Improving N use and performance of arable crops on organic arable farms using an expert group approach (OF0178)

Summary

This is the final report for Defra project OF0178.
Government seeks to support the development of organic farming in the UK, but nitrogen (N) almost always limits productivity on organic farms. This project devised guidance by which farmers could manage N to best effect on organic land. ‘Experts’ in i) organic farming systems, ii) manure management, iii) N cycling in farming systems and iv) crop N responses and N fixation, working through Case Studies representing arable and mixed organic systems and reviewing relevant literature, devised changes which would a) increase the availability of N for crop uptake, b) decrease losses of N to the environment, and c) be acceptable to farmers.
Nitrogen (N), phosphorus (P) and potassium (K) budgets were calculated for 9 organic Case Study farms in the UK. The farms were on sandy loam, silt clay loam and silt loam over chalk soil types and included stockless rotations and cattle, pig and poultry enterprises with a significant proportion of cropping. A soil surface nutrient budget was calculated for the target rotation on each farm using information about field management and measurements of the soil, crops and manure. Losses of N through leaching and volatilization were calculated independently using the NITCAT and MANNER models.
The budgets calculated for these Case Studies indicated no reason for organic systems to be inherently unsustainable with regard to N, P or K. Rotations showed a wide range of nutrient balances, with differences arising from contrasting crop sequences, varied interactions with on-farm livestock and use of supplementary nutrients. There is therefore scope to increase the efficiency of individual organic systems and minimise losses to the environment. Simple rotational budgets, as used in the Case Studies were found to be a useful tool for farmers and their advisors to understand and manage nutrient flows at a rotational level. The results of the Case Study analysis and literature review clearly showed that the supply of available N must be increased during the period of rapid crop growth to improve arable crop productivity in organic systems.
In conclusion, small improvements in efficiency of N retention, redistribution, or relocation were predicted to cause large improvements in output, since the greatest responses in crop production occur at the low levels of N common to organic systems. These improved management strategies were transferred to the organic farming community, through press articles and presentations to organic farmers, consultants and scientists.
There is a more detailed summary at the start of the main report.