

Soil sampling years are not synchronized between theexperiments. The most recent sampling showing the

by 1.72. To obtain organic matter in kg ha¼ 1, a bulkdensity of 1250 kg m3 and a topsoil layer of 20 cm areassumed, giving a conversion factor from % C to kgha¼ 1 of 2.5½106.

At the less favourable sites, Orup, S. Ugglarp andEkebo, there was a loss of organic matter of 10–15 tha¼ 1 in zero N treatments in the rotation withoutlivestock. At Fjardingslov and OÈ rja, representing fa-vourable sites, the losses were around half of thatamount. The differences between the groups werestatistically signi� cant at zero and low N fertilizerlevels (Table 11).

In the rotation without livestock there were consid-erably higher organic matter losses than in the live-stock rotation. At zero and low N rates thedifferences were statistically signi� cant. When thefertilizer level increased, the difference between therotations declined. The positive in� uence of ley onthe soil organic matter was also shown by Persson(1981). Moreover, the addition of organic matterincreases the cation-exchange capacity, which is posi-tively related to soil fertility (Jansson, 1983b).

The in� uence of rotation and N fertilization onhumus balance can be summarized as follows:

y¾32.5x¼4298, n¾24 (with livestock)

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Table 11. Change in organic matter (kg ha¼1) from 1962 to 1988 in topsoils of the � ve south Swedish soilfertility experiments (after Nilsson, 1997)

Initial value N (kg ha¼1)

1962 Rot.1 0 50Site 100 150

60 000 1 »250 ¼3000 »1500 »3500Fjardingslov2 ¼5750 ¼2750 ¼1250 »250

OÈ rja 48 000 1 ¼4300 ¼3450 ¼2580 ¼30002 ¼8600 6030 ¼850 ¼21501 ¼2030Mean ¼3230 ¼540 »2502 ¼7180 ¼4390 ¼1050 ¼950

103 000 1 ¼5000Orup »1200 »500 »5002 ¼10 250 ¼6500 ¼1250 ¼2500

S. Ugglarp 66 000 1 ¼3000 0 »1750 »10002 ¼11 500 ¼4750 0 0

134 000Ekebo 1 ¼12 500 ¼3000 ¼2500 ¼10002 ¼14 500 ¼14 250 ¼7000 ¼22501 ¼6830 ¼1070 ¼80Mean ¼1702 ¼12 080 ¼8500 ¼2750 ¼1580

1 1: rotation with livestock; 2: rotation without livestock.

current situation in the south and central experimentswas done either in 1993 or in 1995. All P, K and Mganalyses are performed using ammonium lactate (AL)extraction (Egner et al., 1960). Topsoil P and Kwere statistically signi� cantly different between treat-ments (Table 12). In treatment A0, without NPKfertilizers, P-AL was about 3.5 mg 100¼ 1 g soil.When N was applied, treatment A2, values werefurther depressed.

In treatments with replacement of P and K at alow N rate, B1, both P and K status were slightlyincreased compared with the A treatments (no NPK

fertilizer additions), although not at a signi� cantlevel. However, in both C and D treatments (replace-ment plus additional PK) signi� cant differences com-pared with A and B treatments were observed. P-ALwas 5–6 units higher in C treatments and 8–10 unitshigher in D treatments than in A. For K-AL, valueswere 5–8 and 8–11 units higher in C and D, respec-tively, than in A.

There was a small difference between crop rota-tions concerning P and K status. Values for thelivestock rotation were usually the largest. Yield andreplacement differences between the rotations are the

Table 12. AL-extractable P and K (mg 100¼1 g soil), in two crop rotations in the south and central Swedishexperiments measured at the latest soil sampling, 1993 or 1995 (sampling year depending on experimental site)

Without livestockWith livestock

P-AL K-ALTreatment1 N2 P3 K3 P-AL K-AL

3.7a 9.0a 3.6a 9.4a0 0A0 02.9a 9.7abA2 100 0 0 3.1a 8.4a

10.7ab4.8a12.5ab4.5aRR50B18.9bc16.0bd8.5bR»40 14.6bcR»150C08.6b 13.8abcC2 100 R»15 R»40 9.0b 17.8cd

C3 150 R»15 R»40 9.5bc 16.8bd 8.1b 13.8abc

17.3cD3 150 R»30 R»80 13.2c 21.6d 11.5c

4.10 5.14LSD 5.063.1110101010n

1 R: replacement of P and K removed in harvested crops. Uptake and hence replacement varies with the Napplied and is approximately 15 P and 40 K (kg ha¼1 year¼1) in C2. Replaced PK in livestock rotation adjustedfor P and K in manure. Manure added once per rotation.2 In central experiments N additions were 0, 41, 82 and 125 kg N ha¼1.3 In central experiments in treatments C0–C3, P and K additions were R»20 P and R»50 K (kg ha¼1 year¼1).

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most plausible explanations. The � ow of P and Kthrough the soil–plant–crop–manure system ishigher in the livestock rotation than in the non-live-stock rotation because of higher yields.

In the north Swedish experiments, clearly differentsoil P and K levels have been established (Table 13).For P, there are now signi� cant differences of 2- and3-fold increases between treatments. For K, differ-ences are also large, with a 2-fold increase, althoughthey are not statistically signi� cant.

Over the years, P has increased steadily with thelargest P addition (Fig. 16). With replacement of P, asmall decrease in P-AL took place during the initialrotation cycles but later values seem to havestabilized.

The balance between K and Mg at Robacksdalen isnot satisfactory and is probably the reason why nega-tive K effects were observed at this site (Table 14).The K Mg ratio indicates that Mg rather than K isneeded for suf� cient growth.

Aspects on phosphorus dynamics. Since the beginningof the experiments in the 1960s, AL-extractable P inunfertilized treatments has decreased by about 1.5units in the livestock rotation and 2.5 units in thenon-livestock rotation in the south and central regionexperiments (Table 15). Increased removal, a conse-quence of increased N rates, made the decrease evenlarger, by 2.5 and 3 mg 100¼ 1 g soil in rotations withand without livestock, respectively.

P-AL was not maintained in the replacement treat-ment, but decreased by about 1 unit, a small but still

Fig. 16. Labile P, P-AL (mg 100¼ 1 g soil) over time in three Plevels. Replacement (solid), replacement »20 P year¼ 1 (� ne dot-ted), replacement »40 P year¼ 1 (course dotted). Means of twoexperiments in north Sweden. Average N application.

evident decrease. The replacement plus 15 P kg ha¼ 1

each year resulted in an average increase of 2.5 P-ALunits. With more P, 30 kg ha¼ 1 annually, the P-ALvalues nearly doubled during the period.

Are there differences in P dynamics between indi-vidual soils? In Table 16 site-individual changes over35–40 years in P-AL in the rotation without livestockare given. The experiments are ranked from numeri-cally small to numerically large changes. Since thereis an impoverishment without fertilizer P in treatmentA2 (100 N, kg ha¼ 1 year¼ 1, no P addition) differ-ences there are negative. Only small changes havetaken place at KlostergaÊ rden and Bjertorp, but largeones at OÈ rja and Ekebo.

Similarly, in treatment C2 (100 N, replacement»15 P, kg ha¼ 1 year¼ 1) there were generally positivedifferences. At Bjertorp and S. Ugglarp, there wereonly small changes in P-AL values. At Bjertorp anegative value was observed, despite surplus P beingapplied. At Orup and Fors, in contrast, P-AL in-creased considerably.

From this, four alternatives concerning P fertilizereffects can be hypothesized, with the change of P-ALover time as the ruling factor.

(a) Small changes both downwards and upwards.Only small P fertilizer effects are anticipatedbecause surplus P is rapidly � xed in less solubleforms and cannot be extracted by the ALmethod. There were only small soil P reserves toexploit from the beginning.

Table 13. Topsoil content of AL-extractable P and K(mg 100¼1 g soil): means for all N levels at Robacks-dalen and Offer, 1996

Treatment P K pH P-AL K-AL

Manure1 plusA R2 18.3R 6.9ab6.6

R»20B 12.7c 15.36.6RC R»40 R 6.6 18.1d 15.8D R R»80 6.5 5.6a 36.8E R»20 R»80 6.6 11.4bc 31.0

33.0R»40 R»80 6.6 19.0dFnsLSD ns 4.8622n 2

Means followed by the same superscript letter withina column are not signi� cantly different (P\0.05).1 Manure added twice per rotation, 20 and 15 t ha¼1,respectively.2 R: replacement of P and K removed in harvestedcrops. Uptake and hence replacement varies with theN applied and is approximately 15 P and 135 K (kgha¼1 year¼1) in treatment A3 with 73 kg ha¼1 N.

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Table 14. AL-extractable K and Mg in topsoil (mg 100¼1 g soil) at Robacksdalen: average for 1969–1996

P K K-ALTreatment Mg-AL K Mg

Manure1 plusR2 RA 15.6abc 2.7 6.23ab

R»20 R 13.6bcB 2.8 5.12b

R»40 R 13.1c 2.8C 5.15b

R R»80 34.9dD 2.6 13.62d

R»20 R»80 30.9ad 3.1 10.26cdER»40 R»80 30.5abdF 3.1 9.58ac

LSD 17.2 ns 3.87n 4 4 4

Means followed by the same superscript letter within a column are not signi� cantly different (P\0.05).1 Manure added twice per rotation, 20 and 15 t ha¼1, respectively.2 R: replacement of P and K removed in harvested crops. Uptake and hence replacement varies with the Napplied and is approximately 15 P and 135 K (kg ha¼1 year¼1) in treatment A3 with 73 kg ha¼1 N.

Table 15. AL-extractable P (mg 100¼1 g soil): 10 sites in the south and central Sweden and two crop rotations,one with and one without livestock

At start Latest

N2 P3 K3 WithTreatment1 Without With Without

0 0 0A0 5.3 6.2 3.7a 3.6a

100 0 0 5.6A2 6.0 3.1a 2.9a

50 R R 5.6 5.9B1 4.5a 4.8a

0 R»15 R»40 5.8C0 6.1 8.5b 8.9bc

C2 100 R»15 R»40 6.4 6.3 9.0b 8.6b

150 R»15 R»40 7.0C3 6.3 9.5bc 8.1b

D3 150 R»30 R»80 7.1 6.7 13.2c 11.5c

LSD ns ns 4.10 3.1110 10 10n 10

Means followed by the same superscript letter within a column are not signi� cantly different (P\0.05).1 R: replacement of P and K removed in harvested crops. Uptake and hence replacement varies with the Napplied and is approximately 15 P and 40 K (kg ha¼1 year¼1) in C2. Replaced PK in livestock rotation adjustedfor P and K in manure. Manure added once per rotation.2 In central experiments N additions were 0, 41, 82 and 125 kg N ha¼1.3 In central experiments, treatments C0–C3, P and K additions were R»20 P and R»50 K (kg ha¼1 year¼1).

(b) Large changes downwards and small changesupwards. At a site where P is easily exploited butdif� cult to raise, slightly larger P fertilizer effectsare anticipated than in case (a). Only a smallfraction of the added fresh P will become plantavailable.

(c) Small changes downwards, large changes up-wards. Plant-available P is easily replenished andnot all freshly applied P is � xed in non-plant-available forms. This leads to moderate P fertil-izer effects.

(d) Large changes both downwards and upwards. Inthis case, � xed P is not easily mobilized. AddedP, however, remains plant available and large Pfertilizer effects are anticipated.

In summary, the P fertilizer effect can be ranked inthe order (d)\(c)\ (b) \(a).

The experimental sites in Table 16 were groupedaccording to the above alternatives (a)–(d) and theaverage P effects for treatment C2 in the most re-cently cropped winter wheat were calculated:

(a) Bjertorp, HogaÊ sa: 360 kg ha¼ 1

(b) OÈ rja, S. Ugglarp: 360 kg ha¼ 1

(c) Kungsangen, Orup, KlostergaÊ rden: 320 kg ha¼ 1

(d) Fjardingslov, Ekebo, Fors: 440 kg ha¼ 1

The assumed differences in P effect were partly con� r-med, in that effects were larger in group (d) than in(a). In group (c), the variation between the sites wasvery large.

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Table 16. AL-extractable P (mg 100¼1 g soil), at thebeginning and 35–40 years later: individual sites inthe south and central experiments; rotation withoutlivestock

At start Latest Difference

Treatment A2KlostergaÊ rden 4.1 3.4 ¼0.7

2.7 1.3Bjertorp ¼1.42.8 1.4 ¼1.4Orup4.1 2.7Kungsangen ¼1.4

HogaÊ sa 3.7 2.2 ¼1.512.0 9.8Fors ¼2.26.7 2.6 ¼4.1Fjardingslov5.5 1.2S. Ugglarp ¼4.38.0 1.5 ¼6.5OÈ rja

10.1 2.6Ekebo ¼7.5

Treatment C25.9 5.4Bjertorp ¼0.55.6S. Ugglarp 6.5 0.97.4 8.6OÈ rja 1.2

HogaÊ sa 4.6 5.8 1.2Ekebo 8.0 9.4 1.4

7.7 9.9KlostergaÊ rden 2.2Fjardingslov 6.8 9.6 2.8

3.6 7.5Kungsangen 3.92.1 6.5 4.4Orup

11.0 16.5Fors 5.5

and irregular. Cd content and fertilization were wellcorrelated. Both increasing PK and increasing Nfertilization raised the beet root Cd content. Cd, ifpresent, is taken up passively as a counter-ion to-gether with negatively charged nitrate and phosphateions. Additions of superphosphate will increase thesoil concentration of Cd (Johnston & Jones, 1992).

In 1991, Cd in winter wheat grain from the southand central experiments was determined (Table 18).Large differences between the sites were observed.High values were found at Kungsangen and S. Ug-glarp, and low values at Ekebo and Fors. Differencesbetween PK levels were smaller than they were insugar beet roots.

Earlier determinations of Cd were carried out in1971 and 1979 (Jansson, 1975, 1980). Average Cdcontents for the years 1975, 1980 and 1991 are givenin Table 19. The most dominant impression is thatCd in winter wheat grain decreased markedly from1971 to 1991. It is also obvious that increased Nfertilization has caused the Cd content to increase.

Topsoil Cd was analysed by Jansson (1980). Theaverage content of the sites was 240 ppb, and variedvery little between sites. As was the case with Cd inthe crop, contents of topsoils were correlated withNPK application and increased on average for � vesites and two rotations from 227 ppb in A0 to 251 inD3.

Summary

Twelve long-term soil fertility � eld experiments insouth, central and north Sweden were started in theperiod 1957–1969 (� ve in the south in 1957, � ve incentral Sweden in 1963 and 1966, and two in northSweden in 1969). The experiments were intentionally

Cadmium in crops and soil

Occasionally, the cadmium (Cd) content in harvestproducts has been analysed, most recently in the 1996sugar beet roots. Only three of the � ve experimentswere harvested in this year because of crop failures.

Cd varied from 150 to 300 ppb in the roots (Table17). Differences between the sites were considerable

Table 17. Cadmium content (ppb) in sugar beet roots, 1996: average of two crop rotations; three sites in thesouth experiments

Site

Treatment1 N P K Fjardingslov OÈ rja Ekebo Average

A0 0 0 0 128 190 171 163A3 150 0 0 144 187 166 166

188221179164RR50B1B3 150 R R 171 182192 182

182R»40R»15100C2 208273169C3 150 R»15 R»40 224 178 278 226

R»80 181 156 242 193D0 0 R»30R»80D3 227 176 288 230150 R»30

Mean 178 178 227 195

1 R: replacement of P and K removed in harvested crops. Uptake and hence replacement varies with the Napplied and is approximately 15 P and 40 K (kg ha¼1 year¼1) in C2. Replaced PK in livestock rotation adjustedfor P and K in manure. Manure added once per rotation.

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Table 18. Cadmium content (ppb) in winter wheat grain, 1991: average of two crop rotations; seven sites fromthe south and central Swedish experiments

Site

N2 P3 K3 Fjardingslov Orup OÈ rja S. UgglarpTreatment1 Ekebo Kungsangen Fors

0 0 0 32 39 37A0 63 25 80 37A3 150 0 0 65 53 41 59 31 95 31

50 R R 43 47 23 43B1 36 94 28150 R R 56 43B3 44 51 24 90 14

C2 100 R»15 R»40 63 53 46 61 24 88 22150 R»15 R»40 61 48 42 79C3 46 96 24

0 R»30 R»80 42 51D0 29 55 26 – –150D3 R»30 R»80 65 62 43 53 28 79 15

1 R: replacement of P and K removed in harvested crops. Uptake and hence replacement varies with the Napplied and is approximately 15 P and 40 K (kg ha¼1 year¼1) in C2. Replaced PK in livestock rotation adjustedfor P and K in manure. Manure added once per rotation.2 In central experiments N additions were 0, 41, 82 and 125 kg N ha¼1.3 In central experiments, treatments C0–C3, P and K additions were R»20 P and R»50 K (kg ha¼1 year¼1).

Table 19. Cadmium content (ppb) in winter wheat grain: average of two crop rotations and six sites in 1971 and1979 and seven sites in 1991; south and central Swedish experiments

Year

N4 P5 K5 19712Treatment1 19793 1991

0 0A0 0 – 62 45150 0 0A3 107 60 5350 R R –B1 55 42

150 R RB3 106 – 46100 R»15 R»40 –C2 64 51150 R»15 R»40C3 109 – 57

D0 0 R»30 R»80 – 58 41D3 150 R»30 R»80 111 71 49

1 R: replacement of P and K removed in harvested crops. Uptake and hence replacement varies with the Napplied and is approximately 15 P and 40 K (kg ha¼1 year¼1) in C2. Replaced PK in livestock rotation adjustedfor P and K in manure. Manure added once per rotation.2 Jansson (1975).3 Jansson (1980).4 In central experiments N additions were 0, 41, 82 and 125 kg N ha¼1.5 In central experiments, treatments C0–C3, P and K additions were R»20 P and R»50 K (kg ha¼1 year¼1).

located at favourable or less favourable sites withregard to climate and natural soil properties.

Two crop rotations, one with and one withoutlivestock, and 16 combinations of inorganic N andPK applications were compared in the south andcentral Swedish experiments. In north Sweden, therewas one livestock rotation including ley and manurewith 30 N, P and K combinations. There was afour-course rotation in the south, a six-course in thecentral parts and a seven-course rotation in northSweden.

Cereal yields in normally fertilized treatments inrotations without livestock were almost twice those of

unfertilized plots. In more abundantly fertilized treat-ments they were even larger. This indicates that fertil-izers accounted for about 50% of the yield, and fornutrient-demanding crops even more. In livestockrotations, mineral fertilizer effects were smaller de-pending on the positive in� uence of manure. Withadequate fertilizer supply the yield development withtime showed sustainability for all crops except for oilseeds in the non-livestock rotations.

Average mean hectare yields over four rotationcycles in the north Swedish experiments were approx-imately 4500 kg ha¼ 1 of barley grain, 9000 kg ha¼ 1

DM of ley, 6000 kg ha¼ 1 DM of green rape and 30

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t ha¼ 1 of potato tubers. Relative yields in treatmentswith no inorganic N were approximately 20–40%lower than yields with an average fertilization of 70 Nkg ha¼ 1. These yield levels were reached soon afterthe experiments had started.

In unfertilized treatments the uptake of N, P and Kin the non-livestock rotation was 25–40, 7–10 and10–25 kg ha¼ 1 year¼ 1, respectively. In livestockrotations values were 50–90, 10–15 and 30–100 kg.In north Sweden, the N removal was even higherowing to the large proportion of ley in the rotation.

Soil % C content decreased during a 30 year exper-imental period by 0.2 percentage units in ley rotationsand 0.3 units in rotation without leys. With increasedNPK application, the decrease was reduced in experi-ments in the south but not in the central parts or inthe north.

In zero N treatments losses of organic matter ofnearly 10 t ha¼ 1 were observed in the non-livestockrotation in south Sweden over a 26 year period andabout half as much in the livestock rotation. With Ninputs of 100 kg ha¼ 1 the losses were reduced tonegligible values.

AL-extractable P was not maintained in replace-ment treatments but decreased by about 1 mg 100g¼ 1 soil over a 40 year period. There were cleardifferences between the sites concerning P dynamics.On the one hand, there were sites where P fertilizerhad no yield effect and soil P status was rigid. Twocentral Swedish sites belonged to this group. On theother hand, there were sites where P fertilizers bothaffected yields and remained in plant-available formsin the soil.

Cd content in sugar beet roots was correlated withNPK fertilization. The content varied from 128 to288 ppb. Differences between sites were larger thandifferences between treatments.

Acknowledgement

The authors are greatly indebted to the SwedishFoundation of Plant Nutrition Research for � nancialsupport.

References

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Carlgren, K. 2001. Is it possible by use of heavy fertilization toboost the small yields normally obtained from arable land withunfavourable natural qualities to the yield levels of favourableland? Arch. Acker- P� . Boden. 46, 289–295.

Cooke, G. W. 1976. Long-term fertilizer experiments in England:the signi� cance of their results for agricultural science and forpractical farming. Ann. Agron. 27, 503–536.

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Egner, H., Riehm, H. & Domingo, W. R. 1960. Untersuchunguber die chemische Bodenanalyse als Grundlage fur dieBeurteilung des Nahrstoffzustandes der Boden 2. ChemischeExtraktionsmethoden zur Phosphor und Kaliumbestimmung.Ann. R. Agric. Coll. Swed. 26, 199–215.

FAO, 1990. Guidelines for Soil Pro� le Descriptions. 3rd edn. SoilResources Management and Conservation Service. Land andWater Development Division, FAO, Rome, 70 pp.

Garz, J., Stumpe, H., Schliephake, W. & Hagedorn, E. 1996. Yielddevelopment in the Halle (Germany) continuous cropping long-term experiment after changes in the fertilizer application in1990. Z. P� anzenernahr. Dung Bodenkunde 159, 373–376.

Ivarsson, K. & Bjarnason, S. 1988. The long-term soil fertilityexperiments in southern Sweden. 1. Background, site descriptionand experimental design. Acta Agric. Scand. 38, 137–143.

Jansson, S. L. 1975. Long-term soil fertility studies. Experiments inMalmohus County 1957–74. J. R. Swed. Acad. Agric. For.,Suppl. 10, 60 pp. (In Swedish with English summary.)

Jansson, S. L. 1978. Long-term � eld experiments as a basis of soilfertility maintenance. J. R. Swed. Acad. Agric. For. 117, 77–93.(In Swedish with English summary.)

Jansson, S. L. 1980. The yearly variations of the cadmium contentin plant husbandry. R. Swed. Acad. Agric. For., Report 4,62–67. (In Swedish with English summary.)

Jansson, S. L. 1981. Guidelines for use of plant nutrients withinSwedish agriculture based on long-term soil fertility experiments.R. Swed. Acad. Agric. For., Report 5, 5–33. (In Swedish withtables and summary in English.)

Jansson, S. L. 1983a. Twenty� ve years of soil fertility studies inSweden. Dept of Soil Sciences, Div. of Soil Fertility, SwedishUniv. of Agric. Sci., Report 151, 29 pp. (In Swedish with tablesand summary in English.)

Jansson, S. L. 1983b. Acidi� cation and liming of arable soils.Experiences from the long-term soil fertility experiments inMalmohus county. Dept of Soil Sciences, Div. of Soil Fertility,Swedish Univ. of Agric. Sci., Report 152, 22 pp. (In Swedishwith tables and summary in English.)

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Johnston, A. E. & Powlson, D. S. 1994. The setting-up, conductand applicability of long-term, continuing � eld experiments inagricultural research. In: Greenland, D. S. & Szabolcs, I. (eds.)Soil Resilience and Sustainable Land Use. CAB International,Wallingford, pp. 395–421.

Kirchmann, H. 1991. Properties and classi� cation of soils of theSwedish long-term fertility experiments: 1. Sites at Fors andKungsangen. Acta Agric. Scand. 41, 227–242.

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Appendix 1

Macronutrients in harvest products (% of dry matter), in cereal grain, oil seeds, forage and sugar beet roots;two crop rotations in the south experiments

Without livestockWith livestock

K P KTreatment NN P

Barley0.51a0.40a1.67cd0.48abA0 1.56c 0.36b

0.45b 1.85b 1 0.34c 0.46bA2 1.81b 1 0.32d

0.37b 0.47b1.64cd0.47abB1 1.60c 0.34cd

0.50ab0.40aC0 1.49c 1 0.36b 0.49ab 1.57d 1

0.47b0.37b1.78bc0.47abC2 1.76b 0.35bc

0.48ab 2.00a 1 0.37b 0.47bC3 1.92ab 1 0.36b

0.39a 0.48ab2.02a0.49aD3 1.98a 0.39a

0.03 0.18 0.02 0.04LSD 0.18 0.0240405040n 50 40

Wheat0.39a1.52d 0.410.41A0 1.61cd 0.37ab

0.40 1.85b 2 0.32cA2 0.391.90b 2 0.33d

0.410.36b1.52d0.40B2 1.67c 0.34c

0.41 1.52d 2 0.40a 0.41C0 1.59d 2 0.37a

0.36b 0.401.73c0.41C2 1.88b 0.36abc

0.40 2.01a 2 0.35bC3 0.402.06a 2 0.35bc

0.400.37b2.05a0.41D3 2.12a 0.37ab

ns 0.12 0.02LSD ns0.12 0.0245 50 45n 4550 45

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Appendix 1 (Continued)

With livestock Without livestock

N PTreatment N P K K

Oil seed3.72b 0.75c 0.77bcA0

0.75c0.67d4.19aA23.71b 0.77bcB1 0.77bc

3.72b 0.84aC0 0.81ab

0.82a3.93b 0.82abC24.21a 0.81ab 0.82abC3

0.85a0.84a4.24aD30.26 0.05LSD 0.0645 45n 45

Ley, 1st cut1.57dA0 2.01a 0.22d

1.43dA2 1.88b 3 0.21d

B1 1.88b 0.23d 2.12c

C0 2.10a 3 0.24c 2.53b

2.56bC2 1.90ab 0.27b

C3 2.03ab 3 0.28b 2.64b

2.77aD3 2.02ab 0.31a

LSD 0.21 0.03 0.25n 49 44 44

Sugar beet0.78d 4 0.62c 0.12ab 0.77abA0 0.69cd 4 0.12c

0.76b 40.09b 40.84a 40.74dA2 0.88a 0.11d

0.66c 0.12abB1 0.74bc 1 0.13c 1 0.83cd 1 0.72b

0.55d 0.15aC0 0.64d 0.15ab 0.84bcd 0.74b

0.14a0.72b 0.76b0.90abcC2 0.80b 0.15b

0.14a 0.80abC3 0.93a 0.14b 0.95ab 0.87a

0.86a0.15a0.87a0.98aD3 0.93a 0.16a

0.01 0.10LSD 0.09 0.01 0.12 0.0741 41n 41 41 41 41

Means followed by the same superscript letter within a column are not signi� cantly different (P\0.05). For anexplanation of treatment symbols, see Table 2.

140 observations; 245 observations; 344 observations; 438 observations.

Appendix 2

Macronutrients in harvest products (% of dry matter), in cereal grain, oil seeds and forage: two crop rotationsin the central Swedish experiments

With livestock Without livestock

N PTreatment N P K K

Barley0.53a 1.60ab 0.42abA0 0.53ab1.52c 0.40ab

0.38c 0.50bA2 1.64ab 1 0.37b 0.49b 1.60ab

0.50ab 1.49b 0.40bB1 0.52ab1.52c 0.38ab

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Appendix 2 (Continued)

With livestock Without livestock

N P KTreatment N P K

1.52c 1 0.41a 0.53ab 1.60abC0 0.43a 0.54a 1

C2 1.60bc 0.39ab 0.50ab 1.56ab 0.41b 0.52ab

1.71a 1 0.39abC3 0.51ab 1.62a 0.40b 0.52ab

1.71a 0.40ab 0.52abD3 1.64a 0.41b 0.52ab

LSD 0.12 0.04 0.04 0.12 0.02 0.0430 30 30 30n 30 30

WheatA0 1.67c 0.36a 0.41 1.72b 0.38ab 0.42

2.00ab 0.33b 0.39 1.95a 0.33d 0.41A21.74c 0.35ab 0.40B2 1.68b 0.35b 0.421.65c 0.37a 0.41 1.70bC0 0.39c 0.431.88b 0.36a 0.40C2 1.79b 0.36a 0.42

C3 2.03a 0.36ab 0.41 2.00a 0.35bc 0.412.02a 0.37a 0.40D3 1.96a 0.36bc 0.42

LSD 0.13 0.03 ns 0.13 0.02 nsn 32 32 77 49 49 49

Oil seedA0 3.68 0.80ab 0.75 3.49b 0.76b 0.74bc

3.96 0.76b 0.76 3.85aA2 0.66c 0.73c

3.69 0.80ab 0.76B1 3.50b 0.75b 0.77abc

C0 3.65 0.82a 0.77 3.54b 0.82a 0.80abc

3.90 0.80ab 0.79 3.62b 0.81a 0.82abC24.00 0.80ab 0.80C3 3.80a 0.79a 0.82ab

3.99 0.82a 0.81 3.81aD3 0.81a 0.83a

ns 0.05 nsLSD 0.37 0.05 0.09n 17 17 17 27 27 27

Ley, 1st cutA0 2.14 0.23bc 1.90c

A2 2.05 0.22c 1.93c

2.10 0.23bc 2.15bB1C0 2.17 0.26ab 2.44a

2.08 0.26ab 2.51aC22.09 0.28a 2.50aC3

D3 2.07 0.27a 2.62a

ns 0.03 0.21LSD54 54 54n

Ley, 2nd cut2.71 0.24 1.83bA0

A2 2.67 0.23 1.82b

2.69 0.24 2.07bB1C0 2.69 0.25 2.35a

C2 2.57 0.25 2.36a

2.57 0.24 2.34aC3D3 2.46 0.25 2.46a

ns ns 0.29LSD24 22 21n

Means followed by the same superscript letter within a column are not signi� cantly different (P\0.05). For anexplanation of treatment symbols, see Table 2.

129 observations.

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