Submitted to: Geoderma
Publication Type: Peer reviewed journal
Publication Acceptance Date: 10/18/2012
Publication Date: 11/19/2012
Publication URL: http://handle.nal.usda.gov/10113/56272
Citation: Hurisso, T.T., Davis, J.G., Brummer, J.E., Stromberger, M.E., Mikha, M.M., Haddix, M.L., Booher, M.R., Paul, E.A. 2012. Rapid changes in microbial biomass and aggregate size distribution in response to changes in organic matter management in grass pasture. Geoderma. 193-194:68-75. Interpretive Summary: The application of organic amendment increases soil carbon (C) and improves soil health. Pasture management that includes the addition of composted dairy manure or interseeding of a legume into grass pasture as a nitrogen (N) source will influence soil quality and nutrient dynamics. The objective of this study is to identify how the rate of composted dairy manure application (10, 15, and 20 t/ac) and the interseeding of legume into grass pasture affect aggregate stability, microbial activity, and soil C and N contents. The results suggest that the addition of composted dairy manure at 20 T/ac and the interseeding a legume (alfalfa) into grass pasture results in higher microbial activity, total microbial C and N, macroaggregates stability, and mean weight diameter compared with other manure rates. Over all, the soil quality was improved with the addition of composted dairy manure and interseeding alfalfa into grass pasture. The improvement accrued rapidly within 1.5 year of study establishment.
Technical Abstract: Adding high quantities of organic matter can increase carbon (C) inputs to soil and help maintain soil structure. This study investigated short-term effects of application of different levels of composted dairy manure (CDM) versus interseeding a legume into grass pasture on aggregate stability and soil C and nitrogen (N) contents. CDM was added to a mixture of perennial grasses at 22.4, 33.6 or 44.8 Mg ha- 1. A grass–legume treatment was established by interseeding alfalfa (Medicago sativa) into the grass mixture. A no-input control was sampled as a reference. Soils (0–5 and 5–15 cm) were sampled approximately 1.5 years after study implementation and wet sieved to obtain four aggregate size classes: large macroaggregates (> 2000 micron), small macroaggregates (250–2000 micron), microaggregates (53–250 micron) and silt and clay fraction (< 53 micron). Significant CDM influences were found in the 5–15 cm depth. The addition of 44.8 Mg CDM ha- 1 and alfalfa resulted in higher proportions of macroaggregates (> 250 micron) and mean weight diameter (MWD) than CDM added at 22.4 or 33.6 Mg ha- 1. Addition of CDM at low dose rate and alfalfa did not affect total soil or aggregate-associated organic C or N. However, addition of CDM at 44.8 Mg ha- 1 and alfalfa resulted interseeding a legume into grass pasture compared to CDM added at 22.4 and 33.6 Mg ha- 1. Large macroaggregates were found to be positively correlated with total soil microbial biomass C (R = 0.81, p = 0.002). In conclusion, compared to a low application rate of CDM, addition of a high application rate of CDM or alfalfa interseeding resulted in higher total soil microbial biomass C and N and macroaggregates, and these changes in microbial biomass and aggregation occurred very rapidly.