Physico-chemical properties and productivity of a Nigerian Typic-Haplustult amended with fresh and burnt rice-mill wastes

In order to arrest the declining productivity of the soils in the Abakaliki agro-ecological zone of S.E. Nigeria, four levels (12.5, 25.0, 37.5 and 50.0 Mg ha−1) of fresh (FW) and burnt (BW) rice-mill wastes abundant in the area, and a mixture of the waste + NPK and NPK alone were added to the soil (Typic-Haplustult) to evaluate their immediate and residual effects on the productivity of the soil using maize (Zea mays L.) as a test crop. Results showed a significant reduction in bulk density as well as improvements in total porosity and water stable aggregates (WSA>0.5 mm) at levels >12.5 Mg ha−1 of the FW amendments. Although both amendments failed to improve the soil pH, significant improvements in soil C, N and BS were obtained at 37.5 Mg ha−1 and above in both amendments. The highest relative increase (TF) of 135.1% and 102.8% in C and N in the first season and 94.4% and 99.3% in the second season were obtained in the FW at 50.0 Mg ha−1. The highest maize grain yields of 2.74 and 2.66 Mg ha−1 were obtained in the waste + NPK mixtures (FW/BW + NPK) in the first season. The residual yield was highest (1.45 Mg ha−1) in the FW amendment at 50.0 Mg ha−1. The results showed that regular and properly planned applications of these wastes can sustain the productivity of soils in this region.