Effect of Long-Term Use of Tillage, Crop Residue and N Application on Phosphorus Fractions in Soil under Sorghum (Sorghum vulgare) (L.)-castor System (Ricinus Communis) in Rainfed Alfisol Soils

A long-term field experiment was conducted at Hayathnagar Research Farm (HRF) of ICAR-Central Research Institute of Dryland Agriculture with the objectives to assess the effect of soil management practices viz tillage, residue application and N levels on soil phosphorus fractions, their interrelationships among themselves, impact on soil P availability pool, crop yields and P uptake. The results of the study clearly indicated that the long-term use of tillage, application of residues and N levels had a significant effect on all the P fractions in soils, except that water-soluble phosphorus (WSP) was not significantly influenced by the tillage practices. The Tillage x Residue x Nitrogen (T x R x N) significantly influenced the reductant soluble phosphorus (RSP) and total phosphorus (TP); however, the remaining P fractions were not influenced significantly. Among the combination of soil management treatments, conventional tillage (CT)+ Gliricidia loppings @ 2 tha(-1) (GL) + N level @ 90 kg ha(-1) (N90) (CTGLN90) gave the highest sorghum grain yield (1432 kg ha(-1)) and P uptake (14.20 kg P ha(-1)). Among the treatment combinations, the order of superiority of treatments in terms of castor yield and P uptake was: CT+ sorghum stover @ 2t ha(-1) (SS) + N90 (CTSSN90) (1788 kg ha(-1), 11.94 kg P ha(-1)) > Minimum Tillage (MT) + sorghum stove @2 t ha(-1) (SS) + N level @ 90 kg ha(-1) (N90) (MTSSN90) (1761 kg ha(-1), 14.24 kg P ha(-1)), respectively. Significant coefficients of multiple determination obtained from regression equations developed between sorghum crop yield and P fractions (R-2 = 0.726, p = .05) and sorghum P uptake and P fractions (R-2 = 0.620, p = .05) highlighted the importance of these fractions in influencing the crop yield and P uptake. Similarly, castor yield (R-2 = 0.748, p = .05) and P uptake (R-2 = 0.783) were significantly influenced by the P fractions. The results of the present study will be useful in understanding the effect of soil management practices on the status of P fractions and their contribution toward P uptake and crop yields.