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Title: THE WORLD'S OLDEST COTTON EXPERIMENT: RELATIONSHIPS BETWEEN SOIL CHEMICAL AND PHYSICAL PROPERTIES AND APPARENT ELECTRICAL CONDUCTIVITY

Author
item SIRI-PRIETO, G - AUBURN UNIVERSITY
item Reeves, Donald
item SHAW, J - AUBURN UNIVERSITY
item MITCHELL, C - AUBURN UNIVERSITY

Submitted to: Communications in Soil Science and Plant Analysis
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/15/2005
Publication Date: 8/5/2006
Citation: Siri-Prieto, G., Reeves, D.W., Shaw, J.N., Mitchell, C.C. 2006. The world's oldest cotton experiment: relationships between soil chemical and physical properties and apparent electrical conductivity. Communications in Soil Science and Plant Analysis. 37:767-786.

Interpretive Summary: Soil scientists and natural resource managers need reliable tools to map and understand the natural variability in soils in order to manage them better. Soil electrical conductivity mapping has been used to rapidly but indirectly measure soil properties like salt content, moisture, texture, and the presence of root-restricting layers. However, for other properties, like soil organic matter, electrical conductivity mapping has been problematic. The 'Old Rotation' is the world's oldest continuous cotton experiment (ca. 1896). Since the experiment has used varying management practices for over 100 years, it provides a unique opportunity to better understand the usefulness of electrical conductivity mapping to predict soil properties. Scientists from Auburn University and USDA-ARS Conservation Systems Research Unit and the J. Phil Campbell Sr. Natural Resource Conservation Center cooperated to map the 'Old Rotation' and determined the relationships with numerous soil chemical and physical properties. They found that electrical conductivity was best related to clay and soil phosphorus content than other soil properties. Soil organic matter and soil nitrogen could not be estimated by electrical conductivity mapping. Historical cropping systems used in the 'Old Rotation' demonstrated the benefit of using intensive crop rotations with wheat, corn and winter legume cover crops to improve soil quality and productivity. This information can be used by soil scientists and agencies like USDA-NRCS to more reliably interpret the usefulness of electrical conductivity mapping as a rapid means to determine the natural variability in soils.

Technical Abstract: Mapping apparent soil electrical conductivity (ECa)can provide information on salinity, moisture, texture, and presence of fragipans, however, for other soil chemical and biological properties, e.g., soil organic matter, results have been conflicting. The 'Old Rotation', the world's oldest continuous cotton (Gossypium hirsutum L.) experiment (ca. 1896), provides a valuable resource for evaluating soil spatial variability. The objective of this study was to determine the relationship between soil chemical and physical properties and ECa in the 'Old Rotation'. Soils at the site classified as fine, kaolinitic, thermic Typic Kanhapludults. Soil ECa was measured at 0-30 and 0-90 cm depths (ECa-30 and ECa-90) using a Veris® 3100 direct contact sensor with geo-referencing. Soils were grid sampled (288 points) at close interval (1.5 x 3.0 m) for chemical properties and grid sampled (65 cells, 7.5 x 6.9 m) for soil texture. Soil organic carbon (SOC) and total nitrogen (N), extractable P, K, Ca, pH, buffer pH and estimated cation exchange capacity (CECest) were measured at two depths (0-5 and 5-15 cm). Soil ECa was highly spatially correlated. The ECa-30 was more highly correlated with clay content (r = 0.58, P 0.01) and P (r = 0.43, P 0.01) than other soil properties. Total N and SOC had little or no relationship with ECa-30. Correlation improved when historical cropping systems or rotations were analyzed separately. Cropping systems affected chemical properties in the 'Old Rotation' indicating that crop rotation and cover crops are beneficial for soil productivity. The relatively poor relationship between soil chemical parameters and ECa suggest that mapping plant nutrients and SOC using ECa is problematic due to strong dependence on clay content.