|Mohanty, B. - U.C. RIVERSIDE|
|Klittich, W. - IOWA STATE UNIV.|
|Horton, R. - IOWA STATE UNIV.|
|Van Genuchten, Martinus|
Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 2, 1994
Publication Date: N/A
Interpretive Summary: Soil temperature is an important physical property that affects crop growth and water movement in soil. Its spatial variability across a plot/field and temporal variability across different time lengths (e.g., day/month/year) need to be understood properly for better soil water management practices. This study was conducted to measure the spatio- temporal variability of soil temperature and its diurnal fluctuation in three different soil management systems including moldboard plowing, chisel plowing, and ridge tillage under continuous corn. Hysteresis (i.e., differences between heating versus cooling periods) was found within diurnal cycle between the mean and the sample variance under all management practices at 1- and 10-cm depths. Better spatial correlation were found along the crop rows than across crop rows. These results will further help in understanding the field-scale nonisothermal water and chemical movement in near-surface soil environment.
Technical Abstract: This study was conducted to measure the horizontal spatial variability of soil temperature and its diurnal fluctuation in three different tillage systems. Soil temperature was measured with copper-constantan thermocouples at 49 positions in each system at the 1- and 10-cm depths. The thermocouples formed by a 7 by 7 grid with a spacing of 3.0 (east-west) by 1.5 m (north-south). The three management systems were fall moldboard plowing followed by spring disking and planter operation (MP), fall chisel plowing followed by spring disking and planter operation (CP), and ridge tillage slot planting (RN). Each management system had been under continuous field corn (Zea mays L.) for 8 yr. A novel finding of the study is that a hysteresis within the diurnal cycle existed between the mean and the sample variance. This hystersis was presumably due to differences in soil surface heating and cooling rates during the diurnal cycle. Although no definitive relationships could be determined, semivariograms appeared to show in a time dependence and anisotropy during the 24-h observation period. Correlation distances were = 9 m in the E-W direction along crop rows and tillage operations but <1.5 m in the N-S direction across crop rows and tillage operations. These spatial correlation distances will be useful in deciding the minimum (lateral) spacing between adjacent soil temperature sensors in the field.