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Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 3/16/2006 Publication Date: 7/1/2006 Citation: Acosta Martinez, V., Harmel, R.D. 2006. Soil microbial communities and enzyme activities under various poultry litter application rates. Journal of Environmental Quality. 35(4):1309-1318. Interpretive Summary: Poultry wastes can be disposed by being applied directly to land, and can also act as a soil fertilizer. In recent years, concern of potential excessive nutrient and/or microbes being added to soil from mismanaged poultry litter application is forcing careful attention of the rates being applied to soil. Thus, it is important to understand the impacts of different rates of poultry litter on soil microbial communities, which are key in the degradation of organic amendments applied to soil. From 2002 to 2004, we studied the microbial communities and several enzyme activities in soils treated with different rates of poultry litter application in pasture (0, 6.7, and 13.4 Mg ha-1) or cultivated (0, 4.5, 6.7, 9.0, 11.2, and 13.4 Mg ha-1) sites in Texas, USA. No differences in soil C content (pasture: 4.39± 0.32% or cultivated: 4.02± 0.67%) or pH (avg: 7.95) were observed during the first four years of litter application at 0-15 cm soil depth. The soil microbial C and N (indicator of amounts of fungi, bacteria, and actinomycetes) increased with application of litter rates greater than 6.7 Mg ha-1 compared to sites with no applied litter. Increases in fungal populations at litter rates of 9.0, 11.2, and 13.4 Mg ha-1 in cultivated sites were found. The activities of enzymes important in the recycling of C and N nutrients from the poultry litter were increased in soils treated with litter rates greater than 6.7 Mg ha-1. Soil enzyme activities of P and S substrates degradation were also increased with litter rates greater than 6.7 Mg ha-1 in pasture, but their activities were only increased at the highest litter application rates (11.2 and 13.4 Mg ha-1) in cultivated sites. While our study demonstrated that rates greater than 6.7 Mg ha-1 provided rapid increases of soil microbial populations and enzymatic activities, they result in P application in excess of crop needs, which increases soil P levels and the potential for excess P loss in runoff. Technical Abstract: In recent years, as a result of the shift to fewer and larger confined animal operations, environmental and economic issues associated with utilization or disposal of animal manures and litters has become a focal point of conservation efforts. The potential excessive nutrient and/or microbial loading from mismanaged land-applied organic fertilizers is forcing changes in animal waste management, and information is needed on the impacts of poultry litter applications in soil quality. Currently, it is not clear to what extent different rates of poultry litter impact soil microbial communities, which control nutrient availability, organic matter quality and quantity, and soil degradation potential, and thus, soil quality and functioning. From 2002 to 2004, this study was initiated to investigate microbial community shifts and several enzyme activities in a Vertisol soil (Fine, smectitic, thermic, Udic Haplustert) at 0-15 cm as affected by different rates of poultry litter application to pasture (0, 6.7, and 13.4 Mg ha-1) and cultivated sites (0, 4.5, 6.7, 9.0, 11.2, and 13.4 Mg ha-1) in Texas, USA. No differences in soil C content (avg. of 3 years: pasture: 4.39± 0.32% or cultivated: 4.02± 0.67%) or pH (avg: 7.95) were observed following the first four years of litter application. Microbial biomass C and N increased at litter rates greater than 6.7 Mg ha-1 (i.e., avg. of 3 years: pasture: MBC = >863 mg kg-1 soil; MBN => 88 mg kg-1 soil) compared to sites with no applied litter (i.e., MBC= 722 mg kg-1 soil; MBN= 69 mg kg-1 soil). Similarly, enzyme activities of cellubiose (beta-glucosidase), chitin (beta-glucosaminidase), and melibiose (alpha-galactosidase) degradation were increased at litter rates greater than 6.7 Mg ha-1. Enzyme activities of P (alkaline phosphatase) and S (arylsulfatase) mineralization showed the same response in pasture, but they were only increased at the highest (11.2 and 13.4 Mg ha-1) application rates in cultivated sites. According to FAME analysis, the microbial community structure under pasture experienced shifts to higher soil bacterial populations at litter rates of 6.7 Mg ha-1, and shifts to higher soil fungal populations at litter rates of 9.0, 11.2, and 13.4 Mg ha-1 in cultivated sites. While our study demonstrated that rates greater than 6.7 Mg ha-1 provided rapid enhancement of soil microbial populations and enzymatic activities, they result in P application in excess of crop needs, which increases soil P levels and the potential for excess P loss in runoff. Thus, studies will continue to investigate whether litter application at rates below 6.7 Mg ha-1, previously recommended to maintain water quality, will result in similar improved soil microbial and biochemical function with continued annual litter application. |
