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ARS Home » Southeast Area » Raleigh, North Carolina » Soybean and Nitrogen Fixation Research » Research » Publications at this Location » Publication #194634
Title: MICROBIAL COMMUNITY ECO-PHYSIOLOGY AND SOIL NITROGEN CYCLING IN A PASTURE: IMPACT OF DUNG DISTRIBUTION

Author
item KANNAN, IYYEMPERUMAL - NC STATE UNIV
item Israel, Daniel
item SHI, WEI - NC STATE UNIV

Submitted to: Soil Biology and Biochemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/15/2006
Publication Date: 1/15/2007
Citation: Kannan, I., Israel, D.W., Shi, W. 2007. Microbial community eco-physiology and soil nitrogen cycling in a pasture: impact of dung distribution. Soil Biology and Biochemistry, 39:149-157.

Interpretive Summary: Grazed pastures are commonly used as receiver crops for nitrogen in swine lagoon effluent. These careful studies on how microbially mediated nitrogen cycling processes function in soil of a grazed pasture have the potential to improved nitrogen management and minimize the pollution of shallow groundwater in swine production areas of North Carolina. This approach may be applied to other animal production systems.

Technical Abstract: Grazing animals recycle a large fraction of ingested C and N within a pasture ecosystem, but the redistribution of C and N via animal excreta is often heterogeneous, being highest in camping areas, i.e. near shade and watering sources. This non-uniform distribution of animal excreta may modify soil physical and chemical attributes, and likely affect microbial community eco-physiology and soil N cycling. A better understanding of microbial biomass and soil N transformations associated with the distribution of animal excreta is fundamental to pasture ecology and improved management decisions. We determined microbial population size, activity, N mineralization, and nitrification in areas of a pasture with different dung concentration. The pasture was cropped with coastal bermudagrass (Cynodon dactylon L.) and subjected to grazing by cattle for 4 y. Soil microbial biomass, activity and N transformations were significantly higher at 0 – 5 cm than at 5 – 15 cm soil depth, and the impacts of cattle dung were more pronounced in the uppermost soil layer. Microbial biomass, activity and net N mineralization were significantly greater in areas with high dung concentration, and were significantly (P < 0.05) correlated (r2 ' 0.50) with the associated changes in total soil C and N. However, gross N mineralization and nitrification potential were highest in areas with low dung concentration. The decrease in gross N mineralization, combined with greater net N mineralization in dung-concentrated areas, implied that microbial N assimilation was lower in those areas than in the other areas. Also, microbial biomass N turned over more slowly in dung-concentrated areas than in other areas. The negative association between microbial N immobilization and soil C as a function of dung concentration is inconsistent with a bulk of publications showing that microbial N immobilization was positively related to the amount of soil C. We hypothesized that this negative correlation was due to changes in soil microbial community composition towards active fungi dominance in dung-concentrated areas.