Watershed-scale soil quality assessment: Assessing reasons for poor canopy development in corn

摘要

Soil quality assessment is a critical component in understanding the long-term effects of soil and crop management practices within agricultural watersheds. Additionally, simple, robust assessment methodologies are needed for policy planning and implementation. 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 were marked. Our objective was to determineif 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 in the field and the fourth from the area with poor canopy. Bulk density (BD), aggregate stability, texture, pH, extractable P, K, Ca, Mg, N03, Cu, Fe, Mn and Zn, electrical conductivity (EC), soil organic carbon (SOC), total N, microbial biomass C (MBC), potentially mineralizable C (C^and N (N^), and (3-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 in all fields. Overall, the SOC, MBC, 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 (SQI, 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 low SOC and other indicationsof poor nutrient cycling: low extractable P, high BD, and low water-filled pore space at time of sampling. When the fields were separated by slope position, most indicators and indicator scores were significantly lower in the poor canopy areas. Using SMAF to determine specific problems will help land managers deyelop management practices to ameliorate poor performing field areas. Policy makers can use information like this to assess overall effectiveness of management systems on ecosystem functions.