Variation in Soil Texture and Microbial Biomass Across An Iowa Agricultural Landscape.

Soil is an essential resource that is described by related biological, chemical, and physical characteristics. For example, soil texture is important to microbial communities, as it defines the soil habitat in which they live.  Despite these types of relationships, biological and physical characteristics are rarely studied in tandem.  To integrate basic biological and physical measurements, we evaluated the distribution of microbial biomass and soil texture across an agricultural landscape, and the extent to which they co-vary at different spatial scales. We hypothesize that 1) variation in microbial biomass and soil texture will change with land management, and 2) the correlation between soil texture and microbial biomass varies with spatial scale.

We sampled soil every meter along a 256-meter transect in Boone County, Iowa in August 2011. The first half of the transect was an uncultivated monoculture of switchgrass (Panicum virgatum) enrolled in the Conservation Reserve Program. The second half was a cultivated field planted in corn (Zea mays). For each sample, we measured microbial biomass using the chloroform-fumigation-extraction method and soil texture using a rapid particle size analysis method. We employed wavelet analysis to test for changes in the variation of these characteristics as well as scale-dependent correlations between them.

Microbial biomass was more variable in the switchgrass portion of the transect compared to the corn field. This difference may reflect a more diverse soil habitat under switchgrass. In addition, most of the variation in microbial biomass was associated with fine spatial scales (2-4 meters) compared to coarser spatial scales (32-64 meters). Soil texture data collection and analysis are ongoing. When combined, results from this study will provide data that integrates soil biological and physical properties. In turn, this knowledge can be used to better inform land management decisions.