Conversion of conservation reserve program land back to cropland: short-term changes in soil carbon and nitrogen dynamic

Authors: LI, CHENHUI - University Of Missouri; Moore, Jennifer; Acosta-Martinez, Veronica; FULTZ, LISA - Louisana State University; KAKARLAA, MAMATHA - Northshore University Health System

Submitted to: Journal of Soil and Water Conservation
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/14/2022
Publication Date: N/A
Citation: N/A

Interpretive Summary: The Conservation Reserve Program (CRP) provides financial and technical support to agricultural producers to protect the natural resources of their lands. An example of such a program is converting cropland into perennial grasses to protect the soils from erosion and to increase soil health. Many of these CRP agreements will end in 2025 and some producers are contemplating to revert to crops. The problem is that we do not know if the benefits from soil health would be lost once these lands go back from grasses to crops. To answer this question, university, and ARS scientists from Lubbock, for 4 years sampled the soil from fields with crops and with grasses. In these soil samples we measured indicators of soil health. Our results indicated that within 1 to 2 years of planting grasses the indicators of soil health increased and that after 4 years, when grass planted fields were converted to crops, the soil health indicators decreased. These results are important and may persuade producers to continue to enroll in the CRP program to maintain their fields in perennial grasses.

Technical Abstract: Texas leads the nation in acreage enrolled as well as expiring from the Conservation Reserve Program (CRP) and the majority of these restored grasslands are located in the Southern High Plains (SHP). The reduction in acres allowed to enroll in CRP and crop market forces have resulted in many farmers considering to place the land under crop production again. Changes in soil health within the first years of conversion from long-term (20+ years) CRP back to cropland have not been well documented. We collected soil (0-10, 10-30, and 30-50 cm) from three sets of CRP and converted CRP (C-CRP) sites from 2012 to 2015 (1-4 yrs of the conversion). Soil health indicators related to soil carbon (C) and nitrogen (N) dynamics were evaluated including soil organic C (SOC), total N (TN), particulate organic matter C and N (POM-C and POM-N), permanganate oxidizable C (POXC), microbial biomass C and N (MBC and MBN), in situ soil CO2 efflux, and metabolic quotient (qCO2). The incorporation of grass residues in C-CRP resulted in greater labile C and N stocks such as MBC and MBN compared to CRP after 1-2 years after conversion. However, all the C and N stocks (SOC, TN, POM-C, POM-N, MBC, MBN, and POXC) overall had a trend of decline in C-CRP compared to CRP over the four years after the conversion, and the responses varied by indicators and depth increments (0- to 10-cm, 0- to 30-cm, and 0- to 50-cm). The cultivation likely relocated the residues from the surface to the subsurface layer, which was indicated by the decline of C and N stocks at the top 10 cm soil in C-CRP but with no difference except POM-N between CRP and C-CRP at the 0- to 30-cm soil increment. However, exploring beyond the tillage, SOC stock showed a 3.4 Mg ha-1 loss from the CRP to C-CRP conversion at 0- to 50-cm depth increment. Precipitation gradually increased in our study, and the soil C and N stocks either decreased in C-CRP or did not substantially increase as in CRP from 2013 to 2015. In 2015, the year of record precipitation, microbial biomass and activity bounced back quickly in both systems, which likely triggered priming soil organic matter decomposition at both systems, but CRP still gained SOC in 2015 compared to 2014. In contrast, C-CRP showed decreases in all variables except MBN in 2015. Overall, this study showed negative impacts on soil C and N stocks within four years after CRP to C-CRP conversion.