EFFECT OF CULTIVATION ON HYDRAULIC PROPERTIES OF AN IOWA SOIL USING TENSION INFILTROMETERS1

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Abstract
The potential for groundwater contamination at a given location is influenced strongly by the hydraulic properties (K) of the soils. The objective of this study was to investigate the effect of field cultivation in a no-till soil on the variability of infiltration rates, fractional porosity distribution, and soil hydraulic conductivity during the growing season. Infiltration rates were measured at different tensions using tension infiltrometers in two no-till plots with cultivation (cultivated) and two no-till plots without cultivation (uncultivated) at two different depths (soil surface and 0.15-m depth). Tension infiltrometer readings were taken at four soil water tensions (0-, 30-, 60-, and 90-mm) and at three different times during the growing season (July, August, and September). Results of this study showed that infiltration rates at 0-mm water tension were significantly larger than infiltration rates at the three other tensions for all plots. The data on infiltration rates show that under saturated flow conditions, macropore flow is a significant pathway for water infiltration. For the cultivated plots, 70 to 80% of the saturated flux at the soil surface occurred though macropores. At 0.15-m depth for the same plots, there was a decrease in macropore flow during the growing season(from 69% in July to 44% in September). However, in the uncultivated plots, macropore flow increased (by almost 52%) at the soil surface during the growing season. In the uncultivated plots, macroporosity increased with time at the soil surface. During the latter part of the growing season, macroporosity values for no-till plots with cultivation were very similar to those of no-till plots without cultivation. The effect of cultivation disappeared with time during the growing season. Although there was great variability in the saturated K values, K values at the surface remained constant in the cultivated plots at the beginning of the growing season and increased during the latter part of the growing season. In the plots without cultivation, there was an increase in the surface-saturated K values from July through September.