Kristofor R. Brye

Measurements and Modeling of Carbon and Nitrogen Cycling in Agroecosystems of Southern Wisconsin: Potential for SOC Sequestration during the Next 50 Years

Landmanagement practices such as no-tillage agriculture and tallgrass prairie restoration have been proposed as a possible means to sequester atmospheric carbon, helping to refurbish soil fertility and replenish organic matter lost as a result of previous agricultural management practices. However, the relationship between land-use changes and ecosystem structure and functioning is not yet understood. We studied soil and vegetation properties over a 4-year period (1995–98), and assembled measurements of microbial biomass, soil organic carbon (SOC) and nitrogen (N), N-mineralization, soil surface carbon dioxide (CO2) flux, and leached C and N in managed (maize; Zea mays L.) and natural (prairie) ecosystems near the University of Wisconsin Agricultural Research Station at Arlington. Field data show that different management practices (tillage and fertilization) and ecosystem type (prairie vs maize) have a profound influence on biogeochemistry and water budgets between sites. These measurements were used in conjunction with a dynamic terrestrial ecosystem model, called IBIS (the Integrated Biosphere Simulator), to examine the long-term effects of land-use changes on biogeochemical cycling. Field data and modeling suggest that agricultural land management near Arlington between 1860 and 1950 caused SOC to be depleted by as much as 63% (native SOC approximately 25.1 kg C m−2). Reductions in N-mineralization and microbial biomass were also observed. Although IBIS simulations depict SOC recovery in no-tillage maize since the 1950s and also in the Arlington prairie since its restoration was initiated in 1976, field data suggest otherwise for the prairie. This restoration appears to have done little to increase SOC over the past 24 years. Measurements show that this prairie contained between 28% and 42% less SOC (in the top 1 m) than the no-tillage maize plots and 40%–47% less than simulated potential SOC for the site in 1999. Because IBIS simulates competition between C3 and C4 grass species, we hypothesized that current restored prairies, which include many forbs not characterized by the model, could be less capable of sequestering C than agricultural land planted entirely in monocultural grass in this region. Model output and field measurements show a potential 0.4 kg C m−2 y−1 difference in prairie net primary production (NPP). This study indicates that high-productivity C4 grasslands (NPP = 0.63 kg C m−2 y−1) and high-yield maize agroecosystems (10 Mg ha−1) have the potential to sequester C at a rate of 74.5 g C m−2 y−1 and 86.3 g C m−2 y−1, respectively, during the next 50 years across southern Wisconsin.

CARBON BUDGETS FOR A PRAIRIE AND AGROECOSYSTEMS: EFFECTS OF LAND USE AND INTERANNUAL VARIABILITY

Midwestern grasslands have undergone dramatic changes in land use and management practices, but the effects of these changes on terrestrial carbon budgets are poorly understood. This study compared, for five years, the effects of land-use type on components of the carbon (C) budget (above- and belowground net primary production [NPP], C leaching, soil surface CO2 flux, vegetation and soil C contents, and C export from burning and grain removal) of a restored tallgrass prairie and maize agroecosystems on a silt loam soil. Interannual variation of the C budget was addressed by correlating annual fluctuations of environmental variables and soil properties with C-budget components. The C losses we estimated, in order of increasing magnitude, were C leaching, grain C removal from the maize agroecosystems, and soil surface CO2 flux. NPP was significantly greater for N-fertilized maize (10.4 Mg C·ha−1·yr−1) than unfertilized maize agroecosystems (6.2 Mg C·ha−1·yr−1), and both were significantly greater than rest...

Carbon and Nitrogen Storage in a Typic Albaqualf as Affected by Assessment Method

Accurate quantification of soil organic carbon (OC) and nitrogen (N) concentrations are necessary to ascertain the effects of land use, crop rotation systems, and management practices on soil C and N sequestration potential. Soil OC and total N were determined by various methods in a Typic Albaqualf under native tallgrass prairie and agricultural soil cropped to a rice (Oryza sativa L.)–soybean (Glycine max L.)–wheat (Triticum aestivum L.)/soybean rotation that has been annually cultivated for 15, 26, and 44 years. Two wet-oxidation methods, the Walkley-Black (WB) and modified Walkley-Black (mod WB), and high-temperature combustion using a Carlo-Erba and LECO analyzer were used to determine the effects of assessment method on soil OC concentration, while the high-temperature combustion method using the Carlo-Erba and LECO analyzer were used to determine the effects of assessment method on total soil N concentration. Soil OC and total N concentrations determined by high-temperature dry combustion using the Carlo-Erba and LECO analyzers did not differ significantly. Soil OC concentrations determined by the modWB method were generally significantly higher than those from the WB or high-temperature combustion methods. Despite significant linear correlation (r>0.74;p<0.001) between soil OC concentrations by wet-oxidation and dry-combustion methods, assessment methodology significantly affected interpretations regarding changes in soil OC storage over time. The results of this study indicate that the choice of assessment methodology is a critical decision for the accurate quantification of soil OC concentration, content, and change over time.

Carbon and Nitrogen Sequestration in Two Prairie Topochronosequences on Contrasting Soils in Southern Wisconsin

Abstract Prairie restoration has the potential to sequester nitrogen (N) and atmospheric carbon (C) in the soil, but the capability of a site to respond positively to prairie restoration depends on numerous factors such as soil parent material, topography and time. Soil bulk density in the top 10 cm and C and N concentrations at several intervals to a depth of 1 m were measured in a tallgrass prairie topochronosequence at fine- and coarse-textured soil locations to evaluate the role of texture, slope and ecosystem age in controlling C and N sequestration following cessation of cultivation and subsequent prairie restoration. Soil C and N concentrations, contents and C:N ratios were significantly greater in fine-textured soils compared to sites with coarse-textured soil. Soil texture generally did not explain variations in the amounts or rates of C and N sequestration in the restored prairies. Soil surface bulk density was significantly correlated with slope, but not ecosystem age, at sites with coarse-textured soil. Within the limits of this study, neither slope nor ecosystem age were correlated to bulk density at sites with fine-textured soil. Soil C content in the top 25 cm increased significantly as ecosystem age increased for the restored and remnant prairies at the fine-textured location, but not at the coarse-textured location. Results demonstrate that a combination of soil parent material, topography and time since cessation of cultivation control the content and accumulation of C and N following prairie restoration. In the context of this study, the bottom line is that significant C sequestration was not achieved, given the current level and types of restoration management, within two and a half decades following conversion of cultivated cropland to prairie.

Native Soil Quality and the Effects of Tillage in the Grand Prairie Region of Eastern Arkansas

Abstract Soil properties were assessed to determine the effects of tillage agriculture on soil-quality-related parameters of former tallgrass prairie. Soil physical, chemical and biological properties were evaluated in the top 10 cm at six native grassland sites within the Grand Prairie region of east-central Arkansas and compared with adjacent tilled agricultural land in a total of 11 prairie-agriculture land-use combinations. Soil organic matter and total C and N concentrations were significantly lower and soil pH, electrical conductivity and extractable soil P, K, Ca, Mg, Fe were significantly higher under tilled agriculture than under native prairie land use. The introduction and continuance of intense mechanized agriculture and its associated practices have significantly, and for the most part negatively, impacted native soil quality in this region. These results will aid prairie restoration efforts by identifying soil properties most impacted by cultivated agriculture and those that may be desirable to restore and providing potential restoration targets based on native soil properties.

Assessing the Progress of a Tallgrass Prairie Restoration in Southern Wisconsin

Abstract Assessments of ecosystem restorations are necessary to improve restoration practices and goals. Restoration assessments, whether quantitative or qualitative, are also a vital part of managing previously degraded ecosystems. This study examined some of the key structural and functional characteristics and processes of a tallgrass prairie restoration near Arlington, Wisconsin for 5 y, 19 to 24 y after beginning restoration from cultivation, including mean annual drainage, N and C leaching, soil organic matter, pH, extractable P and K, total N and C contents, above- and belowground net primary production, leaf area index, soil surface CO2 flux and net N-mineralization. Total soil N and C contents of the prairie restoration were compared to other nearby prairie restorations, remnants and an adjacent agricultural field, all on similar soil, to determine the degree of change in ecosystem properties as a result of ecological restoration. Soil properties and processes and vegetation characteristics varied annually throughout the 5-y assessment period, but most soil properties showed no significant temporal trend. Only soil N content in the 0–30 cm layer increased significantly in the 5-y period, but the rate of N increase did not coincide with the rate typical of N inputs to a prairie. Results suggest that most soil properties have either already come to some equilibrium with the surrounding environment or their rates of change were too small to measure over 5 y. This study demonstrates the difficulties of ascribing changes in ecosystem properties to restoration. The spatial and temporal variability and slow rates of change make it difficult to discern differences between restored, disturbed and natural ecosystems.

Long-term effects of cultivation on particle size and water-retention characteristics determined using wetting curves

Short-term (i.e., seasonal) variations are expected with some soil physical properties, whereas other properties, such as particle size, are considered static. However, less is known about long-term (i.e., decadal) variations in properties, such as particle-size fractions and water-retention characteristics, caused by continuous annual cultivation. The objective of this study was to determine the effect of land use (i.e., undisturbed virgin prairie vs. cultivated agriculture) and years of continuous annual cultivation on soil particle-size fractions and water-retention characteristics determined using soil wetting curves. Particle-size fractions (i.e., 0.05–2 mm, 0.002–0.05 mm, and <0.002 mm representing sand-, silt-, and clay-sized fractions, respectively) were determined on soil samples collected in 1987 and 2001 from the 0- to 10-cm depth along a transect across four adjacent fields representing a range from 0 to 44 years under continuous annual cultivation. Soil wetting curve data, obtained from a dewpoint potentiameter by re-wetting air-dried, crushed, and sieved soil, were fit by nonlinear regression to determine modeled water-retention characteristics for the native prairie and cultivated agricultural soil from samples collected in 2001. Particle-size fractions and water-retention characteristics were significantly affected by land use and years under continuous cultivation. The sand-sized fraction decreased and the clay-sized fraction increased significantly for the agricultural soil that had been annually cultivated the longest. Results indicate that long-term changes in particle-size fractions can occur following decades of continuous annual cultivation and that the effects of tillage on soil-water-retention characteristics can be ascertained after removing the confounding effects of initial differences in soil and pore structure by using soil wetting curves.

Residue Management Practice Effects on Soil Surface Properties in a Young Wheat-Soybean Double-Crop System

ABSTRACT Approximately 25% of the soybean [Glycine max (L.) Merr.] grown in the mid-South is produced in a wheat (Triticum aestivum L.)-soybean double-crop system. Pre-soybean field preparations often consist of removing wheat residue by burning followed by conventional tillage (CT). However, crop residue burning has serious negative environmental consequences and will likely be outlawed in the future. Therefore, the objective of this study was to evaluate the short-term effects of alternative wheat-residue management practices, tillage [no-tillage (NT) and CT], burning (burn and no burn), and wheat-residue level (low and high), on soil surface properties after two full cropping cycles in a wheat-soybean double-crop production system on two silt-loam Alfisols in east-central Arkansas. Soil bulk density increased over time, but the increase was unaffected by imposed treatments. Changes in soil pH and electrical conductivity (EC) were generally unaffected by tillage or burning, whereas soil EC increased by 7% under the high and decreased by 8% under the low wheat-residue level treatment at one location, but not the other. Mehlich-3-extractable Mg and Zn increased more and Na decreased less under NT than CT at one location or the other. Soil organic matter and total N and C also increased more under NT than CT at one location, but not the other. The results of this study indicate that, in a wheat-soybean double-crop production system in a relatively warm and wet environment, numerous soil properties can be improved more under NT than CT and more when crop residues are left unburned than when they are removed by burning. Extended use of alternative wheat-residue management practices that improve soil tilth will result in more sustainable agriculture and likely increase production.

Soil Quality Differences Under Native Tallgrass Prairie Across a Climosequence in Arkansas

Abstract Climate, specifically moisture and temperature, influences plant growth and nutrient cycling; thus, climate also influences prairie development. Relatively little research has been conducted in the ecological transition zone between the Great Plains and the more humid forests. Since moisture and temperature affect many ecosystem processes, the wetter climate of the southern forest region should influence soil biogeochemical cycling quite differently from that in grassland soils. The objective of this study was to evaluate soil quality and the relationships between selected soil properties across a climosequence in a transition zone between tallgrass prairie in humid-temperate (Ozark Highlands) and humid-subtropical (Grand Prairie) climate regimes in Arkansas. Soil physical, chemical and biological properties of the upper 10 cm differed significantly between physiographic regions. Linear relationships between total soil nitrogen (N) and carbon (C), extractable phosphorus and manganese, electrical conductivity and soil organic matter concentration differed significantly between physiographic regions. Total soil N and C decreased with increasing soil bulk density in both physiographic regions. The relationship between total C and bulk density differed by physiographic region, while the relationship between total N and bulk density did not. Soil organic matter concentration, C:N ratio, and many extractable nutrients, were higher and relationships between selected soil properties differed under native tallgrass prairie in a relatively warm and wet climate than that in a relatively cooler and drier climate. The results of this study suggest that prairie preservation, restoration and management practices should differ depending on climate regimes.

Methodological limitations and N-budget differences among a restored tallgrass prairie and maize agroecosystems

Abstract Interpretation of elemental balances requires careful assessment of component terms and their errors, especially for the major terms of the nitrogen (N) budget which has implications for environmental health. This study reports results from independent field measurements of major annual N-budget components, including atmospheric deposition, fertilizer added, net mineralization, residue returned, soil storage changes of inorganic N, leaching, and plant uptake. Measurements were made in a restored tallgrass prairie and optimally and deficiently N-fertilized, no-tillage and chisel-plowed maize (Zea mays L.) agroecosystems on Plano silt loam soil (fine-silty, mixed, superactive, mesic Typic Argiudoll (USDA); Haplic Phaeozem (approximate FAO)) in Wisconsin between 1995 and 1999. Denitrification and N losses due to runoff were assumed negligible and bulk density was assumed uniform with depth and across ecosystems. Annual inorganic N leaching was negligible in the restored prairie, but represented 3–57% of the amount of fertilizer-N applied in the optimally N-fertilized agroecosystems. On an annual basis, closure of the inorganic-N budget yielded cumulative errors that were often undesirably large; indicating methodological problems with quantifying ecosystem N cycling in situ. Increased spatial sampling is required to reduce individual measurement errors of two components with large uncertainties; namely net N-mineralization and soil inorganic N changes. Profile-scaled net N-mineralization generally did not balance with the residue N input from the previous year, but the imbalance agreed with the N-budget imbalance. Both results suggest that the prairie is accumulating N slowly, the deficiently N-fertilized maize plots are losing N more rapidly, and the optimally N-fertilized maize plots have too large an uncertainty to be interpreted confidently. Nitrogen-use efficiency, defined on a N-uptake basis, did not differ among the prairie and deficiently N-fertilized maize for 3 out of 5 years, but the prairie was significantly more efficient than the optimally N-fertilized maize.