Challenges of devising nitrogen recommendation systems for open field vegetables

Large amounts of nitrogen fertiliser are often applied to field vegetable crops to ensure the maximum yield of quality produce. To avoid unnecessary environmental pollution the amounts of N could easily be optimised. However the process of devising N recommendation systems can be complex, as crops are so diverse and can be grown in intensive and varied rotations. An analysis of crop parameters, such as total dry matter yield, and critical N content, of optimally fertilised crops across a relatively small dataset, may be used to define crop requirement. For this purpose, data could be pooled between researchers. Soil N supply needs to take account of the rooting pattern; available N, and what has been released from the soil organic matter, and any fresh residues and manures. Whilst there are many uncertainties in this assessment, data can be pooled across crop sectors to help. Overall, N balance could provide prescriptive recommendations, but there will be situations where recommendations will need fine tuning, a corrective approach, during the season. Tools for such corrective actions will all require the setting of trigger values, which may be difficult to define without specific crop research. All recommended systems will need to be designed with all stakeholders, particularly the users, in mind. Knowledge transfer will require a mix of communication methods to ensure buy in. Systems that bring Win Win benefits to the growers, the industry and the environment will be the most successful. The input required for knowledge transfer cannot be regarded as trivial.