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Effect of organic amendment on soil carbon dynamics in agricultural ecosystems
Review StatusInternal Review
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Soil carbon (C) contents and dynamics are important in the maintenance of health soils. Organic amendments (e.g. crop residue and organic manure) are known as materials to increase soil C. The degradation of organic amendments and physical disturbance of soils, performed by the fauna, can alter soil microbial community, and thus influence rates of the C cycles. However, little is known about the interaction between different soil biological communities (i.e. soil fauna and microbes) regarding soil C dynamics. Hence the objectives of this research were (1) to investigate the effects of different types of earthworms on CO2 emissions and microbial biomass during organic material decomposition, (2) to determine the effects of organic amendments on above-ground ecosystems in two agricultural soils in Zambia and (3) to quantify the interaction between soil C dynamics and microbial community changes after organic amendments in two agricultural soils in Zambia. This first experiment measured the changes in CO2 emissions and soil microbial biomass during barley decomposition with and without earthworms (Metaphire Hilgendorfi and Eisenia Fetida). After 32 days incubation, M. hilgendorfi had a potential to accumulate microbial biomass carbon (MBC) and nitrate-N, compared to E. fetida. The result suggested that the interaction between soil microbes and earthworm is influenced by earthworm species, consequently influencing the soil C and N dynamics. The second experiment investigated the changes aboveground ecosystems after organic amendments (e.g. cattle manure, poultry manure etc.) in two different soils in Zambia. We conducted two field experiments using different organic amendments in sandy loam soils and loamy sand soils in Zambia. A split-plot design was used with crop type (cassava, maize, soybean and control (bare) as the main plot and soil amendment (chemical fertilizer, cattle manure, poultry manure, maize residue, and control) as the subplot factors. The results showed that the total number of soil fauna in each site was totally different; we found around 1000/200 individuals at sandy loam soils/loamy sand soils. Organic amendments stimulate soil fauna abundance. For crop production, the organic amendments had positive effects on crop yields in both soils. Based on the results, organic amendments largely contribute to stimulate soil fauna abundance with the increase in nutrient cycles in sandy loam soils, while organic amendments act as nutrient source for crop production in loamy sand soils. Finally, the third experiment focused on the influence of the organic amendments on C dynamics and soil microbes in C depleted agricultural soils in Zambia (same treatments of second experiments). The results indicate that in the loamy sand soil, organic amendments altered the microbial activity but did not have a major impact regarding the C sequestration in the soil. Contrastingly, the effects of the organic amendments on CO2 emissions and microbial activities in the sandy loam soil were unclear. Factors such as soil texture and moisture ranges controlled the impacts of organic amendments on soil C cycle and bacterial communities. These studies indicate that the response of organic amendments is markedly influenced by soil biological community. Those different response consequently influenced soil C dynamics and agricultural production. To maintain/increase soil C in agricultural systems, the factors affecting the soil biological community have to be taken into account.
I would like to sincerely thank my supervisors, Associate Professor Yoshitaka Uchida, for his great supervision during my study. I would like to thank Prof. Nhamo Nhamo and Dr. Chikoye David, Dr. Suzuki, Petan Hamazakaza, and Friday Simkamba for this work in Zambia. I would like to thank my committee members, Prof. Ryusuke Hatano and Prof. Munehide Ishiguro who reviewed this PhD thesis. This work was mostly performed in International Institute of Tropical Agriculture (IITA), Lusaka, Zambia ...