Changes in soil physical properties and organic carbon status at the topsoil horizon of a vertisol of central India after 28 years of continuous cropping, fertilization and manuring

Balanced application of inorganic fertilizer and organic amendments greatly influence the accumulation of organic matter in soil and also influence the soil physical environment. An investigation was carried out to study the long-term impact of fertilizer and manure application in a soybean-wheat-maize (fodder) crop rotation on soil organic carbon status and physical properties of a vertisol (Typic Haplustert or Pellic Vertisols) in sub-humid sub-tropical India. Five treatments namely, control (no fertilizer and manure), 100% of the optimum rate for nitrogen (100% N), 50% of the optimum rate for nitrogen, phosphorus and potassium (50% NPK), 100% of the optimum rate for NPK (100% NPK) and 100% NPK + farmyard manure at 15 Mg ha-1 (100% NPK + FYM) from a long-term fertilizer experiment continuing at Jabalpur, India, were chosen for this study. Soil samples were collected from the topsoil horizon (0-15 cm) of all the four replications of the selected five treatments in April 2000 after 28 crop cycles and analyzed for physical and chemical properties. The results showed that the soil organic carbon (SOC) content in 100% NPK and 100% NPK + FYM treatments increased, respectively, by 22.5 and 56.3% over the initial level (1.14 kg m-2). The electrical conductivity, SOC content, aggregation, water retention, microporosity and available water capacity of the soil were increased while the bulk density was reduced significantly with the 100% NPK + FYM treatment over all other treatments. However, the use of imbalanced (100% N) and suboptimal rate of inorganic fertilizer (50% NPK) as compared to the unfertilized control showed no significant effect on the physical properties of the soil. The study indicates that application of balanced rate of fertilizers in combination with organic manure could sequester soil organic carbon in the surface layer, improve the soil physical environment and sustain higher crop productivity under this intensive cropping system.