Recent trends in inter-relationship of nutrients with various agronomic practices of field crops in India

The spectacular performance of Indian agriculture witnessed during the second half of the 20th century against the onslaught of rising demographic pressure is a vivid demonstration of the growing effectiveness of our agricultural research and development system. However, the issue of sustainability in agriculture still remains a question. Management of natural resources, especially soil and its fertility status and vegetation following suitable agronomic management practices for sustainable agricultural production, represents a most daunting task and is certainly going to receive much attention in the years to come. Many workers established functional relationships between nutrients and other agronomic factors at different locations in India but systematic compilation of those relationships is a rare effort. The present paper reviews the latest information on inter-relationships between nutrients and other agronomic factors (seed rate, planting density, age of the seedling, planting method, irrigation, weed control, tillage, bacterial inoculation and cultivar etc.) on field crops. Major findings of first and second order interactions are highlighted. None of the second order interaction was found significant; thus only first order interactions were discussed. The interactive effect of nutrients and seed rate varied with soil type. In sandy loam soil when 125 kg seed ha(-1) was used, wheat responded up to 60:30:40 kg N, P2O5 and K2O ha(-1), whereas in clay loam soil it was up to 80:40:30 kg N, P2O5 and K2O ha(-1) with the use of 25 kg higher seed rate. When chickpea was grown with a medium seed rate of 75 kg ha(-1) it responded up to 30 kg N and 60 kg P2O5 ha(-1) saving 10 kg N and 20 kg P2O5 in comparison to when a higher seed rate of 100 kg was used. Younger seedlings (20-25 days) performed better than old seedlings (35-40 days) in timely sown rice with the recommended dose of N, P2O5 and K2O (120:60:40). However, the adverse effect of late transplanted rice with aged seedling (35 days) on yield was nullified by using higher number of seedling/hill (4-5) and using higher dose of fertilizer (150:75:75 kg N, P2O5 and K2O ha(-1)). French bean, a negligible nodule-bearing legume responded to higher dose of N (160 kg) even under medium plant density (30 cm x 10 cm) in the tarai belt of North India. In general, interaction between cultivar and nitrogen level was non-significant in cereal but significant in oilseeds. The optimum dose of N for rapeseed cv. TH-68-8 and cv. TCH-2 was calculated to be 66.0 kg ha(-1), whereas it was 90 kg N ha(-1) for cv. RH-30. Soil moisture influenced the response of crops to fertilizer and vice-versa. Mustard responded up to 40 kg N ha(-1) under residual soil moisture and up to 60 kg N ha(-1) under limited irrigation; sunflower up to 120 kg N ha(-1) when irrigation was applied at 0.4 irrigation water/cumulative pan evaporation (IW/CPE) ratio. However, at 0.6 IW/CPE ratio the crop responded up to 80 kg N. Significant interaction of nitrogen and weed control on grain yield of wheat was observed. Interestingly, isoproturon, an urea group herbicide, along with 75 kg N ha(-1) gave significantly higher grain yield than with 100 and 125 kg N ha(-1) indicating a saving of 25-50 kg fertilizer N. Mustard inoculated with Azotobacter or Azospirillum, and receiving moderate level of fertilizer N (30 kg ha(-1)) gave similar grain yield to the uninoculated crop receiving higher dose of N (60 kg ha(-1)).