Field experiments were conducted to determine the physiological and biochemical basis of the interactive effect of sulphur (S) and nitrogen (N) application on seed and xanthotoxin yield of Ammi majus L. Six treatments were tested (T1 = control-without manure and fertilizers, T2 = manure @ 9 kg plot-1-10~;t~;ha-1,~;T3=A0N50K25P25,~;T4=S40N50K25P25,~;T5=S40N100K25P25~;T6=S20+20N50+50K25P25) ). Nitrate reductase (NR) activity and ATP-sulphurylase activity in the leaves were measured at various phonological stages, as the two enzymes catalyze rate-limiting steps of the assimilatory pathways of nitrate and sulphate, respectively. The activities of these two enzymes were strongly correlated with seed and xanthotoxin yield. The highest nitrate reductase activity, ATP-sulphurylase activity and xanthotoxin yield were achieved with the treatment T4 . Any variation from this treatment decreased the activity of these enzymes, resulting in a reduction of the seed and xanthotoxin yield in Ammi majus L. The higher seed and xanthotoxin yield achieved in Ammi majus L. at treatment T4 could be due to optimization of leaf soluble protein and photosynthetic rate, as these parameters are Influenced by S and N assimilation.

A number of field experiments were conducted to assess the role of combined application of nitrogen and sulfur to increase the seed and oil yield of nonnodulating soybean (Glycine max (L) Merr.) cv. PK-416 (V1) and cv. PK-1024 (V2) . Six combinations of N and S in three replicates each were used for this purpose i.e. 0~;S+23.5kg~;N~;ha-1(T1);~;0~;S+23.5+20kg~;N ~;ha-1(T2);~;40~;S+23.5kg~;N~;ha-1(T3);~;40~;S+23.5+20kg~;N~;ha-1(T4);~;20+20~;S+23.5kg~;N~;ha-1(T5);~;20+20~;S+23.5+20kg~;N~;hal(T6) . Nitrate reductase (NR) and ATP-sulphurylase activities in the leaves were measured at various growth stages as the two enzymes catalyze the rate limiting steps of the assimilatory pathways of nitrate and sulphate, respectively. The activities of these enzymes were strongly correlated with seed yield. The higher seed, oil and protein yields were achieved with the treatment T6 in both the cultivars due to optimization of NR activity and ATP-sulphurylase activity, as these parameters were influenced by N and S assimilation. Any variation from this combination was observed to decrease the activity of these enzymes resulting in reductions in the seed, oil and protein yield of soybean.