Evaluation of Rock Phosphate Enriched Compost on Soil Nutrient Status after Harvest of Finger Millet-Cowpea Cropping Sequence in High Phosphorus Soils of Cauvery Command Area, Karnataka

A field experiment was conducted at Zonal Agricultural Research Station, VC Farm, Mandya during kharif 2017, summer 2018, kharif 2018 and summer 2019 to study the effect of rock phosphate enriched compost on soil nutrient status after harvest of finger millet-cowpea cropping sequence. Prior to initiation of the field experiment, three different composts viz., urban solid waste compost (USWC), vermicompost and farm yard manure (FYM) were enriched with rock phosphate at 5 per cent. Field experiment consisting of eleven treatment combinations comprising recommended N and K, and P through varied levels of enriched composts. The experiment was laid out in RCBD design with three replications and the test crops were finger millet and cowpea. The initial P2O5 of the experimental site was very high (133.58 kg ha-1). The results revealed that application of recommended N and K + 75 per cent P supplied through enriched USWC (T5) had significantly higher organic carbon (0.56 and 0.58%) in pooled data of both finger millet and cowpea, respectively. Available N (241.94 and 224.86 kg ha-1), P2O5 (138.69 and 120.99 kg ha-1) and K2O (153.92 and 135.31 kg ha-1) were recorded significantly higher in T5 of finger millet and cowpea, respectively. Similarly, in pooled mean, exchangeable Ca [4.15 and 4.04 C mol (P+) kg-1] and Mg [2.16 and 2.05 C mol (P+) kg-1] were recorded significantly higher in treatment which received recommended N and K + 75 per cent P supplied through enriched vermicompost (T8) in both finger millet and cowpea, respectively. The decrease of available P2O5 was 20.98 per cent from initial (133.58 kg ha-1) to final crop (summer 2019) (105.55 kg ha-1).