| Organic materials added to soil are a source of nutrients for plants and soil organisms and increase soil organic matter (SOM) which has an important role in improving soil structure and fertility, hence maintaining soil quality for sustainable agriculture.In order to utilize organic materials for increasing SOM more effectively, it is necessary to understand the decomposition mechanisms of organic materials. Organic material decomposition is influenced by several factors such as quality of organic materials, temperature, water availability, soil structure and texture, particularly clay content. Many studies investigated the interaction of soil properties and organic materials quality in laboratory condition as well as under field condition over long periods. Variation in environmental factors may influence the interaction of soil types and decomposition rate of organic materials, thus in most previous studies their effect cannot be separated from the direct effect of soil types and organic materials quality on decomposition. To investigate the effect of soil types and organic materials properties on decomposition rate, several experiments were carried out using nylon mesh bag under field condition with different soil types in the field of Red Soil Experimental Station, Chinese Academy of Agricultural Sciences, Qiyang, Hunan province, China over a12month period of field incubations.Experiments were carried out using seven kind of organic materials viz., wheat straw, corn straw, rice straw, wheat root, corn root, pig manure and cattle manure and four soil types viz, red soil, chao soil or fluvo-aquic soil, black soil and paddy soil. Decomposition of organic materials was carried out with and without mixing the organic materials with different soils. In the first experiment, decomposition characteristics of7organic materials were evaluated with bag burial in soil. Second decomposition experiment was carried out with7types of organic materials (where organic materials were mixed separately with3types of soil viz, red soil, black soil and chao soil) to evaluate the effect of soil types on decomposition rate. Third experiment was carried out with rice straw, pig manure and cattle manure with and without mixing with soil in paddy field to evaluate the mass loss, C decomposition and changes in total nitrogen during decomposition. Fourth experiment was conducted with1month and12month samples of second experiment to know the microbial community composition associated with different organic materials decomposition with different soil types. For the experiment without mixing with soil,20g of ground organic materials of each type was used in litter bag and for with soil (mixed with soil), organic materials were mixed according to the ratio of100:1.5(soil:organic carbon of organic materials). For all the experiments, the mesh bags were retrieved after15days,1month,2month,3month,4month,6month,9month and12month period of burial. After collection of bags, samples were analyzed for organic C, total N, microbial biomass C and N. The remaining C and mass were calculated for estimating the decomposition rate.Decomposition rates (k) were estimated from mass loss data and remaining carbon by fitting a single-pool exponential decay model. The highest decomposition rate (1.01%month-1) was recorded in corn straw and the lowest (0.39%month-1) in pig manure. C decomposition rates, k values followed the order:corn straw> wheat straw> rice straw> cattle manure> corn root> wheat root> pig manure. Carbon loss showed positive and significant relationship with C:N ratio for all the organic materials under study, while it was negatively correlated with lignin:N ratio for rice straw, corn straw and cattle manure. Monthly mass loss and C loss were significantly affected by residue type. Crop straw showed higher decomposability than root and manures.Decomposition rate of crop residues and animal manures were significantly varied among the soil types as well as among the organic materials. In red soil, the highest decomposition rate (0.96%month-1) was found in cattle manure which was identical with crop straw and the lowest (0.69%month-1) in pig manure. Corn straw showed the highest decomposition rate with fluvo-aquic soil (0.83%month-1) and black soil (1.06%month-1). The lowest decomposition rate was recorded in pig manure irrespective of soil types. Regarding types of organic materials C decomposition rate, the highest rate (0.87%month-1) was found in corn straw and rice straw and the lowest (0.55%month-1) in pig manure and the k values followed the pattern like, corn straw=rice straw> cattle manure> wheat straw> wheat root> corn root> pig manure. Regarding to soil types, C loss of organic materials was lower (0.66%month-1) in fluvo-aquic soil (chao soil) and higher (0.85%month-1) in black soil.In this study the changes in organic C, total N and C:N ratio of rice straw, pig manure and cattle manure decomposing with and without soils were evaluated in paddy field. On average, rice straw and pig manure lost a larger proportion of their original organic C than cattle manure. The decomposability increased in order of rice straw> pig manure> cattle manure. The presence soil affects the decomposition rate of organic C of the organic materials. Average rate of C loss was significantly higher in presence of soil which was nearly double of the rate of C loss without soil.Microbial community composition associated with organic materials decomposition with different soil types were assessed using1month and12month samples. Average well color development (AWCD) data revealed that metabolic activities of bacterial communities associated with organic materials decomposition varied both with soil and organic materials types. The crop straws recorded higher AWCD than crop roots and manures. Principal component analysis indicated that organic materials decomposing microbial community grouped by the type of organic materials at two time points as well as three soil types.On the basis of the results it can be concluded that decomposition rates of organic materials were varied among organic materials types and soil types due to organic materials compositions and soil properties as well as soil microbial communities. |
