Dexter B. Watts

Impact of Gypsum Applied to Grass Buffer Strips on Reducing Soluble P in Surface Water Runoff

The threat of P transport from land applied manure has resulted in water quality concerns. Research was conducted to evaluate gypsum as a soil amendment applied to grass buffer strips for reducing soluble P in surface runoff. A simulated concentrated flow was created in an established tall fescue (Festuca arundinacea Schreb.) pasture. Poultry litter (PL) was applied at a rate of 250 kg N ha(-1) to the upper 3.05 m of each plot, while gypsum was applied at rates of 0, 1, 3.2, and 5.6 Mg ha-1to the lower 1.52 m of the plot functioning as a grass buffer strip. Two 30-min runoff events ( approximately 4 L min(-1)) were conducted, immediately after PL application and 4 wk later to determined soluble P concentration in the surface water samples. The greatest concentration of soluble P was in the runoff event occurring immediately after the PL application. Gypsum applied to grass buffer strips was effective in reducing soluble P concentrations (32-40%) in surface runoff, while the untreated buffer strip was somewhat effective in reducing soluble P (18%). No significant differences were observed between gypsum rates, suggesting that land managers would achieve the greatest benefit from the lowest application rate (1Mgha(-1)). In the second runoff event, although concentrations of soluble P in the surface water runoff were greatly reduced, the effect of gypsum had disappeared. Thus, these results show that gypsum is most effective in reducing the initial P losses from PL application when applied to grass buffer strips. The information obtained from this study may be useful in aiding land managers in developing management practices that reduce soluble P loss at the edge of a field.

Soil Microbial Community Dynamics as Influenced by Composted Dairy Manure, Soil Properties, and Landscape Position

Manure applications can benefit crop productivity by adding required nutrients and organic matter to soil. There is a paucity of information on how soil microbial community dynamics will be altered by the application of manure to different landscape positions. Thus, an in situ field study was conducted during the summer and winter months to evaluate microbiological properties of three soil types that have evolved because of different landscape positions in an agricultural field. The three Coastal Plain soils investigated were Bama (sandy loam), Lynchburg (loam), and Goldsboro (loam) representing the landscape position of a summit, drainageway, and sideslope, respectively. Composted dairy manure was incorporated into in situ soil cores at a rate of 350 kg N ha−1 and compared with unamended controls. Soil microbial biomass N and dehydrogenase enzyme activity were determined to evaluate changes in the microbial biomass size and activity, whereas phospholipid fatty acid analysis was used as an indicator of the microbial community structure. Addition of composted dairy manure increased microbial activity and N immobilization, representing a shift in microbial response resulting from changes in substrate availability. This was most evident during summer months, with the composted dairy manure increasing dehydrogenase enzyme activity 21% and microbial activity 20% compared with without manure, suggesting that seasonal timing of application will influence microbial activity. Microbial properties were also impacted by landscape position. The drainageway landscape position soil, a loam, had the highest microbial biomass and microbial activity. Changes in microbial community structure using phospholipid fatty acid profiles were evaluated with canonical discriminate analysis. This analysis indicated that a shift in microbial community structure occurred between season, manure application, and landscape position. Findings from this study suggest that changes in soil variability from landscape positions and season can impact the growth and dynamics of the microbial community when manure is applied to agricultural fields.

US agricultural nitrous oxide emissions: context, status, and trends

The use of commercial nitrogen (N) fertilizers has led to enormous increases in US agricultural productivity. However, N losses from agricultural systems have resulted in numerous deleterious environmental impacts, including a continuing increase in atmospheric nitrous oxide (N2O), a greenhouse gas (GHG) and an important catalyst of stratospheric ozone depletion. Although associated with about 7% of total US GHG emissions, agricultural systems account for 75% of total US N2O emissions. Increased productivity in the crop and livestock sectors during the past 30 to 70 years has resulted in decreased N2O emissions per unit of production, but N2O emissions from US agriculture continue to increase at a rate of approximately 0.46 teragrams of carbon dioxide equivalents per year (2002–2009). This rate is lower than that during the late 20th century. Improvements in agricultural productivity alone may be insufficient to lead to reduced emissions; implementing strategies specifically targeted at reducing N2O emiss...

Mineralization of Nitrogen in Soils Amended with Dairy Manure as Affected by Wetting/Drying Cycles

Abstract Interest in manure management and its effects on nitrogen (N) mineralization has increased in recent years. The focus of this research was to investigate the N‐mineralization rates of different soil types in Coastal Plain soils and compare them to a soil from Illinois. Soils with and without dairy composted manure addition were subjected to different wetting/drying cycles [constant moisture at 60% water‐filled pore space (WFPS) and cycling moisture from 60 to 30% WFPS] under laboratory conditions at three different temperatures (11°C, 18°C, and 25°C). Samples were collected from three different soil types: Catlin (Mollisols), Bama (Ultisols), and Goldsboro (Utilsols). Soil chemical and physical properties were determined to help assess variations in N-mineralization rates. Addition of composted manure greatly impacted the amount of N mineralized. The amount of manure‐derived organic N mineralized to inorganic forms was mainly attributed to the soil series, with the Catlin (silt loam) producing the most inorganic N followed by the Goldsboro (loam) and then Bama (sandy loam). This was probably due to soil texture and the native climatic conditions of the soil. No significant differences were observed between the constant and cycling moisture regimens, suggesting that the imposed drying cycle may not have been sufficient to desiccate microbial cells and cause a flush in N mineralization upon rewetting. Nitrogen mineralization responded greatly to the influence of temperature, with the greatest N mineralization occurring at 25°C. The information acquired from this study may aid in predicting the impact of manure application to help increase N‐use efficiency when applied under different conditions (e.g., climate season) and soil types.

Impact of flue gas desulfurization gypsum application on water quality in a coastal plain soil.

There are growing concerns regarding the fate of nutrients, especially phosphorus (P), from land application of animal waste. One approach being studied to reduce runoff losses of P is to treat manure or the soil receiving manure with chemical amendments such as gypsum. This study used rainfall simulations to examine the impact of flue gas desulfurization (FGD) gypsum application on runoff nutrient losses on a Coastal Plains soil (Luverne sandy loam; fine, mixed, semiactive, thermic Typic Hapludults). Four rates of FGD gypsum (0, 2.2, 4.4, and 8.9 Mg ha) were applied to plots of Coastal Bermudagrass ( L.) that had received application of 13.4 Mg ha poultry litter. Plots with 8.9 Mg ha FGD gypsum but no poultry litter and plots with neither poultry litter nor FGD gypsum were also used. Rainfall simulation was used to generate water runoff for 60 min, and samples were analyzed for soluble reactive P (SRP) and soluble Al, B, Ca, Cu, Fe, K, Mg, Mn, Na, and Zn. Total concentration of Ca, Mg, K, Na, Fe, Mn, and Zn and concentration of heavy metals Ar, Hg, Al, Sb, Ba, Be, Cd, Cr, Co, Cu, Pb, Ni, Si, V, Se, Tl, and hexavalent chromium were also analyzed. Results indicated a maximum of 61% reduction in SRP concentration in runoff with the application of 8.9 Mg ha FGD gypsum. This translated to a 51% reduction in total SRP load during the 60-min runoff event. Concentrations of heavy metals in runoff were all found to be below detection limits. The results indicated that use of 4.4 Mg ha FGD gypsum on Coastal Plains pastures receiving poultry litter could be an effective method of reducing SRP losses to the environment.

Impact of Tillage and Fertilizer Application Method on Gas Emissions in a Corn Cropping System

Abstract Tillage and fertilization practices used in row crop production are thought to alter greenhouse gas emissions from soil. This study was conducted to determine the impact of fertilizer sources, land management practices, and fertilizer placement methods on greenhouse gas (CO 2 , CH 4 , and N 2 O) emissions. A new prototype implement developed for applying poultry litter in subsurface bands in the soil was used in this study. The field site was located at the Sand Mountain Research and Extension Center in the Appalachian Plateau region of northeast Alabama, USA, on a Hartsells fine sandy loam (fine-loamy, siliceous, subactive, thermic Typic Hapludults). Measurements of carbon dioxide (CO 2 ), methane (CH 4 ), and nitrous oxide (N 2 O) emissions followed GRACEnet (greenhouse gas reduction through agricultural carbon enhancement network) protocols to assess the effects of different tillage (conventional vs. no-tillage) and fertilizer placement (subsurface banding vs. surface application) practices in a corn ( Zea mays L.) cropping system. Fertilizer sources were urea-ammonium nitrate (UAN), ammonium nitrate (AN) and poultry litter (M) applied at a rate of 170 kg ha −1 of available N. Banding of fertilizer resulted in the greatest concentration of gaseous loss (CO 2 and N 2 O) compared to surface applications of fertilizer. Fertilizer banding increased CO2 and N2O loss on various sampling days throughout the season with poultry litter banding emitting more gas than UAN banding. Conventional tillage practices also resulted in a higher concentration of CO 2 and N 2 O loss when evaluating tillage by sampling day. Throughout the course of this study, CH 4 flux was not affected by tillage, fertilizer source, or fertilizer placement method. These results suggest that poultry litter use and banding practices have the potential to increase greenhouse gas emissions.

Soil Property and Landscape Position Effects on Seasonal Nitrogen Mineralization of Composted Dairy Manure

To develop better management practices that optimize the N derived from manure, additional research is needed regarding the mineralization and dynamics of N under field conditions. Thus, an in situ field study using three different soil types located in an agricultural field was conducted to evaluate N mineralization patterns during the summer and winter months. The three Coastal Plain soils (Ultisols) investigated were Bama (sandy loam), Lynchburg (loam), and Goldsboro (loam), representing the landscape position of a summit, drainageway, and sideslope, respectively. Composted dairy manure was incorporated into in situ soil cores, at a rate of 350 kg N ha−1, to evaluate mineralization rates of the soils and their landscape position during the summer and winter months. Addition of composted dairy manure on N mineralization was impacted by season and soil type. This was most evident during summer months (N mineralization was 24%), suggesting that seasonal timing of application will influence mineralization. The seasonal patterns of N mineralization were affected mostly by temperature; N mineralization was minimal during winter (N mineralization was 2%) when temperature was low (∼10 °C) but was greater during summer with higher temperatures (25 °C-30 °C). Landscape and soil texture played an additional role in mineralization. The soil type with the greatest percentage of sand and located in a low-lying area, although N mineralization was low during the winter months, significantly lost more of the added N from dairy compost (80%-90% more) compared with the other soils. During the summer, the loam soil with the greatest water-holding capacity mineralized the most N, significantly mineralizing 9% to 10% more than the other soils. These results show that soil variability, temperature, and landscapes need to be considered when applying manure to agricultural fields.

Effects of gypsum on trace metals in soils and earthworms.

Mined gypsum has been beneficially used for many years as an agricultural amendment. A large amount of flue gas desulfurization (FGD) gypsum is produced by removal of SO from flue gas streams when fuels with high S content are burned. The FGD gypsum, similar to mined gypsum, can enhance crop production. However, information is lacking concerning the potential environmental impacts of trace metals, especially Hg, in the FGD gypsum. Flue gas desulfurization and mined gypsums were evaluated to determine their ability to affect concentrations of Hg and other trace elements in soils and earthworms. The study was conducted at four field sites across the United States (Ohio, Indiana, Alabama, and Wisconsin). The application rates of gypsums ranged from 2.2 Mg ha in Indiana to 20 Mg ha in Ohio and Alabama. These rates are 2 to 10 times higher than typically recommended. The lengths of time from gypsum application to soil and earthworm sampling were 5 and 18 mo in Ohio, 6 mo in Indiana, 11 mo in Alabama, and 4 mo in Wisconsin. Earthworm numbers and biomass were decreased by FGD and mined gypsums in Ohio. Among all the elements examined, Hg was slightly increased in soils and earthworms in the FGD gypsum treatments compared with the control and the mined gypsum treatments. The differences were not statistically significant except for the Hg concentration in the soil at the Wisconsin site. Selenium in earthworms in the FGD gypsum treatments was statistically higher than in the controls but not higher than in the mined gypsum treatments at the Indiana and Wisconsin sites. Bioaccumulation factors for nondepurated earthworms were statistically similar or lower for the FGD gypsum treatments compared with the controls for all elements. Use of FGD gypsum at normal recommended agricultural rates seems not to have a significant impact on concentrations of trace metals in earthworms and soils.

Microbial-Based Inoculants Impact Nitrous Oxide Emissions from an Incubated Soil Medium Containing Urea Fertilizers

There is currently much interest in developing crop management practices that will decrease NO emissions from agricultural soils. Many different approaches are being investigated, but to date, no studies have been published on how microbial inoculants affect NO emissions. This study was conducted to test the hypothesis that microbial-based inoculants known to promote root growth and nutrient uptake can reduce NO emissions in the presence of N fertilizers under controlled conditions. Carbon dioxide and CH fluxes were also measured to evaluate microbial respiration and determine the aerobic and anaerobic conditions of the incubated soil. The microbial-based treatments investigated were SoilBuilder (SB), a metabolite extract of SoilBuilder (SBF), and a mixture of four strains of plant growth-promoting spp. Experiments included two different N fertilizer treatments, urea and urea-NHNO 32% N (UAN), and an unfertilized control. Emissions of NO and CO were determined from soil incubations and analyzed with gas chromatography. After 29 d of incubation, cumulative NO emissions were reduced 80% by SB and 44% by SBF in soils fertilized with UAN. Treatment with spp. significantly reduced NO production on Days 1 and 2 of the incubation in soils fertilized with UAN. In the unfertilized treatment, cumulative emissions of NO were significantly reduced 92% by SBF. Microbial-based treatments did not reduce NO emissions associated with urea application. Microbial-based treatments increased CO emissions from soils fertilized with UAN, suggesting a possible increase in microbial activity. Overall, the results demonstrated that microbial-based inoculants can reduce NO emissions associated with N fertilizer application, and this response varies with the type of microbial-based inoculant and fertilizer.

Influence of Flue Gas Desulfurization Gypsum on Reducing Soluble Phosphorus in Successive Runoff Events from a Coastal Plain Bermudagrass Pasture

Controlling the threat that pastures intensively managed with poultry litter (PL) pose to accelerating eutrophication is a major issue in the southeastern United States. Gypsum (CaSO) has been identified as a promising management tool for ameliorating litter P losses to runoff. Thus, research was conducted to elucidate gypsums residual effects on P losses from a bermudagrass ( L.) pasture. Runoff events (60 min) were created using rainfall simulations. Treatments consisted of applying four flue gas desulfurization (FGD) gypsum rates (0, 2.2, 4.4, and 8.9 Mg ha) to bermudagrass fertilized with 13.4 Mg ha PL plus a nonfertilized check (no litter or gypsum) and 8.9 Mg ha FGD gypsum only as controls. Rainfall simulations (∼ 85 mm h) were conducted immediately, 5 wk, and 6 mo (i.e., at the end of growing season) after PL application to determine gypsums effectiveness at controlling P loss over successive runoff events. The greatest dissolved P (DP) in runoff occurred immediately after PL application. Gypsum effectively reduced cumulative DP concentration losses (54%) compared with PL alone in initial runoff events. Gypsum reduced DP concentrations in succeeding runoff events also regardless of timing, suggesting that its effect is persistent and will not diminish over a growing season. Generally, maximum DP reductions were achieved with 8.9 Mg ha. However, it was surmised from this study that optimal P reduction in a bermudagrass pasture can be achieved with 4.4 Mg ha. Information ascertained from this study may be useful in aiding land managers making prescriptions for management practices that reduce DP losses from agricultural fields.