Assessment of soil quality in conservation reserve program and wheat-fallow soils

Chemical and microbial aspects of soil quality are an important consideration when evaluating the benefits of soil conservation efforts such as the Conservation Reserve Program (CRP). The objective of this study was to evaluate the quality of CRP and wheat-fallow (W-F) soils using soil biological and chemical parameters and C and N mineralization processes. The study was conducted on 20 CRP/W-F paired sites in eastern Washington, on Ritzville silt loam (coarse-silty, mixed, mesic Calciorthidic Haploxerolls). Soils collected from the paired fields were analyzed for chemical and biological parameters that have been suggested as indicators of soil quality. Potential enzyme activities and soil N were higher in the CRP soil than the W-F soil. Although there were no significant differences in total organic carbon (TOC) or microbial biomass carbon (MBC) the C mineralization potentials and C pools mere significantly different between the CRP and W-F soils. Soil biota measurements showed there was greater active bacterial biomass in the CRP soil but greater fungal-feeding nematodes, flagellates, and amoebae in the W-F soil. The C mineralization study suggests that there is a significant increase in the secondary C pool of the CRP soil, which may indicate a buildup of higher quality soil organic matter and the potential for higher enzyme levels. When grass or straw was added to each soil type, the W-F soil produced more CO2 with either substrate than the CRP soil, indicating C limiting conditions in the W-F soil. Since it is unknown what constitutes good soil quality, these shifts in chemical and biological parameters may seem subtle. However, in general, trends in the data indicated that soil quality in the CRP was improved after 4 to 7 yr, compared with its previous management in W-F cropland.