Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/24/2004
Publication Date: 5/1/2005
Citation: Jung, W.K., Kitchen, N.R., Sudduth, K.A., Kremer, R.J., Motavalli, P.P. 2005. Relationship of apparent soil electrical conductivity to claypan soil properties. Soil Science Society of America Journal 69:883-892.
Interpretive Summary: Over the past decade, agricultural producers have been adopting new technologies that enable on-the-go changes in inputs (often called site-specific management or precision farming). While most crop producers are primarily interested in using precision farming methods to improve management efficiency and profitability, some are also interested in using these same methods for assessing and managing soil resources. Claypan soils in the U.S. Midwest are particularly environmentally sensitive to crop farming. On these soils, historic cropping practices have caused soil quality to degrade, usually to variable degrees within fields. This study was conducted to see if sensor-based soil electrical conductivity (EC) could be used to predict soil quality indicators for claypan soil. Soil EC measures the flow or resistence of a weak electrical current introduced to the soil, and its measurement is proportional to several soil properties. We were especially interested in those soil quality indicators that had a direct effect on grain crop production. We found that EC was well-related to these soil quality indicators: soil bulk density, soil texture, cation exchange capacity, and at the deepest soil layer sampled, soil-test phosphorus. Several of these same soil properties were also related to yield. However, the type of relation (either positive or negative) depended on July and August precipitation. When less than about 6 inches of precipitation fell during these months, some soil properties were positively related with yield. When more than about 6 inches of rain fell, then these same soil properties were negatively related to yield. This provided direct evidence of a 'drought boundary' of about 6 inches of rainfall during these two months for claypan soils. This information may help producers and their consultants as they consider various management options (e.g., irrigation, crop loss for insurance claims). Farmers and crop consultants will benefit by having sensor tools to help them understand soil resource variability. Characterizing variability provides a basis for considering management options to help solve the challenges in developing profitable and environmentally friendly site-specific management.
Technical Abstract: Understanding relationships between sensor-based measurements and soil properties related to soil quality may help in developing site-specific management options. The objective of this research was to examine whether sensor-based apparent soil electrical conductivity (ECa) could be used to predict soil quality indicators for claypan soil fields in the U.S. Midwest. Soil samples were obtained in 2002 at three depths (0 - 7.5 cm, 7.5 - 15 cm, and 15 - 30 cm) and at 65 locations within a 4-ha area of an agricultural field located in north central Missouri. Samples were analyzed for numerous physical, chemical, and microbiological properties that serve as soil quality indicators. ECa measurements were also collected with an electromagnetic induction-based sensor in different orientations and at different heights above the soil. Yield, obtained using a combine equipped with a yield-sensing system, was available for corn (Zea mays L.)(4 years) and soybean (Glycine max (L.) Merr) (5 years) crops. At the deepest sampling depth, soil bulk density (BD), clay, silt, cation exchange capacity (CEC), and Bray-1 P were the most significantly correlated (r>0.55) with ECa. Soil properties were regressed against ECa, and R2 values were often improved by including a quadratic term of ECa, especially at the 0- to 7.5-cm depth. Some soil properties (e.g., clay and CEC) and ECa that were positively correlated to yield in years with average or greater than average cumulative July to August precipitation (>15 cm), were negatively correlated to yield for years with less than average precipitation (<15 cm). We found that our best results were when we used the EC sensor near the soil surface, as opposed to lifting the sensor above the ground. Our results suggest that sensor-based ECa can be an efficient way of estimating some claypan soil quality measurements.