BENEFITS OF

Name of site 1. Boxworth 2. Bridgets 3. Gleadthorpe 4. Pwllpeiran 5. Rosemaund 6. Watsonfoot 7. Garrionhaugh

BlOSOLlDS TO SOIL QUALITY AND FERTILITY

Location Topsoil texture Cropping Boxworth, Cam bridgesh ire Clay (Hanslope) Arable Martyr Worthy, Hampshire Silty clay loam (Andover) Arable Meden Vale, Nottinghamshire Sandy loam (Wick) Arable Cwmystwyth, Ceradigion Clay loam (Denbigh) Grassland Preston Wynne, Hereford Silt loam (Bromyard) Grassland Lana rks h ire Clay loam (Rowanhill) Grassland Lana rks hire Sandy loam (Peebles) Grassland

B. J. Chambers, BSc, PhD. FI SoilSci*, F. A. Nicholson, BSc. PhD*. M. Ahken, BSc.

MI Soil Sci**. E. Cartinell, BSc, PhD*** and C. Rowlands. BSc. MSc, PhD. C Biol. MlBiol (Member)****

INTRODU CTl ON Biosolids are an important source of essential plant nutrients, and repeated applications add organic matter to soils. There is a significant amount of scientific literature which reports the effects of biosolids applications on soils and crops, but this has mainly focused on environmental and health issues related to potentially toxic elements and pathogens, with fewer studies on the beneficial effects. Studies on agronomic values have concentrated on nitrogen (N) and phosphorus (P) contributions to crop nutrition, with limited reference to the beneficial effects of other plant nutrients such as sulphur, magnesium and sodium, and additions of organic matter.

An extensive review of the international literature confirmed that biosolids applications can improve the physical, chemical and biological properties of the soil and crop production. However, only a few studies had been carried out at normal agronomic rates of application or under UK conditions" z). The field studies reported here provide comprehensive information on the beneficial effects of biosolids applications at normal agronomic rates under UK conditions.

ABSTRACT Research in the UK on the beneficial aspects of biosolids additions to land has primarily concentrated on nitrogen and phosphorus supph Biosolids have other beneficial effects on soil through the addition of organic matter and other plant nutrients such as sulphur; magnesium and sodium. This study evaluates the effects of biosolids additions on soil quality and fertility at seven established field experimental sites where biosolids have been applied for a t least four years. These addi- tions influenced several physical properties of the soil, increasing topsoil water-infiltration rates, plant-available water supply on a light sandy soil, soil porosity and bearing strength. There were also increases in the level of plant-available sulphuc magnesium, copper and boron. Liquid digested biosolids applications also increased the concentrations of major nutrients in grass.

Key words: Biosolids; crop qua#& soil feitilik soil quali&

*ADAS Gleadthorpe Research Centre, Meden Vale, Mansfield, UK. **Scottish Agricultural College, Auchincruive, Ayr, UK.

***WRc PIC, Henley Road, Medmenham, Bucks, UK. Current address: School of Water

****Severn Trent Watel; Sheldon, Birmingham, UK. Sciences, Cranfield University, Cranfield, Beds., UK.

MATERIALS AND METHODS Experimental Sites The project was undertaken at seven established field experimental sites throughout the UK where biosolids dressings had previously been applied for at least four years and could be compared with inorganic fertiliser control plots. The sites (Table 1) were representative of major agricultural soil types, under both arable cropping and grassland management.

The five sites in England and Wales had received biosolids and inorganic fertiliser P additions annually between the autumns of 1994 and 1996, supplying 60-90 kg/ha P per annum, with applications being made for a further two years (autumns of 1998 and 1999). At the two Scottish sites (Scottish Agricultural College and SAC), three rates of digested liquid biosolids (67, 135 and 270 m3/ha) had been applied annually between 1985 and 1995 and compared with a control receiving inorganic fertiliser and no sludge additions. The biosolids applications (Table 2) were above the minimum level reported in the scientific literature (10 t/ha dry solids or 5 t/ha organic matter) for detectable effects on soil physical properties" *I.

Table 1. Site locations, topsoil textures and cropping

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Table 2. Mean application rates at sites

Biosolids treatment England and Wafes (5 sites) Digested liquid Digested cake Thermally dried

Scotland (2 sites) Digested liquid

Fresh weight applied (m3 or t/ha

676 68 20

0 737 1485 2970

DS applied (t/ha)

11.5 13.8 18.3

0 24 48 96

N.B. OM =organic matter

Treatments The five sites in England and Wales had a randomised block design,

with three replicates of each treatment: (a) inorganic P fertiliser (control), (b) digested liquid (DL), (c) digested cake (DC), and (d) thermally dried (TD). The two Scottish sites had a randomised block design, with four replicates of the DL biosolids and inorganic fertiliser control treatments. The soils at both sites had been maintained a t pH 5.5 and 6.5. A pH of 5.5 was used for the physical-property measurements of the soil (4 treatments x 4 replicates = 16 plots) in this study, although the grass-quality assessments were made on samples from both pH values.

Assessments Physical-property assessments of the soil were made a t each site

using standard methodsi3' and included:

(i) Soil-water infiltration rate; (ii) Soil-moisture retention and available water capacity; (iii) Bulk density and porosity; (iv) Soil strength: (a) shear strength at 100 m m depth; and (b)

(v) Soil temperature a t 100 mm depth. penetration resistance at different depths; and

Representative topsoil samples were collected during autumn 1999 from each plot to a depth of 150 mm at the arable sites and 75 mm at the grassland sites for measurement of the following soil chemical properties('):

(i) Total organic matter (OM); (ii) Total nitrogen (N); (iii) Total sulphur (S) and extractable S concentrations; (iv) Total phosphorus (P), potassium (K), magnesium (Mg), sodium (Na),

calcium (Ca), cobalt (Co), selenium (Se), iodine (I) and boron (B); (v) Extractable P, K, Mg and Na, and water-soluble B; and (vi) EDTAextractable trace elements -zinc (Zn), copper (Cu) and nickel (Ni).

Analyses for total P, CA, K, Mg and Na were carried out on archived grass samples collected at first cut in 1993 at the two Scottish sites, using standard methodsi4'.

RESULTS AND DISCUSSION Soil Physical Properties Water-infiltration rate The water-infiltration rate determines the maximum rate a t which

OM (t/ha)

6.2 7.2 8.8

0 12 24 48

Total N (kg/ha) I Total P (kg/ha) I

863 577 61 1

0 1367 2734 5467

307 322 302

0 336 67 1 1342

rainfal l or irrigation water can be accepted by the soil surface without causing ponding (which could result in anaerobic conditions developing in the root zone), or surface runoff which might result in soil-water erosion.

At Boxworth and Bridgets (Table 11, al l the applications increased the soil-water infiltration rate compared with the inorganic fertiliser control, although these increases could not be confirmed statistically (p>0.05). Similarly, a t Watsonfoot and Garrionhaugh the long-term DL applications increased the soil-water infiltration rate by about 50 mm/h above the inorganic fertiliser control. These data indicate that repeated biosolids applications a t normal agronomic rates can increase topsoil water- infiltration rates, decreasing the potential for surface runoff and the susceptibility of soils to water erosion and associated sediment losses.

Available water capacity The moisture-retention characteristics of soils are controlled by a

number of physical properties which influence pore space distribution, particularly particle-size analysis (i.e. % sand, silt and clay), organic matter, stone content and bulk density. By measuring the soil-water content at a number of tensions, a moisture-retention curve can be determined to assess the pattern of water release from a soil and the plant-available water capacity.

The plant-available water capacity (AWC) of a soil is defined as:

(1) AWC = ev(O.05 bar) - 8v(15 bar)

where f3v is the volumetric water content a t a specified pressure step.

The AWC of a soil horizon or profile is the quantity of water held between the field capacity (0.05 bar) and permanent wil t ing point (15 bar), which i s assessed to be plant available. One of the most important benefits that farmers ascribe to the recycling of biosolids to land is an increase in plant-available water supply. Indeed, drought is a major l imi t ing factor for crop yields in lowland Britain, particularly on sandy textured soils i n low rainfall areas.

At Gleadthorpe, on a sandy textured and low organic matter soil, the repeated applications increased the topsoil AWC (18.1-18.8%) compared with the inorganic fertiliser control (17.6 %). The AWC increased (p4I.05) in relation to the biosolids organic matter loading rates (Fig. 1). A similar, but smaller effect, was also seen a t Rosema u nd.

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y = O 14X+ 175 D F P L O S P 188

18 4 i 176

17 4 I 0 2 4 6 8 10

Organic matter loading rate (ma)

Fig. 1. Relationship between AWC and organic matter loading rates a t ADAS Gleadthorpe

An increase in topsoil AWC can improve crop yields, particularly on low AWC sandy soils where vegetable crops are grown. For example, the yield response of potatoes (a high value crop) to applied irrigation water on sandy textured soils is 0.25 t/ha. mm. Where the topsoil AWC is increased by 1% in the top 300 m m (as measured a t Gleadthorpe), this would increase the soil-water supply by 3 m m - leading to an increase in yield of 0.75 t/ha. At current prices (€80/t), this would result in an increased crop output of €6O/ha. Similarly, the average yield response of carrots and cereals to irrigation water is 0.13 and 0.007 t/ha. mm, re~pectively'~'. These translate into crop-output value increases of about €36/ha and €2/ha a t current prices, €90/t and €70/t, respectively.

Soil bulk density and porosity Soil bulk density is directly related to total porosity, which is a

measure of the space available within the soil for gas and water movement, and for root development. Increases in bulk density impose the following stresses on plant root systems: (a) increased resistance to root penetration, (b l reduced air supply which might facilitate the build-up of toxic products and ethylene, (c) increased proportion of fine pores, which leads to an increased proportion of the total porosity being occupied by water at a given tension, and (d) reduced permeability increasing the risk of waterlogging. Under certain circumstances, permeability could be governed by the size and abundance of macropores such as cracks and earthworm channels.

The topsoil bulk density (0-50 mm) was measured a t al l the sites by determining the dry weight of a known volume of soil. Total porosity at the field-capacity moisture content (0.05 bar a t ADAS sites and 0.06 bar at SAC sites) was calculated from the bulk density and moisture- retention data, respectively:

Total porosity (T,) = 1 - (Bd/Pd) x 100 (2)

where Bd is the soil bulk density and Pd i s the estimated soil-particle density (2.65 g/cm')].

At most ADAS sites, there were indications that the biosolids applications had lowered bulk density and increased porosity, although these differences could not be confirmed stat ist ical ly (p>0.05). At Garrionhaugh (sandy soil), the topsoil bulk density was reduced (p<O.Ol) by 0.09 g/cm3 and porosity increased (p<O.OOl) by over 7% on the DL treatments compared with the inorganic fertiliser control.

Soil strength Soil strength can be defined as the resistance of a soil to fracture

by an applied shear stress or to deformation by a compressive force.

The strength of a soil varies systematically with changes in moisture content and bulk density, and measurement of soil strength provides a quant i ta t ive assessment of the degree of soil consolidation or compaction. Shear strength measurements quanti fy the internal resistance of a soil to external forces where two adjacent areas of soil move relative to each other. Shear strength controls (a) the bearing capacity of a soil, (b) its ability to provide traction and support for vehicles, and (c) i ts resistance to cultivation.

At the Pwllpeiran grassland site, the DL and TD treatments increased shear strength compared with the inorganic fertiliser control (p= 0.06). Similarly a t Bridgets, shear strength was increased on al l the biosolids treatments compared with the inorganic fertiliser control, although this could not be confirmed statistically.

The penetration resistance of a soil i s closely related to other strength measurements (e.g. shear strength), and is of most value in obtaining comparative data in contrasting situations, rather than absolute values of soil strength.

At Bridgets, Gleadthorpe and Pwllpeiran, there was evidence that the DL and DC applications had increased penetration resistance, although the differences could not be confirmed statistically at the individual sites (p>0.05). However, results from the cross-site statistical analysis showed that there were significant increases (p<0.05) in penetration resistance a t 100 m m depth on the DL treatment compared wi th the inorganic fertiliser control - indicating greater soil cohesion and increased bearing strength as a result of the biosolids organic matter additions.

At Garrionhaugh (sandy soil), t he long-term DL applications increased (p <0.05) penetration resistance a t 6 depths between 60 and 160 mm, particularly on the highest DL addition rates (135 and 270 m3/ha), which had consistently greater penetration resistances than the inorganic fertiliser control (Fig. 2). At Watsonfoot (clay soil), the highest DL application rate increased the penetration resistance at al l depths down to 140 mm, although these increases were not statistically significant (p>0.05).

5000 .. 4500 -. 4000 -_

- 3500 -. 30M3 -_ 8 2500 -.

2 2000 --

I 0 50 100 150 200 250 300

Depth (mm)

Fig. 2. Penetration resistance (kPa) a t successive depths (mm) at Garrionhaugh

Soil temperature Topsoil temperatures were recorded on one day each month over the

spring period (February to May) a t the ADAS sites. During May (and April a t Gleadthorpe), there was an indication that temperatures were lower on the biosolids treatments compared wi th the inorganic fertiliser control, being most noticeable on the DL treatment. The daily temperature measurements a t Boxworth indicated that th is effect only persisted for about three weeks from late April until early May. The temperature decreases might reflect the increased water-holding capacity of the topsoils from the biosolids organic matter additions.

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Table 3. Effects of biosolids applications on soil physical properties

Measurement- Water-infiltration rate Available water capacity Bulk density

Total porosity

Strength-shear vane

Strength-penetrometer

Temperature (April - May)

Boxworth +NS NS .LNS (DL + DC) +NS (DL + DC) NS

NS

J/NS (DL + TD)

Bridgets +NS NS .LNS (DL + DC) +NS

+NS

+NS (DL + DC) .LNS (DL + DC)

(DC) NS

!:l 1 N:" (DL + DC) (DL + DC)

4 N S (DL + TD)

Notes, Nd =Not determined

NS = Not significant * =Signif icant a t 5% level (pc0.05)

=Signif icant at 1% level (pc0.01)

=Signif icant a t 0.1% level (pcO.001) = Biosolids applications increased value

= Biosolids applications decreased value =Treatments where effects were measured, otherwise all treatments affected.

i*

* * *

+ 3. ( )

Soil Chemical Properties Organic matter i s one of the most important components of soils,

inf luencing soil structural development, aggregate stability, moisture supply, and nutrient turnover and availability. Biosolids appl ications increased the topsoil organic-matter contents on a l l treatments a t Garrionhaugh, Pwllpeiran, Bridgets, Gleadthorpe and Watsonfoot (range 8-23%), compared wi th the inorganic fert i l iser controls.

The value of biosolids as a source of major p lant nutr ients was confirmed by increases i n soil to ta l N on most of the treatments, which in the long term w i l l increase crop avai lable N supply through the mineral isat ion of soil organic N reserves. Also, there were increases (p <0.05) i n soil-extractable phosphorus levels at the SAC sites and on a l l the biosolids treatments a t Pwllpeiran, compared with the inorganic fert i l iser controls.

There were increases in soil total sulphur on a l l the biosolids treatments at Pwllpeiran and Bridgets, and a t Watsonfoot and Garrionhaugh where the DL applications a t the highest rate increased soil to ta l sulphur concentrations by 90 and 63 mg/kg respectively (Fig. 3). In almost a l l the biosolids treatments, plant-avai lable sulphur concentrations were increased compared wi th the inorganic fertiliser controls. The presence of sulphur wi l l be part icularly important to crops which are a t r isk of deficiency, e.g. c u t grass, oilseed rape and cereals grown on l ight textured sandy or shallow soils, in areas of low atmospheric deposition. Biosolids addit ions should enable farmers to reduce or replace the need for inorganic sulphur fertiliser additions.

Soil-extractable magnesium concentrations were increased by the addit ions a t three sites (Bridgets, Pwllpeiran and Watsonfoot), indicating tha t biosolids can be a useful source where susceptible crops (e.g. potatoes or sugar beet) are grown, or to mainta in adequate herbage levels i n catt le diets.

Rosemaund NS TNS 4 (DL + TD) + (DL + TD) +NS (DC + TD) NS

J.NS

7w c_

Watsonfoot +NS NS J/NS

4"s

NS

+NS

nd

Bridgets Fwllpeiran Watsonfor Site

Garrionhaugh + NS NS 4* *

+* *

nd

+*

nd

Inorganic fettiliser control

DL or 136 m'hlhalyr DL

DC or 270 m 3ihaiyr DL

0 TD

Garrionhaugh

Fig. 3. Soil total sulphur concentrations

Biosolids also contain a number of minor nutr ients and trace elements (Table 4). About 5% of t h e cereal-growing area in England and Wales and 30% in Scotland has been estimated to be deficient i n copper, predominantly on sandy, shal low chalk and peaty soils'6'. Soil-extractable copper (Cu) levels were increased by biosolids addit ion to the shal low soil over chalk a t Bridgets.

Boron can be important to the growth of root and combinable crops (e.g. sugar beet, oi lseed rape). Extractable boron concentrations were increased on the DL and DC treatments a t a l l the ADAS sites and a t Watsonfoot. The TD biosolids d id not increase soil- extractable boron concentrations a t any of the ADAS sites - reflect ing the lower content compared wi th the DL or DC products. Soil concentrations of cobalt, selenium and iodine were also increased a t some sites fol lowing the DL and DC applications, ind icat ing that these products could provide a benefi t to livestock grazing, and as a source of addit ional selenium in UK diets.

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Table 4. Effects of biosolids applications on soil chemical properties

Watsonfoot

Measurement Organic matter Total nitrogen Extractable phosphorus Total sulphur Extractable sulphur Extractable calcium Extractable magnesium Extractable copper Extractable boron Extractable cobalt Extractable selenium Extractable iodine

~-

Garrionhaugh

Boxworth NS +NS +NS NS NS NS NS +* +NS NS NS NS

+ * * *

Notes: NS = Not significant

* * * * *

nd = Not determined

= Significant at 5% level (p<0.05) = Significant at 1% level ( ~ ~ 0 . 0 1 ) =Significant at 0.1% level (p<O.OOl)

+ * * *

9 \L

= Biosolids applications increased value = Biosolids applications decreased value.

Bridgets + NS +NS NS +NS +NS NS NS +* NS NS NS +*

Gleadthorpe +"S NS NS J/NS +NS NS NS +NS +NS ND +* NS

S'elected mkasurements on the effects of the DL applications on crop quality were made on archived grass samples taken in 1993 from the two Scottish sites. The long-term DL applications at Watsonfoot increased ( ~ ~ 0 . 0 5 ) the grass concentrations of P (mean 1.1 g/kg), Ca (mean 1.3 g/kg), Mg (mean 0.75 g/kg) and Na (mean 0.3 g/kg). Similarly at Garrionhaugh, the DL applications increased (p<0.05) grass concentrations of P (mean 0.8 g/kg), Ca (mean 2.3 g/kg), Mg (mean 0.75 g/kg) and Na (mean 1.85 g/kg). The DL applications increased Mg levels in herbage from 1.5 g/kg to 2.2 g/kg, which is above the dietary requirement for grazing animals (2.0 g/kg)(''. Sodium concentrations on all the treatments were above the minimum dietary requirement of 1.5 g/kg and, on the biosolids, treatments were closer to the 6 glkg figure suggested as a requirement for palatability's'. A summary of the effects of biosolids on crop quality is provided in Table 5. The measurements show that the repeated use of biosolids has produced grass with a higher nutritional quality at both sites, compared with the inorganic fertiliser treatments.

Table 5. Summaiy of effects of biosolids applications on crop quality

Measurement Phosphorus Calcium Magnesium Sodium

+ * * * + * * * +*

+* * + * * * + * * *

Notes:

* * * * *

+

* =Significant at 5% level (p<0.05) =Significant at 1% level (p i0 .01)

= Significant at 0.1% level ( ~ ~ 0 . 0 0 1 ) = Biosolids applications increased value

Pwllpeiran +NS +NS +** + * +* +* + * + * * * +* NS NS nd

Rosemaund 1 Watsonfoot NS 1 +NS NS NS NS +* NS J/NS + NS NS NS NS +NS

1.

2.

3.

4.

5.

6 .

+NS +* +* +NS NS +NS +* +NS +NS + * * * +NS

CONCLUSIONS

Garrion haugh + * +* +*** +* +NS NS NS +* +NS +NS +* +NS

At the five ADAS sites in England and Wales, the three biosolids products added 10-19 t/ha of dry solids (5-9 t/ha organic matter), and at the two Scottish sites the digested liquid biosolids added up to 96 t/ha dry solids (48 t l h a organic matter). Biosolids applications increased the topsoil organic matter at five sites (range 8-23%) compared with inorganic fertiliser controls. There was a trend towards higher water-infiltration rates on all the biosolids treatments at four of the sites, decreasing the potential for surface runoff and susceptibility of the soils to water erosion and associated sediment losses. On the lightest textured soil, topsoil available-water capacity was increased (mean 5% above the control treatment) on all the biosolids treatments, increasing in order with the organic matter addition. If potatoes and carrots were grown, the improved water supply was estimated to translate into a yield increase of 0.75 t/ha and 0.4 t/ha, which is worth about €6O/ha and €36/ha in increased crop output value, respectively, At a number of sites there were indications that the biosolids additions had increased soil porosity and strength, improving the potential for air and water movement through the topsoil. The greater soil-bearing strength would lead to improved trafficability for vehicles and livestock. On almost all the biosolids treatments, plant-available sulphur concentrations were increased; soil-extracta ble magnesium concentrations at three of the sites increased; extractable copper levels on a low copper status shallow soil over chalk increased; and extractable boron concentrations were increased on the digested liquid and cake treatments at most sites. Liquid digested biosolids applications increased grass concentrations of phosphorus, calcium, magnesium and sodium compared with the inorganic fertiliser controls, demonstrating that

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the repeated use of biosolids can produce grass wi th enhanced nutr i t iona I quality.

ACKNOWLEDGEMENTS The authors wish to thank the United Kingdom Water Industry Research for funding the work under UKWIR Project SL06/1.

REFERENCES (1) CARTMELL, E., DAVIS, R. D., GENDEBIEN, A,, HALL, J. AND RIDDELL

BLACK, D. Beneficial Effects of Biosolids on Soil Quality and Fertility - Literature Review. UKWR Repoi? 99/SU08/I1. 1999.

(2) GENDEBIEN, A. H., CARTMELL, E., CHAMBERS, B. J . , NICHOLSON, F. A. AND AITKEN, M. N. Beneficial effects of biosolids on soil quality and fertility. In: Agriculture and Waste - Management for a Sustainable Future. Scottish Agricultural College, p149. 2000.

(3) ANON. Techniques for Measuring Soil Physical Properties. MAFF Reference Book 441. HMSO, London. 1982.

(4) ANON. The Analysis of Agricultural Materials. MAW Reference Book 427. HMSO, London. 1986.

(5) BAILEY, R. lrrigated Crops and Their Management. Farming Press, Ipswich. 1990.

(6) CHAMBERS, A. G., SINCLAIR, A. H. AND CARVER, M. Nutrients Other Than Nitrogen, Phosphorus and Potassium (NPK) for Cereals. Home Grown Cereals Authority Research Review No. 41, July 1999.

(7) AGRICULTURAL DEVELOPMENT AND ADVISORY SERVICE. Hypomagnesaemia in Cattle and Sheep. p499. 1998.

(8) SCOTTISH AGRICULTURAL COLLEGE. Sodium in Soils, Crops and Animals. Technical Note - Fertiliser Series 10. 23. The Scottish Agricultural College, Edinburgh. 1993.

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