Organic Arable Systems at ADAS Terrington OF0112

Summary

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.