COMPARISONS OF SOIL PHYSICAL CHARACTERISTICS IN LONG-TERM TILLAGE WINTER WHEAT-FALLOW TILLAGE EXPERIMENTS

Soil physical characteristics resulting from tillage of fallow-wheat ( Triticum aestivum L.) cropping systems were compared for two soils in western Nebraska. The soil physical environment influences the amount of water entering soil and the microenvironment that influences soil b iological processes important to plant response. Effects of tillage on physical properties varied with soil type and depth of soil tillage. Generally, the 0-76 mm surface layer has the largest number of physica l properties that differ as a result of tillage; however, only a few p roperties differed at greater depths. The Alliance silt loam (fine sil ty, mixed, mesic, Aridic Arguistoll) soil at the Previously Cultivated site, for example, showed differences in bulk density, hydraulic cond uctivity, ratio of air to water permeability, and total porosity for t he 0-76 mm layer but only hydraulic conductivity was different at the 76-152 mm depth. A similar frequency of differences in physical proper ties was also true in the 0-76 mm layer for the Duroc loam (fine silty , mixed, mesic, Pachic Haplustoll) soil at the Native Sod site. Compar ed among treatments, water content, bulk density, and pore space diffe red in the 0-76 mm layer, while all properties different in the 76-152 mm layer, and there were fewer differences in the 152-304 mm layer in the Native Sod site. The sod treatment usually was the most extreme v alue with the tillage treatment values clustered together. Air to wate r permeability ratio, as an indicator of structural stability (ratio o f 1 being stable), for the Alliance soil ranged from 18 to 43 in the 0 -76 mm layer and from 31 to 152 in the 76-152 mm layer. For the Duroc soil, the ratio ranged from 5 to 6 in the 0-76 mm layer and 6 to 22 in the 76-152 mm layer. The Duroc soil has not been cropped as long as t he Alliance soil and showed a tendency to be more structurally stable. Based on precipitation intensity records and infiltration characteris tics, water would seldom run off the Duroc soil when in sod and with s ub-till or no-till. Results show that the runoff would occur most freq uently from the plow treatment. (C) 1998 Published by Elsevier Science B.V. All rights reserved.