Jason P. Wight

Simulation of Biomass Yield and Soil Organic Carbon under Bioenergy Sorghum Production

Developing sustainable management practices including appropriate residue removal and nitrogen (N) fertilization for bioenergy sorghum is critical. However, the effects of residue removal and N fertilization associated with bioenergy sorghum production on soil organic carbon (SOC) are less studied compared to other crops. The objective of our research was to assess the impacts of residue removal and N fertilization on biomass yield and SOC under biomass sorghum production. Field measurements were used to calibrate the DNDC model, then verified the model by comparing simulated results with measured results using the field management practices as agronomic inputs. Both residue removal and N fertilization affected bioenergy sorghum yields in some years. The average measured SOC at 0–50 cm across the treatments and the time-frame ranged from 47.5 to 78.7 Mg C ha−1, while the simulated SOC was from 56.3 to 67.3 Mg C ha−1. The high correlation coefficients (0.65 to 0.99) and low root mean square error (3 to 18) between measured and simulated values indicate the DNDC model accurately simulated the effects of residue removal with N fertilization on bioenergy sorghum production and SOC. The model predictions revealed that there is, in the long term, a trend for higher SOC under bioenergy sorghum production regardless of residue management.

Comparison of Near Infrared Reflectance Spectroscopy with Combustion and Chemical Methods for Soil Carbon Measurements in Agricultural Soils

ABSTRACT As interest in soil organic carbon (SOC) dynamics increases, so do needs for rapid, accurate, and inexpensive methods for quantifying SOC. Objectives were to i) evaluate near infrared reflectance (NIR) spectroscopy potential to determine SOC and soil organic matter (SOM) in soils from across Tennessee, USA; and ii) evaluate potential upper limits of SOC from forest, pasture, no-tillage, and conventional tilled sites. Samples were analyzed via dry-combustion (SOC), Walkley–Black chemical SOM, and NIR. In addition, the sample particle size was classified to give five surface roughness levels to determine effects of particle size on NIR. Partial least squares regression was used to develop a model for predicting SOC as measured by NIR by comparing against SOM and SOC. Both NIR and SOM correlated well (R2 > 0.9) with SOC (combustion). NIR is therefore considered a sufficiently accurate method for quantifying SOC in soils of Tennessee, with pasture and forested systems having the greatest accumulations.Abbreviations SOC, soil organic carbon; NIR, Near Infrared Reflectance Spectroscopy; MTREC, Middle Tennessee Research and Education Center; RECM, Research and Education Center at Milan; PREC, Plateau Research and Education Center; PLS, Partial least squares.

Mobility of Poultry Litter Phosphorus in a Coastal Plain Forest Soil

Abstract Loss of phosphorus (P) to surface waters from forest soils fertilized with P-rich poultry litter (PL) is likely less than P loss from pasture because forest soils are typically lower in P. This study examined P mobility where PL was applied to forest soil in amounts constituting disposal. Triplicate plots (13.4 × 3.1 m) of 4-year-old loblolly pine (Pinus taeda) were amended once per year at 0, 5, 10, and 20 Mg PL/ha in 1996 and 1997–2001. Surface soil (0–15 cm) P was monitored annually during the application period and at varying frequencies until 2013. Cores to 1 m were taken in 2002 and 2013. Phosphate sorption in surface and subsoil was measured, and transport in surface soil was investigated. Sorption after 24 h followed the Langmuir model, which described retention during transport better than a linear model but not as well as a two-site kinetic Langmuir model with sorption capacity based on oxalate-extractable aluminum (Al) + iron (Fe). Phosphate sorption was least in 15- to 30-cm depth soil; sorption increased deeper into the Bt horizon. Neither the increase nor the decrease in surface soil P showed a clear effect of sorption nonlinearity. Treatment effects were significant to a depth of 45 cm in 2002 except for organic P (surface only). The profile distribution of P was generally consistent with sorption, with some evidence of preferential flow. Leaching from 2002 to 2013 was slow, moving P in 20-Mg ha−1 plots to 60 cm. However, leaching was likely increased by initial concentrations and fast relative to tree uptake.

Simulating Impacts of Bioenergy Sorghum Residue Return on Soil Organic Carbon and Greenhouse Gas Emissions Using the DAYCENT Model

Different residue management practices can affect carbon (C) allocation and thus soil C and nitrogen (N) turnover. A biogeochemical model, DAYCENT, was used to simulate the effects of bioenergy Sorghum [Sorghum bicolor (L.) Moench] residue return on soil temperature and water content, soil organic carbon (SOC), and greenhouse gas (GHG) [carbon dioxide (CO2) and nitrous oxide (N2O)] emissions under bioenergy Sorghum production. Coefficient of determination (r2) was used to test model performance. Coefficients of determination between the observed and simulated soil temperature, soil water content, SOC, and annual CO2 and N2O emissions were 0.94, 0.81, 0.75, 0.97, and 0.0057, respectively, indicating that the DAYCENT model captured the major patterns of soil environmental factors and C turnover but was less accurate in estimating N2O emissions. Compared with the simulated control (0 % residue return), the simulated 50 % residue return treatment had 7.77 %, 15.12 %, and 1.25 % greater SOC, annual CO2, and N2O emissions, respectively, averaged over 2 years’ data (2010 and 2011). Similar patterns in the simulated outputs were also observed in our field trials, with percentages being 4.52 %, 15.98 %, and 12.89 %, respectively. The model also successfully reflected the daily GHG flux variation affected by treatments, management practices, and seasonal changes except for missing some high growing season fluxes. In addition, annual variations in the simulated outputs were comparable with field observations except the N2O emissions in the 50 % residue return treatment. Our study indicated that DAYCENT reasonably simulated the main effects of residue return on soil C turnover but underestimated N2O emissions.

Long-Term Soil Organic Carbon Changes as Affected by Crop Rotation and Bio-covers in No-Till Crop Systems

Soil organic carbon (SOC) sequestration is a potential negative-feedback for climate-warming gases in agriculture. The rate of no-tillage SOC storage is not well known due to large temporal and spatial biogeochemical and management variations. Therefore our objective was to compare long-term SOC fluxes at a no-till field site in Milan, Tennessee on Oxyaquic Fragiudalfs, in a split-block design with four replications. The whole-block was cropping sequences of corn, soybeans, and cotton with split-block bio-cover treatments of: winter wheat, hairy vetch, poultry litter, and a fallow control. Soil carbon flux was calculated at soil surfaces (0–5 cm) for years-0, 2, 4, and 8. During the first 2 years, small annual losses occurred in carbon over all treatments (1.40 Mg ha−1). During this time, cotton sequences lost significantly more surface SOC than other rotations. However, by year-4, SOC began to stabilize. By year-8, sequences with high frequencies of soybean and with greater temporal complexity generally gained greater SOC levels at 0–5 cm. Also, poultry litter bio-cover gained more surface SOC compared to wheat, vetch and fallow covers. Across all sequences and bio-covers, SOC had increased 1.47 Mg ha−1 after 8 years from pre-experimental levels of 9.20 Mg ha−1; suggesting long-term beneficial effects on C storage under no-till and diverse cropping sequences.