Effect of application of plant residues on chemical and biological fractions of organic carbon in soil

An option for improving soil physical, chemical and biological properties and carbon sequestration is by increasing organic carbon (OC) input through recycling of crop residues and organic manures. The objective of this study was to determine the degradation of some plant residues and the influence of application of plant residue on different chemical and biological forms of OC in soil. The sampled soil from the top 30-cm layer of an agricultural land treated with mild alfalfa, wheat and sawdust residues, at a rate of 20 g kg-1 (dry weight basis) and incubated in field capacity and lab temperature conditions. After 1, 20, 60 and 120 days of incubation a portion of each soil were taken for analysis. The experiment was considered a completely randomized design as factorial in three replicates. The factors were residues type and the passing time of incubation. Biomass C increased in all treatments significantly. Plant residue application increased cold water and hot water extractable OC significantly. They were relatively lower in sawdust treatment compared to alfalfa and wheat treatments in 1st day of soil incubation. Both of fulvic acid and humic acid in soil increased in plant residue treatments compared to those in control. However this increase was greater for humic acid especially in late stages of soil incubation. The study of changes of different chemical and biological fractions of OC during soil incubation and their correlations revealed that microbial secreted C and biomass C had coherence with cold water and hot water extractable OC.