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Long-term effects of soil management practices on soil Zn chemical fractions and their availability to grain sorghum {Sorghum vulgare (L.)} grown in a yearly rotation with castor (Ricinus communis) in rainfed red Alfisol soils

ABSTRACT A study was conducted at Hayathnagar Research Farm of ICAR-Central Research Institute for Dryland Agriculture to assess the long-term effects of soil management practices viz. tillage, residue application and N levels on soil Zn fractions and their contribution to soil Zn availability and uptake by grain sorghum grown in a yearly rotation with castor. Results of the study clearly revealed that tillage significantly influenced the Water soluble + Exchangeable Zinc (Zn-CA), zinc specifically sorbed by inorganic sites (Zn-ACC) and available Zinc (Zn-DTPA). However, the remaining Zn fractions were not influenced significantly. Residue application on long-term basis significantly increased the amount of zinc in all the fractions except water soluble + exchangeable Zinc (Zn-CA), and residual zinc (Zn-Res). The application of N @ 90 kg ha−1resulted in a higher amount of zinc in different fractions compared to control. The multiple regression analysis conducted between Zn-DTPA and zinc fractions revealed that the order of magnitude of the positive contribution of the zinc fractions toward zinc availability pool (DTPA-Zn) was: Zn-CA > Zn-ACC > Zn-OX > Zn-Res. The coefficient of multiple determination (R2 = 0.89) was significant at p = .05 level of significance. The order of percent contribution of Zn fractions toward the sum total of all the fractions was: Zn-Res > Zn-PYR > Zn-OX > Zn-ACC > Zn-CA. The multiple regression studies also revealed that all the zinc fractions studied significantly contributed toward Zn uptake by the sorghum crop (R2 = 0.99). Relatively, significantly higher Zn uptake was recorded by sorghum crop under minimum tillage (0.11 kg ha−1) as compared to conventional tillage (0.10 kg ha−1). The results of this study will be highly useful in regulating the Zn availability in soil through soil management practices.