EFFECT OF TILLAGE-INDUCED SOIL MACROPOROSITY ON WATER INFILTRATION

In some areas of the inland Pacific Northwest, surface runoff is a major source of water loss. Chiseling or plowing in the fall of the year, following wheat harvest, are farming practices to increase water infiltration especially in areas where frozen soil is anticipated. Water infiltration, overwinter water storage, and soil macroporosity were measured in fall tillage treatments of: (1) no tillage (NT); (2) chiseled stubble (C); (3) Paraplowed stubble (P). In spring, final infiltration rates for the respective treatments were 9.2, 22.8 and 23.5 mm h-1. Over winter, all treatments stored the same amount of water in the 3.35-m profile, however there were differences in the distribution of water in the profile. The fraction of macroporosity in a horizontal cross-section of soil, was different for each treatment and depth of cross-section. For the C treatment, macroporosity decreased from about 20% at the 7.6-cm depth to <1.0% at 25.4 cm, In contrast, macroporosity decreased with depth to a minimum of 6.9% at the 12.7-cm depth and increased to a maximum of 17.2% at 25.4 cm for the P treatment. NT had <1.0% macroporosity. Over winter soil settling is uncertain, however, water infiltration and macroporosity measurements conducted in March attest to the overwintering stability of the macropore structure of both C and P treatments. © 1990.