Carbon and nitrogen dynamics in agricultural soil after application of cattle manure and eastern redcedar wood chips.

Uncontrolled proliferation of eastern redcedar tree (Juniperus virginiana) in the Midwest United States requires new alternatives for utilization of waste wood, such as mulching, that promotes efficient tree management by landowners. Similarly, efficient use of manure from animal feeding operations in cropping systems can reduce negative environmental impacts and increase cropland productivity. The objectives of this study were to quantify the nitrogen (N) and carbon (C) decomposition rates, availability, and effects on soil chemical properties of eastern redcedar wood chips (WC), cattle manure (CM), and the combination of cattle manure and wood chips (MW). A 120-day incubation and a 12-month field experiment were conducted in Nebraska. In the incubation study, CM decomposed the fastest, followed by MW and WC. At the end of the experiment, WC induced N immobilization. In the field experiment, most decomposition for all amendments occurred during the period between May and August (spring/summer). Decomposition was most rapid for CM and WC with 44% and 55% organic-C loss by mass, respectively. Approximately, 40% of the organic N in CM mineralized during the 1-year field study. Wood chips induced N immobilization after 6 months for shallow soil layers compared to control (no amendment) but did not induce N immobilization when combined with manure. Changes in soil organic matter concentration due to amendment application were not observed at any stages of the field experiment, likely due to the length of the experiment. However, consecutive applications of comingled MW may provide benefits of C contribution to the soil without inducing N limitations.

Differences in soil biological activity by terrain types at the sub-field scale in central Iowa US.

Soil microbial communities are structured by biogeochemical processes that occur at many different spatial scales, which makes soil sampling difficult. Because soil microbial communities are important in nutrient cycling and soil fertility, it is important to understand how microbial communities function within the heterogeneous soil landscape. In this study, a self-organizing map was used to determine whether landscape data can be used to characterize the distribution of microbial biomass and activity in order to provide an improved understanding of soil microbial community function. Points within a row crop field in south-central Iowa were clustered via a self-organizing map using six landscape properties into three separate landscape clusters. Twelve sampling locations per cluster were chosen for a total of 36 locations. After the soil samples were collected, the samples were then analysed for various metabolic indicators, such as nitrogen and carbon mineralization, extractable organic carbon, microbial biomass, etc. It was found that sampling locations located in the potholes and toe slope positions had significantly greater microbial biomass nitrogen and carbon, total carbon, total nitrogen and extractable organic carbon than the other two landscape position clusters, while locations located on the upslope did not differ significantly from the other landscape clusters. However, factors such as nitrate, ammonia, and nitrogen and carbon mineralization did not differ significantly across the landscape. Overall, this research demonstrates the effectiveness of a terrain-based clustering method for guiding soil sampling of microbial communities.