Abstract:
Abstract: In many crops, nitrogen concentration decreases with increasing plant mass. A critical N concentration in plant above-ground biomass, which is defined as the minimum N concentration required for maximum plant growth, can be found at any time in the growth cycle. To determine the critical N concentration dilution curve for drip-irrigated processing tomato, three years of field experiments with five levels of N applications (0, 75, 150, 300, 450, 600 kg/hm2) were carried out in Shihezi city, northern Xinjiang. Results showed that N concentration in above-ground biomass declined with accumulated physiological development time after emergence. The relationship between the above-ground biomass and critical N concentration can be described by the power equation (%Nc=4.352DW-0.274), with ac=4.352 and b=0.274 for three experiments. Taking into account all data from the three experiments, we observed a large variability in total N concentration for a given biomass. Using the observed maximum, %Nmax and the minimum N concentration, %Nmin at each sampling date, the following two boundary curves were determined. The boundary curve model also followed a power equation (%Nmax=5.063DW-0.246, %Nmin=3.522DW-0.163), with amax=5.063, bmax=0.246, and amin=3.522, bmin=0.163 for all three experiments. Based on the critical N concentration dilution model, a model of the allometric relationship between crop N uptake at each N application level and above-ground biomass, and a model of nitrogen nutrition index (NNI), were developed. The former can be used as an index for controlling N application, and the latter can be used to express the N status of the drip-irrigated processing tomato plants. If NNI=1, N nutrition is considered to be optimum; NNI>1 indicates excess N, and NNI<1 indicates N deficiency. Based on the critical N concentration model, the model of N uptake at growth period for potential growth and yield was developed. According to the N-uptake model coefficient, NNI, and N uptake under critical N concentrations, we concluded that 300 kg/hm2 could be used as the optimum N application rate of drip-irrigated processing tomatoes in northern Xinjiang. Furthermore, there existed agreement between our model and the reference relationship for C3 crops. Thus our results could be used to guide the dynamic precision fertilization and provide a theoretical basis for optimal nitrogen management of drip-irrigated processing tomato in Xinjiang.