Effect of Application of Nitrogen and Different Nitrogen–Sulfur Ratios on the Quality and Quantity of Mustard Seed

Abstract

A greenhouse experiment was conducted on a calcareous chernozem soil to investigate the effects of nitrogen (N) and sulfur (S) fertilization and their ratios on the yield and quality of white mustard (Sinapis alba L.). Four levels of N [0.5, 1, 1.5, and 2 g pot−1 N as ammonium nitrate (NH4NO3) and ammonium phosphate (NH4H2PO4)] in combination with three levels of applied N–S ratios [8, 4, 2; S as potassium sulfate (K2SO4) and sodium sulphate (Na2SO4)] were tested as treatments. Results indicated that a significant response to seed yield was observed for N and S application. Maximum yield, 24.8 g pot−1, was found when full doses of N and S were applied. Increasing N supply from 0.5 g pot−1 to 1 g pot−1 had little increasing effect in the oil content of the seed. Higher application of N doses (>1 g pot−1) decreased these values significantly. The maximum oil content (28%) was achieved with the 1 g N pot−1 treatment; the lowest values were observed in the pots applied with the highest N doses. Changes in the N content of the seed and straw showed a statistically significant increase with increasing N and S fertilization. Highest values in the seed and straw (5.96% and 0.87%, respectively) were observed by applying highest N and S doses. Seed and straw S levels were also observed to increase with increasing N rates and decreasing N–S ratio. Nitrogen doses significantly improved the quantities of essential amino acids with the exception of threonine, tyrosine, phenylalanine, and methionine. The amounts of these amino acids decreased with increasing N supply. When the N–S ratio decreased by increasing S, the quantities of valine, isoleucine, leucine, lysine, methionine, and cysteine increased significantly and the amount of tyrosine decreased. The quantities of nonessential amino acids with the exception of proline, histidine, and glycine increased with increasing N doses. In contrast, N rates decreased the amount of glycine. Decreasing the N–S ratio lowered the proline and arginine contents. The total amounts of essential amino acids slightly increased with increasing N rates and decreasing N–S ratio.