Influence of Conservation Reserve Program Age and Conversion to Cropland on Soil Quality, Microbial Diversity and Metabolic Capacity: Implications for Our Decisions about Soil Conservation.

The conservation reserve program (CRP) has reduced soil erosion and increased aboveground biodiversity and carbon (C) storage. The Texas High Plains (THP) region leads the nation with >890,000 hectares enrolled in CRP. After these contracts expire, some land may be converted back to cropland. In the THP, conversion of grasslands that had year-round cover to cropland that is disturbed by tillage and exposed for part of the year may have a negative impact on many of the ecosystem benefits established during CRP restoration. Assessments of soil microbial community composition and diversity are often coupled to the assessment of soil processes (C storage and nutrient cycling) to better address the ecosystem response to disturbances and recovery. Our first objective was to measure these sensitive soil quality indicators to determine if age of CRP influenced soil quality by comparing soil samples from 7 non-irrigated croplands (0 years restored), 16 CRP lands (range in age from 6-26 years) and 3 native rangelands (NR). Our second objective evaluated the same soil parameters during the first few years when CRP land is converted to cropland.  Preliminary results of our first objective suggest that the CRP lands have not reached soil C levels of the NR and require decades longer to reach these levels. Additionally, CRP lands had lower ecological stress indicators than cropped fields and stress decreased with increasing CRP age. CRP age also positively influenced enzymatic activities involved in nutrient cycling and key soil organisms such as arbuscular mycorrhizal fungi (AMF) that are important for soil stability and water and nutrient uptake. Preliminary results from our second objective demonstrated lower indicators of ecological stress in converted fields than CRP. However, CRP had higher AMF biomass during the first year. In the second sampling year, one of the stress ratios was lower in CRP fields. These findings indicate that the initial measures of improved soil quality in the converted fields may be only short lived.