Infiltration Rate of a Sandy Loam Soil: Effects of Traffic, Tillage, and Plant Roots

Settling and trafficking of a soil after tillage causes rapid changes in the soil physical condition until a new equilibrium is reached. In the soil studied, a Wasco (coarse-loamy, mixed, nonacid, thermic Typic Torriorthent) sandy loam, soil compaction reduces infiltration rates, which under grower conditions could result in inadequate infiltration of irrigation water to supply crop requirements. Our objective was to evaluate important management practices as they relate to changes in the infiltration rate of a sandy loam soil. Factors evaluated were traffic, tillage between crops, and the formation of channels by roots of per- ennial crops. Tillage between crops increased the infiltration rate dur- ing the first part of the season in trafficked soils but decreased or had no effect on nontrafficked soil. Alfalfa (Medicago saliva L.) increased the infiltration rate fourfold during a 2-yr period in a heavily com- pacted soil. An increase in bulk density from 1.6 to 1.8 Mg m~3 decreased infiltration rate 54% in the field. Hydraulic conductivity of undisturbed cores was at least seven times larger than that measured in columns of disturbed soil (same bulk density). This difference is believed to be the result of natural channels in the undisturbed soil that are destroyed when the soil is disturbed. Under controlled traffic, when surface seal is not a problem, tillage will not be necessary to obtain adequate infiltration rates except in the wheel paths.