crop yield and soil fertility response to reduced tillage under organic management
TRANSCRIPT
Soil & Tillage Research 101 (2008) 89–96
Crop yield and soil fertility response to reduced tillage under organic management
A. Berner *, I. Hildermann, A. Fließbach, L. Pfiffner, U. Niggli, P. Mader
Research Institute of Organic Agriculture (FiBL), Ackerstrasse, CH-5070 Frick, Switzerland
A R T I C L E I N F O
Article history:
Received 14 February 2007
Received in revised form 16 June 2008
Accepted 21 July 2008
Keywords:
Reduced tillage
Organic farming
Soil organic carbon
Soil microbial activity
Soil microbial biomass
A B S T R A C T
Conservation tillage (no-till and reduced tillage) brings many benefits with respect to soil fertility and
energy use, but it also has drawbacks regarding the need for synthetic fertilizers and herbicides. Our
objective was to adapt reduced tillage to organic farming by quantifying effects of tillage (plough versus
chisel), fertilization (slurry versus manure compost) and biodynamic preparations (with versus without)
on soil fertility indicators and crop yield. The experiment was initiated in 2002 on a Stagnic Eutric
Cambisol (45% clay content) near Frick (Switzerland) where the average annual precipitation is 1000 mm.
This report focuses on the conversion period and examines changes as tillage intensity was reduced. Soil
samples were taken from the 0–10 and 10–20 cm depths and analysed for soil organic carbon (Corg),
microbial biomass (Cmic), dehydrogenase activity (DHA) and earthworm density and biomass. Among the
components tested, only tillage had any influence on these soil fertility indicators. Corg in the 0–10 cm soil
layer increased by 7.4% (1.5 g Corg kg�1 soil, p < 0.001) with reduced tillage between 2002 and 2005, but
remained constant with conventional tillage. Similarly, Cmic was 28% higher and DHA 27% (p < 0.001)
higher with reduced than with conventional tillage in the soil layer 0–10 cm. In the 10–20 cm layer, there
were no significant differences for these soil parameters between the tillage treatments. Tillage had no
significant effect on total earthworm density and biomass. The abundance of endogeic, horizontally
burrowing adult earthworms was 70% higher under reduced than conventional tillage but their biomass
was 53% lower with reduced tillage. Wheat (Triticum aestivum L.) and spelt (Triticum spelta L.) yield
decreased by 14% (p < 0.001) and 8% (p < 0.05), respectively, with reduced tillage, but sunflower
(Helianthus annuus L.) yield was slightly higher with reduced tillage. Slurry fertilization enhanced wheat
yield by 5% (p < 0.001) compared to compost fertilization. Overall, Corg, Cmic, and DHA improved and
yields showed only a small reduction with reduced tillage under organic management, but long-term
effects such as weed competition remain unknown.
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1. Introduction
Soil management regimes based on conservation tillage (no-till and reduced tillage) are highly suited to integratedproduction systems in order to conserve soil fertility andprevent erosion (Cannel et al., 1986; Carter, 1994; Pekrun andClaupein, 1998). Soil organic matter (Corg) is an importantindicator for soil fertility. It is strongly affected by tillage as wellas temperature, moisture, soil texture, plant residue quantityand quality. The effect of conservation tillage systems on Corg istherefore still a matter of some controversy. While conservationtillage enhanced Corg on many sites (Alvarez, 2005; Ogle et al.,2005), other studies were unable to demonstrate such a positiveeffect (Angers et al., 1993, 1997; Wright et al., 2005). Angers
* Corresponding author at: FiBL, Postfach, CH-5070 Frick, Switzerland.
Tel.: +41 62 865 72 23; fax: +41 62 865 72 73.
E-mail address: [email protected] (A. Berner).
0167-1987/$ – see front matter � 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.still.2008.07.012
et al. (1993) reported changes in the distribution of Corg in theprofile, with increased levels near the surface and lower valueswith depth. This resulted in a similar total Corg content in soils toa depth of 60 cm after 10 years of conservation tillage at eightsites. In some cases plant material left on the field was likely tobe insufficient for Corg enrichment of the soils (Angers et al.,1993; Salinas-Garcia et al., 2001).
In reduced tillage or no tillage systems, carbon sequestrationtakes 25–30 years to reach a new steady state (Alvarez, 2005).These soils contained up to 12 t ha�1 more Corg under conservationtillage than under conventional tillage. In a meta-analysis based on126 articles, Ogle et al. (2005) pointed out the variations caused bydifferent temperature regimes. Twenty years after conversion fromconventional tillage to no tillage, soils contained 16% more Corg
under a temperate wet climate and 10% more under a temperatedry climate. The soils of 161 experiments with conservation tillage(no-till and reduced tillage) under various climatic conditionscontained on average 2.1 t Corg ha�1 more than the conventionallyploughed soils (Alvarez, 2005).
A. Berner et al. / Soil & Tillage Research 101 (2008) 89–9690
Angers et al. (1993) investigated the form of organic carbonsequestered under conservation tillage in Canada. The carbon wasnot bound in organo-clay complexes, but was merely contained asparticulate organic matter in the sand-size fraction. Stockfischet al. (1999) claimed that this fraction is rapidly and easilymineralized after ploughing. Therefore the Corg build-up underconservation tillage over years may drop to initial values within ayear as a result of a single intervention. This is of great importancefor organic farming, where mouldboard ploughing is commonpractice and may be necessary from time to time to reduce weedpressure.
Organic farming systems offer many benefits to the environment(Mader et al., 2002). Conservation tillage systems could provide newopportunities in organic farming as well, but they have beendeveloped under conventional farming systems involving the use ofagrochemicals (Pekrun and Claupein, 1998). Problems with weeds(Hampl, 1999; Zwerger, 1996), slugs (Jourdan et al., 1997) and adelay in soil nitrogen mineralization in spring are more difficult tosolve under organic farming conditions. Few experiments have beenconducted to investigate conservation tillage under organic farmingconditions (Hampl, 2005; Kainz et al., 2005; Pekrun et al., 2003). Inall of these cases, only reduced tillage was applied; no tillage systemswere not tested. One long-term experiment was abandoned after 12years due to severe weed problems (Kainz et al., 2005). Based on datafrom all the tillage experiments in organic farming systems, Hampl(2005) concluded that occasional use of the mouldboard plough isinevitable because of its weed-regulating effect. As alreadymentioned, this may counteract the positive effects of reducedtillage on soil carbon (Stockfisch et al., 1999). Hence, reduced tillagesystems need to be developed further under organic management. Inagricultural practice, farming system elements are cross-linked withothers. In our new system approach, we integrated specific organicfarming practices such as reduced tillage, the use of different formsof organic manure and the application of biodynamic preparations tosolve the problems. Long-term experiments on organic farming haveshown that the application of cattle manure compost exerts positiveeffects on Corg and soil microbial activity (Fließbach et al., 2007).Biodynamic preparations (fermented plant material and mineralcompounds) have shown some influence on soil fertility andcompost quality (Carpenter-Boggs et al., 2000; Zaller and Kopke,2004). By combining the three factors, potential interactions can beelucidated and optimal combinations discerned.
Our objective was to quantify effects of tillage, fertilization, andbiodynamic preparations on soil fertility indicators and crop yieldduring the conversion phase of a long-term field trial.
2. Materials and methods
2.1. Field experiment
In autumn 2002 a field experiment was established in Frick,Switzerland (478 300 N, 88 010 E) comprising the following factors:
Tillage
Conventional: mouldboard plough (operating at15 cm depth) followed by rotary harrow (5 cm)Reduced: chisel plough (15 cm) followed by rotaryharrow (5 cm)
Fertilization
Slurry: slurry aloneManure compost: composted farmyard manureand slurry (both systems at a level of 1.4livestock units ha�1)
Preparations
Without preparationsWith biodynamic compost and field preparations
The three factors – tillage, fertilization and preparations – werefully factorized. This resulted in eight treatments, each replicatedfour times. The 32 plots were arranged in a split-plot design. Theplot size was 12 m � 12 m, allowing the use of regular-sizedfarming equipment. Soil samples were taken and yields measuredin an inner 8 m � 8 m parcel.
2.2. Site conditions
The soil type at the experimental site was a Stagnic EutricCambisol. At the start of the experiment, in autumn 2002, Corg andpH were measured in a maize crop in each experimental plot(n = 32), and texture and soil nutrients in the four replicate blocks(n = 4) at the experimental site. The soil contained 2.2% Corg
(coefficient of variance (cv.) 15%), 22% sand (cv. 8%), 33% silt (cv.12%), 45% clay (cv. 13%) and had a pH (H2O) of 7.1 (cv. 4%) in 0–20 cm soil depth. The soil was enriched in ammonia acetate-ETDAextractable phosphorus (116 mg P kg�1 soil; cv. 15%), and potas-sium (434 mg K kg�1 soil; cv. 5%) due to extensive application ofmanure from livestock (swine) in pre-study management.
Before the experiment started, the field, as part of the wholefarm, had been managed organically for 7 years in accordance withEuropean Union Regulation (EEC) No. 2092/91. Before conversionto organic farming, the farm was conventional with livestock and agrass-clover rotation. Ploughing depth was 25 cm under conven-tional farming and 15 cm under organic farming prior to the startof the experiment. Corg was therefore distributed quite homo-genously through the soil profile down to 20 cm.
The mean annual precipitation at the site was 1000 mm. Inrainy periods in winter and spring the soil can be waterlogged forsome days. Mean annual temperature was 8.9 8C.
2.3. Soil tillage
The conventional tillage system was a treatment with amouldboard plough to a depth of 15 cm and, for seedbedpreparation, with a ‘rototiller’, a horizontally rotating harrow(Rau company, DE-73235 Weilheim, Germany) to a depth of 5 cm.
In the reduced system, a chisel plough (WeCo-Dyn-System fromthe EcoDyn company, DE-77963 Schwanau, Germany) was used toloosen the dry soil to a depth of 15 cm; for the seedbed, the samerototiller was used as in the conventional system. Only after wheatin summer 2003 the soil was dry enough to use the chisel plough(for rotation see Section 2.6). After sunflower (autumn 2004) andafter spelt (summer 2005), only the rototiller was used, withoutchiselling.
Seedbed preparation using the rototiller was done at the sametimes in both tillage systems (Table 1).
2.4. Fertilization
Cow manure was applied at an annual average intensitycorresponding to 1.4 livestock units (LU) ha�1. The dry matterportion in cow excrement was assumed to be 67% in manure and33% in slurry, in accordance with the Swiss guidelines forfertilization (Walther et al., 2001). Before application, the slurrywas stored for about 4 weeks in a silo. The cow manure wascomposted at the beginning for 4 months in two windrows, each of2 m3 volume. Dry matter losses of 30% and total nitrogen losses of20% were calculated in accordance with Walther et al. (2001).Whereas identical amounts of mineral N were applied in bothfertilization systems, dry matter and organic matter inputs werenearly twice as high in the compost system as in the slurryfertilization system alone (Table 2). This was for technical reasons:stable manure, the raw material for composting, contained much
Table 1Dates of soil tillage in the different systems
System Crop Tillage Date
Conventional Winter wheat Plough 11 October 2002
Rototiller 30 October 2002
Intercrop Rototiller 19 August 2003
Sunflower Plough 26 February 2004
Rototiller 22 April 2004
Spelt Plough 8 November 2004
Rototiller 16 November 2004
Reduced Winter wheat Rototiller 30 October 2002
Chisel 06 August 2003
Intercrop Rototiller 19 August 2003
Sunflower Rototiller 22 April 2004
Spelt Rototiller 16 November 2004
A. Berner et al. / Soil & Tillage Research 101 (2008) 89–96 91
straw, used for animal bedding, which did not enter into the slurryphase. In comparing these two systems, the differences in amountsand forms of the fertilizers have to be kept in mind.
2.5. Preparations
The biodynamic preparations (P) consist of the following: P500: Cow-manure fermented in a cow horn; P 501: silica stored in acow horn. These were applied at rates of 250 and 4 g ha�1,respectively and sprayed three times per season on the relevantplots. Composting additives are yarrow flowers (P 502, Achillea
millefolium, L.), camomile flowers (P 503, Matricaria recutita, L.),stinging nettle (P 504, Urtica dioica, L.), oak bark (P 505, Quercus
robur, L.), dandelion flowers (P 506, Taraxacum officinale, Wiggers)and valerian flowers (P 507, Valeriana officinalis, L.); these wereadded at the start of manure composting (Carpenter-Boggs et al.,2000; Zaller and Kopke, 2004).
2.6. Crops
Before the experiment started, the field site was uniformlyplanted in 2002 with silage maize. The following crops werecultivated: winter wheat (Triticum aestivum L. cv. ‘Titlis’, 2002–2003), oat–clover intercrop (Trifolium alexandrinum L. mixed withAvena sativa L., 2003–2004), sunflower (Helianthus annuus L. cv.‘Sanluca’, 2004) and spelt (Triticum spelta L. cv. ‘Ostro’, 2005). For2006 and 2007, grass-clover was planted. The crop rotation willthen start again with maize, and the experiment will continue until2011.
Cereal and sunflower grains, cereal straw, grass-clover and theintercrop were harvested and removed from the field. Untreatedseeds were sown. Weeds were controlled mechanically by atractor-driven hoe in cereals and sunflowers, and also by handwithin the sunflower crop row. In the case of the sunflowers,
Table 2Average yearly input of dry matter, organic matter and plant nutrients via slurry and m
System DM (kg ha�1) OM (kg ha�1) Nt (kg ha�1) Nmin
Tillage
Conventional 2579 1624 110 39
Reduced 2719 1717 116 42
Fertilization
Slurry 1767 1290 94 41
Manure compost 3531 2052 131 40
Preparations
Without 2648 1676 114 41
With 2650 1665 112 41
Nt = N total; Nmin = NO3–N + NH4–N.
labour for hand weeding in the reduced tilled plots was 28, and15 h ha�1 in conventional plots.
2.7. Earthworms
To investigate earthworms in 2005, the method of hand sortingwas used inaccordance withPfiffner andMader (1997). The samplingunit was 0.40 m� 0.40 m per experimental plot to a soil depth of20 cm. Due to the humidity in spring and the high clay content of thesoil, it could only be sorted in the last days of May. In addition, amustard solution was left to infiltrate into the bottom of theburrowed hole to catch the fast-moving earthworms, e.g. Lumbricus
terrestris, as described by Emmerling (1995). Because this methodwas very labour-intensive, we sampled only in the plots with manurecompost of the tillage and biodynamic preparations plots.
The ecological classification into endogeic, unpigmentedhorizontally burrowing worms inhabiting the upper soil layerand anecic, brown-pigmented, vertically burrowing worms wasdone in accordance with Bouche (1977). The individuals in thegroups were divided into adult worms with a scutellum andjuvenile worms without.
2.8. Soil sampling
Soil samples were taken at the beginning of the experiment onOctober 1st 2002 (standing crop:silage maize) and on March 15th
2005 (standing crop:spelt) in all 32 plots. Twelve individual coresper field plot were separated into 0–10 cm and 10–20 cm soildepth layers and thereafter bulked to one composite soil sampleper plot. Soils were then sieved through a 5-mm mesh and kept at3 8C until they were analysed.
2.9. Chemical soil analyses
2.9.1. Measurement of pH and Corg
The pH of dried samples (60 8C, 24 h) was measured in a soilsuspension with deionized water (1:10, w/v). Soil organic carbonwas measured after wet oxidation of 1 g dry soil in 20 mlconcentrated H2SO4 and 25 ml 2 M K2Cr2O7 in accordance withSwiss standard protocols (FAL et al., 1996).
2.10. Soil microbial analyses
All soil microbial analyses were done on moist soil samples at awater content corresponding to 40–50% of maximum waterretention capacity.
2.10.1. Chloroform fumigation extraction
Soil microbial biomass C (Cmic) and N (Nmic) were estimated bychloroform fumigation extraction (CFE) in accordance with Vance
anure compost as fertilizers (2002–2005)
(kg ha�1) P (kg ha�1) K (kg ha�1) Mg (kg ha�1) Ca (kg ha�1)
32 168 35 61
33 180 39 62
27 150 24 36
38 198 49 87
33 175 37 61
32 174 37 62
Table 3pH, Corg in 2005 and difference of Corg 2005–2002 (Diff Corg) in soil depth layers 0–10 and 10–20 cm
System pHH2O Corg Diff Corg
0–10 cm 10–20 cm 0–10 cm (%) 10–20 cm (%) 0–10 cm (%) 10–20 cm (%)
Tillage
Conventional 7.42 7.43 2.11 2.08 �0.008 0.030
Reduced 7.35 7.39 2.34 2.17 0.149 0.006
Fertilization
Slurry 7.43 7.44 2.18 2.10 0.065 0.015
Manure compost 7.35 7.38 2.26 2.15 0.076 0.021
Preparations
Without 7.39 7.42 2.22 2.13 0.086 0.022
With 7.38 7.40 2.22 2.12 0.054 0.014
Tillage
Reduced (%) (100% = conventional) 99 99 111 104 7.4a �1.1a
Fertilization
Manure compost (%) (100% = slurry) 99 99 104 102 0.5a 0.3a
Preparations
With (%) (100% = without) 100 100 100 99 �1.4a �0.4a
ANOVA
Tillage ** ns *** ** *** ns
Fertilization ** ns * ns ns ns
Preparations ns ns ns ns ns ns
*p < 0.05; **p < 0.01; ***p < 0.001.a Diff Corg � 100%/Corg (conventional, slurry or without).
A. Berner et al. / Soil & Tillage Research 101 (2008) 89–9692
et al. (1987). CFE was done in triplicate on 20 g (dry matter) sub-samples that were extracted with 80 ml of a 0.5 M K2SO4 solution.Total organic C (TOC) in soil extracts was determined by infraredspectrometry after combustion at 850 8C (DIMA-TOC 100, Dimatec,45276 Essen, DE). Total N was subsequently measured in the samesample by chemoluminescence (TNb, Dimatec, 45276 Essen, DE).Soil microbial biomass was then calculated according to theformula: Cmic = EC/kEC where EC = (TOC in fumigated sam-ples � TOC in control samples) and kEC = 0.45 (Joergensen andMueller, 1996a). Nmic = EN/kEN where EN = (Nt in fumigatedsamples – Nt in control samples) and kEN = 0.54 (Joergensen andMueller, 1996b).
Table 4Microbial biomass Cmic and Nmic, Cmic-to-Nmic, Cmic-to-Corg and dehydrogenase activity
System Cmic (mg Cmic kg�1) Nmic (mg Nmic kg�1)
0–10 cm 10–20 cm 0–10 cm 10–20 c
Tillage
Conventional 780 754 114 104
Reduced 996 800 143 106
Fertilization
Slurry 883 780 128 106
Manure compost 893 775 130 104
Preparations
Without 895 775 130 105
With 882 779 128 105
Tillage
Reduced (%) (100% = conventional) 128 106 126 102
Fertilization
Manure compost (%) (100% = Slurry) 101 99 102 99
Preparations
With (%) (100% = Without) 99 101 98 101
ANOVA
Tillage *** (*) *** ns
Fertilization ns ns ns ns
Preparations ns ns ns ns
(*)p < 0.1; *p < 0.05; ***p < 0.001.
2.10.2. Soil dehydrogenase activity
Dehydrogenase activity (DHA) was measured in accordancewith Tabatabai (1982) in 5 g soil samples incubated at 30 8C for24 h in the presence of an alternative electron acceptor (triphe-nyltetrazoliumchloride). The red-tinted product (triphenylforma-zan) was extracted with acetone and measured in a spectro-photometer at 546 nm.
2.11. Statistics
The data were analysed by a three-way ANOVA. The main effects(tillage, fertilization and preparations) and their interactions were
in the soil depth layers 0–10 and 10–20 cm in 2005
Cmic-to-Nmic Cmic-to-Corg (%) Dehydrogenase activ-
ity (mg TTF g�1 d�1)
m 0–10 cm 10–20 cm 0–10 cm 10–20 cm 0–10 cm 10–20 cm
6.85 7.26 3.7 3.6 349 317
6.96 7.57 4.3 3.7 442 305
6.90 7.39 4.0 3.7 392 315
6.90 7.45 3.9 3.6 400 307
6.90 7.42 4.0 3.6 403 315
6.90 7.42 4.0 3.7 388 307
102 104 115 102 127 96
100 101 98 97 102 97
100 100 98 101 96 97
ns (*) *** ns *** (*)
ns ns ns ns ns ns
ns ns ns ns * ns
Table 5Density and biomass of earthworms at soil depth of 0-20 cm, total and divided into ecological groups: adult, juvenile and cocoon in 2005
System Density (Individuals m�2) Biomass (g m�2)
Total
numbers
Vertically
burrowing
adult
Vertically
burrowing
juvenile
Horizontally
burrowing
adult
Horizontally
burrowing
juvenile
Cocoons Total
biomass
Vertically
burrowing
adult
Vertically
burrowing
juvenile
Horizontally
burrowing
adult
Horizontally
burrowing
juvenile
Tillage
Conventional 424 26 57 55 287 38 129 44.1 44.4 22.8 17.9
Reduced 582 19 70 93 400 71 101 34.8 35.7 10.8 19.8
Preparations
Without 533 23 69 80 361 56 124 43.1 42.9 18.7 19.3
With 473 22 57 68 326 52 106 35.6 37.1 14.9 18.3
Tillage
reduced (%)
(100% = conventional)
137 75 123 170 139 188 78 79 80 47 111
Preparations
With (%) (100% = without) 89 93 83 85 90 93 85 83 86 80 95
ANOVA
Tillage (*) ns ns * (*) * ns ns ns * ns
Preparations ns ns ns ns ns ns ns ns ns ns ns
(*)p < 0.1; *p < 0.05.
A. Berner et al. / Soil & Tillage Research 101 (2008) 89–96 93
tested for significance using the JMP 5.0.1 software (SAS, 2002). Thefactorial design of the field trial allowed for statistical differentiationof small differences based on 16 replicates for each of the three mainfactors.
3. Results and discussion
The major issue in the conversion period of this long-termexperiment was to elucidate the changes in soil fertility indicatorsand crop yield performance provoked by conventional and reducedtillage under different fertilizer practices and with the use ofbiodynamic preparations. While tillage manifested significanteffects, fertilization by slurry or compost only occasionally showedsmall effects on yield but had hardly any effect on soil fertilityindicators. We measured no effects resulting from the biodynamicpreparations, neither on crop yield nor on soil fertility indicators. Inthe results section we will therefore merely describe the tillageeffects and, where they exist, fertilizer effects. In the relevant datatables, the effects of all three factors (tillage, fertilization andbiodynamic preparations) are shown (Tables 3–7). As expected,tillage affected the upper 0–10 cm soil layers much more stronglythan the lower 10–20 cm soil layers. Statistical analysis revealedno interaction between the three factors tillage, fertilization andpreparations.
Table 6Individual biomass of earthworms, divided into ecological groups: adult and juvenile
Individual biomass (g Individ
Vertically
burrowing
adult
Tillage
Conventional 1.73
Reduced 1.83
Tillage
Reduced (%) (100% = conventional) 106
ANOVA
Tillage ns
*p < 0.05.
3.1. Corg and pH
To monitor changes in the content of Corg and pH, soil sampleswere taken initially for the baseline assessment and again after theexperiment had been running for three winters and two summers.Even after this short period of 21/2 years, Corg at 0–10 cm soil depthincreased by 7%, corresponding to 1.5 g Corg kg�1 soil (p < 0.001)(Table 3) under reduced tillage. Under conventional tillage Corg
remained almost constant. No significant changes were observedat 10–20 cm soil depth in both tillage treatments.
The relatively high Corg increase in reduced tillage plots can beexplained by the high amount of plant residues left on the fieldplots, complementing the input via manure. In addition to croproots, winter wheat stubbles and large amounts of shreddedsunflower residues were incorporated into the soil. Heavy rainfallresulted in temporary waterlogging of that clay soil. This in turnresulted in limited oxygen concentrations, preventing fasterdecomposition in the reduced tillage plots. Ploughed sunflowerresidues were still partly undecomposed in the spring, 9 monthsafter the sunflower harvest. In contrast, they were completelydecomposed in the reduced tillage plots, where they were onlysuperficially mixed into the upper 0–5 cm soil layer by rototiller.We assume, that during the vegetation period, ploughed soils werebetter aerated, inducing a mineralization of plant material and of
ual�1)
Vertically
burrowing
juvenile
Horizontally
burrowing
adult
Horizontally
burrowing
juvenile
0.79 0.42 0.062
0.51 0.12 0.050
65 28 79
ns * *
Table 7Yields of winter wheat 2003, intercrop 2003, sunflower 2004 and spelt 2005
System Winter wheat (mg dm ha�1) Intercrop (mg dm ha�1) Sunflower (mg dm ha�1) Spelta (mg dm ha�1)
Tillage
Conventional 5.18 0.82 3.19 2.43
Reduced 4.43 0.87 3.33 2.23
Fertilization
Slurry 4.92 0.81 3.30 2.28
Manure compost 4.69 0.88 3.22 2.38
Preparations
Without 4.84 0.86 3.31 2.39
With 4.77 0.84 3.20 2.27
Tillage
Reduced (%) (100% = conventional) 86 106 105 92
Fertilization
Manure compost (%) (100% = slurry) 95 109 98 104
Preparations
With (%) (100% = without) 99 98 97 95
ANOVA
Tillage *** ns (*) *
Fertilization *** (*) ns ns
Preparations ns ns ns ns
(*)p < 0.1; **p < 0.05; ***p < 0.001.a Grain.
Table 8Correlation matrix (r) of chemical and microbiological soil parameters at soil depth
of 0–10 cm
Corg pH Diff Corg DHA Cmic Nmic Cmic/Nmic
Corg 1
pH �0.835 1
Diff Corg 0.282 0.066 1
DHA �0.194 0.363 0.176 1
Cmic 0.711 �0.469 0.427 0.423 1
Nmic 0.253 0.033 0.430 0.803 0.831 1
Cmic-to-Nmic 0.865 �0.929 0.023 �0.489 0.451 �0.115 1
Cmic-to-Corg �0.400 0.466 0.143 0.814 0.355 0.738 �0.544
A. Berner et al. / Soil & Tillage Research 101 (2008) 89–9694
easily decomposable soil organic matter fractions, explaining thelower Corg values as compared to the reduced tilled plots.
In our experiment, carbon sequestration accounted for2.0 t C ha�1 in the 0–20 cm soil layer under reduced tillage within21/2 years, whereas no carbon was sequestered under conventionaltillage. This corresponds closely to the average Corg increase underreduced tillage found by Alvarez (2005) in his literature surveycomprising 161 experiments.
Soil acidity (pH) decreased by 0.1 units (p < 0.01) in reducedversus conventional tillage plots and also in compost versus slurry-fertilized plots at 0–10 cm depth (p < 0.01). Our findings confirmthe results of Pronin (2003), who also observed lower pH valueswith the accumulation of organic acids in the organic matter in thesuperficial soil layers in no-till soils. The leaching of basicsubstances into deeper soil layers without ploughing may beanother cause of pH decrease.
3.2. Soil microbial biomass and dehydrogenase activity
Soil microbial biomass was increased under reduced tillage inall soil layers when compared to conventionally tilled treatments.At 0–10 cm soil depth, Cmic increased by 28% (p < 0.001) and at 10–20 cm it increased slightly, by 6% (p < 0.1). Nmic increased by 26% at0–10 cm (p < 0.001) (Table 4). Dehydrogenase activity (DHA) alsoshowed 27% higher activity at 0–10 cm (p < 0.001) under reducedtillage compared to conventional tillage, whereas it was 4% lower(p < 0.1) at 10–20 cm.
Weber and Emmerling (2005) studied soil microbial activity ina 10-year tillage experiment. In the 0–15 cm surface layer, soilmicrobial activity was enhanced by 30% following layer cultivationwith a chisel plough, and by 21% following two-layer ploughing. Ata depth of 15–25 cm, microbial activity fell by 11% under layercultivation versus plough and layer ploughing.
We calculated the Cmic-to-Corg ratio, which is suggested as anindicator of biological soil fertility (Sparling, 1992; Stockfisch et al.,1999; Weber and Emmerling, 2005). In our tillage experiment, theratio Cmic-to-Corg was 15% higher (p < 0.001) at 0–10 cm soil depthunder reduced tillage due to the addition of organic plant biomassto the soil surface. Weber and Emmerling (2005) obtained similar
results, with 16% enhancement of Cmic-to-Corg using layercultivation versus plough. Stockfisch et al. (1999) postulated theCmic-to-Corg ratio as an early indicator of an enhancement of Corg. Infact, the differentiation of Corg was much smaller than the one ofCmic-to-Corg between reduced and conventional tillage in both theexperiments of Weber and Emmerling (2005) and our experiment.Accordingly, Mader et al. (2002) and Fließbach et al. (2007) found asharp discrimination in Cmic-to-Corg of minerally and organicallyfertilized soils, while Corg was differentiating only little in a long-term field experiment. This finding supports the hypothesis ofStockfisch et al. (1999). We also found that the changes in Corg
(differences in Corg between 2005 and 2002 = Diff Corg) showed thehighest positive correlation with Cmic and Nmic (Table 8), indicatingthat the microbial biomass is a regulator of carbon transformationprocesses in the soil, but also strongly depends on Corg as pointedout by Mader et al. (2002).
The Cmic-to-Nmic ratio may serve as an indicator of a change insoil microbial populations (Fließbach et al., 2007; Joergensen,1995). Higher values indicate a higher proportion of fungi or oldercells in relation to bacteria or younger cells in the microbialbiomass (Joergensen, 1995). In the lower, less disturbed 10–20 cmsoil layer of the reduced-tilled soils, Cmic-to-Nmic was 4% higher(p < 0.1) than in the conventionally tilled soils. In the upper soillayer of 0–10 cm, both systems treated by the rototiller, nodifferences could be measured. This indicates that the fungi-to-bacteria ratio may have changed in 10–20 cm soil depth due to
A. Berner et al. / Soil & Tillage Research 101 (2008) 89–96 95
reduced disturbance of the fungal hyphae. This indicator washighly negatively correlated with soil pH (Table 8), reflecting thefact that fungi in general are better adapted to acidic soil conditionsthan bacteria. In a study of Ahl et al. (1998) reduced soil microbialactivity and increased fungal activity in the 7–30 cm soil layer wasobserved in fields under horizontal axis rotary cultivationcompared with conventionally ploughed neighbouring fields.
3.3. Earthworms
Total earthworm density and biomass were not significantlyaffected (p > 0.05) by tillage in our experiment (Table 5). However,numbers of endogeic, horizontally burrowing adult worms were70% higher (p < 0.05) under reduced tillage (Table 5), and numbersof juvenile worms were 39% higher (p < 0.1). The total biomass ofthe endogeic, horizontally burrowing adult worms fell by half(Table 5), and individual biomass decreased to one-third (p < 0.05)(Table 6) under reduced tillage when compared with conventionaltillage. Anecic, vertically burrowing worms were not influenced bythe tillage schemes. Eighty-eight percent (p < 0.05) more cocoonswere counted under reduced tillage.
While earthworm density (400–600 individuals m�2) was quitehigh in our experiment, the biomass was in the average range forcomparable arable sites (Chan, 2001; Kainz et al., 2003; Maurer-Troxler et al., 2005). In general, higher populations of earthwormshave been found in clay loam than in sandy loams (Chan, 2001;Gerhard and Hay, 1979). The high share of horizontally burrowing,endogeic and smaller species in the population is typical for heavysoils under plough (Chan, 2001). The higher earthworm biomass ofendogeic earthworms in the conventional tillage system mayindicate that the shallow ploughing system was well adapted tothis clayey soil, although tillage in the late autumn (Table 1) couldharm the earthworm populations (Chan, 2001; Curry et al., 2002;Pfiffner and Luka, 2007).
The divergence of density and biomass of horizontallyborrowing earthworms under reduced tillage is quite striking.As expected, the density decreased under the plough in thisecological group, while the biomass increased. This can beexplained by the food situation. Under conventional tillage,organic residues were incorporated into the soil down to 15 cm.The food conditions therefore may have been more beneficial forendogeic, horizontally burrowing earthworms, as found in a highertotal and individual biomass (Table 6). Stimulated growth ofearthworm populations following addition of organic matter wasalso measured by Schmidt et al. (2003).
To summarize, total earthworm density and biomass were notaffected by the tillage scheme applied. Density of endogeicearthworms decreased due to mechanical disturbance and biomassincreased due to better food conditions in ploughed plots. A markedincrease in cocoons and juveniles suggests favourable developmentof earthworm populations under reduced tillage.
3.4. Crop yield
Yields differed between crops and systems within the first yearsof the experiment. Under reduced tillage, the grain yield of winterwheat in 2003 was 14% lower (p < 0.001) than under conventionaltillage (Table 7). While the subsequent oat–clover intercrop yieldwas equal between tillage systems, the yield of the sunflowers inthe next year was 5% higher (p < 0.1) under reduced tillage acrossall fertilization and preparations levels. The grain yield of spelt in2005 was again 8% higher (p < 0.01) in conventionally tilled plots.
These yield results may be explained by the temporallydifferent N mineralization under the different tillage schemesand the likewise different N demand of the crops cultivated in the
time course. In other words, N release from soil, residue andmanure-bound N is expected not to be synchronous to the cereal Nneeds under reduced tillage, leading to an N shortage. As plantswith high N demand in early spring, cereals had higher yieldsunder conventional tillage due to improved N mineralization inspring in ploughed soils (Zihlmann and Weisskopf, 2006). Later Nmineralization in no-till soils was reported by Anken et al. (2003)and Zihlmann and Weisskopf (2006). This may have supported thelate sown oat–clover intercrop and the sunflowers, both crops thathave N demand later in the season, resulting in the same yieldunder reduced tillage or even, in the case of sunflowers, a yield thattends to be higher.
Application of slurry resulted in a 5% higher wheat grain yield(p < 0.001) when compared to the system with less slurry andmore organic N-containing manure compost. The slurry contains ahigher proportion of N in ammonia form that can be taken updirectly by the plant in early summer, resulting in a growthpromotion and higher yields. The fertilization forms did not affectsunflower or spelt yield.
Manure compost, however, also tended to raise intercrop yieldby 9% (p < 0.1). Organic N in compost is only mineralized slowly(Warman, 2001). Compost was given to wheat in the early spring.Higher yields in the following unfertilized intercrop may indicate along-term fertilization effect of the compost. In subsequent years,however, no further effects on yield resulting from the differentforms of fertilizer could be observed. In a no-till system fertilizedwith manure compost, no effects on yield could be measured(Wahlen, 2007). We expect that applying larger amounts ofmanure or manure compost to the reduced-tilled plots in theconversion time could enhance yields, as shown by Wang et al.(2006). Compost may also enhance yields in the long term.
4. Conclusion
The aim of our long-term tillage experiment was to assess theeffect of tillage, fertilization and the use of the biodynamicpreparations on soil fertility parameters and yield under organicfarming conditions. While indicators of soil fertility wereenhanced, average yield of cereals and sunflowers achieved underreduced tillage was 97% of those obtained under conventionaltillage. Based on these first results, we can conclude that reducedtillage is applicable under organic farming conditions in theconversion phase, even on a clay soil.
Furthermore, the results suggest that reduced tillage is feasibleboth with manure compost and slurry fertilization. Since therewere no interactions between the three factors tillage, fertilizationand biodynamic preparations, we are unable to suggest anycombinations of these farming practices for optimal conversion toreduced tillage under organic farming conditions. It is important tonote that the findings only reflect the situation during theconversion period from conventional to reduced tillage. Long-term effects of the system need to be assessed to elucidate theirimpact on soil fertility and yield performance from the point ofview of carbon sequestration and weed competition. The resultssuggest that reduced tillage systems may be a valid option forsequestering organic carbon in the soil, which is of paramountimportance with respect to climate change (Barker et al., 2007).
Acknowledgements
We sincerely thank the farmers involved in the project,especially Pius Allemann, Rainer Sax and Daniel Bohler. For helpfuldiscussions we are grateful to Bernhard Streit, Nikolai Fuchs andHartmut Spiess. We also thank Francoise Okopnik for assessing thesoil type at the experimental site. This work was funded by the
A. Berner et al. / Soil & Tillage Research 101 (2008) 89–9696
Swiss Federal Office for Agriculture and the following institutions:Stichting Demeter (NL), Stiftung zur Pflege von Mensch, Mitweltund Erde (CH), Sampo Verein fur anthroposophische Forschungund Kunst (CH), Software AG–Stiftung (DE) and Evidenzge-sellschaft (CH).
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