Twenty—eight years long chemical fertilization effects on soil potassium status under rice-wheat-green gram cropping sequence

Abstract

ABSTRACT A long-term experiment was initiated on potassium (K)-rich clay soils in a rice-wheat-green gram cropping sequence to assess the feasibility of K fertilizer recommendation. Treatment consists of absolute control, farmyard manure to rice (25 t ha−1), 50% nitrogen and phosphorus (NP), 100% NP (257:160 kg NP ha−1), 50% NPK (Nitrogen, Phosphorus and Potassium), 100% NPK (257:160:135 kg NPK ha−1), NP (257:127 kg NP ha−1) and NPK (257:120:67 kg NPK ha−1) as per soil test, 50% N, 100% N (257 kg N ha−1) to the sequence. NP and NPK application as per soil test significantly increased the yield of rice (4.15 and 3.92 t ha−1), wheat (2.59 and 2.56 t ha−1), green gram (0.66 and 0.62 t ha−1) and rice equivalent yield (8918 and 8660 kg ha−1) and net returns (1018 and 959 US $ ha−1), respectively. Sustainable yield index for rice, wheat and green gram was 0.53–0.63, 0.32–0.45 and 0.10–0.23, respectively. Apparent nutrient balance for N (38.7–120.9 kg ha−1) and P (43.6–113.5 kg ha−1) was positive and negative for K (−34.9 to −154.8 kg ha−1). Residual water-soluble (3.3 and 4.0 mg kg−1), exchangeable (84.2 and 95.1 mg kg−1) and available K (87.2 and 98.9 mg kg−1) were higher with full K dose.