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

Summary

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).