Can Dense Topographical Information and Long-Term Yield Monitor Data Substantially Improve Total Soil C Mapping?.
Alexandra N. Kravchenko and G. Philip Robertson. MSU, Crop & Soil Sciences Dept, 376 Plant & Soil Science Bldg, East Lansing, MI 48824-1325
Accurate mapping of total soil carbon (C) on field-scale level is essential for evaluating efforts to sequester soil C and for providing individual producers with information on C sequestration potentials of their fields. Data on easily measured secondary variables that are strongly related to soil C are believed to be helpful in improving mapping accuracy. The objective of this study was to assess improvement in mapping accuracy due to dense topographical and long-term yield monitor information. Approximately 1,200 total C measurements at 0-5 cm depth along with topographical and 7-year crop grain yield data were collected at twelve 60x60 m plots at the Long Term Ecological Research Site, MI. Total C was found to be significantly related to topography and/or 7-year average standardized yield in all studied plots with regression R2 exceeding 0.5 in approximately half of the plots. However, accounting for either topographical or yield information in regression kriging produced only modest (<10%) improvement in mapping accuracy as compared to that of ordinary kriging. Regression kriging was demonstrated to perform poorly in data sets with highly spatially continuous primary variable even when the regression with a secondary variable was relatively strong. Studied plots with promisingly strong relationships of total C with topography or yield were also found to be the ones where spatial distributions of total C were highly continuous. The results indicated that in soil and topographical conditions similar to those of this study dense topographical data or dense long-term yield data might not lead to substantial improvement in C mapping accuracy.