|Mohanty, B. - U.C. RIVERSIDE|
|Ankeny, M. - DANIEL B STEPHENS & ASSOC|
|Horton, R. - IOWA STATE UNIV.|
|Kanwar, R. - IOWA STATE UNIV.|
Submitted to: Water Resources Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 15, 1994
Publication Date: N/A
Interpretive Summary: Surface positions (crop row, trafficked interrow, and nontrafficked interrow) in an agricultural field influence the amount of downward infiltration (of water) versus overland runoff. Using ponded and tension infiltrometers (disc infiltrometry) we measured the saturated and unsaturated hydraulic conductivity at four different soil water tensions in nthe three surface positions in a no-till field under continuous corn production. Hydraulic conductivity measurements were maximum in the corn rows and minimum in wheel track interrows, with no-track interrows intermediate. The rates of decrease of hydraulic conductivity from saturated to unsaturated conditions were similar for corn row and no-track interrow positions which are significantly higher than that of wheel-track positions. In general, no spatial structure was found for saturated and unsaturated hydraulic conductivity, in all three field positions. Small spatial structures for "rate of change of hydraulic conductivity with tension" were somewhat associated with traffic pattern (in corn rows) and soil type (in nontrafficked interrows). Spatial structure was absent in wheel track interrows, indicating the destruction of pore structure due to wheel compaction. Our findings could help quantifying field-scale water and chemical transport at the filed site under row crop cultivation using farm machinery.
Technical Abstract: To examine and differentiate the factors contributing to spatial structure under different field conditions 296 infiltration measurements were made in the corn rows, no-track interrows, and wheel track interrows of a field using four different soil water tensions h (0, 30, 60, and 150 mm). Unsaturated hydraulic conductivity (K) and saturated hydraulic conductivity (Ks) were maximum in the corn rows and minimum in wheel track interrows, with no-track interrows intermediate. Exponents (alpha parameters) of Ks and K relationships (K = Ks exp - (alpha h) for corn rows and no-track interrows were not significantly different from each other but were significantly different from alpha for the wheel track interrows at P = 0.01 level. Spatial variability of K and Ks values showed some pseudo proportional effect in nugget variance for all three field conditions. No-track interrows clearly showed an inverse trend for semivariogram of K with changing tension (h) values, whereas differences were found for corn rows and wheel traffic interrows. Under corn rows, in addition to random variation, a small five-row periodic variation at the P = 0.20 level, matching the five-row traffic configuration, was discovered. The spatial structure of alpha was influenced by soil type for the no-track interrows. Spatial structure was absent in wheel track interrows, indicating the destruction of pore structure due to compaction.