Vol. 7, Issue 1 (2019)

The field experiments were conducted at the Main Agricultural Research Station, Dharwad during kharif season of the year 2015 and 2016 to study the effect of different fertilizer recommendation approaches to soybean on NPK transformation in soil. The treatments consisted of different fertilizer recommendation approaches viz., site specific nutrient management (SSNM) and soil test crop response (STCR) each targeted yield at 20, 25. 30 and 35 q ha-1 and soil test laboratory (STL) approach and these were compared with graded levels of fertilizer (125 and 150 % of RDF) and control (RDF). The experiment laid out in randomized completely block design with twelve treatments replicated thrice.

Pooled data of two years indicated that inorganic forms of nitrogen, phosphorus and potassium significantly influenced due to different fertilizer recommendation approaches. In most of the soils, more than 90 per cent of nitrogen is mainly organic in nature and only a small portion is in inorganic form. Inorganic forms (mineralizable-N) of nitrogen are ammonium (NH4) and nitrate (NO3) and plants normally utilize nitrogen in only nitrate and ammonical forms. Different inorganic forms of nitrogen viz., NH4-N and NO3-N and mineral-N and total-N contents in soil was recorded significantly higher in the treatment with target yield 35 q ha-1 under SSNM which was on par with 30 q ha-1 under the same management practice and both the treatments differed significantly to the remaining treatments. All the inorganic forms of phosphorus such as saloid-P, Al-P, Fe-P, Ca-P, occluded-P and reductant-P were recorded significantly higher in the treatment received 150 per cent RDF and were at par with the treatment 125 per cent RDF and SSNM yield target at 35 q ha-1but differed significantly to other treatments. ¬Soil potassium exists in dynamic equilibrium in four different forms viz., water soluble-K, exchangeable-K (exch-K), non-exchangeable-K (non-exch-K) and lattice-K and all these forms are recorded higher in yield target at 30 and 35 q ha-1 under SSNM compared to other remaining approaches.