Mineralization rate constants, half-lives and effects of two organic amendments on maize yield and carbon-nitrogen status of loamy ultisol in Southeastern Nigeria
Mineralization rate constants and half-lives of cattle dung (CD) and swine wastes (SW) and their effects on soil organic Carbon (SOC), Nitrogen (STN) and maize yield were evaluated for two years. The study was conducted on a deep, coarse-textured, porous and brownish red soil in Nsukka, southeastern Nigeria. Each of CD and SW was applied at four rates (0, 10, 20 and 40 t ha-1) in a split-plot design as main plot and sub-plot treatments, respectively. The organic materials were only added the first year and residual effect evaluated the second year. The results showed that SW had less C and more N than CD. Also the C/N ratio of CD (5:1) was higher than SW (3:1). Sole SW had higher mineralization rate constants and lower half lives than sole CD but their combined application enhanced both parameters. Mineralization rate constants also increased with increasing rate of application while the half-lives decreased. The CD increased SOC in both years while SW increased SOC and STN in the first year and only SOC in the second year. In addition, C and N contents of the organic materials contributed 45% and 40% changes in SOC and STN, respectively at the end of first year cultivation. In the second year, only SOC was affected by the C content of the organic material thus contributing 28% of changes in SOC. Both C and N contributed 85% changes in grain yield of first season maize with N contributing 69% improvement. In the second year, N alone contributed 56% of the change in grain yield. So SW had less half-lives than CD depicting faster decomposition and release of plant nutrients. There were significant interactions of CD and SW on SOC, STN and maize grain yield.
Keywords: cattle dung, swine waste, mineralization rate constants, soil organic carbon, maize yield