Effect of Conjunctive Use of Inorganic and Organic Sources of Nutrients on Soil Quality Parameters, Key Indicators and Soil Quality Indices (SQIs) under Sorghum + Cowpea Intercropping System in Rainfed Vertisol Soils of Southern India

Abstract

The present study was conducted at Kovilpatti Centre of All India Coordinated Research Project for Dryland Agriculture (AICRPDA) to assess the impact of conjunctive nutrient management practices on soil quality parameters, to identify the key indicators of soil quality, to compute the soil quality indices (SQIs) and to identify the best conjunctive nutrient management practices from the view point of soil quality improvement in sorghum + cowpea intercropping (C1), sorghum sole cropping (C2) and cowpea sole cropping (C3) systems. The treatments were comprised of T1: control, T2: 100% N (inorganic), T3: 25 kg N (compost), T4: 15 kg N (compost) + 20 kg N (inorganic) and T5: 15 kg N (green leaf) + 20 kg N (inorganic). The results of the present study clearly indicated that the conjunctive nutrient treatments significantly influenced organic carbon (OC), available phosphorus (P), sulphur (S), zinc (Zn) and copper (Cu) contents of soil in all the three systems; the potassium (K) and manganese (Mn) were significantly influenced in the C2 and C3 cropping systems. The dehydrogenase activity (DHA) was significantly highest under T3 in sole sorghum system with highest value of 1.41 μg TPF ha−1 g−1 of soil, which was on par with T4. The microbial biomass carbon (MBC) was significantly influenced by sole cowpea and sole sorghum systems, with highest values of 125.1 and 114.0 μg g−1 of soil under T3, respectively. However, the labile carbon (LC) content was significantly influenced in all the three cropping systems, with the highest LC content of 338.3 (T3), 285.2 (T3) μg g−1 and 339.64 (T4) of soil under sorghum + cowpea, sole sorghum and sole cowpea systems, respectively. The mean weight diameter of soil aggregates (MWD) was significantly influenced by the treatments in the sole sorghum system with the highest value of 0.50 mm with the T5 treatment. When all the cropping systems were viewed together, the final set of key soil quality indicators for these Vertisol soils emerged were: EC, OC, available P, available S, available Zn, LC, MBC and BD. From the view point of RSQI, the order of superiority of the conjunctive nutrient management treatments was: T3: 25 kg N (compost) (0.95)=T4: 15 kg N (compost) + 20 kg N (inorganic) (0.95) > T5: 15 kg N (green leaf) + 20 kg N (inorganic) (0.84) > T2: 100% N (inorganic) (0.73) > T1: control (0.55).