Citrus nutrition: An Indian perspective

Diagnosis and management of nutrient constraints are the two important pillars of sound citrus fertilizer program, although its history in India is as old as cultivation of citrus. Of the different diagnostic tools (leaf nutrient standards, soil thresholds of soil available nutrients, metalloenzyme activity, inflorescence analysis, juice nutrient standards, xylem sap analysis); leaf and soil-based nutrient standards have established their superiority over rest of the diagnostic methods. Optimum leaf nutrients standards developed for different commercial cultivars in Indiahave further warranted the necessity of identifying nutrient constraints through cultivar specific diagnostics in order to inflict precision diagnosis. Similar observations were envisaged through optimum soil fertility limits suggested for Indian citrus cultivars, primarily governed by prevailing soil fertility constraints. Multi-location nutrient specific field response studies lacked heavily on the point of uniformity in yield and quality improvements when replicated at other locations. Site-specific nutrient management studies demonstrated soil type-based fertilization, suggesting the fertilizers to be tailored as per canopy size within an orchard to derive rationality in fertilizer use within an orchard. Fertigation has further reduced the optimum fertilizer requirement by 30-40%, in addition to microbial consortium-based integrated nutrient management saving 30% cut from conventional RDF. Many other significant advances have taken place to improve the fertilizer-use-efficiency e.g. sensor-based variable rate application, fertigation using magnetized irrigation, open field hydroponics and dual purpose microbially loaded substrate (organic manure) enriched with limited inorganic fertilizers collectively known as INM a plausible alternative.