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 th e 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 activit y in the leaves were measured at various growth stages, as the two enzymes catalyse rate-limiting steps of the assimilatory pathways of nitrate and su lphate, respectively. The activities of these enzymes were strongly correla ted with seed and oil yield. The highest nitrate reductase activity, ATP-su lphurylase activity and yield were achieved with the combination T-3 in bot h species. Any variation from this combination decreased the activity of th ese 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 co uld be due to optimization of leaf soluble protein and photosynthetic rate, as these parameters are influenced by N and S assimilation.