A field study was conducted during the winter (rabi), spring (zaid) and rainy (kharif) seasons of 1999 to 2003 at New Delhi, to evaluate the direct, residual and cumulative effect of recommended doses of phosphorus (40 kg P2O5/ha) and sulphur (30 kg S/ ha) alone and in combination of the Indian mustard [Brassica juncea (L.) Czernj. and Cosson.]-sunflower (Helianthus annuus L.)-urdbean [Vigna mungo (L.) Hepper] annual crop rotation, repeated continuously on the fixed plot for three and half years. Main plot treatments to Indian mustard were control, 40 kg P-2,O-5, 30 kg S and 40 kg P2O5, + 30 kg S/ha and same treatments were applied to succeeding sunflower by dividing main-plots into 4 sub-plots. Urdbean, third crop of the sequence was grown on residual fertility. Recommended dose of 40 kg P2O5, and 30 kg S/ha alone and in combination caused significant increase in the seed yield of Indian mustard and sunflower over the control. Direct effect of phosphorus on the seed yield of Indian mustard and sunflower was more pronounced than direct effect of sulphur. Based on three years average, Indian mustard recorded 32.8, 23.9 and 43.2% increase in seed yield due to P, S and P+S application over the control respectively. In case of sunflower, corresponding increase in seed yield was 42.0, 22.4 and 54.2%. Residual effect of P alone and in combination with S on Indian mustard become visible during third year only while in sunflower, these were found perceptible during second and third year. Cumulative residual effect of S application was not observed both on Indian mustard and sunflower. Residual effect of P applied to Indian mustard became visible on urdbean after 2 applications while residual effect of S application to same crop did not cause marked increase in the seed yield of urdbean. On the contrary residual effect of P and S applied to sunflower induced significant increase in seed yield of urdbean. Annual system productivity in term of mustard seed equivalent recorded increasing trend due to P and S application across the years. On an average P and S application alone and in combination either to Indian mustard or sunflower recorded net returns of Rs 31 881, Rs 28 242 and Rs 34 935/ha respectively. Available P in the soil recorded perceptible build up after 3 years when both the crop received recommended dose of P. Available P remained at initial level when P was applied either to Indian Mustard or sunflower. Indian mustard-sunflower urdbean crop sequence recorded slight improvement in available S, where S was applied to both the crop.
