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Long-term straw management effects on yields of sequential wheat (Triticum aestivum L.) crops in cla


Soil & Tillage Research 71 (2003) 59–69

Long-term straw management effects on yields of sequential wheat (Triticum aestivum L.) crops in clay and silty clay loam soils in England
D.B. Turley a,? , M.C. Phillips a , P. Johnson b , A.E. Jones b , B.J. Chambers c
a c

ADAS High Mowthorpe, Duggleby, Malton, North Yorkshire YO17 8BP, UK b ADAS Drayton, Stratford-upon-Avon, Warwickshire CV37 9RQ, UK ADAS Gleadthorpe, Meden Vale, Mans?eld, Nottinghamshire NG20 9PF, UK

Received 16 May 2001; received in revised form 20 November 2002; accepted 30 November 2002

Abstract The incorporation of chopped wheat (Triticum aestivum L.) straw into soil by tine cultivation (non-soil inversion) or ploughing was compared with burning straw followed by tine cultivation at six sites in England over a period of 11 years. Three sites had clay soils and three silty clay loam soils. Effects of straw management on weed incidence, take-all (Gaeumannomyces graminis var. tritici) infection and grain yield of following wheat crops and occasional break crops were studied. Soil mineral nitrogen and organic matter contents were measured at the end of the study. Incorporating straw by tines rather than burning reduced mean yield at all but one site. The yield reduction from tine incorporation ranged from 5 to 8% on clay soils and 3–18% on silty clay loam soils. Ploughing straw into soil only had an occasional adverse effect on yield of following crops. Much of the yield penalty associated with tine incorporation of straw was attributed to weed competition by Bromus spp. Dif?culties in preparing a good seedbed, resulting in variable plant emergence, was the other main cause of lower yields with tine incorporation and in situations where plough incorporation reduced yields compared to burning straw. Method of straw disposal had no consistent effect on take-all infection. The effects of straw incorporation on soil mineral nitrogen and organic matter contents were small and inconsistent. There was no consistent effect of straw management practice on yield response to additional autumn application of nitrogen fertiliser. These results demonstrate that on those soils where ploughing is preferred, it is a suitable option for disposing of straw. Where non-ploughing methods have traditionally been used after straw burning they can still be employed with success, but occasional ploughing or planting of suitable break crops may be required to control grass weeds. ? 2003 Elsevier Science B.V. All rights reserved.
Keywords: Straw incorporation; Weeds; Take-all; Nitrogen; Organic matter; Tillage

1. Introduction During the 1970s and 1980s, declining demand for cereal straw in the UK and increased production of
? Corresponding author. Present address: 25 Broughton Way, Osbaldwick, Yorkshire Y017 8BP, UK. E-mail address: turley-dc@supanet.com (D.B. Turley).

cereals resulted in a surplus of straw, the majority being burnt in the ?eld. By 1984, 6 million tonnes of straw was being burnt, representing 60% of the wheat growing area (Anon., 1992). This highly visible activity occasionally caused signi?cant damage to hedges, trees and property, and caused public outcry each year. A report by The Royal Commission on Environmental Pollution (1984) recommended a ban on straw burning

0167-1987/03/$ – see front matter ? 2003 Elsevier Science B.V. All rights reserved. doi:10.1016/S0167-1987(03)00018-7

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and this was introduced from autumn 1992. By 1992 the amount of straw burnt had reduced to about 2 million tonnes. Previous work had demonstrated the potential for buried straw to affect the growth and yield of following wheat crops (Oliphant, 1982). With changes in farming practices and a much wider range of soil cultivation equipment available, a new study was designed jointly by ADAS (formerly known as the Agricultural Development and Advisory Service) and the former Agriculture and Food Research Council (AFRC). This started in autumn 1983 and tested, on large plots, a range of options appropriate to different soil types and sites. This paper reports some of the results obtained during a 11-year period at six sites. The experiment investigated method of incorporating or burning straw on crop establishment, grain yield, weed and disease incidence, and soil mineral nitrogen and organic matter contents.

the soils at Bridgets and High Mowthorpe are shallow (30–50 cm deep) and overlay chalk, while the soil at Terrington is a deep marine silt clay loam. 2.2. Cropping The intention was to grow winter wheat continuously throughout the period of the experiment. This had to be modi?ed by including break crops in order to control grass weeds, which could not be adequately controlled by chemical means in wheat. Therefore at several sites oilseed rape (Brassica napus L.), peas (Pisum sativum L.), linseed (Linum usitatissimum L.) or sugar beet (Beta saccharifera) breaks were introduced into the cropping sequence. Table 2 gives details of the crops grown in each harvest year. The crop cultivars grown varied among sites and years, but were typical of commercial practice. The whole trial area at Rochford had to be ploughed after the 1988 harvest and treatments were re-established. These later data are not reported here. 2.3. Treatments and design

2. Materials and methods 2.1. Sites Six sites across England, ADAS Boxworth in Cambridgeshire, ADAS Bridgets in Hampshire, ADAS Drayton in Warwickshire, ADAS High Mowthorpe in North Yorkshire, ADAS Terrington in Norfolk and a farm at Rochford in Essex were selected to represent the main cereal growing areas of England. Descriptions of the soil type and particle size distribution for each site are given in Table 1. The sites divide into two broad soil types—clays and silty clay loams. While the textural descriptions of the soils are similar,
Table 1 Description of soils at experiment sitesa Site Soil texture

The number of cultivation treatments tested varied from 4 to 12 among sites. Three core treatments were included at each site in each year studied: (1) tine/disc cultivation to 15 cm on chopped straw, (2) ploughing to 20 cm on chopped straw and (3) straw burning followed by tine/disc cultivation to 10 cm. Only the results of these treatments are reported here. In these treatments, off-set discs and spring-tine cultivators were used. Ploughing was by reversible mouldboard plough, followed by secondary cultivations as necessary.

UK soil series

Soil particles (%) Sand Silt 31 28 40 56 63 60 Clay 45 52 56 32 23 29

1. 2. 3. 4. 5. 6.

Boxworth Drayton Rochford Bridgets High Mowthorpe Terrington

Clay Clay Clay loam Calcareous silty clay loam Stony calcareous silty clay loam Silty clay loam

Hanslope Evesham Wallasea Andover Wold Agney

24 20 4 12 14 11

a Size groupings were clay <2 m, silt 2–63 m and sand 63–2000 m. FAO soil descriptions by site—(1) and (2) ?ne textured Calcaric Gleysol, (3) ?ne textured Eutric Fluvisol, (4) and (5) medium textured Calcaric Regosol, and (6) medium textured Calcaric Fluvisol.

D.B. Turley et al. / Soil & Tillage Research 71 (2003) 59–69 Table 2 Crops grown at each site over harvest years 1984–1994a Site Harvest year 1984 Boxworth Drayton Rochford Bridgets High Mowthorpe Terrington ww ww ww ww ww ww 1985 ww ww ww ww ww ww 1986 ww ww ww ww ww ww 1987 ww ww ww ww ww ww 1988 osr ww peas ww ww wb 1989 ww ww osr ww ww osr 1990 ww sw ww ww ww ww 1991 osr ww ww sw ww ww 1992 ww ww osr lin ww beet 1993 ww ww ww trit osr sb

61

1994 lin ww – ww ww ww

a ww: winter wheat; sw: spring wheat; wb: winter barley; sb: spring barley; trit: triticale (winter); osr: oilseed rape; lin: linseed; beet: sugar beet; peas: spring peas.

The treatments were applied to main plots that varied in size from 486 to 1728 m2 among sites. The aim was to have large enough plots to operate machinery at speeds used under commercial conditions. Nitrogen (40 kg ha?1 ) was applied in the autumn to sub-plots at all sites except Bridgets. This nitrogen was deemed to be in excess of that required to optimise yield. Spring nitrogen application rates varied across sites and season, but were designed to optimise yield, taking account of soil type, previous cropping and anticipated yield. There were three replicates of each treatment on the clay sites and four replicates on the silty clay loam sites. 2.4. Management Straw was burnt in the swath as soon as possible after harvest and cultivations were carried out as soon as possible. Where straw was incorporated, straw was chopped and spread by combine-mounted straw choppers. The cultivation operations were then carried out promptly after harvest to allow the chopped straw maximum time in contact with soil before sowing wheat. Soil conditions determined the number and direction of passes required each year. For the non-inversion cultivation treatments this was usually two passes of spring-tines followed by one or two passes of disc cultivators. A ?nal seedbed was prepared before drilling in October. Sites were treated as a whole for drilling date and all fertiliser and pesticide applications. Crops were managed according to best local practice in respect of inputs to minimise the incidence of weeds, pests and diseases and produce optimum yields.

2.5. Assessments Assessments and measurements were made of the success of the cultivation treatments at incorporating straw and their effects on subsequent plant growth. Yield of grain was measured by one to three plot-combine cuts per plot each of between 55 and 69 m2 depending on the width of the combine cut at each site. Grain samples were taken for oven determination of moisture content (40 h at 100 ? C). Soil samples were collected at all sites in July 1990 and November 1994. Soil mineral nitrogen was determined by KCl extraction of samples taken from 6 points per plot at four depths (0–15, 15–30, 30–60 and 60–90 cm). Organic matter was determined by standard potassium dichromate digest method from soil samples bulked from 25 points per plot, to cultivation depth (0–15 cm for tines and 0–20 cm for ploughing). Crops were monitored regularly for weeds, pests and diseases, and levels were formally assessed where incidence was deemed likely to in?uence yield potential and/or differences between treatments were observed. Weed numbers were counted in 10 randomly chosen 0.1 m2 quadrats per plot and disease assessments made on 25 plants lifted at random per plot in spring. Infection of roots by take-all (Gaeumannomyces graminis var. tritici) was assessed, recording the percentage of plants affected by take-all. Data were subjected to analysis of variance each year. Yields were pooled over years for each site to demonstrate the long-term effects of the treatments. Standard errors for treatment means are given together

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with the associated least signi?cant difference (LSD) where analysis of variance indicated differences were statistically signi?cant. 3. Results 3.1. Grain yield on clay soils 3.1.1. Boxworth Mean yield across eight seasons was 5% lower with chop/tine than with burn/tine and chop/plough. Yield varied substantially from year to year, but to a much lesser extent among treatments. Dry soil conditions in autumn 1983 made incorporating straw dif?cult, particularly by tines, resulting in poorer plant establishment where straw was incorporated and yields were reduced in all cases compared to where straw was burnt. By 1987 meadow brome (Bromus commutatus) was well established on the site. Ploughing straw and burning both effectively controlled brome but yields were still low. Oilseed rape was sown in autumn 1987 to allow more effective herbicide control measures. Oilseed rape was sown again in autumn 1990 to control grass weeds. However, herbicide residues and pigeon damage affected both this crop and the following wheat so data for harvests 1991 and 1992 were not presented. The ?nal wheat crop in 1993 again suffered from poor plant establishment on chop/tine, and the recurring presence of meadow brome, and also blackgrass (Alopecurus myosuroides) reduced yield (Table 3). 3.1.2. Drayton Across 11 years chop/tine yielded almost 8% less than burn/tine and chop/plough. Grain yield differed little in the ?rst 5 years, with the relative ranking varying from season to season. By 1989 sterile brome (Bromus sterilis) infestation on the chop/tine treatment was serious, though the effect on yield was not statistically signi?cant. Both ploughing and burning kept populations of sterile brome under control on this site. Sterile brome continued to be abundant on the chop/tine treatment from 1992 until 1994. The effect of the weed infestation on grain yield became progressively worse resulting in a signi?cant yield loss of up to 2.46 t ha?1 in 1994 (Table 3).

3.1.3. Rochford There was no consistent or signi?cant effect of straw disposal method on grain yield during 3 years at Rochford (Table 3). 3.2. Grain yield on shallow silty clay loam soils 3.2.1. Bridgets Incorporating straw with tine cultivation resulted in an average 18% yield reduction compared with burn/tine. Ploughing straw had no adverse effect on mean yield compared with burn/tine. For the ?rst 3 years, poor seedbeds on the chop/tine treatment, due to dif?culties in incorporating all the straw into soil, resulted in poor establishment of the crop. There was also a build up in volunteer wheat and sterile brome plants. This resulted in severe lodging and brome infestation that signi?cantly reduced grain yield. The site was abandoned in autumn 1990 in an attempt to reduce the level of sterile brome and spring break crops were sown until autumn 1993. In 1994, plant population in the chop/tine treatment was only 25% of that in other treatments. The autumn was wet and the loss of plants was possibly due to slug grazing. A high population of sterile brome was also recorded. In this situation, yield was signi?cantly reduced by tine incorporation of straw (Table 4). 3.2.2. High Mowthorpe Problems with straw incorporation by tines were encountered where the 8-year mean yield reduction was 13% compared with burning straw. Incorporating straw by ploughing was generally satisfactory, though some negative effects were recorded in 1986 and 1993. Yield reductions with chop/tine in the ?rst 4 years were attributed to poorer seedbeds, with straw in the surface layer affecting soil consolidation. A cultivation pan that formed under the non-plough treatments was broken after the 1989 harvest, and this may have contributed to the tine treatments out-yielding chop/plough in 1990, though moisture loss may also have been a factor in this dry autumn. In 1992, sterile brome and volunteer infestation led to lodging in the tine incorporation treatment. Oilseed rape was sown in autumn 1992. Cleavers (Galium aparine) were not well controlled in the oilseed crop and were most abundant on the chop/tine treatment, resulting in signi?cant yield loss (Table 4).

D.B. Turley et al. / Soil & Tillage Research 71 (2003) 59–69

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Table 3 Yield of grain (t ha?1 at 85% DM for cereals and peas, 91% DM for oilseed rape) for three cultivation treatments at the three clay soil sitesa Year Treatment Chop/tine Boxworth 1984 1985 1986 1987 1988b (osr) 1989 1990 1993 Mean Drayton 1984 1985 1986 1987 1988 1989 1990b (Sp.W) 1991 1992 1993 1994 Mean Rochford 1985 1986 1987 1988b (peas) Mean
a b

S.E. Chop/plough 10.16 7.42 7.29 5.87 3.33 8.29 7.45 7.43 7.70 7.75 7.69 8.37 7.63 7.50 5.68 4.09 7.43 7.06 9.51 8.12 7.35 5.90 6.80 5.60 4.85 6.10 Burn/tine 10.81 7.32 7.69 5.62 3.27 8.04 7.96 7.43 7.84 8.22 7.20 8.54 7.24 7.54 6.48 4.15 7.24 6.99 8.93 8.53 7.37 5.38 6.94 6.12 4.65 6.15 0.149 0.127 0.267 0.191 0.286 0.215 0.187 0.288 0.080 0.272 0.384 0.170 0.071 0.134 0.399 0.121 0.176 0.237 0.166 0.271 0.072 0.105 0.283 0.178 0.050 0.117

P

LSD0.05

9.89 6.92 7.36 5.27 3.42 8.39 7.45 6.77 7.43 8.21 7.98 8.09 7.47 7.37 4.69 4.19 6.71 6.64 7.42 6.07 6.80 5.61 6.42 6.32 4.82 6.12

<0.05 ns ns ns ns ns ns ns <0.01 ns ns ns <0.05 ns ns ns ns ns <0.01 <0.01 <0.001 ns ns ns ns ns

0.587

0.230

0.276

0.653 1.063 0.207

osr: oilseed rape; Sp.W: spring wheat. Excluded from mean.

3.2.3. Terrington Compared to straw burning, a mean yield reduction of 3% was observed with chop/tine, mainly due to effects on crops grown in 1984 and 1994. Incorporation of straw generally presented no dif?culties and plant establishment was always good across all treatments. Slug activity resulting in loss of plants was noted in 1986, 1987 and 1988, but this did not affect yields adversely. Oilseed rape was sown in autumn 1988 to combat the build up of blackgrass. No dif?culties were encountered establishing wheat after incorporating oilseed rape straw. Burning straw was replaced by baling in autumn 1991. Sugar beet was sown the following spring and the proportion of plants emerging

was found to be signi?cantly higher where the straw was baled. However, thinning was still necessary on all treatments to achieve the desired plant population. There was no signi?cant treatment effect on yield or sugar content of roots. For the ?nal wheat crop following spring barley, burning was again replaced by baling straw. Tine incorporation of straw had a small negative effect on grain yield (Table 4). 3.3. Grain yield with autumn applied nitrogen Nitrogen at 40 kg ha?1 applied in autumn was tested in 32 site years. On two occasions it resulted in small but signi?cant (P < 0.05) increases in yield of the

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Table 4 Yield of grain (t ha?1 at 85% DM cereals, 91% DM oilseed rape) or clean beet/sugar (t ha?1 ) (Terrington 1992), for three cultivation treatments at the silty clay loam sitesa Year Treatment Chop/tine Bridgets 1986 1987 1988 1991 (Sp.W) 1993 (trit) 1994 Mean High Mowthorpe 1986 1987 1988 1989 1990 1991 1992 1993b (osr) 1994 Mean Terrington 1984 1985 1986 1987 1988 (W.bar) 1989b (osr) 1990 1991 1992b (SB-sugar) 1992b (SB-roots) 1994 Mean
a b

S.E. Chop/plough 7.37 5.82 6.68 4.42 5.61 8.24 6.36 5.98 8.61 8.07 5.56 7.20 8.47 7.25 2.43 9.28 7.55 10.57 8.86 9.83 8.74 7.00 3.30 10.28 9.16 11.73 66.47 9.95 9.30 Burn/tine 6.45 6.15 6.51 4.25 5.38 8.07 6.13 6.89 8.63 8.20 6.19 7.61 8.92 7.33 3.04 9.43 7.90 10.66 8.71 10.04 8.63 7.07 3.48 10.43 8.93 12.25 68.18 10.13 9.32 0.350 0.423 0.295 0.228 0.108 0.219 0.118 0.110 0.181 0.171 0.307 0.123 0.155 0.451 0.161 0.247 0.086 0.148 0.265 0.155 0.180 0.137 0.351 0.332 0.043 0.146 1.531 0.160 0.069

P

LSD0.05

4.20 4.91 5.16 4.29 5.42 6.16 5.03 5.19 7.86 6.95 4.62 7.86 7.86 5.21 1.94 9.33 6.86 9.63 8.51 9.98 8.72 7.22 3.78 9.90 9.01 11.71 66.57 9.43 9.05

<0.01 ns <0.05 ns ns <0.001 <0.001 <0.001 <0.05 <0.05 <0.05 <0.05 <0.01 <0.05 <0.05 ns <0.001 <0.01 ns ns ns ns ns ns <0.05 ns ns <0.05 <0.05

1.171 1.020

0.759 0.337 0.382 0.626 0.591 1.064 0.427 0.535 1.561 0.559 0.247 0.511

0.149

0.552 0.197

Sp.W: spring wheat; trit: triticale; osr: oilseed rape; W.bar: winter barley; SB: sugar beet. Excluded from mean.

chop/tine treatment. These occurred in the ?rst year of the experiment at Terrington, and in 1989 at High Mowthorpe. In all other comparisons there was no effect. Lack of response to autumn applied nitrogen where tested was therefore consistent. 3.4. Weed populations 3.4.1. Clay soils At Boxworth, meadow brome was present in low numbers on the trial site in the early years of the

experiment. By 1986 the weed was more abundant (Table 5). In most cases, chop/tine had higher levels of brome grasses than burn/tine and lowest populations were in chop/plough. However, the high level of variability typically associated with assessment of weed populations meant none of the effects were statistically signi?cant. Blackgrass appeared on the site in 1993 and populations were highest where straw was burnt (Table 5). Ploughing was an effective way of controlling both grass weeds in all years.

D.B. Turley et al. / Soil & Tillage Research 71 (2003) 59–69 Table 5 Grass weed populations by species at each site (plants/m2 or panicles/m2 ) Site/year Species Treatment Chop/tine Boxworth 1986 1987 1990 1993 (plants/m2 ) B. B. B. B. B. A. B. B. B. B. B. commutatus commutatus commutatus commutatus sterilis myosuroides sterilis sterilis sterilis sterilis sterilis 4.7 98.8 29.0 97.1 38.7 23.4 192.0 21.7 45.2 100.6 96.2 0.0 0.2 0.0 6.8 0.0 0.0 42.0 3.6 0.3 0.5 0.5 2.4 22.6 83.0 16.8 3.2 61.3 27.0 0.2 0.2 1.0 0.9 0.7 1.8 25.10 174.34 – 34.32 11.56 8.75 52.75 5.35 6.10 11.50 9.09 0.315 10.55 ns ns – ns ns <0.05 <0.05 <0.05 <0.05 <0.001 <0.001 ns <0.01 Chop/plough Burn/tine S.E. P

65

LSD0.05

25.53 172.00 20.65 19.67 34.89 27.57

Drayton 1989 1991 1992 1993 1994

(panicles/m2 )

Bridgets (plant numbers/m2 (1993) and panicles/m2 (1994)) 1993 B. sterilis 1.5 0.0 1994 B. sterilis 71.2 0.0

33.75

At Drayton a similar build up of grass was experienced with sterile brome (Table 5). High populations built-up by 1987 and treatment differences were observed in following years. Panicle populations were highest in chop/tine. Burning and ploughing were equally effective at reducing brome populations at Drayton. Grass weeds were adequately controlled at the Rochford site. 3.4.2. Silty clay loam soils At Bridgets, sterile brome was abundant with chop/tine treatment from the start of the experiment and caused the abandonment of the site in 1989, as the infestation was the overriding treatment effect. Data for 1994 shows how quickly re-infestation occurred when straw was incorporated by tine cultivation (Table 5). No formal record of grass weed populations were made at High Mowthorpe, but build-up of sterile brome with chop/tine and to a lesser extent with burn/tine treatments was ?rst noted in 1992. Blackgrass was the main grass weed problem at Terrington and non-cereal break crops were grown in 1989 and 1992 to prevent weed build-up. In subsequent years good control of blackgrass was achieved and weeds were not a problem in any treatment.

3.5. Take-all infection Wheat plants in spring (April/May) from 1987 to 1992 were sampled at High Mowthorpe to assess take-all (G. graminis var. tritici) infection of roots. Take-all levels were low, except in 1991. The level of infection varied among years but in all cases was not signi?cantly affected by straw disposal treatment. Take-all was not recorded regularly at Terrington, but in 1984 there was a suggestion that higher plant infection with chop/tine (57% plants infected) compared chop/plough and burn/tine (27–33% infected) may have contributed to a yield reduction that year. Take-all infection was assessed at Boxworth in the early years of the experiment. Levels of infection were generally low and the proportion of infected plants was unaffected by treatment. However, in 1990, infection levels were higher where straw was shallowly incorporated (27% plants infected) rather than burnt (15% plants infected). Take-all was not observed to be a limiting factor on grain yield in any season. 3.6. Soil organic matter and mineral nitrogen Soil mineral nitrogen (NO3 -N and NH4 -N) was determined on four sites in November 1994 (Table 6). Similar measurements were made at all sites in July

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Table 6 Soil mineral nitrogen content (kg ha?1 N) (NO3 -N plus NH4 -N) in 0–15 and 0–90 cm soil layer in November 1994 Site Soil horizon 0–15 cm Boxworth Chop/tine Plough Burn/tine S.E. Drayton Chop/tine Plough Burn/tine S.E. Bridgets Chop/tine Plough Burn/tine S.E. Mowthorpe Chop/tine Plough Burn/tine S.E. 14.8 15.2 14.1 1.39 (ns) 33.5 43.6 26.4 5.33 (ns) 20.7 21.2 31.9 3.14 (P < 0.05) 55.2 45.0 32.7 5.45 (P < 0.05) 0–90 cm 82.8 83.7 66.4 6.77 (ns) 174.5 141.2 110.1 9.46 (P < 0.05) 95.2 89.9 93.6 6.24 (ns) 147.6 135.8 154.0 8.15 (ns)

worth and Drayton. Drayton was the only site where there was signi?cantly more nitrogen in the 0–90 cm soil pro?le following incorporation of straw. Soil organic matter in 1994 are shown in Table 7. Estimates for 1990 are in Rule et al. (1990). Eleven years of incorporating straw did not produce a measurable increase of organic matter in the cultivated layer at any of the sites. The slightly lower ?gures for ploughing compared with tine incorporation may be due to dilution with soil at greater depths and greater mineralisation of organic matter. There was generally either little change in organic matter content between 1990 and 1994 or organic matter levels declined. The decline in soil organic matter was most consistent with chop/plough (observed at all sites except High Mowthorpe) and ranged from 0.27 to 0.47%. This was probably due to stimulation of organic matter mineralisation by the increased level of soil disturbance. At the Boxworth and Terrington sites, soil organic matter levels also declined with tine cultivation (by between 0.6 and 0.8%), irrespective of whether straw was burnt or incorporated. 4. Discussion

1990 and reported in Rule et al. (1990). There was wide variation among the sites in the total amount of soil mineral nitrogen and at most sites differences among treatments were not signi?cant. Where differences did occur they were most noticeable in the upper 0–15 cm layer, so only data for this layer and the whole pro?le (0–90 cm) are presented. Chop/tine resulted in the highest levels of mineral nitrogen in the topsoil layer at High Mowthorpe, while at Bridgets the highest level was after burning. There were no signi?cant differences in mineral N at BoxTable 7 Soil organic matter (%) in the cultivated layer, August 1994 Site Treatment Chop/tine Boxworth Drayton Bridgets High Mowthorpe Terrington 3.37 4.93 4.40 4.20 2.35 Chop/plough 3.03 4.43 4.28 4.05 2.35

Prior to the ban on burning straw in ?elds in the UK, burning was considered crucial to the success of popular non-ploughing cultivation for growing cereal crops on heavier soils (Harper and Lynch, 1981; Oliphant, 1982). Concern was based on the potential of decomposing cereal straws to produce a phytotoxin under anaerobic conditions that could stunt or kill cereal seedlings. These effects were most marked when the seed was direct drilled into chopped straw. In practice, damage was only seen occasionally in the ?eld in wet autumns. In this series of experiments, at none

S.E. Burn/tine 3.27 5.07 4.65 4.00 2.20 0.139 0.160 0.174 0.091 0.064

P

ns ns ns ns ns

D.B. Turley et al. / Soil & Tillage Research 71 (2003) 59–69

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of the sites during 11 years, nor at other long-term sites (Prew et al., 1995), were phytotoxic effects seen following the surface incorporation of straw. Effects of different soil types on crop establishment after straw incorporation were noted. Ploughing clay soils in dry conditions sometimes led to dif?culty in preparing a seedbed. Under these conditions tine cultivation was more appropriate. At High Mowthorpe and Bridgets, poorer establishment was consistently experienced with chop/tine. This was attributed to the physical conditions resulting from trying to mix all straw shallowly into soil, which resulted in a less consolidated seedbed, reducing plant emergence. Effects of weed competition dominated the effects of straw incorporation for several seasons at four sites. In the absence of grass weeds on the clay soil sites there was only one case where incorporation of straw reduced yield compared with burning. This was in contrast to previous experiments at Drayton between 1975 and 1977 when the presence of straw adversely affected yield following wet autumns (Oliphant, 1982). Compared to burning straw, a yield penalty from tine incorporation of straw occurred in 2 out of 7 years at Terrington. On the shallower and stony silty clay loams, a yield penalty was recorded in 3 out of 4 years at Bridgets and in 6 out of 8 years at High Mowthorpe. While there was no obvious explanation for the cause of this at Terrington, grass weed infestation was the main cause at Bridgets and at High Mowthorpe in 1991. Poorer, less consolidated seedbeds seem to be the likely reason for the reduced yields in other cases. Ploughing was a more reliable method of incorporating straw at all sites, though it too suffered yield penalties in certain years. Averaged across years, yield of winter wheat after ploughing was less than with burning only at High Mowthorpe. In a comparable long-term study Prew et al. (1995) found few treatment effects on yield in the ?rst few years of straw incorporation. In later years on a silt loam soil, lower yield after tine incorporation was attributed to take-all and grass weeds. On a sandy soil, on only one occasion did disc/tine incorporation yield signi?cantly less than where straw was burnt. In another experiment studying the incorporation of winter barley straw during 5 years, Jenkyn et al. (1995) reported increased yield from incorporation in 2 out of 3 years. In a 1 year experiment on a clay soil and a silt loam soil, yield was not different from incorporat-

ing chopped straw by tines or plough (Christian and Bacon, 1991). Reviewing the results of 52 ?eld experiments undertaken between 1983 and 1987, Lord (1988) found that in 24 cases there was a small yield increase and in 22 a small yield decrease due to ploughing-in chopped straw rather than burning it. Yield penalties ranged from 1% on the heaviest to 10% on the lightest soil type. The reasons for the yield depressions were not always identi?ed, but included weed competition, compaction from use of discs and poorer plant establishment and growth. From the limited number of comparisons made in this series of experiments, it can be concluded that establishing spring-sown cereals and non-cereal crops after incorporating straw presents few problems. Other experiments on clay soils have shown that wet or dry autumns can cause dif?culties in establishing oilseed rape after incorporating straw with associated yield reduction (Jarvis, 1988). Inconsistent effects of straw incorporation on yields of sugar beet has been demonstrated (Allison and Hetschkun, 1995). The factor with most in?uence on crop yields in these experiments was the presence of grass weeds, particularly Bromus species. Sterile Brome is well adapted to a regime of surface cultivations (Peters et al., 1993). It produces a large quantity of seed with little dormancy. Some seed will germinate before drilling if there is suf?cient moisture, but in dry autumns most will germinate after crop drilling. Burning easily destroys the seeds, and if placed 15 cm or more below the surface they will germinate but are unable to emerge. Hence both burning and ploughing are good methods of control, which was also demonstrated in these experiments. In the absence of good selective herbicides for brome grass control in cereals, alternative control strategies have to be used after a number of years of surface incorporation of straw. Brome populations of 115 plants/m2 are capable of reducing cereal yields by 35–47% (Peters et al., 1993). In other experiments at Boxworth, yield losses of 2–4.5 t ha?1 were attributable to brome infestation (Rule, 1991). In this study there was no signi?cant effect of straw disposal method on levels of take-all infection, con?rming results found in other studies (Prew et al., 1995; Prew, 1988). This study con?rms that additional autumn nitrogen is not required where straw is incorporated as long as

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spring applied nitrogen is adequately tailored to meet yield expectation. This ?nding is in keeping with other experiments (Lord, 1988). When straw is incorporated with soil, nitrogen is both immobilised by soil micro?ora breaking down the straw, and released as the nitrogen in the straw is mineralised. In theory up to 9 kg N t?1 straw could be immobilised (AFRC, 1985), but this level of immobilisation has not been seen in recent ?eld experiments in the UK. There is evidence in the literature that incorporating straw can reduce nitrate leaching. Powlson et al. (1985) measured a reduction in nitrate leaching loss of 13% when straw was incorporated into soil. Lysimeter experiments on a highly permeable sandy loam soil have shown that nitrate leaching from winter wheat could be reduced by 25–50% by incorporating chopped straw (Jarvis et al., 1989). Although such effects decline with time, the effects have not been reversed after 11 years of study (Lord and Shepherd, 1996). The results from our study indicate a trend towards increasing soil mineral nitrogen with regular incorporation of straw. According to the Rothamsted model of soil organic matter, over a period of 5 years an increase of 0.2% organic matter should be expected from incorporation of straw (AFRC, 1985). However, at 11 years, no signi?cant difference was noted where straw was incorporated or burnt. At least a proportion of the incorporated straw may therefore be mineralised relatively quickly in soil and repeated cultivations may stimulate mineralisation of organic matter. These results demonstrate that straw can be incorporated successfully by a variety of cultivation methods. On those soils where ploughing is preferred, it is a suitable option. Where non-ploughing methods have traditionally been used after straw burning because of reduced costs and increased work rates, they can still be employed, but occasional ploughing or planting of suitable break crops may be required to control grass weeds. If straw incorporation reduces groundwater contamination by nitrates then wider bene?ts could be realised.

in the completion of these experiments. The former Ministry of Agriculture, Fisheries and Food (now Department for Environment Food and Rural Affairs) funded the work. References
AFRC, 1985. Straw, Soils and Science—Current Research into Viable Alternatives to Disposing of Cereal Straw by Burning. AFRC, London. Allison, M.F., Hetschkun, H.M., 1995. Five years of straw incorporation and its effects on growth, yield and nitrogen nutrition of sugar beet. J. Agric. Sci. Camb. 125, 61–68. Anon., 1992. Straw disposal survey 1992—England and Wales. Report of Government Statistical Service. MAFF, London. Christian, D.G., Bacon, E.T.G., 1991. The effects of straw disposal and depth of cultivation on the growth, nutrient uptake and yield of winter wheat on a clay and a silt soil. Soil Use Manage. 7, 217–222. Harper, S.H.T., Lynch, J.M., 1981. The kinetics of straw decomposition in relation to its potential to produce the phytotoxin acetic acid. J. Soil Sci. 32, 627–637. Jarvis, R., 1988. Other autumn crops. In: HGCA Research Review 11. Changing Straw Disposal Practices, Home-Grown Cereals Authority, London, UK, pp. 41–43. Jarvis, S.C., Barraclough, D., Unwin, R.J., Royle, S.M., 1989. Nitrate leaching from grazed grassland and after straw incorporation in arable soils. In: Germon, J.C. (Ed.), Management Systems to Reduce Impact of Nitrates. Elsevier, Amsterdam, pp. 110–125. Jenkyn, J.F., Gutteridge, R.J., Todd, A.D., 1995. Effects of incorporating straw using different cultivation systems, and of burning it, on disease of winter barley. J. Agric. Sci. Camb. 124, 195–204. Lord, E.I., 1988. Crop nutrition. In: HGCA Research Review 11. Changing Straw Disposal Practices, Home-Grown Cereals Authority, London, UK, pp. 24–28. Lord, E.I., Shepherd, M.A., 1996. Effect of long term straw incorporation and drilling date on nitrate leaching: lysimeter study. In: Aspects of Applied Biology 47. Rotations and Cropping Systems, Association of Applied Biologists, Warwick, UK, pp. 417–420. Oliphant, J.M., 1982. The effect of straw and stubble on the yield of winter wheat after cultivations or direct drilling. Expl. Husb. 38, 60–68. Peters, N.C.B., Froud-Williams, R.J., Orson, J.H., 1993. The rise of barren brome Bromus sterilis in UK cereal crops. In: Proceedings of the British Crop Protection Conference on Weeds, vol. 2, Brighton, UK, 22–25 November 1993, pp. 773–779. Powlson, D.S., Jenkinson, D.S., Pruden, G., Johnston, A.E., 1985. The effect of straw incorporation on the uptake of nitrogen in winter wheat. J. Sci. Food Agric. 36, 26–30. Prew, R.D., 1988. Diseases. In: HGCA Research Review 11. Changing Straw Disposal Practices, Home-Grown Cereals Authority, London, UK, pp. 37–40.

Acknowledgements The authors wish to acknowledge the valuable contributions of many past and present members of ADAS

D.B. Turley et al. / Soil & Tillage Research 71 (2003) 59–69 Prew, R.D., Ashby, J.E., Bacon, E.T.G., Christian, D.G., Gutteridge, R.J., Jenkyn, J.F., Powell, W., Todd, A.D., 1995. Effects of incorporating or burning straw, and of different cultivation systems, on winter wheat grown on two soil types, 1985–91. J. Agric. Sci. Camb. 121, 355–362. Rule, J.S., 1991. The effect of straw disposal method on weed populations and the ef?cacy of herbicides on Alopecurus myosuroides, Bromus sterilis and Bromus commutatus in winter wheat crops. In: Proceedings of the British Crop Protection

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Conference on Weeds, vol. 2, Brighton, UK, 18–21 November 1991, pp. 799–806. Rule, J.S., Turley, D.B., Vaidyanathan, L.V., 1990. Straw incorporation into soils compared with burning during successive seasons—impact on crop husbandry and soil nitrogen supply. In: Wilson, W.S. (Ed.), Advances in Soil Organic Matter Research: The Impact on Agriculture and the Environment. The Royal Society of Chemistry, London, pp. 291–298.


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