Abstract
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: T-1 = control (without manure and fertilizers), T-2 = manure @ 9 kg plot(-1) (10 t ha(-1) T-3 = So N-20 K-40 P-40 T-4 S-20 N-20 K-40 P-40, T-5 S20+20 N-20 K-40 P-40, and T-6 S20+20 N20+20 K40 P-40. 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 T-5. This might be attributed to the optimization of leaf soluble protein and photosynthetic rate, both of which are influenced by S and IN assimilation.