CRP Land Research Articles

Effects of Land Use on Greenhouse Gas Flux in Playa Wetlands and Associated Watersheds in the High Plains, USA

In the High Plains, U.S., native prairie conversion to cropland agriculture has resulted in a loss of service delivery capabilities from most depressional wetlands as a result of sedimentation. Restoring historic hydrological conditions to affected wetlands may rejuvenate some services, however, there may be tradeoffs due to emissions of CH4 and N2O. We evaluated the influence of two predominant conservation programs (Wetlands Reserve Program, WRP and Conservation Reserve Program, CRP) on gas emissions (CO2, CH4, N2O) from 42 playas and uplands in the High Plains of Nebraska. Because playa restoration through the WRP is most prevalent in the Rainwater Basin (RWB), we studied 27 playas/uplands among reference condition, cropland, and WRP land uses. We studied 15 playas/uplands within native grassland, cropland, and CRP land uses in the Western High Plains (WHP) of Nebraska. Emissions were collected bi-weekly from April-October of 2012 and 2013 from four landscape positions extending outward from the wetland center into upland. In RWB playas, CH4 and N2O emissions were similar among land uses but CO2 was 28% higher in cropland than WRP wetlands. Cropland uplands emitted 648% more N2O than reference and WRP uplands. Overall, net CO2-equiv emissions were lower in playas/uplands in WRP, suggesting that benefits of playa restoration may include climate mitigation services as well as increased water storage capacity and biodiversity provisioning. In the WHP, cropland and grassland playas emitted 46 and 23 times more CH4, respectively, than CRP in 2013. Playas in CRP emitted 43% less N2O than cropland playas. In 2013, net emissions for cropland and native grassland playas were 75% and 39% greater, respectively, than CRP playas. In the WHP, the benefits of lower gas emissions must be appropriately weighted against tradeoffs of ecosystem services related to shorter hydroperiods as a result of reduced runoff into playas in CRP.

Relationships among land use, soil texture, species richness, and soil carbon in Midwestern tallgrass prairie, CRP and crop lands

Accumulation of soil carbon (C) in ecosystems could help mitigate climate change, particularly in agricultural landscapes, but accumulation rates are thought to depend on land cover and management practices. To uncover relationships between soil properties and vegetation management strategies in the Midwestern USA, we examined soil C and nitrogen (N) content on lands under five management types that produced different levels of plant species diversity: remnant prairies, high-, medium- and low-diversity grassland restorations, and crop fields. We examined the relationships of soil C, labile C, and N with plant species richness, aboveground biomass production and silt+clay content on land under each of the five management types, in two non-adjacent counties. Field plots were located in sites predicted to have mid-range soil C contents for each county (2.0–2.5% or 2.4–2.9%) based on a SOLIM (Soil Land Inference Model) C model (Libohova, 2010), in an effort to limit variability among sites. However, we found that soil texture data from the Soil Survey Geographic Database (SSURGO; the base data layer for SOLIM) frequently overestimated silt+clay content relative to the hydrometer-measured silt+clay content of our collected soil samples. We found that the low-diversity restorations (which were the most productive sites) had the greatest soil C and N content over the full soil profile (to 90cm depth). On average soil C was 1.3 and 1.9 times greater, and soil N was 3.7 and 1.5 times greater, in the low diversity restorations compared to remnant prairies in Newton and Lee Counties, respectively. This was likely a consequence of (and a driver of) the high biomass production of the grasses that tended to dominate these fields. We attribute low soil C content in the remnant prairies and high diversity restorations in large part to the patterns of soil texture that led to the historical patterns of land use change, in which less productive areas were left as prairie and the more productive areas tilled. Labile C was highest in the low-diversity restorations at the 0–15 and 15–30cm depths in both counties. Labile C was greatest from 0–15cm and decreased with soil depth. Patterns of soil C across the intensely cultivated Midwestern landscape depend on the interaction between the suitability of soil for cultivation, and historical land management in terms of both the soil and vegetation. Our results suggest that the more heavily managed and productive fields in this region often harbor the greatest soil C, and that this soil C cannot be accurately predicted from the SSURGO database, highlighting the challenges and opportunities associated with maintaining and sequestering soil C in the Midwestern agricultural landscape.

Soil organic carbon in playas and adjacent prairies, cropland, and Conservation Reserve Program land of the High Plains, USA

Soil organic carbon (SOC) is an important reservoir for atmospheric CO2 associated with climate warming. The High Plains, USA, lacks region-wide SOC estimates within playa wetlands and their adjacent watershed. Croplands often have less SOC than grasslands, and the Conservation Reserve Program (CRP; former croplands planted to grass) may return SOC. Our goals were to estimate SOC within playa wetlands and investigate small scale differences within wetland catchments across a broad agriculturally modified landscape. We estimated SOC (kgm−2) to 50cm depth from 4 soil cores/catchment (in playas and 10, 40 and 100m into uplands) at 56, 52, and 54 sites in native grassland, CRP and cropland, respectively. At a subset of sample locations within each land use type, we estimated SOC to 1m depth to characterize SOC missed by shallow sampling. In playa wetlands, CRP SOC from 0 to 50cm was 18% greater than croplands, but native grassland playa SOC did not differ from other land-uses. From 0 to 1m, SOC in native grassland wetlands and uplands was 20% greater than the same habitats within croplands, while CRP lands were intermediate. Native grassland playa SOC also was 16% greater than in surrounding native short grass prairie. Playas therefore represent an important SOC repository in the High Plains ecoregion. CRP playas and uplands may require an additional 10–30 years to resemble native grassland SOC. SOC increased with playa area throughout CRP and native grassland catchments, suggesting playa hydrogeomorphology influences adjacent upland SOC. High Plains playas store 20.8Tg C and cropland conversion caused a cumulative loss of 2.0Tg C from 82,000ha of playas. Currently, CRP enrollment on over 25,000ha of playas has returned 0.2Tg C (95% CI: 0.1–0.3), only half the historic SOC lost by cropland conversion within CRP playas. To promote SOC storage, native grasslands and large playas should be preserved and CRP enrollments should be maintained over long timescales.

Simulated impact of the renewable fuels standard on US Conservation Reserve Program enrollment and conversion

AbstractA socioeconomic model is used to estimate the land‐use implications on the U.S. Conservation Reserve Program from potential increases in second‐generation biofuel production. A baseline scenario with no second‐generation biofuel production is compared to a scenario where the Renewable Fuels Standard (RFS2) volumes are met by 2022. We allow for the possibility of converting expiring CRP lands to alternative uses such as conventional crops, dedicated second‐generation biofuel crops, or harvesting existing CRP grasses for biomass. Results indicate that RFS2 volumes (RFS2‐v) can be met primarily with crop residues (78% of feedstock demand) and woody residues (19% of feedstock demand) compared with dedicated biomass (3% of feedstock demand), with only minimal conversion of cropland (0.27 million hectares, <1% of total cropland), pastureland (0.28 million hectares of pastureland, <1% of total pastureland), and CRP lands (0.29 million hectares of CRP lands, 3% of existing CRP lands) to biomass production. Meeting RFS2 volumes would reduce CRP re‐enrollment by 0.19 million hectares, or 4%, below the baseline scenario where RFS2 is not met. Yet under RFS2‐v scenario, expiring CRP lands are more likely to be converted to or maintain perennial cover, with 1.78 million hectares of CRP lands converting to hay production, and 0.29 million hectares being harvested for existing grasses. A small amount of CRP is harvested for existing biomass, but no conversion of CRP to dedicated biomass crops, such as switchgrass, are projected to occur. Although less land is enrolled in CRP under RFS2‐v scenario, total land in perennial cover increases by 0.15 million hectares, or 2%, under RFS2‐v. Sensitivity to yield, payment and residue retention assumptions are evaluated.

Potential ecological impacts of switchgrass (Panicum virgatum L.) biofuel cultivation in the Central Great Plains, USA

Switchgrass (Panicum virgatum L.) is a broadly adapted warm-season grass species native to most of the central and eastern United States. Switchgrass has been identified as a potential biofuel species because it is a native species that requires minimal management, and has a large potential to sequester carbon underground. Since the 1990’s, switchgrass has been bred to produce cultivars with increased biomass and feedstock quality. This review addresses potential ecological consequences of widespread switchgrass cultivation for biofuel production in the central United States. Specifically, this review address the ecological implications of changing use of marginal and CRP land, impacts on wildlife, potentials for disease and invasions, and changes in soil quality through reductions in erosion, decomposition rates, and carbon sequestrations. A central theme of the review is the utility of maintaining landscape heterogeneity during switchgrass biofuel production. This includes implementing harvest rotations, no till farming, and mixed species composition. If negative ecological consequences of switchgrass cultivation are minimized, biofuel production using this species has economical and environmental benefits.

Using DAYCENT to quantify on-farm GHG emissions and N dynamics of land use conversion to N-managed switchgrass in the Southern U.S.

Use of a simulation model to predict long-term yield, greenhouse gas (GHG) emissions, and water quality impacts can be valuable for assessing land use conversion to bioenergy crops. The objective of this study is to assess the usability of DAYCENT for measuring environmental impacts due to land conversions from cotton and CRP lands (as unmanaged grasses) to switchgrass in the Southern U.S. We use published yield data to calibrate the crop growth parameters and test the calibrated model on independent data sets. We then apply the model to predict other relevant C and N parameters. In the case of cotton, the model simulates long-term mean cotton lint yield within 25% of observed yields across the South and within 4% of yields in the case study area of Darlington County, SC. DAYCENT also matches observed mature switchgrass yields within 25% of the mean in the range of expected fertilization rates across the region and within 6% in the case study area. Long-term simulations predict a decrease in GHG emissions (1.0–3.8 MtCO 2-e/ha-yr) and a reduction of nitrate runoff (up to 95%) for conversions from cotton to switchgrass at N application rates of 0–135 kgN/ha. Conversely, conversion from unmanaged grasses to switchgrass resulted in annual increases of net GHG emissions (0.2–1.4 MtCO 2-e/ha-yr) for switchgrass at no and low (45 kgN/ha) fertilization rates. Sequestration occurs due to increased soil organic C when higher levels of N are applied. At all levels of fertilization, a reduction of nitrate (50–70%) occurs when converting from unmanaged, unharvested grasses. The amount of nitrate leaching is only slightly sensitive to the fertilization rate applied to the perennial switchgrass. DAYCENT sufficiently models the “carbon debt” from land use conversion from CRP grasslands to managed switchgrass and highlights the importance of fertilization rate. Both C and N parameter results fall within published observed ranges. Thus, the long-term (10–15-year) accuracy of the model for both cotton and switchgrass offers promise as a tool for analyzing land use conversions in terms of N-managed yields and subsequent environmental impacts and benefits.

CO2 fluxes of transitional bioenergy crops: effect of land conversion during the first year of cultivation

The present study examined the effect of land conversion on carbon (C) fluxes using the eddy covariance technique at seven sites in southwestern Michigan (USA). Four sites had been managed as grasslands under the Conservation Reserve Program of the USDA. Three fields had previously been cultivated in a corn/soybean rotation with corn until 2008. The effects of land use change were studied during 2009 when six of the sites were converted to soybean cultivation, with the seventh site kept as a grassland. In winter, the corn fields were C neutral while the CRP lands were C sources, with average emissions of 15gCm � 2 month � 1 . In April 2009, while the corn fields continued to be a C source to the atmosphere, the CRPs switched to C sinks. In May, herbicide (Glyphosate) was applied to the vegetation before the planting of soybean. After tilling the killed-grass and planting soybean in mid June, all sites continued to be C sources until the end of June. In July, fields previously planted with corn became C sinks, accumulating 15‐50gCm � 2 month � 1 . In contrast, converted CRP sites continued to be net sources of C despite strong growth of soybean. The conversion of CRP to soybean induced net C emissions with net ecosystem exchange (NEE) ranging from 155.7 (� 25) to 128.1 (� 27)gCm � 2 yr � 1 . The annual NEE at the reference site was � 81.6 (� 26.5)gCm � 2 yr � 1 while at the sites converted from corn/soybean rotation was remarkably different with two sites being sinks of � 91 (� 26) and � 56.0 (� 20.7)gCm � 2 yr � 1 whereas one site was a source of 31.0 (� 10.2)gCm � 2 yr � 1 . This study shows how large C imbalances can be invoked in the first year by conversion of grasslands to biofuel crops.

Post‐Contract Grassland Management and Winter Wheat Production on Former CRP Fields in the Southern Great Plains

Integrated management guidelines for postcontract land use Conservation Reserve Program lands in semiarid regions are generally lacking. We determined the relative efficacy of four systems of transitional conservation practices for producing ‘Old World' bluestem (OWB) (Bothriochlora ischaemum L.) and dryland wheat (Triticum aestivum L.) and cotton (Gossypium hirsutum L.) on former CRP fields. The sites were located on Dalhart fine sandy loam (Aridic Paleustalf) and La Casa–Aspermont clay loam (Typic Paleustoll) near Forgan and Duke, OK, respectively. Removing old growth increased cumulative OWB yields between 1994 and 1997. Applications of 67 kg N and 16.5 kg P ha−1 increased yields by 0, 70, and 180% at Forgan and 290, 70, and 280% at Duke in 1995 to 1997, respectively. Removing the old dry matter and regrowth vigor also enhanced chemical suppression and killing of the grass, the performance of conservation tillage, and achieving a uniform crop stand. Early OWB suppression conserved stored water that was vital to cool‐season crop production in the year the contract expired. First‐year wheat yields averaged 970, 490, and 1002 kg ha−1 at Forgan and 1590, 600, and 830 kg ha−1 at Duke under unfavorable weather conditions (i.e., drought, late freeze) of 1995 through 1997, respectively. No‐till generally produced higher yields, averaging 10 and 35% greater than conservation systems at Forgan and Duke, respectively. In variable semiarid environment, the chance of success for agronomic production decreased in the order of grass production, NT wheat, tilled wheat, and dryland cotton on former CRP lands.

Summary of grazing research on Kansas CRP land (1997)

Summary of grazing research on Kansas CRP land (1997)

An Evaluation of Post Conservation Reserve Program Alternatives In The Texas High Plains

AbstractFour policy alternatives for CRP lands upon expiration of the current contracts in Hale County, Texas are evaluated using chance-constrained programming. It was found that if CRP contracts are extended at the current average rental rate, 40 percent of the current enrollment would be expected to return to crop production, while 66 percent would return to crop production if the program were eliminated. The results also indicate that the marginal value of CRP payments to producers is lower than the marginal value of deficiency payments.

Grasshopper Control, 1988

Abstract Fifty ft × 0.5 mile plots were arranged in a randomized complete block design. Two replicates were placed in an 80 acre soybean field and 2 replicates were placed in 160 acres of CRP land. Treatments were applied by air with an Ag Cat flying at 100 mph on 2 Aug. Five gal total material/acre was applied. Air temperature was 69-79°F with overcast skies; wind speed was 5°8 mph. 2 sets of 25 sweeps each using a standard 15 inch sweep net were collected in each plot by 2 different people. Counts were averaged and control calculated as a % reduction from untreated. Populations at 72 h posttreatment were so low in the untreated that comparisons were not meaningful.

Grasslands: The Future of CRP Land after Contracts Expire

Grasslands: The Future of CRP Land after Contracts Expire