Increased Corn Rotation Frequency Cropping System Impacts on Soil Functional Propertie

Corn (Zea mays L.) intense rotations have become more common in the southern region of the U.S Corn Belt due to high grain production levels and economic benefits (Zhang & MacKenzie, 1997). As a result of increasing corn demand and economic competitiveness to soybean (Glycine max), many producers are altering management practices and implementing crop rotations which include more corn. This increase in corn adoption has raised concerns about the long-term sustainability of corn-intense cropping systems, and their overall impact to soil function. The objective of this study was to determine the influence of crop rotations with varying frequencies of corn and soybean on soil function in a long term (nine year) no-till management system. Soil samples were collected in the spring of 2014, at 0 to 5cm (Layer 1) and 5 to 15cm (Layer 2) depths. Soil function was represented by measurements of physical, chemical, and biological soil properties. Indicators were analyzed for previous crop effects and by calculating corn rotation frequency (CRF) ratings which were assigned to each treatment based on the total number of corn (C) years within a completed 6 year rotation cycle (e.g. S-S = 0.0, S-S-C = 0.33, C-S = 0.50, C-S-C = 0.66, C-C = 1.0). By calculating frequency, long term impacts of increased corn within rotations could be more easily identified. Plots previously in soybean averaged 33% greater water stable aggregates (WSA) in Layer 1 and 40% greater in Layer 2 compared to those previously in corn. In addition, greater electrical conductivity (EC1:1) levels were observed at 0 to 5cm when soybeans were planted previously (0 to 5cm). Surface residues, potassium (K), and magnesium (Mg) concentrations were all larger following corn. As CRF increased, favorable trends in a majority of the soil properties examined at the surface layer were observed. Soil organic carbon (SOC), water filled pore space (WFPS), soil organic matter (SOM), active carbon (AC), beta-glucosidase (beta-g), and phospholipid fatty acids (PLFA) (estimation of microbial biomass and diversity) displayed increasing trends with greater corn frequency while bulk density (BD) and EC1:1 values decreased. In addition, continuous corn had the highest concentrations of soil total nitrogen (TN). Unfavorable effects with increasing CRF included reduced soil extractable phosphorus (P) at both depths. No significant differences were observed in pHw, cation exchange capacity (CEC), calcium (Ca), or Mg based on CRF at either sampled depth. Greater CRF indicated the potential for better soil functional capacity in Layer 1, while Layer 2 showed similar functional potential among all rotation treatments.