Optimisation of nitrogen mineralisation from winter cover crops and utilisation by subsequent crops

Summary

Winter cover crops are integral to organic cropping systems; however, lack of knowledge concerning the fate of N following their incorporation presents a major barrier for efficient use of these crops in practice. Use of this N source is not only limiting to the production systems itself, but can also lead to loss of N via groundwater. This study will aim to quantitatively assess the fate of N from winter cover crops and investigate ways of optimising utilisation of this N source by subsequent organically-grown crops. The study will involve a mixture of field experimentation and computer modelling which will be carried out concurrently.
A series of field experiments will be conducted over 24 months on an organic site in order to quantitatively assess the fate of N from 2 winter cover crops (rye (Secale cereale) and winter vetch (Vicia sativa)). Mineral N content in soil following incorporation of these winter cover crops will be monitored at weekly or monthly intervals. Studies will be conducted to determine how effectively N mineralised from incorporated winter cover crops is used by subsequent arable and horticultural crops.
The cover crops will be followed by sequences of cash crops covering a cropping period of up to 24 months. Cash crop sequences will consist of one of the following:
• a short term summer crop utilising rapidly mineralised N, followed by 2 successive winter cereals
• a series of horticultural crops (including winter crops) maintaining as much ground cover during the year as possible
• short term crops, maintaining ground cover during spring and summer only
• bare soil (control)
Nitrate leaching will be assessed in these different crop sequences using ceramic cup samplers. Effects of cultural techniques (especially time of incorporation) on the pattern of N mineralization from incorporated winter cover crops will also be investigated. The existing HRI computer model for N mineralization will be refined and tested using experimental data as it becomes available during the course of the project. Experimental data and information from computer modelling will be evaluated in the context of current farming advice on the use of winter cover crops and will also help to provide a basis which could aid future government policy development on related farming issues.