The effects of land management, organic compost addition and soil series on the soil ecology of cotton (Gossypium hirsutum) fields in dryland production in Georgia (USA)
Simmons, Breana Lee
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Conservation tillage involves a reduction or elimination in tillage combined with use of a cover crop and is becoming more common in areas prone to severe erosion. A common concern when transitioning to conservation tillage is the delay in nutrient mineralization associated with a change in the soil food web. The main objective of this study was to assess the ability of a one-time compost application to accelerate the accumulation of organic matter, reducing the delay in nutrient cycling by facilitating an increase in soil biota, due to increased habitat and substrate. Additionally, we sought to differentiate between the effects of tillage and soil series using a comparative study between soils from the Piedmont and the Coastal Plain. Compost was added at three rates to five fields across a chronosequence of tillage in Coffee County, Georgia. Compost application appeared to have a minimal effect on the soil ecology at any site, but results indicate that soil biota benefit from a decrease in tillage. The conventionally tilled site had the highest C/N ratio, the lowest amount of soil organic matter, and low microbial biomass compared to sites in conservation tillage. N-mineralization was highest in sites in conservation tillage for 10 and 30 years. Fungi were typically lowest in the conventionally tilled soil, probably due to disruption of the fungal hyphae by tillage. In all soils, microbial functional groups were most heavily influenced by soil C, % soil organic matter and soil moisture, and most sites in conservation tillage were not significantly different from each other, regardless of time in no-till. This is encouraging, because it implies that sites in transition to a reduced tillage regime may not have to wait as long as expected for stabilization of the soil food web. In the comparison study between the Piedmont and the Coastal Plain, abundances of nematodes, microarthropods and microbial community composition were assessed from each site. Results indicate that soil series has a potentially greater effect on soil food webs than tillage for most biota, and decisions about land management regime should include the best available data for that particular soil type.