Transformation of Phosphorus Fractions in Various Soil Types of Kerala: An Incubation Study

Aims: Research study was undertaken to examine the dynamic changes and transformations of applied phosphorus (P) in soil, spanning a comprehensive period of 75 days, to understand its interactions and potential impact on nutrient availability.

Study Design: Factorial CRD.

Place and Duration of Study: Department of Soil Science and Agricultural Chemistry, Vellanikkara, Thrissur, between September 2023 and December 2023.

Methodology: Soil samples collected from three different agroecological units (AEU) of Kerala varying in physicochemical properties were selected for the study Plastic containers filled with 300g of processed soil were treated with four levels of phosphorus as KH2PO4, with three replications for each treatment. The experiment was laid under factorial completely randomized design (CRD). On 15th, 45th and 75th day, each treatment combinations were analysed for pH, Electrical conductivity (EC), Available P (Av. P) and different fractions of phosphorus viz. Saloid-bound P (SB-P), Aluminum phosphate (Al-P), Iron phosphate (Fe-P), Reductant soluble phosphate (RS-P), Calcium phosphate (Ca-P) and Organic P (OP).

Results: Soil types had significant influence on pH, electrical conductivity, available phosphorus and various phosphorus fractions. The levels of phosphorus had significant influence on pH, EC, Av. P and phosphorus fractions except RS-P. Incubation period had significant effect on EC, Av. P and all phosphorus fractions but did not influence pH. The interaction among soil type, phosphorus levels and incubation period did not have significant influence on pH, available P and RS-P. Formation of Fe-P and Al-P was found highest on 15th day.

Conclusion: EC, SB-P, OP was found to be highest on 75th day of incubation due to the slow dissolution, desorption as well as immobilisation and mineralisation reactions in the soil. The rapid precipitation of available phosphorus as Fe and Al phosphates reduces the likelihood of RS-P formation. Due to slow diffusion of P into sesquioxide, the highest value of RS-P was recorded on 75th day of incubation. It was also notable that RS-P was not influenced by the level of P. Ca-P formation was found lowest in Kuttanad soil due to ultra-acidic condition.