Quantification of the effects of management factors on maize (Zea mays L.) and cotton(Gossypium hirsutum L.) residues decomposition rate

Efforts to quantify management effects on decomposition rate of added substrates to the soil is important especially where such information is to be used for prediction in mathematical or simulation models. Using data from a short term (60 days) greenhouse simulation study, a procedure for quantifying effects of management on SOM and substrate decomposition is presented. Using microbial growth rate u (q), microbial efficiency in substrate utilization e (q), specific decomposition rates for added plant residues to two contrasting soils, red earth (Ferrasol) and black earth (Acrisol) were estimated. The treatments included straw addition + buried, (T1); straw addition + mineral N (T2); and straw addition + tillage, (T3). Sampling was done every 15 days. Straw decomposition rate was affected by external mineral N sources (Urea 46% N). Addition of an external N source significantly increased decomposition rates. The study could not, however, fully account for the effect of tillage on residues because of the limited effect of the tillage method due to the artificial barrier to mechanical interference supplied by the mesh bags. It is concluded that using few decomposer parameters, decomposition rates and consequently SOM trends in a soil system can be monitored and quantification of the influence of perturbations on decomposition rate of added substrates possible.

Characteristics of maize residue decomposition and succession in the bacterial community during decomposition in Northeast China

Microbes are decomposers of crop residues,and climatic factors and residue composition are known to influence microbial growth and community composition,which in turn regulate residue decomposition.However,the succession of the bacterial community during residue decomposition in Northeast China is not well understood.To clarify the property of bacterial community succession and the corresponding factors regulating this succession,bags containing maize residue were buried in soil in Northeast China in October,and then at different intervals over the next 2 years,samples were analyzed for residue mass and bacterial community composition.After residue burial in the soil,the cumulative residue mass loss rates were 18,69,and 77%after 5,12,and 24 months,respectively.The release of residue nitrogen,phosphorus,and carbon followed a similar pattern as mass loss,but 79%of residue potassium was released after only 1 month.The abundance,richness,and community diversity of bacteria in the residue increased rapidly and peaked after 9 or 20 months.Residue decomposition was mainly influenced by temperature and chemical composition in the early stage,and was influenced by chemical composition in the later stage.Phyla Actinobacteria,Bacteroidetes,and Firmicutes dominated the bacterial community composition in residue in the early stage,and the abundances of phyla Chloroflexi,Acidobacteria,and Saccharibacteria gradually increased in the later stage of decomposition.In conclusion,maize residue decomposition in soil was greatly influenced by temperature and residue composition in Northeast China,and the bacterial community shifted from dominance of copiotrophic populations in the early stage to an increase in oligotrophic populations in the later stage.

Nutrient Export with Logs, and Release from Residues, after Harvest of a <i>Pinus taeda</i>Plantation in Uruguay

In Uruguay, Pinus taeda is usually planted a few months after harvest of the former turn, therefore;decomposing residues represents a nutrient source for the new plantation. The aim of this study was to determine the biomass and nutrient extraction off site, following the harvest of a P. taeda plantation. Residue decomposition patterns, and nutrient release were also examined. The site will be referred as S1, corresponding to the clear cut of a 22-year-old P. taeda plantation. Before the clear cut 10 trees were harvested, and logs, branches, twigs, and needles separately weighed. Additionally, forest litter at harvest time was quantified in three different areas. To assess decomposition, mesh bags with residues were allocated in three areas over the forest litter, and samples were taken periodically for 26 months. The remaining biomass, N, P K, Ca, and Mg contents were determined in the different fractions, calculating decompositon rates. Most of the harvested biomass was removed in logs, but the proportion of nutrients exported was considerably lower. Needles showed the highest biomass loss and only 39.1% remained after 26 months, while branches presented high rates in the first two months after cut, but slower thereafter, and at the end of the study more than two thirds of the woody residues remained. Potassium was rapidly released from the residues, while Ca, and Mg, were slowly released, and there was evidence of N and P immobilization in the early stages of decomposition. It was concluded that, although a lower proportion of nutrients were exported, compared to biomass, in the long term, nutrient export with logs could be significant for the sustainability of this production system. While K release from residues did not depend on biomass decay, the slow decomposition, and release of the other nutrients, indicates that this process could have been delayed by nutrient scarcity.