Interactive effect of sulfur and nitrogen on nitrate reductase and ATP-sulfurylase activities in relation to seed yield from Psoralea corylifolia L.

Field experiments were conducted to determine the interactive effect of sulfur (S) and nitrogen (N) applications on seed yield from Psoralea corylifolia L. Six treatments were tested: T1 = control (without manure and fertilizers), T2 = manure @ 9 kg plot-1 (10 t ha -1), T3 = S0 N20 K40 P40, T4 = S20 N20 K40 P40, T5 = S20+20 N20 K40 P40, and T6 = S20+20 N20+20 K 40 P40. Activities of nitrate reductase (NR) and ATP-sulfurylase in the leaves were measured at various phenological stages. These two enzymes catalyze the rate-limiting steps in the respective assimilatory pathways for nitrate and sulfate. Enzyme activity was strongly correlated with seed yield, with the greatest performance being achieved with treatment T5. This might be attributed to the optimization of leaf soluble protein and photosynthetic rate, both of which are influenced by S and N assimilation