Optimization of N fertilisation through fertigation and green manuring: case studies in processing tomato.

In conventional cropping systems fertigation with drip irrigation represents an efficient tool to optimize vegetable crop nutrition and limit nitrogen pollution to the environment. In fact this technique allows to split and adjust the rate according to crop requirements during the growth cycle, to localize the fertilizers and thus to improve N use efficiency. In organic systems green manure crops can have a strategic role both to reduce the risk of nitrate leaching and to supply N for a subsequent cash crop so improving the environmental sustainability and self-sufficiency of the system. Recently, there has been an increased interest in fertigation in organic agriculture due to the availability of reliable water soluble organic fertilizers as well as in cover crops in conventional agriculture mainly due to a rise in the price of fertilisers and to the increased awareness of environmental issues. As a consequence, within a sound strategy for a conservative horticulture, fertigation and green manure crops could be suggested as complementary tools in order to guarantee both adequate vegetable crops N nutrition and environmental benefits. Nitrogen dynamics in crop-soil system when fertigation, green manuring and fertigation+green manuring were applied in processing tomato is discussed on the basis of published and unpublished evidences from field experiments carried out in the last decade in Central Italy. Particular attention is given to N leaching risk as affected by fertigation frequency, green manuring by legumes and grass species as pure stands or mixtures, and green manures coupled with fertigation.