Agronomic and physiological responses of a tomato crop to nitrogen input

Abstract

Two field experiments were carried out during 2005 and 2006 to study the effect of four N-fertilization rates (0 (N0), 100 (N100), 200 (N200), and 300 (N300)kgha−1) on yield, growth, N uptake, and N use efficiency of processing tomato in a silty-clay soil under Mediterranean conditions. N supply positively affected LAI (leaf area index), radiation use efficiency (RUE), above-ground dry weight (DW) and N accumulation. The respective maximum values 4.6, 1.16gMJ−1, 13.4Mgha−1, and 383kgha−1 were detected with N300. However, passing from the N200 to the N300 rate, the DW and the N tissue content mostly increased in the vegetative organs resulting in lower total and marketable yield, attributable mainly to the lower number of fruit in N300 plants. N excess exacerbates the unbalanced vegetative/reproductive plant growth which occurred when seasonal temperatures negatively affected crop productivity by reducing fruit load. Maximum total and marketable yield were obtained with the N200 rate and were respectively 155 and 119Mgha−1 in 2005 and 135 and 104Mgha−1 in 2006 season. N supply quadratically decreased the agronomical (NUEa) and physiological (NUEp) N use efficiency, these indices reaching a maximum with the N200 rate (NUEa=11.8kgkg−1, NUEp=15.1kgkg−1). However, increasing N supply decreased partial factor productivity and the efficiency in N fertilizer recovery linearly to 24 and 0.55kgkg−1. Nitrogen nutrition index (NNI) was 0.8 in N0 plants and increased up to 1.3–1.4 with N300. Under Mediterranean conditions and with the specific tomato cultivar, the N200 rate can be considered the most efficient both in terms of yield and NUE, and the respective NNI values of 1.15–1.23 (in the period from maximum LAI to harvest) could be associated with the optimal N nutritional status of the crop indicating that the minimal N concentration to obtain the maximum above-ground DW is higher than that proposed as critical for this crop. From an environmental standpoint, a 200kgha−1 of nitrogen fertilizer dose would put this production system in N balance, with N removal from the field being close to 200kgha−1 with a yield goal of 100–120kgha−1 of marketable fruits containing 1.97kgMg−1 of N.