Response of dryland wheat to small supplemental irrigation and fertilizer nitrogen in submontane Punjab

Abstract

In northern India, the monsoon rains recede much earlier than the sowing time of post-rainy crops and the seed-zone gets dried. Excess rain water collected in near-farm or on-farm reservoirs permits small presowing and/or postsowing irrigation(s) to increase yield which is also limited by N supplies. Field experiments were conducted to match N application rates with available water supplies to optimise wheat (Triticum aestivum L.) yields. Five rates of fertilizer N (0, 25, 50, 75 and 100 kg ha⁻¹) were combined with five irrigation treatments (no-irrigation; 5 cm and 10 cm presowing irrigation, 5 cm irrigation 30 days after sowing and; equal presowing and postsowing irrigations totalling 10 cm). The yield was regressed over crop water supply inclusive of irrigation (W) or exclusive of irrigation (W₁) and applied nitrogen (N). Grain yield increased with increase in both water supply and N-rate. Within certain limits N and W₁ substituted each other for yield and so did irrigation and W₁. Irrespective of irrigation, the amount of N required to substitute for given W₁ to maintain a given yield decreased with increasing W₁. At low W₁, irrigation substituted for small changes in W₁ but with increased W₁, irrigation substituted for larger changes in W₁. Also with increase in N level given irrigation substituted for smaller amount of W₁. These regressions permit recommendations of N in relation to stored water and seasonal rain with or without limited irrigation. The latter was most useful at intermediate W₁.