SOIL MICROBIAL COMMUNITIES: KEY INDICATORS OF SOIL CARBON TRANSFORMATIONS WHEN CONSERVATION RESERVE PROGRAM LAND IS CONVERTED TO CROPLAND

The purpose of this project is to evaluate the soil microbial communities and their influence on biogeochemical cycling and carbon (C) sequestration in Conservation Reserve Program (CRP) sites representing different years of establishment, from 0 (cotton croplands) to 26 years. Additionally, we will evaluate short-term soil microbial community and soil C changes as CRP is converted to cotton during the first four years. The USDA's CRP was introduced by the Food and Security Act of 1985 with the goal of reducing erosion by converting highly erodible croplands to perennial grasslands. As of April 2011, there were 12.6 million hectares of active and expiring CRP cropland contracts. Despite an overall increase in the acreage under CRP contracts, currently there are between 0.8 and to 2.6 million CRP hectares scheduled to expire annually between 2011 and 2014. Texas leads the Nation with the highest total active hectares under CRP contract (1.4 million hectares as of April 2011); the majority of this land is located within the Southern High Plains (SHP) region. Texas, however, also leads the nation with expiring contracts with more than 277,000 hectares scheduled to expire in September 2011 and an additional 334,000 hectares with expiring contracts in 2012. As these CRP contracts expire, soils which have been under long-term grassland production for 10-20 years will be plowed and cropped or grazed. These management conversions may result in the reversal of some of the ecological benefits previously established. The SHP region is representative of semiarid regions currently facing complex challenges to maintain sustainable agriculture while conserving natural resources. Agricultural practices such as fallow periods, monoculture and/or intensive tillage, have focused on water conservation and less on soil conservation due to low water availability from the Ogallala Aquifer. These practices contribute to a deterioration of soil structure and fertility while increasing soil erosion potential to the detriment of crop yields and sustainability. Wind erosion is a national problem that currently threatens agricultural sustainability and environmental quality, contributing to annual cropland soil losses of approximately 776 million tons year-1. Although application of conservative management is a challenge in the SHP region, this region has > 4.7 million hectares of cropland and more than 30% of the cotton that is produced in U.S. To sustain future agricultural activities, research requires evaluating both the short- and long-term impact of management practices, e.g., CRP land, crop rotations and tillage practices. Particularly, the effectiveness of the CRP program in improving soil quality has not been thoroughly evaluated in the SHP region, where significant amount of CRP contracts will be expiring. Therefore, this research effort is crucial because of the increasing challenges that face soil and water conservation efforts for semi-arid agroecosystems regions of North America.