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A common passive sampler used to measure NH3 volatilization losses in field studies has a nozzle with a 1‐mm, round orifice that reduces air flow to increase NH3 adsorption. This reduction in air flow, measured by the orifice's K value (0–1), implies a reduction in the amount of NH3 entering the sampler per unit of time, which may require a longer exposure to accumulate measurable quantities of NH3. Increasing the diameter of the orifice would increase the NH3 entering the sampler and possibly allow shorter exposure times, but it may also lead to increased NH3 bypass. The objectives of this research were to (1) determine the effect of wind speed on NH3 bypass in samplers with 1‐ or 2‐mm orifices, (2) determine the reduction in air speed in samplers with 1‐ or 2‐mm orifices by determining their K values, and (3) compare field NH3 volatilization losses measured with 1‐ and 2‐mm orifices. A laboratory study with wind speeds ranging from 0.6 to 10 m·s−1 showed that both orifice sizes had NH3 bypass at low and high wind speeds. Results from wind tunnel studies determined that flow was reduced to 63% (K = 0.63) in 1‐mm orifices and to 74% (K = 0.74) in 2‐mm orifices. Field studies indicated that 1‐mm orifices may measure greater NH3 volatilization losses than 2‐mm orifices at average low wind speeds when maximum wind speeds <10 m·s−1, but may measure equal or lower losses than 2‐mm orifices when several days occur with maximum wind speeds >10 m·s−1. Core Ideas: Field NH3 loss measured with 1‐ and 2‐mm orifices depended on maximum wind speeds.Ammonia bypass occurred at low and high wind speeds with both orifice sizes.Wind speed through sampler was reduced to 63% with a 1‐mm orifice and to 74% with a 2‐mm orifice. [ABSTRACT FROM AUTHOR]

The production and application of fertilizers are not only costly but can be harmful to the environment if misapplied; therefore, sustainability research has aimed to investigate alternatives to traditional nitrogen fertilizer applications. Biostimulants, including microbial inoculants, have been touted to enhance plant nutrition, growth, and stress tolerance, but research on warm‐season turfgrass is limited. Therefore, the objective of our research was to compare the establishment, quality, and function of bermudagrass (Cynodon spp.) in response to commercially available microbial inoculants (Klebsiella variicola, Gluconacetobacter diazotrophicus, and Azospirillum brasilense) in field and controlled environment experiments. Microbial inoculant applications in the field did not consistently increase the normalized vegetation difference index, turfgrass color, or turfgrass quality of hybrid bermudagrass [Cynodon dactylon (L.) Pers. × Cynodon transvaalensis Burtt Davy] compared with the nontreated check. However, although the difference was not always significant, inoculated hybrid bermudagrass often exhibited higher carbon efflux measurements than the nontreated check, but the results were inoculant‐specific. No microbial inoculant resulted in greater common bermudagrass [Cynodon dactylon (L.) Pers.] root or shoot production in the greenhouse. Perennial cropping systems such as turfgrass may create greater challenges for microbial inoculant use and performance because of the presence of endemic microbial populations that are already adapted to survive and proliferate in turfgrass environments. Consequently, future research should examine inoculation frequency, soil and plant persistence, and the use of microbial blends to determine best management practices leading to the greatest opportunity for colonization and subsequent turfgrass benefits. Core Ideas: Field‐applied inoculants did not consistently increase bermudagrass NDVI, color, or quality.No microbial inoculant increased bermudagrass root or shoot production in the greenhouse.Future research should examine inoculation frequency, soil persistence, and microbial blends. [ABSTRACT FROM AUTHOR]

Most biogeochemical models simulate water dynamics using the tipping bucket approach, which has been often found to be too simplistic to represent vadose zone dynamics adequately under shallow groundwater conditions. Recently, a solution to the Richards equation using the Mualem–van Genuchten model (Rich‐vGM) has been added into the EPIC (Environmental Policy Integrated Climate) model to address this shortfall. Its performance was tested using lysimeters operating under free drainage (FD) and at a shallow water table (60‐ [WT60] and 120‐cm depth [WT120]). Model accuracy was also compared with the upgraded tipping bucket‐based method implemented into EPIC (the variable saturation hydraulic conductivity method [VSHC]). Soil water content (SWC) data were split into calibration and validation subsets. Model evaluation also included annual evapotranspiration (ET), percolation (PRK), and upward water movements to assess underlying soil water balance factors. The submodels provided accurate and similar results upon comparison with SWC measures under FD (Nash–Sutcliffe coefficient [NSE] = 0.26 and 0.61 using VSHC and Rich‐vGM, respectively). The Rich‐vGM model accurately reproduced observed SWC and ET (e.g., NSE = 0.70 and percentage bias [PBIAS] = −3.7% for WT120, respectively) although it slightly overestimated PRK (PBIAS = 47.8%, on average). Instead, VSHC proved unable to correctly simulate shallow groundwater conditions (e.g., NSE = −1.85 for WT60 SWC). Under shallow groundwater conditions, the Rich‐vGM method is recommended, despite the additional data required and the need to define the bottom boundary conditions according to water table fluctuations. In conclusion, the Richards solver introduced and tested in EPIC improved the model's ability to represent complex biophysical and biogeochemical processes in terrestrial ecosystems associated with the hydrological balance. Core Ideas: EPIC Richards solver was tested in a 9‐yr experiment under different groundwater conditions.The new Richards algorithms were compared with the tipping‐bucket based method.Both methods predicted similar soil water content under free drainage.Water content and ET were better predicted by Richards under shallow water table.Under specific conditions, percolation was overestimated for both approaches. [ABSTRACT FROM AUTHOR]

Quantification of nitrogen mineralization at the field scale is necessary to improve current N fertilizer recommendations. The objective of this study was to identify a suitable set of explanatory variables and an appropriate modelling framework to estimate the average daily amount of N mineralized (DANM) during a corn (Zea mays L.) growing season. In six field experiments in Flat Inland Pampas, Argentina, DANM was evaluated in three different homogeneous zones (HZ), which were defined based on terrain elevation. Mixed‐effect generalized linear models were developed that included growing season as random effect as well as HZ, sand, clay, silt, soil organic carbon, and normalized difference vegetation index (NDVI) as fixed effects. Results showed that DANM ranged from 0.19 to 1.25 kg N ha−1 day−1 with a mean of 0.64 kg N ha−1 day−1, which is equivalent to 110 kg N ha−1 for the corn growing season. The best model included HZ, sand, and early NDVI measurements, and predicted DANM with an RMSE of 0.19 kg N ha−1 day−1. Thus, the model should be improved and tested in the Inland Flat Pampas before it could be used to assess N fertilizer application rates. [ABSTRACT FROM AUTHOR]

Understanding the role of clipping biomass in nutrient budgets of turfgrass systems is critical to improving N use efficiency (NUE). The objective of this study was to evaluate the effect of mowing frequency on clipping tissue characteristics, N mineralization (NMin, %), and NH3 volatilization (AV, %) from decomposing 'TifTuf' bermudagrass [Cynodon dactylon (L.) Pers. × Cynodon transvaalensis Burtt Davy] clippings applied to the soil surface. Turfgrass clippings were collected from two research facilities in Athens, GA, at 3‐, 7‐, 10‐, and 14‐d mowing intervals (MIs). A subsample of clippings from each plot was ground and analyzed using near‐infrared spectroscopy to determine tissue characteristics. Soil from each location was packed into polyvinyl chloride cylinders, treated with grass clippings on the surface or left unamended, and incubated for 90 d. Cumulative evolved NH3 was trapped, and inorganic N was extracted from each cylinder and analyzed colorimetrically after 90 d. Rates of NMin varied significantly across treatments and locations, making it difficult to generate informed recommendations for reducing N fertilization based on MI. Although dry yield (g m–2) and tissue characteristics (carbohydrates, cellulose, and lignin) were found to be significant parameters in predicting NMin, no clear relationship was established between MI and tissue characteristics in this study. More frequent mowing (3‐d MI) appeared to support more vigorous turfgrass growth through greater net clipping yield and may also decrease AV as a function of smaller clipping yield for unique mowing events. Mowing more than one time per week may be more N‐use efficient and promote healthier turfgrass systems overall. Core Ideas: Mowing interval does not appear to affect turfgrass clipping tissue composition.More frequent mowing may bolster turfgrass health and reduce NH3 volatilization losses.Nitrogen mineralization can be highly variable, even in a controlled environment. [ABSTRACT FROM AUTHOR]

Computer models are commonly used for predicting risks of runoff P loss from agricultural fields by enabling simulation of various management practices and climatic scenarios. For P loss models to be useful tools, however, they must accurately predict P loss for a wide range of climatic, physiographic, and land management conditions. A complicating factor in developing and evaluating P loss models is the relative scarcity of available measured field data that adequately capture P losses before and after implementing management practices in a variety of physiographic settings. Here, we describe the development of the P Loss in runoff Events from Agricultural fields Database (PLEAD)—a compilation of event‐based, field‐scale dissolved and/or total P loss runoff loadings from agricultural fields collected at various research sites located in the US Heartland and southern United States. The database also includes runoff and erosion rates; soil‐test P; tillage practices; planting and harvesting rates and practices; fertilizer application rate, method, and timing; manure application rate, method, and timing; and livestock grazing density and timing. In total, >1800 individual runoff events—ranging in duration from 0.4 to 97 h—have been included in the database. Event runoff P losses ranged from <0.05 to 1.3 and 3.0 kg P ha−1 for dissolved and total P, respectively. The data contained in this database have been used in multiple research studies to address important modeling questions relevant to P management planning. We provide these data to encourage additional studies by other researchers. The PLEAD database is available at https://doi.org/10.15482/USDA.ADC/1482380. Core Ideas: Development of database containing P loss from agricultural fields is described.We provide public access to P loss data for individual runoff events.The data can be used to evaluate P loss models and P Indices. [ABSTRACT FROM AUTHOR]

Uneven spatial distribution of soil N in conventionally managed pastures is a function of various biotic and abiotic factors and results in poor land use efficiency. In this study, we measured soil inorganic N (at depths of 05, 5-10, and 10-20 cm) in a 50-m grid and specific areas of interest from eight conventionally managed beef pastures (~17 ha each), four near Eatonton and four near Watkinsville in the southern Piedmont of Georgia, USA, to assess the effects of management, landscape, and cattle locus in spatial distribution of soil inorganic N. Significant spatial autocorrelation was observed in the soil inorganic N indicating that the regions of high inorganic N deposition were near (within 91 m of) one or more pasture equipage (hay, shade, and water). In the Watkinsville pastures, inorganic N was 65% higher within 5 m of shade than the rest of the pastures, down to a 10-cm soil depth. In the Eatonton pastures, inorganic N (0-5 cm) was 22% higher within 30 m of a hayfeeding areas than the rest of the pasture. Cattle locus calculated as cattle density (cow ha-1 yr-1) was a function of pasture equipage and had a significant positive relationship with soil inorganic N. Landscape parameters (slope and elevation) significantly affected inorganic N distribution; however, the effect was small and was masked by management factors. Our results suggest that strategic placement of pasture equipage (hay, shade, and water) can effectively distribute N where needed in beef pastures, thereby increasing land use efficiency. [ABSTRACT FROM AUTHOR]

Broiler (Gallus gallus domesticus) litter is subject to ammonia (NH3) volatilization losses. Previous work has shown that the addition of gypsum to broiler litter can increase nitrogen mineralization and decrease NH3 losses due to a decrease in pH, but the mechanisms responsible for these effects are not well understood. Therefore, three laboratory studies were conducted to evaluate the effect of gypsum addition to broiler litter on (i) urease activity at three water contents, (ii) calcium carbonate precipitation, and (iii) pH. The addition of gypsum to broiler litter increased ammonium concentrations (p < 0.0033) and decreased litter pH by 0.43 to 0.49 pH units after 5 d (p < 0.0001); however, the rate of urea hydrolysis in treated litter only increased on Day 0 for broiler litter with low (0.29 g H2O g-1) and high (0.69 g H2O g-1) water contents, and on Day 3 for litter with medium (0.40 g H2O g-1) water content (p < 0.05). Amending broiler litter with gypsum also caused an immediate decrease in litter pH (0.22 pH units) due to the precipitation of calcium carbonate (CaCO3) from gypsum-derived calcium and litter bicarbonate. Furthermore, as urea was hydrolyzed, more urea-derived carbon precipitated as CaCO3 in gypsum-treated litter than in untreated litter (p < 0.001). These results indicate that amending broiler litter with gypsum favors the precipitation of CaCO3, which buffers against increases in litter pH that are known to facilitate NH3 volatilization. [ABSTRACT FROM AUTHOR]

Many crops in volcanic regions exhibit symptoms of B deficiency but do not respond to B fertilizer rates that solve deficiency problems in non–volcanic-influenced soils. The US recommended rates are routinely adopted in these regions without accounting for differences in soil B dynamics. Because of the paucity of investigations and the resulting lack of understanding of B adsorption/desorption dynamics in volcanic ash–derived soils over the past 40 yr, it would be incorrect to extrapolate the few data available to all volcanic ash–derived soils because they have not been analyzed as a function of andic character. This paper aims to create an understanding of what soil properties govern B availability in volcanic-influenced soils and to establish if there are low-cost testing methods that can help estimate appropriate field B application rates in these soils. Boron adsorption/desorption isotherms were constructed for a group of volcanic ash–derived and non-volcanic ash–derived soils, and the derived parameters were compared with various standard soil tests. Our results show that soil B availability in volcanic-influenced soils is governed mainly by strong and stable B complexation with short-rangeorder (SRO) minerals. Boron adsorption maxima exhibit a wide variability not directly correlated with clay content but rather with reactivity quantified by SRO mineral and organic matter contents. Organic matter is not a significant variable explaining specific surface area for the overall group of soils, but it becomes significant for soils containing <200 g clay kg-1, suggesting that a new approach to analyzing whole-soil reactivity based on mineral surface abundance is needed. The maximum adsorption capacities of volcanic-influenced soils can be as much as 18-fold higher than for non-volcanic soils, with the reversibility of adsorption reactions decreasing as andic character increases. These findings explain why standard B fertilizer rates fail to solve deficiency problems in volcanic-influenced soils. Because pH in NaF is strongly related with acid-oxalate Al (SRO minerals) and B desorption index, this low-cost test can potentially be used as a measure of soil andic character to better reflect B availability and corresponding field application rates. [ABSTRACT FROM AUTHOR]

Poultry litter (PL) is widely used as an alternative to inorganic fertilizers (IF) in conventional (CT) and no-tillage systems (NT). The objective of this work was to evaluate the legacy effect of a 16-yr factorial study that combined fertilization (PL or IF) and tillage (CT or NT) treatments on soil C and N pools and microbial communities. Soil samples were collected from the 0 to 5 and 5 to 20 cm depths after 8 and 3 yr of suspending fertilization and tillage, respectively. Samples were analyzed for total organic C (TOC), total organic N (TON), N mineralization rate (k0) and abundance of ammonia-oxidizing bacteria (AOB) and archaea (AOA). The TOC and TON concentrations (range: 5.8-20.8 and 0.5-1.8 g kg-1, respectively) were affected by tillage system and fertilizer source. Legacies of fertilization and tillage affected k0 (range: 0.20-0.87 mg kg-1 d-1) which was correlated with TOC and TON (r2 ∼ 0.9). The abundance of AOA (5.3-7.6 log10 copies g-1) and AOB (7.1-8.9 copies log10 g-1) was greater in CT than NT in the 0 to 5 cm layer, whereas the opposite was observed in the 5 to 20 cm layer. Both AOA and AOB were associated with k0 (r2 = 0.5 and 0.8, respectively), suggesting the dependence of ammonia oxidizers on mineralization of the organic N pool. Our results indicate that 8 and 3 yr after fertilization and tillage treatments were suspended, soil C and N and microbial dynamics were still being influenced by previous management practices. [ABSTRACT FROM AUTHOR]

Urea-based fertilizers have replaced ammonium nitrate (AN) as the most common N source used in forage crops. However, urea-based fertilizers are less efficient and result in greater N loss as ammonia. Environmentally Smart Nitrogen (ESN, Agrium Advanced Technologies) is a polymer-coated urea-N fertilizer that controls N release through temperature-controlled diffusion. This study assessed the effect of different proportions of ESN and untreated urea (0, 50, 75, and 100% ESN with the balance as urea) on yield and nutritive quality of bermudagrass [Cynodon dactylon (L.) Pers.], as compared with conventional applications of AN and urea. The experimental design was a randomized complete-block design with four replications on each of two sites and 3 yr (2010-2012). Nitrogen was applied at 336 kg ha1 season1, but was split over the season into two equal applications for the ESN treatments and four equal applications for the AN and urea conventional treatments. As the proportion of ESN increased, the amount of N lost through volatilization decreased. Relative to conventionally applied AN, the 50 and 75% ESN blends resulted in similar yields and 16.8% lower nitrate (NO3-N) levels in the harvested for-age. Relative to conventionally applied urea, the 50 and 75% blends produced 10 and 6.1% more yield and 14.4 and 19.5% greater N removal, respectively. The 50 and 75% ESN blends were also the most cost-effective blend systems. These results support a recommendation of blending ESN at a rate of 50 and 75% with urea as a substitute for AN. [ABSTRACT FROM AUTHOR]

In a pine forest, urea hydrolysis rates can vary widely. The rate of urea hydrolysis is controlled by the amount of urease enzyme, temperature, pH, urea concentration, but at the soil surface, soil water potential is an especially critical factor because it may vary widely in short periods of time due to precipitation, dews, and rapid evaporation. The objective of this study was to describe the quantitative relationship between soil water and urea hydrolysis rates in a loblolly pine (Pinus taeda L.) forest floor. Hydrolysis rates were measured in a pine forest with time after urea was applied in seven studies performed at different times that varied widely in soil water content and temperature. Separately in a laboratory study, the urea hydrolysis rates were measured in pine needles and in the humified layer at different water potentials. Results showed that although well-defined relationships were found between urea hydrolysis rates and forest floor water potentials, the urea hydrolysis rates measured in the field could not be predicted based on these relationships and the water potential of the forest floor pine needles at the time of urea application. However, the percent of urea hydrolyzed at 3 and 29 d could be predicted accurately from the initial water potential of new needles and an interaction between initial water potential and relative humidity days. [ABSTRACT FROM AUTHOR]

Soil water availability affects NH3 loss from surface applied urea, partly due to its influence on urea hydrolysis rates. However, the quantitative effects of soil water on hydrolysis rates are not well understood. Our objective was to quantify how soil matric potential affects urea hydrolysis rates across a wide range of soil matric potentials. Urea hydrolysis rates were measured based on disappearance of urea at various soil water potentials in soils limed to a pH of 8.2 to eliminate confounding by soil pH. Urea-N was applied on a soil mass basis (1200 µg urea-N g-1 soil, 0.2-2.4 mol urea L-1) in Exp. I and at a constant urea-N soil solution concentration of 40,000 µg urea-N g-1 soil solution (1.43 mol urea L-1) in Exp. II. Differences in relative rates of urea hydrolysis between both experiments suggested that in Exp. I there was a confounding effect of urea-N solution concentration on the response of urea hydrolysis to soil matric potential. In Exp. I, relative rates of hydrolysis changed little at intermediate soil matric potentials between -0.1 and -1.0 MPa because urea-N concentration in solution increased as matric potential decreased. In Exp. II, relative rates were greatest at the highest matric potentials (>-0.24 MPa) and decreased more rapidly as matric potential decreased, approaching zero at a matric potential of approximately -10 MPa. These results also suggest that research to describe urea hydrolysis rates as affected by soil water content should be based on urea-N concentrations in soil solution and not urea-N concentrations on a soil mass basis. [ABSTRACT FROM AUTHOR]

Broiler litter is commonly surface applied to grasslands as fertilizer in the southeastern United States. Surface application may lead to losses of P in surface runoff and to losses of N through NH3 volatilization. Adding gypsum to broiler litter can reduce water-soluble P and, therefore, the potential for surface water contamination, but no information is currently available on the effect of gypsum on NH3 volatilization when broiler litter is applied to soil. We conducted three laboratory studies to evaluate the effect of adding flue-gas desulfurization (FGD) gypsum to broiler litter or soil on NH3 volatilized and N mineralized. In two studies, soil with or without 0.01 g FGD gypsum g-1 soil was packed into acrylic columns and broiler litter with or without 0.25 g FGD gypsum g-1 litter was applied on the soil surface and incubated at 25°C for 15 d. In a third study, litter with or without 0.25 g FGD gypsum g-1 litter was mixed with soil and incubated at 25°C for 63 d. Our results showed that the addition of FGD gypsum to broiler litter or soil did not affect net N mineralized or NH3 volatilized when litter was surface applied. Similarly, the addition of FGD gypsum to broiler litter did not affect net N mineralized when broiler litter was incorporated into soil. Thus, the addition of FGD gypsum at these rates does not change NH3 loss or N mineralized from broiler litter. [ABSTRACT FROM AUTHOR]

The article discusses research into mineralization and incorporation of 17-Β estradiol and testosterone in soil organic matter (SOM) and pure broiler litter. It cites abiotic factors which may influence hormone mineralization including water potential and temperature. It reports experimental procedures conducted which include preparation of necessary chemical materials and processing of broiler litter collected. A chart listing broiler litter and soil characteristics is presented. It is also observed that cumulative testosterone mineralization led to increase in water content unlike with estradiol.

A reliable laboratory index of N availability would be useful for making N recommendations, but no single approach has received broad acceptance across a wide range of soils. We compared several indices over a range of soil conditions to test the possibility of combining indices for predicting potentially mineralizable N (N0). Soils (0-5 and 5-15 cm) from nine tillage studies across the southern USA were used in the evaluations. Long-term incubation data were fit to a first-order exponential equation to determine N0, k (mineralization rate), and N0 (N0 estimated with a fixed k equal to 0.054 wk-1). Out of 13 indices, five [total C (TC), total N (TN), N mineralized by hot KCI (Hot N), anaerobic N (Ana_N), and N mineralized in 24 d (Nmin_24)] were strongly correlated to N0 (r > 0.85) and had linear regressions with r2 > 0.60. None of the indices were good predictors of k. Correlations between indices and N0 improved compared with N0, ranging from r = 0.90 to 0.95. Total N and flush of CO2 determined after 3 d (FLCO2) produced the best multiple regression for predicting N0 (R2 = 0.85) while the best combination for predicting N0 (R2 = 0.94) included TN, Fl_CO2 Cold_N, and NaOH_N. Combining indices appears promising for predicting potentially mineralizable N, and because TN and Fl_C02 are rapid and simple, this approach could be easily adopted by soil testing laboratories. [ABSTRACT FROM AUTHOR]

Poultry litter (PL) can supply N, P, K, and other plant nutrients; however, excessive application may cause environmental problems, depending on management and crop nutrient demand. Changes in soil test (ST) nutrient content in a Cecil soil (a fine, kaolinitic, thermic Typic Kanhapludult) during a 10-yr period of PL use was evaluated at the USDA-ARSJ. Phil Campbell, Sr., Natural Resource Conservation Center, Watkinsville, GA. During the cotton (Gossypium hirsutum L.) cropping phase (1995-2000), 4.4 Mg PL ha-1 yr-1 resulted in small changes in ST nutrient content in the surface 15 cm. Differences were observed between tillage treatments, with less accumulation of Ca, Mg, and Mn and greater accumulation of Zn for no-till (NT) than conventional tillage (CT). During the corn (Zea mays L.) cropping phase (2001-2005), average annual PL inputs (11.2 Mg hat) increased P and Zn contents, with changes being similar for CT and NT After 10 yr, ST nutrient contents in the surface 15 cm reflected 25, 4, 45, 26, 17, and 97% of the input from PL for P. K, Ca, Mg, Mn, and Zn, respectively. Changes in soil profile nutrient content (to a depth of 60 cm) from 1997 to 2005 were predominantly at 0 to 15 cm, where P and Zn increased >200%. Accumulation of Ca, K, P, and Zn at lower depths was also observed. Strategies for increasing nutrient removal following repeated long-term application of PL should be considered to avoid excessive levels of nutrients. [ABSTRACT FROM AUTHOR]

The use of urea fertilizers in grasslands is likely to increase in areas with concentrated animal feeding operations as restrictions on manure applications are implemented. Concerns have been raised about the economic and environmental impacts of NH3 loss from these urea fertilizers. This study evaluated NH3 losses from Nitamin (a urea polymer), urea-N H4N03 (UAN), and granular urea applied to tall fescue (Festuca arundinacea Schreb.) plots at 50 kg N ha1 in fall and spring for 2 yr. Fertilizers were applied to circular plots (30-rn diameter) and NH3 loss was measured by the modified passive flux method for 69 to 120 d after application. In a separate laboratory study, Nitamin, UAN, and urea were surfaced applied to fescue thatch at 100 kg N ha1 and treatments were incubated at 24°C and 90% relative humidity for 31 d. In fall applications, urea lost more NH3 (19% in 2004, 46% in 2005) than UAN or Nitamin, which were not different from each other (6% in 2004, 34% in 2005). In contrast, there were no differences among fertilizers in spring applications, with average losses of 13% in 2005 and 17% in 2006. In the laboratory study, urea lost significantly more NH3 (24%) than UAN or Nitamin, which were not different from each other (average 9% loss). These results indicate that Nitamin and UAN undergo similar NH3 losses, and that both fertilizers may lose less NH3 than urea under conditions favorable to volatilization. Abbreviations: CRH, critical relative humidity; RH, relative humidity; UAN, urea-ammonium nitrate. [ABSTRACT FROM AUTHOR]

The relationship between soil test P (STP) and dissolved reactive P (DRP) in runoff has been shown to vary with soil type due to differences in soil properties. This study was conducted to determine the effect of mineralogy on P sorption behavior and DRP losses in runoff using simulated rainfall. Nine different soft types were sampled from four different fields to provide a range in STP. Unamended soils were packed into runoff boxes for use in a rainfall simulation study (7.5 cm h-1 for 30 min). A mineralogical analysis and adsorption-desorption isotherm was conducted on one representative sample from each soil type. Results indicated that P retention for adsorption and desorption in separated day fractions and whole soils was well correlated to Al bearing minerals such as hydroxy-interlayered-vermiculite (HIV), gibbsite, and amorphous Al. However, P retention was negatively related to kaolinite content, which was also confirmed by isotherms conducted on pure day minerals. Based on the isotherm results, all soils were split into two groups based on the ratio of HIV/ksolinite. Soils with a HIV/kaolinite ratio >0.5 had a significantly lower concentration of DRP in runoff for a given soil water soluble P level compared with soils with a ratio <0.5. [ABSTRACT FROM AUTHOR]

Previous work showed that simulated rainfall applied immediately after urea application to a pine forest floor decreased NH3 losses to negligible levels. The same work also showed that unless rain occurs before urea is dissolved, it might not be effective at leaching urea into the forest floor and decreasing NH3 losses. This study evaluated the effects of diurnal humidity cycles and rainfall amounts on the proportion of urea leached from loblolly pine (Pinus taeds L.) forest floor fractions, and on subsequent ammonia volatilization. New and old pine needles, as well as the partially decomposed (Oe) horizon, were collected from a loblolly pine forest floor in Georgia, USA. Control samples and samples treated with urea at 200 kg N ha-1 were exposed to zero, two, four, or eight simulated humidity cycles, after which they were leached with nine 20-mm increments of simulated rain. Rainfall (180 mm) applied immediately after urea application (0 humidity cycles) leached >98% of the urea from the three forest fractions. Increasing the number of simulated humidity cycles from zero to eight decreased the percentage of urea leached from new pine needles from 98 to 49%, but did not have a major effect on the amount of urea leached from old needles or partially decomposed fraction. All of the urea not leached from new pine needles by 180 mm of simulated rainfall was extractable by water when the new needles were ground. When new needles treated with urea were leached with 180 mm of simulated rainfall and then incubated at 25°C and 95% relative humidity (RH) for 15 d, NH3 losses amounted to 8% of the urea applied. These results suggest that urea retained by recently dropped pine needles is found inside the needles, where it can be hydrolyzed and subsequently lost as NH3. [ABSTRACT FROM AUTHOR]

Analyzes the relationship between soil test phosphorus and phosphorus runoff. Value of including other soil properties in phosphorus loss prediction equations; Soil test phosphorus levels; Influence of the inclusion of site-specific information about soil aluminum and iron content on the relationship between soil test phosphorus and runoff phosphorus.

Spray irrigation of forested land can provide an effective system for nutrient removal and treatment of municipal wastewater. Evolution of N2 + N2O from denitrifying activity is an important renovation pathway for N applied to forested land treatment systems. Federal and state guidance documents for design of forested land treatment systems indicate the expected range for denitrification to be up to 25% of applied N, and most forest land treatment systems are designed using values from 15 to 20% of applied N. However, few measurements of denitrification following long‐term wastewater applications at forested land treatment sites exist. In this study, soil N2 + N2O–N evolution was directly measured at four different landscape positions (hilltop, midslope, toe‐slope, and riparian zone) in a forested land treatment facility in the Georgia Piedmont that has been operating for more than 13 yr. Denitrification rates within effluent‐irrigated areas were significantly greater than rates in adjacent nonirrigated buffer zones. Rates of N2 + N2O–N evolved from soil in irrigated forests ranged from 5 to 10 kg ha−1 yr−1 N on the three upland landscape positions and averaged 38 kg ha−1 yr−1 N within the riparian zone. The relationship between measured riparian zone denitrification rates and soil physical and chemical properties was poor. The best relationship was with soil temperature, with an r2 of 0.18. Overall, on a landscape position weighted basis, only 2.4% of the wastewater‐applied N was lost through denitrification. [ABSTRACT FROM AUTHOR]