Effects of N fertilizers and rates on yield, safety and nutrients in processing spinach genotypes

Two field experiments were carried out at the Experimental Field, Department of Food Science (TE, Italy) in 2004 and 2005 to evaluate the effects of genotypes, different N forms and N rates on yield, safety and nutritional features of processing spinach. Experiment 1, as treatments, included spinach genotypes and N forms (CO(NH2)2; Agricote; NH4NO3); experiment 2 included three N forms (Ca(NO3)2; (NH4)2SO4; NH4NO3) applied at rates of 0, 75, 150, 200 kg N ha−1. This research work confirmed differences among spinach genotypes in terms of efficiency in N use and oxalate and nitrate accumulation. Spinach accumulated much more nitrate in petioles and much more oxalate in blades indicating that nitrate and oxalate might play a counterrole to each other. Fertilizers containing N under forms not readily available to the crop, i.e. Agricote, CO(NH2)2 and (NH4)2SO4, increased nitrate and oxalate accumulations less than fast N-release fertilizers, but their effect on yield was limited. Highest yield with contents of nitrate and oxalate lower than the limits imposed to avoid health problems, were achieved with Ca(NO3)2, at rates of 130 and 150 kg N ha−1 NH4NO3.A good accumulation in some important macronutrients for the human diet such as Ca, K and P were allowed by application of Ca(NO3)2, at rates of 130 and 150 kg N ha−1 NH4NO3. The glucose, fructose, sucrose as well as Mg accumulation were not alterable in spinach with nitrogen fertilization or with genotype choice.