Abstract

Decomposition of maize straw incorporated into soil with various nitrogen amended carbon to nitrogen (C/N) ratios under a range of moisture was studied through a laboratory incubation trial. The experiment was set up to simulate the most suitable C/N ratio for straw carbon (C) decomposition and sequestering in the soil. The purpose of this study was to determine organic C decomposition by measuring CO₂ evolution using alkali traps. Maize straw mixed with clay loam topsoil was supplied with four initial nitrogen rates (40, 80, 160, 320 mg N/0.5 g C) using (NH₄)₂SO₄, to adjust its C/N ratio to 80, 40, 18 and 9. The soil moisture content was maintained at four moisture levels to achieve 60, 70, 80 and 90% of field capacity. Each of the four nitrogen rates were tested against four moisture levels, arranged in complete randomized design and incubated at 20°C for 52 days. Results reveal that decomposition rates and cumulative CO₂-C was increased by about 40% in straw amended treatments as compared to the controls. On average, about 34.56% of the added straw C was mineralized to CO₂-C. Also, there was highly significant relationship between CO₂-C emission and incubation period (R² = 0.98). Further, straw addition with interactive effect of nitrogen and moisture had significant relationships (p < 0.05) with cumulative amounts of CO₂-C, soil organic C and microbial biomass nitrogen. In conclusion, straw returning with appropriate N doses and optimum moisture can sequester and restore organic C in soil, thereby improving soil quality.

Key words: CO₂ evolution, C/N ratio, microbial biomass, moisture, straw decomposition.