THE EFFECT OF ORGANIC FERTILIZATION ON YIELDS OF TOMATO CROPS IN THE SELE RIVER PLAIN

Several sustainable agricultural practices, such as crop rotations and green manure, have been suggested to avoid nitrogen losses and water pollution. The present study investigates N dynamics in the soil and the yield of a tomato crop in Southern Italy as affected by green manure applied as horse bean (Vicia faba var. minor L.) in comparison with mineral fertilization. Trials were carried out during the summer of 2002 in Southern Italy. A split plot design was used, with green manure vs. uncultivated as the main factor and three levels of mineral N fertilization (0, 90 and 180 kg ha^-1 of N) as the sub-factor. The analysis of tomato yield showed a significant interaction between green manure and mineral fertilization. Yields gained after green manure or mineral fertilization were not significantly different. Mineral fertilization increased yields up to 90 kg ha^-1, suggesting that the maximum yield could be reached with lower N supplies than those normally used in the area. N balances for both the mineral and organic fertilization systems show N surpluses which are mainly determined by mineral N in the former. The high organic N remaining in the soil after green manuring will be subjected to slow mineralization which could make N available in post-harvest periods, so determining nitrate leaching and pollution hazard, which must be also considered in organic systems.