EFFECT OF CULTIVATION ON HYDRAULIC-PROPERTIES OF AN IOWA SOIL USING TENSION INFILTROMETERS

The potential for groundwater contamination at a given location is inf luenced strongly by the hydraulic properties (K) of the soils. The obj ective of this study was to investigate the effect of field cultivatio n in a no-till soil on the variability of infiltration rates, fraction al porosity distribution, and soil hydraulic conductivity during the g rowing season. Infiltration rates were measured at different tensions using tension infiltrometers in two no-till plots with cultivation (cu ltivated) and two no-till plots without cultivation (uncultivated) at two different depths (soil surface and 0.15-m depth). Tension infiltro meter readings were taken at four soil water tensions (0-, 30-, 60-, a nd 90-mm) and at three different times during the growing season (July , August, and September). Results of this study showed that infiltrati on rates at 0-mm water tension were significantly larger than infiltra tion rates at the three other tensions for all plots. The data on infi ltration rates show that under saturated how conditions, macropore dow is a significant pathway for water infiltration. For the cultivated p lots, 70 to 80% of the saturated flux at the soil surface occurred tho ugh macropores. At 0.15-m depth for the same plots, there was a decrea se in macropore flow during the growing season (from 69% in July to 44 % in September). However, in the uncultivated plots, macropore flow in creased (by almost 52%) at the soil surface during the growing season. In the uncultivated plots, macroporosity increased with time at the s oil surface. During the latter part of the growing season, macroporosi ty values for no-till plots with cultivation were very similar to thos e of no-till plots without cultivation. The effect of cultivation disa ppeared with time during the growing season. Although there was great variability in the saturated K values, K values at the surface remaine d constant in the cultivated plots at the beginning of the growing sea son and increased during the latter part of the growing season. In the plots without cultivation, there was an increase in the surface-satur ated K values from July through September.