Soil and plant nitrogen dynamics of a tomato crop under different fertilization strategies.

A field experiment was conducted in 2007 to investigate the effects of the N fertilizer source on the soil and plant N dynamics of a tomato crop grown in a sandy loam soil. The fertilization treatments were: mineral N-fertilization applied by fertigation (TM); organic N-fertilization (TO) with compost obtained from the organic fraction of urban waste (OFUW); and a combined treatment (TC) with half organic and half mineral N. Compost was incorporated in November 2006. Plants were drip irrigated with well water. The nitrate concentrations in the irrigation solutions were determined on a weekly basis. Soil samples were taken before planting and at harvest from depths of up to 90 cm in order to determine moisture and N-NO 3 levels. The estimated amounts of total N-NO 3 - available in the different treatments, including the initial content in the 0-90 cm soil layer, were 560 (TC), 570 (TO) and 610 (TM) kg N ha -1 . The N contents of plants sampled on three occasions during the growing period and those of marketable fruits were also analyzed. Total marketable yield was determined at the end of the harvest period. The EU-Rotate_N model was used to predict the effects of the applied treatments. The model was calibrated using data from a previous experiment. No differences between treatments were observed with respect to yield or N content in marketable fruits. The amount of N left in the field at the end of the cropping period was significantly lower in TO than in TC and TM. Simulated plant growth, marketable yield and N uptake were similar to observed data. N leaching predicted by the model for the TM treatment was 50% higher than in the TC and TO treatments. However, an underestimation of residual N contents was found in all treatments. It was concluded that tomato fertilization with compost obtained from the OFUW could offer a suitable strategy for reducing N leaching without affecting yield when there is sufficient mineral N available throughout the growing period. The EU-Rotate_N model may be a valuable tool for evaluating N fertilizer practices for tomato crops.