The decomposability of three types of animal manures and their influences on microbial biomass in calcareous soils with clay and sandy loam texture

The decomposability of soil organic matter and animal manure plays a vital role in ecosystem processes and functions. The current study explored the decomposability of three types of organic manures including poultry litter، cow and sheep dung and their impacts on microbial biomass and metabolic quotient in calcareous soils with clay and sandy loam texture. The two soils were collected from a winter wheat field and amended with organic manures. The C decomposition rates of the manures were evaluated over 60 days of laboratory incubation، and the amount of soil biomass C was assayed at the end of the incubation period. The total amount of C mineralized (i. e. CO2 production) at the end of soil incubation showed a significant difference between control soils and soils amended with animal manures. The added organic manures resulted in higher microbial activity and CO2 production، which was more sustainable in sandy loam soil with low organic C content than clay soil with higher organic C content. At the beginning of incubation period، the decomposition rate of poultry litter C in both soils was significantly greater than that of cow and sheep dung، whereas similar amounts of C was mineralized in animal manure-treated soils at the end of incubation time. The decomposition rate of cow dung in clay soil was higher than that of sheep dung at the initial stages، while the decomposition rate of the two manures in sandy loam soil was equal. The main effects of soil texture and manure type، and their interactions on microbial biomass C were statistically significant (P<0. 01). The microbial biomass C in sandy loam soil (10. 4) was about 2. 5 times higher than that in clay soil (4. 2). Results indicate the addition of organic manure to both soils had no influence on microbial biomass C. In sandy loam soils، the addition of cow dung and poultry litter produced microbial biomass C equally but higher than sheep dung. However، there were not significant differences in soil microbial biomass C among the three manures with clay soils. The two soils did not show a significant difference (P=0. 53) in the metabolic quotient (qCO2)، but the addition of manures significantly increased this parameter. The highest values for the metabolic quotient were found in sandy loam soil amended with sheep dung، and the least values were observed in the same soil amended with cow dung. In summary، results of the current study illustrate that the decomposability of the three organic manures differs significantly and may depend on soil texture. The changes in the amount of soil microbial biomass C and metabolic quotient are better related to organic manure type and soil texture.