Submitted to: Applied Soil Ecology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 8/31/2011
Publication Date: 9/29/2011
Citation: Pengthamkeerati, P., Motavalli, P.P., Kremer, R.J. 2011. Soil microbial biomass nitrogen and Beta-Glucosaminidase activity response to surface compaction and poultry-litter application in a claypan soil. Applied Soil Ecology 51(1):79-86. Interpretive Summary: Soils compaction in crop production fields is a consequence of heavy 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 activity involved in plant nutrient cycling. Addition of organic material such as poultry litter and other livestock manure to soil may reduce effects of compaction by maintaining soil structure and providing organic nutrients, including nitrogen (N), to sustain microbial activity and provide available N for plant growth. We investigated the effects of compaction on soil microbiological activity involved in N cycling 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 measured as enzymatic release of N from a common organic compound known as glucosamine increased slightly under field compaction indicating that the microorganisms were somewhat resistant to the stress at the field compaction level. Similar effects of high soil bulk density on N release from glucosamine were observed under laboratory conditions. Addition of poultry manure further improved N release by microorganisms subjected to soil compaction and increased N stored in the microbial cells by providing additional organic N sources and improving soil structure. Increased N in the microbial biomass (MBN) is beneficial because it is available for plant uptake when the MBN is later decomposed and the N recycled in the soil environment. The results suggest adverse effects on soil microbial N cycling activity may occur to a slight degree but can be overcome with addition of organic materials to soil. 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 to provide good soil structure for microbial N cycling, which can involve the application of an important agricultural resource, poultry litter, as an effective soil amendment.
Technical Abstract: Compaction-induced changes in soil physical properties may significantly affect soil microbial activity, especially nitrogen-cycling processes, in many agroecosystems. The objective of this study was to determine the effect of soil compaction on soil microbiological properties related to N in a claypan soil amended with poultry litter (consisting of poultry excrement mixed with pine shavings) and cropped to corn. In laboratory incubation studies, a silt loam soil was compacted to four different bulk density levels (1.2, 1.4, 1.6 and 1.8 Mg m-3), amended with and without poultry litter and incubated at 25C for 28 d. A complementary field experiment was conducted in 2001 and 2002 on a Mexico silt loam claypan soil that was amended with litter (0 and 19 Mg ha-1), uniformly or not compacted, and planted to corn (Zea mays L.) or allowed to remain fallow. Soil compaction reduced microbial biomass N (MBN) and soluble organic N (Sol N) and shifted soil microbial community structure to favor fungi as the microbial C:N ratio increased. In contrast, soil Beta-glucosaminidase activity increased as a result of soil compaction. In the field, MBN and microbial C:N ratio significantly correlated (P<0.001) with soil water content (r = 0.49*** and -0.32***, respectively), while soil Beta-glucosaminidase activity was significantly correlated (P <0.001) with total soil organic C (r = 0.39***). Under controlled soil water content and temperature in the laboratory, all soil microbiological properties had a linear relationship with soil bulk density. Litter-amended or cropped soil had higher MBN and soil Beta-glucosaminidase activity compared to unamended or fallow soil, while Sol N increased only with litter application. The results showed that N-related soil microbiological properties were sensitive to changes induced by soil compaction, but the compaction effect was reduced with addition of litter to soil and with cropping.