Agronomic and physiological responses of a tomato crop to nitrogen input

Two field experiments were carried out during 2005 and 2006 to study the effect of four N-fertilization rates (0 (N-0), 100(N-100), 200(N-200), and 300 (N-300) kg ha(-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, 1.16 g MJ(-1), 13.4 Mg ha, and 383 kg ha(-1) were detected with N-300. However, passing from the N-200 to the N-300 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 N-300 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 N-200 rate and were respectively 155 and 119 Mg ha(-1) in 2005 and 135 and 104 Mg ha(-1) in 2006 season. N supply quadratically decreased the agronomical (NUEa) and physiological (NUEp) N use efficiency, these indices reaching a maximum with the N-200 rate (NUEa = 11.8 kg kg(-1), NUEp = 15.1 kg kg(-1)). However, increasing N supply decreased partial factor productivity and the efficiency in N fertilizer recovery linearly to 24 and 0.55 kg kg(-1). Nitrogen nutrition index (NNI) was 0.8 in No plants and increased up to 1.3-1.4 with N-300. Under Mediterranean conditions and with the specific tomato cultivar, the N-200 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 200 kg ha(-1) of nitrogen fertilizer dose would put this production system in N balance, with N removal from the field being close to 200 kg ha(-1) with a yield goal of 100-120 kg ha(-1) of marketable fruits containing 1.97 kg Mg-1 of N. (C) 2012 Elsevier B.V. All rights reserved.