Review Article

Abstract

Phosphorus (P) is generally incorporated by plants through the root system from soil solution as orthophosphates, chiefly H2PO4 and HPO4 2, the latter to a somewhat lesser degree. As this depends on several innate factors, the precise recovery following an initial application of P-fertilizer can get affected. As stated by [1], the lowest concentration of P which the soil P content can get reduced to at the rhizosphere of terrestrial plants is around 1 μM. Since roots in the rhizosphere only exploit about 25 % of the topsoil, the P-contents there needs to be replenished often through fertilization to meet the nutritional demands of crops cultivated in such soils, as was observed by [2]. Nutrients acquisition by plant roots follows two different paths [3] mass flow (depends largely on the rate of water flow through the roots) and diffusion (the main process of nutrient mobilization across a concentration gradient). Diffusion depends on the absorption capability of the roots, creating a sink to which nutrient can get pooled [4] and even this process is heavily reliant upon the soil characteristics in addition to plant metabolism [5]. A sub-continental country like India is bestowed with a diverse array of soil types which is largely responsible for the plethora of agricultural produce obtained. At the same time phosphorus availability is limited (around 50%) in majority of the arable soil types found in India due to the P-fixation (as well as buffering) capacity of the various soils, none more so than in acidic soil, (mostly resultant of leaching of base forming cations) which incidentally dominates the global cultivable lands and is a matter of great concern due to its adverse effect on crop productivity [6]. Red (or omnibus group) and lateritic soils occupy an area of about 3.5 lakh sq. Km and 2.48 lakh sq. Km (1 lakh = 100,000) respectively, accounting for more than 26 % of the total arable land area (1.597 million sq. Km) of India. Productivity of these soils is usually low because of their clastic crystalline origin, sandy texture, moderate to high porosity, low organic matter content, low cation exchange capacity (CEC), low water retention and acidic products in reaction as well as inadequacy of nitrogen (N), phosphorus (P) and potassium (K), along with the presence of some micronutrients in toxic concentrations [7]. Abstract Phosphorus (P) is almost never found in elemental state owing to its highly reactive nature. It is available at a concentration of about 1000 mg per Kilogram in the Earth’s crust. Various soil types such as acidic, lateritic, calcareous etc are characteristically low in bioavailable phosphorus due to their veritable P-fixation rates. At the same time it also is quintessential to living organisms, being a structural component of nucleic acids and ATP as well as aiding in many physiological and biochemical processes. Hence, an adequate supply of phosphorus in the soil and water is required to sustain life on earth. Phosphorus factions play major roles in the solubility and transformation of phosphorus in various soils, thus governing the management of phosphorus fertilization based on soil types. Various microbial symbioses such as with bacteria, fungi etc are responsible for the solubility of phosphorus from Apatite and related minerals but are solely not adequate in many cases to overcome the dearth in supply of bioavailable phosphorus. As we are aware that eutrophication in water bodies has transcended as a major environmental issue in dire need of resolution in recent decades, the prudent usage of phosphorus in agriculture was never more a mandate than now. In this context the data on the availability of phosphorus in various Indian soils is very important given the agriculture buttressed economy of the country and may serve as future reference while formulating policies for remedying ecological ailments.