Effects of N sources and management strategies on crop growth, yield and potential N leaching in processing tomato

A 2-year field experiment was carried out in Central Italy on processing tomato (Lycopersicon esculentum Mill., cv PS1296). The aim was to assess the effects of various N sources and methods of distribution on crop growth and yield, as well as on the potential risks of nitrate leaching. Processing tomato was fertilized by using (i) green manuring with several cover crops (vetch and barley alone and in several mixtures), (ii) broadcast organic fertilizers (poultry manure and by-product of leather factory), (iii) fertigation with organic fertilizer (by-product of leather factory) and (iv) fertigation with a mineral N fertilizer. N accumulation and C/N ratio were measured in the cover crops at killing date. Tomato growth and N accumulation were determined fortnightly. The concentration of NO3-N in the soil solution was measured by a suction lysimeter at 0.9 m N supply from pure barley or from mixtures with high proportion of barley (i.e. 50% or higher) were inadequate for tomato growth. Pure vetch ensured an optimal N status to the succeeding crop, but led to nitrate leaching. The mixture vetch 75%+ barley 25% ensured an adequate amount of N for tomato, while reducing the NO3-N concentration in soil solution. Poultry manure and by-product of leather factory at low N rate (i.e. 100 kg N ha−1) were both inadequate to fulfil tomato requirements. At the same N rate, fertigation with the organic fertilizers gave the same good efficacy of fertigation with the mineral fertilizer, ensuring higher environmental sustainability. The integrated use of fall-winter cover crops and fertigation could represent a sound strategy for conservative horticulture.