Submitted to: Applied Soil Ecology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 1/30/2011
Publication Date: 5/1/2011
Citation: Pengthamkeerati, P., Motavalli, P.P., Kremer, R.J. 2011. Soil microbial activity and functional diversity changed by compaction, poultry litter and cropping in a claypan soil. Applied Soil Ecology. 48(1):71-80. Interpretive Summary: Soils in crop fields may be compacted when subjected to the weight of farm machinery travelling over the field during routine land preparation for planting, weed and pest control, and harvest. The likelihood of compaction increases if the soil is moist or wet during these field operations. Compaction increases soil density and weakens soil structure leading to reduced water infiltration and aeration, and reduced soil microbial composition (diversity) and activity involved in plant nutrient cycling. Addition of organic material such as poultry litter and other livestock manure to soil may minimize effects of compaction by maintaining soil structure and providing energy sources, primarily as available carbon (C), to sustain microbial activity. We investigated the effects of compaction on soil microbiological activity and diversity in a field soil amended with poultry litter and planted to corn. Field soils were either amended or not amended with poultry litter and compacted using a tractor-drawn water wagon of known weight. Soils in the various treatment combinations were sampled periodically for two years. In the laboratory, soils similar to those at the field site were amended with or without poultry litter, then artificially compacted using a hydraulic press, moistened and incubated at ambient temperature for 28 days prior to sampling. Soil microbial activity and functional diversity (the ability to use a wide range of energy or food sources) increased slightly under field compaction indicating that the microorganisms were somewhat resistant to the stress at the field compaction level. However, the higher compaction values achieved in the laboratory greatly reduced soil microbial activity and diversity. Addition of poultry manure appeared to offset the detrimental effects of compaction by providing readily available C as an energy source and a more favorable soil structure. The results suggest adverse effects on soil microbial activities are likely with increasing soil compaction that may be associated with continuous or annual cultivation of corn in the same field. This information is important for scientists, extension personnel, consultants, and farmers because it will be useful in managing soil compaction to maintain plant nutrient availability by providing good soil structure for microbial activity, which can involve the application of an important agricultural resource, poultry litter, as an effective soil amendment.
Technical Abstract: Changes in soil physical characteristics induced by soil compaction may alter soil microhabitats and, therefore, play a significant role in governing soil microorganisms and their activities. Laboratory incubation and field experiments were conducted in 2001 and 2002 to investigate the effects of soil compaction on soil microbiological properties in a claypan soil amended with poultry litter and cropped to corn. Laboratory and field studies revealed that moderate soil compaction (bulk density = 1.40 Mg m-3 ) increased total soil organic C, Beta-glucosidase activity, microbial biomass C (MBC), and microbial functional diversity, but decreased soluble organic C (Sol C). However, more severe soil compaction imposed in the laboratory (bulk density = 1.60 to 1.80 Mg m-3 ) adversely affected these soil microbiological properties, except for Sol C. Poultry litter application and cropping significantly increased soil Beta-glucosidase activity, MBC, Sol C and microbial functional diversity, partly due to inputs of labile C substrates from litter and root exudates from the growing corn. Overall, modification of soil microhabitat by compaction may change soil microbial growth and activity relative to available C and alter soil microbial functional diversity; however, the positive effects of poultry litter addition and crop cultivation could overcome the effects of compaction on soil microbiological properties.