SPATIAL-ANALYSIS OF HYDRAULIC CONDUCTIVITY MEASURED USING DISC INFILTROMETERS

Spatial variability of surface hydraulic properties and the extrinsic (e.g., traffic, cropping, etc.) and intrinsic (e.g., soil type, pore s ize distribution, etc.) factors; associated with these properties are important for infiltration and runoff processes in agricultural fields . Disc infiltrometers measured infiltration at 296 sites arranged on t wo parallel transects. To examine and differentiate the factors contri buting to spatial structure under different field conditions these mea surements were made in the corn rows, no-track interrows, and wheel tr ack interrows of the field using four different soil water tensions Ps i (0, 30, 60, and 150 mm). Unsaturated hydraulic conductivity (K) and saturated hydraulic conductivity (K-s) were maximum in the corn rows a nd minimum in wheel track interrows, with no-track interrows intermedi ate. Exponents (alpha parameters) of K-s and K relationships (K = K-s exp(-alpha Psi)) for corn rows and no-track interrows were not signifi cantly different from each other but were significantly different from ct for the wheel track interrows at P = 0.01 level. Spatial variabili ty of K and K-s values showed some pseudoproportional effect in nugget variance for all three field conditions. No-track interrows clearly s howed an inverse trend for semivariogram of K with changing tension (P si) values, whereas differences were found for corn rows and wheel tra ffic interrows. The spatial structure of a: for all three field condit ions were mostly white noise. Under corn rows, in addition to random v ariation, a small five-row periodic variation at the P = 0.20 level, m atching the five-row traffic configuration, was discovered. The spatia l structure of ct was influenced by soil type for the no-track interro ws. Spatial structure was absent in wheel track interrows, indicating the destruction of pore structure due to compaction.