Influence of tillage on soil properties under agricultural and natural prairie systems

Over the last 130 years, agriculture practices in the Palouse region of Washington State have caused remarkable changes in soil properties and soil processes. No-till (NT) is an alternative to conventional tillage (CT), mainly with the objective of reducing soil erosion. However, the impact of NT practices on soil hydraulic properties and increased soil acidity in the seed zone is not completely known. Surface application of lime to correct for soil acidification may not be practical under NT. One alternative is to place the lime near the seed zone. Soil hydraulic properties were studied in a long-term NT soil, a long-term CT soil, and a never-tilled natural prairie (NP) soil. The effect of sample size on the near-saturated K of a NT silt loam soil was also analyzed. Finally, laboratory experiments were conducted to characterize the effect of lime on chemical and biological soil properties in a long-term NT soil. Hydraulic conductivities under the NP soil were about one order of magnitude larger than for cultivated soils. Under NT, saturated K in the top 5 cm of soil was significantly higher than under CT. No-till and CT soils had similar unsaturated K, indicating that restoration of original hydraulic properties in these soils may take a long time. Determination of K in an undisturbed soil core was affected by the length of the soil column. The heterogeneity of the soil with depth affected mostly the saturated K. Unsaturated K at low hydraulic heads was less affected by the length of the soil core due to increased homogeneity of the porous media. Lime increased soil NO3--N consistently at only at the highest rate of 17.6 Mg ha-1. Greater microbial respiration rates and greater microbial biomass-C were found in lime-treated than in non-limed soils. When soil was limed and mixed over larger depths (0-10, 0-20 cm), NO3 --N, soil respiration rates, and microbial biomass-C, decreased significantly. Organic matter turnover was faster in the lime-treated than in the non-limed soil.