Identifying suitable soil quality indicators in an Indian rice-wheat system as influenced by long-term (30 years) inorganic-organic fertilization

A long-term experiment was initiated in a sub-humid tropical Indian rice-wheat system to identify suitable soil quality indicators for determining yield and sustainability of the system as influenced by chemical fertilizers (NPK) alone or in combination with organic amendments viz. farmyard manure (FYM), paddy straw (PS) and green manure (GM). Soil samples were analysed for physical, chemical and biological indicators after 30 crop cycles and the soil quality index (SQI) was calculated by nonlinear scoring functions following the methodology of principal component analysis and multiple regression analysis-based minimum data set selection. Application of NPK fertilizers in combination with FYM and GM significantly increased systems yield and sustainability (sustainable yield index or SYI) as well as improved soil properties compared to the control and other combinations. The value of the dimensionless SQI varied from 2.0 in the control plot to 3.1 in the NPK+FYM. A greater SYI and SQI in the NPK+FYM treatment suggested that FYM in combination with chemical fertilizers has an edge over GM and PS. Among all the indicators (30) under study, available-N, soil organic carbon, available-B and aryl-sulfatase were screened as suitable indicators which contributed 24, 29, 24, 22%, respectively to the SQI in NPK+FYM treatment.