Physiological investigation of the impact of nitrogen and sulphur application on seed and oil yield of rapeseed (Brassica campestris L.) and mustard (Brassica juncea L-Czern. and Coss.) genotypes

Field experiments were conducted to determine the physiological basis of the effects of N and S interactions on seed and oil yield of Brassica species. Five combinations of N and S (in kg ha(-1)) 0S + 100N (T-1), 40S + 60N (T-2), 40S + 100N (T-3), 60S + 100N (T-4) and 60S + 150N (T-5), were used for this purpose. Nitrate reductase (NR) activity and ATP-sulphurylase activity in the leaves were measured at various growth stages, as the two enzymes catalyse rate-limiting steps of the assimilatory pathways of nitrate and sulphate, respectively. The activities of these enzymes were strongly correlated with seed and oil yield. The highest nitrate reductase activity, ATP-sulphurylase activity and yield were achieved with the combination T-3 in both species. Any variation from this combination decreased the activity of these enzymes, resulting in a reduction of the seed and oil yield of Brassica species. The higher seed and oil yield achieved in these species at T-3 could be due to optimization of leaf soluble protein and photosynthetic rate, as these parameters are influenced by N and S assimilation.