Cover Crops and Manure Combined with Commercial Fertilizers Differently Affect Yield and Quality of Processing Tomato ( Solanum lycopersicum L.) Organically Grown in Puglia

Nitrogen is crucial for the productivity of agricultural systems, although there is a growing demand for alternative cultural practices that reduce the off-farm inputs of this fertilizer. Cover crops provide a suite of services; among these, they can affect soil nitrogen content. In addition, the use of manure can contribute to a decrease in nitrogen loads from external inputs. The aim of this study was to evaluate, in processing tomato grown under an organic system, the combined use of cover crops (i.e., Vicia faba var. minor , Triticum aestivum , and Raphanus sativus ) or cattle manure, with reduced rates of commercial nitrogen fertilizers. The yield and some important qualitative characteristics of the tomato fruits were considered. V. faba was able to enhance the effects of the external input of nitrogen with respect to the yield. External inputs increased tocopherol content with respect to the control but only when it was integrated with manure. The content of carotenoids was not affected by commercial fertilizer alone; however, when it was supplied in addition to cattle manure or incorporation of R. sativus , a decrease in β-carotene was observed. Moreover, lycopene also decreased when T. aestivum or R. sativus were used as cover crops. We conclude that the sowing of nitrogen-fixing cover crops or the use of manure are good strategies for combining internal and external inputs for the sustainable production of processing tomato.