Contribution of Nutrients through Critical Irrigation from Diverse Water Sources in Selected Watersheds of Semi-arid Tropical India

Critical irrigation is one of the most important management options to protect the crop during weather aberrations like dry spells at critical stages of the crop growth in semi arid condition. Various water harvesting structures are useful in watershed areas to cope up with mid-season droughts. These structures provide critical irrigations at sensitive crop growth stages by which they supply essential nutrients to some extent. We estimated the contribution of various sources of water in terms of plant nutrients and to what extent critical irrigations meet nutrient requirements of various crops. By giving 4 cm irrigation, the maximum major nutrient (kg ha⁻¹) addition in the studied watersheds is of the following order NO₃ (5.2, Kothapalli); SO₄ (15.2, Kolar); Na (72.0, Haveri); K (3.6, Govardhanapura); Ca (38.5, Semli and Shyamapura); Mg (20.5, Kothapalli) and for micronutrients (g ha⁻¹) Fe (109, Kolar); Zn (40, Kothapalli); Mn (90, Kolar); Cu (120, ICRISAT) and B (190, ICRISAT). Percentage of recommended dose of nutrients which can be met by three irrigations in cereal crops (510, 15–100, 10–20% in N,S,K respectively); legumes (5–30,10–100, 5–10% of N,S,K respectively); cotton (10–15, 25–30, 5–10% of N,S,K, respectively) and micronutrients such as Fe, Zn, Mn, Cu and B to the full extent. With the number of critical irrigations increased, application of secondary and micro nutrients should be avoided which otherwise leads to higher cost of alleviation and environmental pollution.