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.
Highlights
Soil organic carbon (SOC) is a key indicator of fertility and quality of the arable fields
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 research findings show that C/N ratio of 18 and moisture level of 70 to 80% of field capacity seems to be most suitable for effective straw decomposition rates and cumulative CO2 production
Summary
Soil organic carbon (SOC) is a key indicator of fertility and quality of the arable fields. It has crucial role in nutrient cycling, improving soil physical, chemical and biological properties, crop productivity, and reducing green house gases (GHGs) (Rivero et al, 2004; Lal, 2006; Battacharyya et al, 2010). Crop residues were traditionally used in China, including Guanzhong Plain for animal feed or fuel and returned to soil as organic manures. This practice of straw addition to arable fields has declined since the 1980s due to ever increasing population and indiscriminate use of inorganic fertilizers (Ju et al, 2005; Wang et al, 2008).
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