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

Summary

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.