Relationship of Apparent Soil Electrical Conductivity to Claypan Soil Properties

tantly, subsets of indicators could be related to a specific soilfunction(KarlenandStott,1994;Brejdaetal.,2000). Understanding relationships between sensor-based measurements Indicator measurements used to assess soil quality must and soil properties related to soil quality may help in developing siteberesponsivetomanagementpracticestoobservechanges specific management. The primary objective of this research was to that might either improve or impair the soil (Karlen examine whether sensor-based apparent soil electrical conductivity (ECa) could be used to predict soil properties for claypan soil. Soil et al., 1997; Wander and Bollero, 1999). Soil quality samples were obtained at three depths intervals (0- to 7.5-, 7.5- to indicators could be described into inherent soil proper15-, and 15- to 30-cm depths) at 65 locations within a 4-ha area of an ties, those that change slowly over time (e.g., soil texture agricultural field located in north central Missouri in 2002. Samples and hydraulic characteristics), and dynamic soil properwere analyzed for numerous physical, chemical, and microbiological ties such as those that management can influence (e.g., properties that serve as soil quality indicators. The ECa measurements pH, soil water use from the tillage, and plant nutrient were also collected at the coring locations with an electromagnetic levels). A list of basic soil properties that meet many induction-basedsensor.Acombine equippedwithacommercialyieldof the requirements for screening soil quality was develsensing, GPS based recording system was used to map corn (Zea oped by Doran and Parkin (1994). A framework for evalmays L.) and soybean [Glycine max (L.) Merr.] yields from 1993 to uatingsite-specificchangesinsoilqualitywasalsodevel2002. At the deepest sampling depth, soil bulk density (Db), clay, silt, cation exchange capacity (CEC), and Bray-1 P were the most oped by Karlen and Stott (1994), where high-quality significantly correlated (r 0.55) with ECa. Soil properties were soil was defined as one that accommodates water entry, regressed against ECa, and R 2 values were often improved using a retains and supplies water to plants, resists degradation, quadratic term of ECa, especially at the 0- to 7.5-cm depth. Selected and supports plant growth. regression models were validated with an independent soil sample An evaluation of how various management practices data set (n 20). Soil properties were similar between measured and affect soil quality in claypan soils is important because predicted. Some soil properties (e.g., clay and CEC) and ECa that these soils are highly sensitive to soil degradation from were positively correlated to yield in years with average or greater processes such as runoff and erosion (Nikiforoff and than average cumulative July to August precipitation (15 cm) were Drosdoff, 1943; Kitchen et al., 1998). The central claynegatively correlated to yield for years with less than average precipipan soil region occupies about 4 million ha in Missouri tation (15 cm). Our results suggest that sensor-based ECa can be a quickandeconomicalwayofestimatingsomeclaypansoilqualitymea- and Illinois and is identified as Major Land Resource surements.