Assessing the sustainability of a stockless arable rotation (OF0318)

The majority of organic conversions have been on upland grass-based livestock farms resulting in a shortage of UK-grown cereals and pulses. Across northern Europe, conventional agriculture has developed a specialised structure with many areas having no livestock, or knowledge or facilities to support livestock. Sustainable organic production on these farms has particular challenges for nutrient supply, for the management of weeds, pests and diseases and for economically viability. This report covers a three and a half year period (four crop harvests) of a longer-term programme of work, which began in 1990. The overall objective was to identify and overcome factors limiting the sustainability of a stockless arable rotation. Specific objectives were to 1) quantify crop yield and quality, 2) quantify the financial performance of the rotation and contrast with Farm Business Survey data from comparable non-organic arable farms, 3) to monitor and evaluate indicators of sustainability; particularly for nutrients, weeds, pests and diseases and 4) to communicate results, and their implications, to Defra and other stakeholders. These were all achieved. The study was located on the ADAS Research Centre at Terrington St Clement, Norfolk. The soil is a deep stoneless silty clay loam of the Wisbech series. It is derived from marine alluvium, has a naturally high pH of around 7.5 and is retentive of water and nutrients. The project was an unreplicated study with field-scale plots. There were five plots, each of 2 ha, each in a different phase of a five-year rotation. This design, with no replication within-year, whilst allowing more meaningful crop husbandry and economic evaluation than a conventional small-plot replicated experiment, did limit statistical analysis. This was a deliberate choice as economic evaluation and demonstration were the principal initial objectives of the project. Despite this limitation, it has provided a long-term data-set gathered under realistic conditions that gave useful indicators of crop performance in a stockless rotation, and provided data for other Defra-funded projects, such as economic modelling. The project was managed by a steering group chaired by the Defra project officer. Other members included Roger Unwin, policy adviser on soil protection and organic farming in the Defra Rural Development Service, three organic farmers, and representatives of the Soil Association and Elm Farm Research Centre (EFRC). Meetings were held twice per year. Detailed written reports were submitted to each meeting for discussion. All changes to cropping and management were agreed by the group. The crop sequence from 2002 to 2004 was: potatoes and calabrese (split ⅔ potatoes and ⅓ calabrese) winter wheat spring beans spring wheat (undersown) white clover (fertility building crop). The clover was mown three to four times per year and left as a mulch. Organic registration was with the Soil Association. All crop management operations were done using normal farm machinery; the aim was to simulate typical commercial practice. No fertilisers were applied apart from aluminium calcium phosphate (“Redslaag”) once per rotation, at 625 kg/ha. No irrigation was applied. Undersown white clover thrived only in one year (2002) out of five. Establishment was affected variously by slug grazing, insufficient rain, and excessive rain. It was successfully re-sown in 2003 but had to be replaced by spring sown vetch in 2004 and 2005. Of all the crops grown post-conversion, fertility-building crops have been the most difficult to establish. Over the life of the programme, clover failed to successfully establish in four of the eleven years from 1995 to 2005, even when re-sown in some years. Vetch was sown in spring as a (reputedly) rapidly-growing replacement in three of the years but it was slow to establish, competed poorly with weeds and had a considerably lower accumulated nitrogen in the mulched foliage. The mean accumulated nitrogen in vetch was 102 kg/ha (range 90 to 121), whereas in clover it was 175 kg/ha (range 0 to 274). Despite the poor performance of some of the fertility-building crops, this was not clearly reflected in the performance of following cash crops. This conclusion was supported by results from replicated experiments comparing legume species over different seasons, done at Terrington in the 1990s as part of this programme (and published in a peer reviewed journal), and by results from a stockless arable study on fertile soil in Germany. Yield of winter wheat was good with an average of 7.0 t/ha; this compares with a typical organic yield of 4.0 t/ha. Yield was relatively consistent, and reflected environmental conditions, with lowest yields in the very dry 1995 and the wet and dull 1997 and 2001. The highest yield of 9.8 t/ha was in 1996 when a dry and sunny early summer was followed by rain in July and August ensuring good grain fill. Grain nitrogen content ranged from 1.7% (1995 and 1997) to 2.2% (2003). This was generally below the 2.2 to 3.3% typically required for bread making and as a result it was sold for organic livestock feed. Potato saleable yield was very variable (from 7 to 40 t/ha) depending on the impact of rainfall pattern, slugs and blight. Beans generally established and grew well with yields of over 3 t/ha in all but two years. Yield was reduced in 1995 by drought, in 1997 by poor pollination and pod set in a very dull June, and in 2004 and 2005 by weeds. The spring cereal yielded considerably less than the winter wheat. This was expected as it was at the end of the crop sequence when nitrogen availability would be least. Crop prices declined through the programme, particularly from 1999 (e.g. winter wheat price fell from £205/t in 1996 to £129/t in 2005). Non-organic prices also declined, but at a slower rate. The stockless rotation had a substantially greater gross margin than comparable non-organic farms until 2000 (e.g. £1,881/ha vs. £601/ha in 1997). From 2000, the advantage decreased as prices fell. From 2003 to 2005, gross margin was less than for non-organic farms (£561/ha vs. £601/ha in 2005). High margin crops such as potatoes and calabrese made a large contribution to the rotation gross margin and were necessary to balance the low income from the 20% of fertility-building crops in the stockless rotation. The introduction of the Single Payment Scheme in 2005 changed the economic picture making the inclusion of 20% fertility-building crops look even less attractive. New designs of stockless rotation are needed with better integration of fertility-building, and ideally with all crops earning revenue from sales. Relatively stable crop yields and nitrogen contents suggested that the rotation was in balance for nitrogen. However, crop offtake of nitrogen was substantially greater than the estimate of nitrogen supply from the fertility-building crop mulched foliage, suggesting that this measure was underestimating nitrogen supply. Soil available potassium was consistently in Index 2 despite no additions, showing that the clay minerals were releasing potassium to replace offtake. Soil available phosphorus declined sharply initially and calcium ammonium phosphate was applied annually from 1995. It continued to decline but more slowly, and by 2005 was just in Index 1. Soil carbon showed a slow upward trend. In the longer term, sustainable additions of plant-available phosphorus and potassium will be needed in a stockless rotation, even on nutrient retentive and potassium rich soils as at ADAS Terrington. Diseases and pests had little impact on cereals and beans. Significant pest issues were slugs on potatoes, calabrese and clover, and stem nematodes and Sitona spp. weevils on clover. The lack of an organic control for slugs makes production of root and vegetable crops on such slug-prone soils unreliable. Strategies to avoid stem nematode, such as alternating clover species, should be adopted in stockless systems with a high frequency of clover crops. Total numbers of weeds did not increase, but the dominant species of annual weeds changed from those of autumn-sown arable crops to those of spring-sown crops. Perennial weeds, particularly creeping thistles, progressively increased from an initial sparse and patchy distribution to cover the whole study area at a dense population. By 2005, it was clear that the creeping thistle population could not be managed without substantial change to the rotation, such as the introduction of a cultivated fallow or a longer fertility building period, both of which would be costly. Strategies to avoid domination by perennial weeds should be put in place at the start of conversion. That would be more likely to succeed in the long term rather that trying to contain a well-established population at a manageable level. Any new rotations designed in response to the introduction of the Single Payment Scheme would also have to be more competitive against perennial weeds. Two papers were published in peer-reviewed journals, and papers were presented at two Colloquium of Organic Researchers conferences. A web site dedicated to the project was established and maintained. Further research is needed on: 1) An integrated strategy for the management of perennial weeds, particularly to prevent infestations spreading. This is likely to require research to clarify aspects of weed biology and spread mechanisms, and the interaction of those with crop husbandry practices; 2) Reliable and affordable controls for slugs, particularly to protect product quality in root and vegetable crops; 3) New designs of rotation with fertility building better integrated with cash crops to a) eliminate unproductive and failure-prone dedicated fertility-building crops, and b) offer better competitive ability against perennial weeds

Testing the sustainability of stockless arable organic farming on a fertile soil (Extension to OF0 145)

This work contributes to DEFRA’s policy objective of promoting a sustainable, competitive and safe food supply chain which meets consumers’ requirements. It helps to identify sound methods of organic farming, limiting factors and ways of overcoming them. To expand in the arable east of England, where the knowledge, infrastructure and capital for livestock are not available, viable stockless systems will be necessary. Projects OF0145 showed that in the first crop sequence after conversion, a stockless arable rotation was consistently more profitable that a comparable conventional rotation on the fertile silty clay loam soil at ADAS Terrington. However, sustainability in terms of nutrient supply, perennial weed control, soil-borne pests, and other pests and diseases will be increasingly challenged in subsequent crop cycles. Also, as UK organic crop production increases, and imports become more available, difficult market conditions are challenging economic sustainability. Project OF0301 was a one-year extension to OF0145 study to maintain core monitoring pending the DEFRA review of Organic Farming Research in 2001. Following the review, a proposal was submitted to DEFRA for a longer-term development of the core activities of this project. The project was a combination of an unreplicated system study, replicated experiments and monitoring of commercial farms. A steering group consisting of representatives of DEFRA, Soil Association, Elm Farm Research Centre and three farmer members guided the project. The core of the project was an unreplicated system study with field-scale plots to allow meaningful study of patchy problems such as perennial weeds and give confidence to farmers that the system could work on a farm scale. Conversion to organic methods was started in 1990 and was completed in 1995; the land is currently certificated by the Soil Association. The rotation is clover, potatoes and calabrese, winter wheat, spring beans, undersown spring cereal. There are five plots, each of 2 ha, and each is a different phase of the five-year rotation. In a study of ten commercial organic farms (‘Linked-farms’), costings were done to Net Farm Income level, and compared with results for similar conventional farms from Farm Business Survey data and with Terrington organic and conventional crops. Linked-farm results are for 2000, due to the unavoidable time delay in collecting and analysing data. Rainfall at Terrington between September 2000 and April 2001 was particularly high with some months having double the long-term average. This led to very few days with the soil dry enough to travel on, or to work with machinery, increased leaching losses of nitrogen (not measured in this project) and delayed sowing into poor seedbeds. The summer of 2001 was also wet, particularly July. This led to ideal conditions for slugs and for potato blight. This was the most difficult year for organic production since the start of the project. Disease levels in cereals were again very low and posed minimum threat to yields. However, slugs caused serious problems, eating virtually all calabrese plants after one particularly wet day in May when 30 mm of rain fell, writing off the crop. Potatoes could not be planted until early May and were then affected by both blight and slugs. This reduced saleable yield to only 18.8 t/ha. Marketing as organic produce proved impossible, mainly due to over-supply, and the crop was sold for only £16/t for conventional processing. Despite these problems, rolling average crop yields remain good at 24.3 t/ha for potatoes, 7.3 t/ha for winter wheat, 3.5 t/ha for spring beans and 4.1 t/ha for spring cereals. This represent a reduction, compared to conventional, of 20% for winter wheat and 43% for potatoes. Despite the poor potato crop in 2001, weighted rolling-average gross margins still showed an advantage to a modelled organic rotation including potatoes (£855/ha conventional rotation at Terrington vs. £1568/ha stockless organic with potatoes). However, the generally lower profitability of vegetables, and the write-off of the 2001 calabrese crop, resulted in an average weighted rolling-average gross margin of £859/ha from a modelled organic rotation including vegetables, similar to the performance of the conventional rotation. Soil fertility as measured by carbon content has shown little change since the start of conversion in 1990. The lack of a marked increase is not unexpected, as returns of crop residues were not significantly greater than in the conventional cropping replaced. Soil available P and K have remained at ADAS Index 1 to 2 despite continued crop offtakes. However, both are showing a slow progressive decline. Further assessment will be necessary to determine how this will develop, what impact it may have on productivity and to test solutions. The perennial weeds; couch grass, creeping thistle and docks are increasing. These weeds are common problems in organic arable systems in northern Europe and it will be essential to better understand their biology to allow them to be managed to acceptable levels in a cost effective way. Crop yields in 2000 on ten monitored organic Linked-farms were similar to Terrington apart from winter wheat which averaged only 3.5 t/ha compared to 6.7 t/ha at Terrington. Input costs, crop husbandry and sale prices were also similar to Terrington. The overall gross margins of the Linked-farms were lower than at Terrington, principally because of their higher proportion of fertility building crops and the general lower profitability of livestock enterprises. The need for more fertility building crops, the inclusion of livestock and lower wheat yields compared with Terrington are all functions of the lighter, less nutrient retentive soils on these farms. Compared to conventional Farm Business Survey data, the Linked-farms again showed a significant advantage in whole-farm gross margin (£980/ha vs. £625/ha). The distribution of potato cyst nematodes (PCN) was mapped within all five plots in January 2001. PCN showed a similar distribution to sampling between 1998 to 2000 in OF0145 and there as was no evidence of a significant multiplication of PCN following potatoes. However, the growing of non-PCN resistant cultivars may have resulted in a more significant build-up and future research should consider the impact of variety choice on PCN infested land. Technology transfer activities in 2001 were severely restricted by the FMD outbreak. However, results were presented at the DEFRA organic framing research review in Warwick in July 2001, at the COR conference at Aberystwyth in March 2002, and in the farming press. The study has contributed data to several other DEFRA studies such as OF0164 – Understanding soil fertility in organically farmed systems, and OF0190 – Economics of organic farming. A CSG7 proposal for a further extension to the project has been submitted to DEFRA. This concentrates on key sustainability measurements on the core study at ADAS Terrington. Specific challenges deserving further study include: • The ecology of perennial weeds and agronomic strategies for their control. • Quantification of net nitrogen fixation by legumes and subsequent release to crops (covered by CTE 0204). • The impact of potato cultivar on PCN multiplication. • Effective management of slugs and potato blight

Constraints to the sustainability of a stockless arable rotation

The sustainability of an organic stockless arable rotation on a fertile soil in eastern England was assessed from 1990 to 2005. The good water and nutrient holding characteristics of the silty clay loam soil were well suited to a stockless organic rotation. Fertility-building clover crops were the most difficult to establish, and failed completely in some years despite one or two re-sowings. Crop yields were good, particularly for cereals, with an average for winter wheat of 7 t ha-1. Crop yield did not show any particular trend with time; there was no evidence of either a post conversion adjustment period, or a fall in yield due to declining fertility. High organic crop prices in the 1990s, resulted in significantly higher gross margins than from comparable non-organic farms. However, falling organic crop prices from 2000 resulted in profitability only similar to non-organic. Supply of N, P and K was probably not a major limitation to crop growth and yield. However, in the longer term, additions of sustainable sources of plant-available phosphorus and potassium would be necessary, even on the nutrient retentive and potassium rich soil. Effective mechanical weeding was difficult on the silty soil. The rotation favoured perennial weeds, particularly creeping thistle which increased progressively despite efforts at control with mechanical and hand weeding

Testing the sustainability of stockless arable organic farming on a fertile soil (OF0145)

This is the final report of Defra project OF0145. If organic farming is to expand in the arable east of England, where the knowledge, infrastructure and capital for livestock are not available, viable stockless systems will be needed. The aim is to maximise economic performance and in turn encourage conversion. Project OF0112 showed that a stockless arable rotation was consistently more profitable that a comparable conventional rotation on the fertile silty clay loam at ADAS Terrington. Project OF0145 researched challenges to sustaining that level of performance into the second crop rotation. The project was a combination of systems comparison, replicated experiments and monitoring of commercial farms. The core of the project was an unreplicated systems comparison with field-scale plots to allow meaningful study of patchy problems such as perennial weeds and give confidence to farmers that the system could work on a farm scale. Conversion was completed in 1995 and the rotation has since been clover, potatoes, winter wheat, spring beans, undersown spring barley. The greatest agronomic challenges continued to be with the establishment of fertility-building legumes. Despite these problems, crop yields have been maintained with good rolling average yields of 25 t/ha for potatoes, 7.5 t/ha for winter wheat, 3.5 t/ha for spring beans and 4.1 t/ha for spring cereals. Disease levels in cereals have remained low and posed minimum threat to yields. Slugs and blight have affected potatoes in wet years; control of these is particularly difficult in an organic system leading to greater yield variability than would be expected in a non-organic rotation. Calabrese has grown and yielded well with few problems but weed control in onions proved both difficult and expensive and they have been dropped in the successor project OF0301. Weighted rolling-average gross margins show a consistent and large advantage to organic (£912/ha conventional, £1757/ha stockless with potatoes and £1148/ha stockless with vegetables). The advantage to organic has increased with time as yields and prices have been maintained whilst conventional crop prices have fallen. Soil fertility as measured by carbon and nitrogen contents has shown little change since the start of conversion in 1990. Soil available P and K have remained at ADAS Index 1 to 2 despite continued crop offtakes. However both are showing a slow progressive decline, less so with P, perhaps partly due to the rotational applications of Aluminium Calcium Phosphate. Annual weeds are proving relatively easy to control, being worst where crop growth is poor for reasons such as compaction on headlands. However, the perennial weeds couch grass, creeping thistles and docks are an increasing problem. Hand pulling of thistles and docks is containing the problem but the cost of this has risen dramatically in the last two years. The distribution of potato cyst nematodes (PCN) was mapped within all five plots in January 1998, 1999 and 2000. Sampling was in 25 m x 25 m sub-plots. In January 2000 viable cysts were found in 7.6 % of sub-plots, all at fewer than 10 eggs per g of soil. There was no evidence of a significant multiplication of PCN following potatoes. Growing a variety other than the resistant Sante may have allowed multiplication. A manure utilisation booklet was compiled in association with Elm Farm Research Centre. The text was agreed with MAFF in May 2001 and it should be published by July 2001. Specific challenges deserving further study include: • The ecology of perennial weeds and agronomic strategies for their control. • Quantification of net nitrogen fixation by legumes and subsequent release to crops. • The impact of potato cultivar on PCN multiplication. • Better and more reliable grain quality. • Control of slugs and potato blight. The development of companion and bi-cropping systems for arable rotations (linked to results from OF0181 and OF0173)

Effect of mowing a legume fertility-building crop on shoot numbers of creeping thistle (Cirsium arvense (L.) Scop.)

This report was presented at the UK Organic Research 2002 Conference. Perennial weeds with spreading root systems, e.g. Cirsium arvense, are difficult to control in organic arable rotations, particularly in those without grazed leys. Competitive crops and repeated mowing are proven methods of control that can be applied to the legume fertility-building crops in stockless rotations. An experiment at ADAS Terrington in 2000 compared a standard treatment of mowing at 45 cm legume height (x4) with mowing every two weeks (x8), and mowing when thistle flower buds were visible (x3). Thistle shoot numbers counted in July 2001 were around 75% less than at start of mowing in April 2000 (mean of 9.5 shoots per m2). The results suggest that achieving and maintaining a dense competitive crop has more influence than mowing frequency on creeping thistle survival under a clover fertility-building crop

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Choice of cereal and pulse species and varities

All the main cereal crops - wheat, barley and oats, triticale, rye and spelt - can be grown organically in the UK. Until recently, the most important organic cereals were wheat and oats, with premiums paid for samples which reached milling quality. In the last year or two, more livestock farmers than arable farmers have converted to organic production so that feed grain has been in short supply, and the range of cereals grown organically has increased. New markets have also developed. Malted organic barley has been used for some time to produce beer, and now barley malt and wheat have been processed into organic whisky

Organic Arable Systems at ADAS Terrington OF0112

Project OF0112 contributes to MAFF's main policy focus of encouraging conversion to organic farming methods. It is part of a long term rotational study that began in 1990 as OF0102 and has recently been extended to 2001 as OF0145. The overall objective of these three projects is to evaluate the cost of conversion to organic arable production on a fertile soil, to assess the physical and financial performance of the organic rotation, to identify and overcome limitations to sustainabilty and to compare the results with conventional arable production. The project comprises a field-scale unreplicated systems comparison and associated replicated experiments at ADAS Terrington, and a financial analysis of ten commercial 'linked' organic farms. The silty clay loam soil at Terrington has proved ideal for organic production, primarily because it has very good water and nutrient and retention. As expected, organic crop yields have been less than conventional, averaging 70% for winter wheat; yields have been, on average, double that of the linked farms, and reached a peak of 10 t/ha in 1996. Variable costs have been lower and organic prices have been twice or more that for conventionally grown potatoes and wheat. Crop grossmargins (i.e. the value of the crop harvested minus the drect variable costs of growing it) have been consistently higher from organic than conventional. Even allowing for the lower value of the other three crops in the rotation, i.e. beans, spring cereal and clover (Set aside), overall gross margin from organic was higher than from conventional (average from 1993 to 1997 was 1,878 v 1,290 #/ha). Crop yields and gross margins were generally lower on the linked farms, probably mainly because they were on lighter soils more prone to leaching losses. However, all were viable businesses and had similar profitabilities to conventional farms of their size. The most profitable rotations in cluded potatoes and/or vegetables. In the absence of animal manures and synthetic fertilisers, the main driver of crop yield and key to sucess, will be the fixation of sufficient atmospheric nitrogen by the Rhizobium bacteria in the root nodules of legumes. Replicated experiments comparing a range of species have shown that in terms of gross accumulation of nitrogen in the cut foliage, and in the yield of a following wheat crop, red clover, lucerne and white clover are all very effective fertility builders, with red clover on average just the best. A second experiment has compared wheat, barley and oats as the cover crops for the undersowing of red clover. In 1997 clover dry matter at harvest uder oats was only 4.5kg/ha compared with 88 under wheat and 74 under barley. Baley was also the most profitable crop, however this was affected by relative grain prices which vary between years. A third experiment tested timing of manure application across the rotation. The modest quantity applied (30 t/ha per rotation) was chosen as what could have been produced from animals fed on crops grown within the rotation. There was only one isolated response in crop yield over four different crops. This was probably a reflection of the high inherent fertility and nitrogen retention capacity of the silty clay loam soil at Terrington. There are real current business opportunities for conversion to arable production. The linked farms, mostly with mixed arable livestock rotations, show profitability comparable with conventional; stockless arable production was consistently more profitable than conventional on the fertile nutrient retentive soil at Terrington. However there remain questions about the longer term sustainability of a stockless arable rotation, even on such a well suited soil. The next phase of the project (OF0145), which has just started, will focus on sustainability studying potential threats from perennial weeds, nutrient supply and soil-borne pests and diseases. The use of manure will be discontinued and, in that part of the study area, vegetables will be introduced in place of potatoes to test an alternative rotation

Companion cropping for organic field vegetables (OF0181)

Typical organic crop rotations are extensive with at least one year in four as a fertility building crop. However, the economic viability of organic systems may be compromised by having 75% or less of the farm productive at one time, limited further by the absence of the Arable Area Payments Scheme, particularly Set-aside, for vegetable crops. In addition, the system gives rise to a high fertility/low fertility sequence which is inefficient in terms of nutrient management (particularly nitrogen). To try to address this, the use of permanent beds of companion crop grown alongside the vegetable crops has been developed under various conditions around the world and is perceived as a possible alternative in organic husbandry. Companion crops also have the potential to reduce the impact of pests and weeds. A potential disadvantage of companion crops is competition with crop plants for space, light, water and nutrients. The companion crop, therefore, is likely to have to be mown or grazed to control competition and encourage nutrient transfer. On the positive side, companion crops have the potential to reduce the impact of pests, and weeds. The challenge is, therefore, to develop appropriate crop layouts and machinery to balance these interactions and result in profitable crop production. Project OF0181 was delivered with Elm Farm Research Centre and was guided by a Steering Group. The core of the project was the further development and evaluation of a seven-crop companion crop system initially developed by Professor Martin Wolfe at Wakelyns Agroforesty, Fressingfield, Suffolk, a Soil Association registered organic farm. The system was based on 1.5 m beds, with three 20 cm vegetable rows alternating with 30 cm leguminous companion strips. Within each bed, there was a seven-course crop rotation: potatoes, alliums, Umbellifers, spring oats, legumes, brassicas and spring wheat. To establish and manage this system, Martin Wolfe and his co-workers (P. J. & M. J. Wards) had by spring 1999 developed a range of purpose-built machinery including a strip rotavator, 3 row precision seed drill, straight tine or L-blade strip cultivator with/without discs, rotary strip mower, strip irrigator and a strip compost spreader. Two large experiments were established at Wakelyns in spring 1999; it was planned that these be continued for the full three years of the project. One experiment compared a factorial combination of a) three companion crops: white clover, vetch and nil, b) companion crop mowings left to fall, or deflected onto the vegetable rows, and c) the presence or absence of added composted manure. A second experiment compared factorial combinations of winter cover crops of rye and vetch grown in the vegetable rows with additional approved inputs of phosphorus and potassium. All seven crops were grown but assessments were made only on brassicas, alliums and carrots. Conclusions Companion cropping has the potential to improve economic viability, and pest, disease and annual weed control in organic cropping systems, particularly in field vegetables which are not supported by the Arable Area Payment Scheme. However, in practice, in project OF0181 these benefits were not realised: • Grass weeds were favoured and were difficult to control once established. • There were problems with seedbed preparation and crop establishment; these may be less on lighter soils. • Some crop species were better suited to companion cropping. In 2000 and 2001, there was: - a high yield in both years from beetroot, spinach, chard and kale; - a high yield in one year from Brassicas (some cabbage, swede, turnip), endive, lettuce, parsley and parsnip; - a low yield in both years from Allium crops (leeks, onions), Brassica (sprouts, some cabbage, calabrese), carrots, celeriac, broad and dwarf beans. • Clover used soil available nitrogen in preference to fixed nitrogen, starving less competitive crops such as alliums of the nutrient and resulting in very low yields. • Even with reliable yields, companion cropping in the form tested may only be suited to small-scale labour-intensive production. A system with greater spatial separation of companion and vegetable crops, with vegetables and companion crops grown alone in separate beds or strips, may give the reported benefits of companion cropping with less competition and be practical for large scale production