Fate of Micronutrients in Alkaline Soils

Abstract

Elements essentially required for the proper functioning of plants are termed as “essential nutrients” that are classified into macro (H, O, C, P, K, N, Ca, Mg, S) and micro (B, Fe, Cu, Mn, Zn, Ni, Mo, Cl) nutrients. Micronutrients though required in minute quantity are an integral part of plant nutrition, and their absence from the system significantly affects plant growth and biochemical functioning. Metallic micronutrient availability in soil being dependent upon soil pH and redox potential has become an issue for alkaline soils. In general, all micronutrients are bioavailable in acidic to neutral soil pH except Mo. Thus, making the nonsignificant supply of these nutrients in alkaline soil a constraint for sustainable agriculture. Besides soil chemical properties, soil biota and rhizosphere root chemistry and plant symbiotic associations also affect micronutrient solubilization and uptake by plants. Modification of rhizosphere chemistry, the introduction of mycorrhizal association and biofertilizers can be an option for increasing bioavailability of these nutrients in alkaline soils. Using biofertilizers and screening, enrichment and incorporation of Fe, Zn, Cu, and Mn solubilizing, and S reducing bacteria are only useful if we can sustain proper microbial count per gram of soil. Application of different inorganic and organic amendments, fertigation of synthetic nutrient formulation, and foliar application of micronutrient products are acceptable and economical options for tackling this issue in alkaline soils. This chapter is an effort to summarize all issues associated with the availability of micronutrients in alkaline soils and possible options for enhancement of bioavailable fraction, uptake and assimilation of these nutrients by various crop plants.