Effects of ammonium sulphate and urea on NO3− and NO2− accumulation, nutrient contents and yield criteria in spinach

In this study, effects of ammonium sulphate (AS) and urea fertilizers on NO3− and NO2− accumulation, N, P, K, Ca, Mg, Fe, Cu, Zn, Mn contents and some yield criteria in spinach were investigated. Increments in nitrogen doses of AS and urea from 0 (control) to 150 kg N level ha−1 increased NO3−, NO2−, total N contents and yield of spinach significantly, but usually decreased P, Zn and Mn contents. NO3− contents of spinach in 120 and 150 kg N ha−1 of urea applications were higher than that of AS applications, while the NO3− contents of spinach in the lower application doses of AS were higher than that of urea applications. Increasing phosphorus availability in the higher doses of AS applications due to possibility of decreasing soil pH might be decrease NO3− accumulation in spinach by assimilating NO3− in protein form. NO3− and NO2− contents also gave the significant negative relationships with yield and P content in spinach. Decreasing micronutrient contents in spinach at the higher nitrogen doses might be due to dilution effect by increasing the plant biomass.