ABSTRACT
Amelioration of micronutrient deficiencies involves two approaches. The first approach aims at correction of deficiencies through application of the limiting micronutrients or amendments that increase their availability to plants. The second approach aims at raising crop genotypes with high nutrient efficiency on soils lacking in their availability. Once a micronutrient has been identified to be deficient in a soil and the extent of deficiency has been evaluated by appropriate methods (Chapter 10), it can be applied to the soil (soil amendment) or the plant (foliar amendment) to overcome the deficiency. This approach has been followed since the beginning of cultivation by man and is still the most widely followed method for amelioration of micronutrient deficiencies (Murphy and Walsh, 1991). Where the availability of micronutrients is limited by some soil chemical condition (e.g. high pH), deficiencies can be ameliorated through soil amendments (e.g. liming), causing an increase in the availability of micronutrients through modification of the soil chemical conditions. Micronutrient deficiencies caused by excessive salinity can be ameliorated by application of gypsum (CaS04.7H20), which increases exchangeable Ca2+ and decreases exchangeable Al (Shainberg et al. 1989). Availability of micronutrients (Fe, Zn) can also be increased through biological methods such as VAM associations or microbial siderophores. Rhizosphere microorganisms can affect plant nutrition by influencing the availability of plant nutrients, growth and morphology of roots and nutrient uptake processes (Rovira et al. 1983). Organic manures provide another potential source of micronutrients. They have an edge over the artificial fertilizers in that they also improve soil conditions to favour enhanced availability of native as well as applied micronutrients.
