Submitted to: World Congress of Soil Science
Publication Type: Proceedings
Publication Acceptance Date: January 15, 2010
Publication Date: August 1, 2010
Citation: Stott, D.E., Cambardella, C.A., Tomer, M.D., Karlen, D.L. 2010. Watershed-Scale Soil Quality Assessment: Assessing Reasons for Poor Canopy Development in Corn [abstract]. In: Proceedings of the World Congress of Soil Science, August 1-6, 2010, Brisbane, Australia. CD ROM. Technical Abstract: Soil quality assessment is a critical component in understanding the long-term effects of soil and crop management practices within agricultural watersheds. In the South Fork of the Iowa River Watershed, an aerial survey was conducted during the summer of 2006, and fields that were planted to corn and appeared to have sections with underdeveloped canopy within the corn crop were marked. Our objective was to determine if a soil quality assessment could suggest the reasons for the poor canopy development. Fifty-one marked fields were assessed in autumn of 2006. Four composite samples were taken at the 0-10 cm depth in each field, three from the dominant soil types and the fourth from the area with poor canopy. Bulk density, aggregate stability, texture, pH, extractable P, K, Ca, Mg, NO3, Cu, Fe, Mn and Zn, electrical conductivity, soil organic carbon (SOC), total N, microbial biomass C(MCB), potentially mineralizable C (Cmin) and N (Nmin), and ß-glucosidase (BG) activity were measured. The Soil Management Assessment Framework (SMAF) was used to assess soil quality. There was no single cause for poor canopy across all fields. Overall, the SOC, MCB, Cmin, Nmin, and BG activity were lower in the areas with poor canopy development. SMAF indicator scores for carbon, which compensate for differing soil types, were significantly lower for the poor canopy areas. When the data means were analysed, SOC, MBC, BD and EC, as well as the soil quality index (mean of the 11 scored indicators) were significantly different between the normal and poor canopy areas. On a field to field basis, there were specific problems such as lower SOC and other indications of poor nutrient cycling, low extractable P, high bulk density, and low water-filled pore space at time of sampling. Using SMAF to determine specific problems will help land managers develop management schemes to ameliorate the poor performing areas of the fields.