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A common passive sampler used to measure NH3volatilization losses in field studies has a nozzle with a 1‐mm, round orifice that reduces air flow to increase NH3adsorption. This reduction in air flow, measured by the orifice's Kvalue (0–1), implies a reduction in the amount of NH3entering 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 NH3entering the sampler and possibly allow shorter exposure times, but it may also lead to increased NH3bypass. The objectives of this research were to (1) determine the effect of wind speed on NH3bypass 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 Kvalues, and (3) compare field NH3volatilization losses measured with 1‐ and 2‐mm orifices. A laboratory study with wind speeds ranging from 0.6 to 10 m·s−1showed that both orifice sizes had NH3bypass 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 NH3volatilization 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. Field NH3loss 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.

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 NH3volatilization (AV, %) from decomposing ‘TifTuf’ bermudagrass [Cynodon dactylon(L.) Pers. × Cynodon transvaalensisBurtt 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 NH3was 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. Mowing interval does not appear to affect turfgrass clipping tissue composition.More frequent mowing may bolster turfgrass health and reduce NH3volatilization losses.Nitrogen mineralization can be highly variable, even in a controlled environment.

Ammonia (NH3) volatilization from broiler (Gallus gallus domesticus) litter is a microbially mediated process that can decrease bird productivity and serves as an environmental pollutant. The release of NH3is strongly influenced by the pH of litter. Flue‐gas desulfurization gypsum (FGDG) has been suggested as a potential amendment to reduce NH3volatilization due to the pH buffering capacity of calcium carbonate (CaCO3) precipitation. However, its effect on litter pH is not as pronounced as acidifying agents, such as aluminum sulfate (alum). The main objective of our study was to develop an acidified‐FGDG amendment that has a more pronounced effect on litter pH and NH3volatilization than FGDG alone. We conducted a 33‐d incubation in which litter pH, NH3volatilization, nitrogen mineralization, PLUP‐ureCgene abundance, and CaCO3precipitation were measured. Treatments in the study included: broiler litter (BL), broiler litter + 20% FGDG (BL+FGDG), broiler litter + FGDG‐alum mixture (BL+FGDG+A6), broiler litter + 6% alum (BL+A6), and broiler litter + 10% alum (BL+A10). Our FGDG+alum amendment decreased litter pH (0.68 pH units) and PLUP‐ureCgene abundance (>1 log) compared with FGDG alone and the control (p< .05). This led to a 25% decrease in cumulative NH3loss after 33 d. The addition of FGDG alone did not have an effect on litter pH (p= .36) or cumulative NH3loss (p= .29) due to a lack of significant CaCO3precipitation. Treating litter with 6 and 10% alum was the most effective amendment for reducing pH and cumulative NH3loss. Acidified gypsum decreases ammonia volatilization from broiler litter.FGD gypsum and acidified gypsum reduce urease‐producing bacteria in broiler litter.Calcium carbonate does not form in gypsum amended litter with a pH <8.Litter pH has a strong effect on ammonia volatilization.

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−1for 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. 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.

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 0–5, 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 hay‐feeding areas than the rest of the pasture. Cattle locus calculated as cattle density (cow ha−1yr−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. We found uneven spatial distribution of soil inorganic N in conventionally grazed pastures.Management is key to spatial distribution of soil inorganic N.Landscape parameters are important for soil inorganic N distribution.Cattle locus shapes soil inorganic N distribution in pastures.

Core IdeasSoil B availability in volcanic soils is governed by SRO minerals.Analyzing whole‐soil reactivity based on mineral surface abundance is proposed.Volcanic soils adsorb as much as 18‐fold higher than non‐volcanic soils.The reversibility of adsorption reactions decreases as andic character increases.pH in NaF can be used to reflect field B availability and application rates. 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‐range‐order (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.

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 NH3losses 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 CaCO3in 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 NH3volatilization. The rate of urea hydrolysis briefly increases when gypsum is added to broiler litter.Treating broiler litter with gypsum causes an immediate decrease in litter pH.Calcium carbonate precipitation in gypsum‐amended litter decreases litter pH.

Core IdeasSoil C and N dynamics were still affected by past fertilization treatments (8 yr).Soil C and N dynamics were still affected by past tillage systems (3 yr).Ammonia‐oxidizing bacteria were affected by ammonium concentration and pH.Ammonia‐oxidizing bacteria and archaea were associated with N mineralization. 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−1d−1) which was correlated with TOC and TON (r2∼ 0.9). The abundance of AOA (5.3–7.6 log10copies g−1) and AOB (7.1–8.9 copies log10g−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.

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 ha−1season−1, 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 forage. 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.

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 taedaL.) 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.

Soil water availability affects NH3loss 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−1soil, 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−1soil 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.

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 NH3volatilization. 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 NH3volatilization 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 NH3volatilized and N mineralized. In two studies, soil with or without 0.01 g FGD gypsum g−1soil was packed into acrylic columns and broiler litter with or without 0.25 g FGD gypsum g−1litter 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−1litter 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 NH3volatilized 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 NH3loss or N mineralized from broiler litter.

Surface application of urea to pine forests may lead to ammonia (NH3) volatilization, which can reduce forest production. The objective of this study was to characterize the effect of rate of urea application on urea hydrolysis rates and the loss of nitrogen (N) by NH3volatilization under a range of environments in the field. Three field studies were performed in a mid‐rotation loblolly pine (Pinus taedaL.) plantation with treatments consisting of urea‐N application rates of 50, 100, and 200 kg N ha−1applied to NH3volatilization chambers that were designed to adjust the rate of air flow through the system based on wind speed at 1 cm above the soil surface. Overall, there was a tendency during some periods of measurement for urea hydrolysis to be slower at the high rate compared with the lower rates of application, but this effect was small. There was, however, no effect of rate of N application on NH3loss, expressed as a percentage of the N applied, during any of the three studies. The main factor controlling NH3loss was water availability as reflected by the interaction between pine needle water potential and relative humidity.

The presence of the hormones estradiol and testosterone in the environment is of concern because they adversely affect vertebrate sexual characteristics. Land spreading broiler litter introduces these hormones into the environment. We conducted two studies. The first study determined the mineralization of 14C‐labeled estradiol and testosterone at three water potentials and three temperatures in four broiler litter‐amended soils. With a few exceptions, the mineralization of each hormone either stayed the same or increased with increasing water content (both hormones) and increasing (estradiol) or decreasing (testosterone) temperature. Mineralization was dependent on soil type. The second study determined the incorporation of 14C‐labeled estradiol and testosterone into (i) three soil organic matter (SOM) fractions (fulvic acid, humic acid, and humin) at two water potentials, two temperatures, and one sampling time, and (ii) at one water potential, one temperature, and seven sampling times. As time increased, higher temperature and water potential decreased percentages of 14C estradiol and testosterone in water‐ and acetone‐soluble fractions and increased percentages in SOM fractions. However, the distribution of the two hormones in SOM fractions differed. For estradiol, higher temperature and water potential increased the percentage in all three SOM fractions. For testosterone, higher temperature and water potential increased the percentage of hormone in fulvic acid and humin. Although the mineralization studies suggest the potential for these hormones to still have environmental effects, the incorporation of the two hormones into SOM suggest that land spreading these hormones may actually be less of an environmental concern.

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* (N0estimated with a fixed kequal to 0.054 wk−1). Out of 13 indices, five [total C (TC), total N (TN), N mineralized by hot KCl (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 kCorrelations between indices and N0* improved compared with N0, ranging from r= 0.90 to 0.95. Total N and flush of CO2determined after 3 d (Fl_CO2) 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_CO2 are rapid and simple, this approach could be easily adopted by soil testing laboratories.

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‐ARS J. Phil Campbell, Sr., Natural Resource Conservation Center, Watkinsville, GA. During the cotton (Gossypium hirsutumL.) cropping phase (1995–2000), 4.4 Mg PL ha−1yr−1resulted 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 maysL.) cropping phase (2001–2005), average annual PL inputs (11.2 Mg ha−1) 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.

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 NH3loss from these urea fertilizers. This study evaluated NH3losses from Nitamin (a urea polymer), urea–NH4NO3(UAN), and granular urea applied to tall fescue (Festuca arundinaceaSchreb.) plots at 50 kg N ha−1in fall and spring for 2 yr. Fertilizers were applied to circular plots (30‐m diameter) and NH3loss 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 ha−1and 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 NH3losses, and that both fertilizers may lose less NH3than urea under conditions favorable to volatilization.

Corn (Zea maysL.) producers in the southeastern United States must overcome soil and water limitations to take advantage of the expanding corn market. In this 2001 to 2005 study on a Cecil sandy loam (fine, kaolinitic, thermic Typic Kanhapludult) near Watkinsville, GA, we compared dry land corn biomass and yield under conventional tillage (CT) vs. no‐tillage (NT) with ammonium nitrate or sulfate (based on availability) as conventional fertilizer (CF) vs. poultry litter (PL). In a randomized complete block split plot design with three replications, main plots were under tillage and subplots under fertilizer treatments. The cover crop was rye (Secale cerealeL.). Over 5 yr, NT and PL increased grain yield by 11 and 18%, respectively, compared with CT and CF. Combined, NT and PL increased grain yield by 31% compared with conventionally tilled and fertilized corn. Similarly, soil water was 18% greater in NT than CT in the 0‐ to 10‐cm depth. In 2 yr of measurements, dry matter of stalks and leaves and leaf area index under PL were an average of 39 and 22% greater, respectively, than under CF during reproduction. Values were 21 and 6% greater, respectively, under NT than CT but during tasseling. Analysis of 70 yr of daily rainfall records showed that supplemental irrigation is needed to meet optimal water requirement. Our results indicate that corn growers can use rainfall more efficiently, reduce yield losses to drought, and expect increased corn yields with a combination of no‐tillage management and long‐term use of poultry litter.

Because surface‐applied manures can contribute to phosphorus (P) in runoff, we examined mechanical aeration of grasslands for reducing P transport by increasing infiltration of rainfall and binding of P with soil minerals. The effects of three aeration treatments and a control (aeration with cores, continuous‐furrow “no‐till” disk aeration perpendicular to the slope, slit aeration with tines, and no aeration treatment) on the export of total suspended solids, total Kjeldahl P (TKP), total dissolved P (TDP), dissolved reactive P (DRP), and bioavailable P (BAP) in runoff from grasslands with three manure treatments (broiler litter, dairy slurry, and no manure) were examined before and after simulated compaction by cattle. Plots (0.75 × 2 m) were established on a Cecil soil series with mixed tall fescue (Festuca arundinaceaSchreb.)‐bermudagrass [Cynodon dactylon(L.) Pers.] vegetation on 8 to 12% slopes. Manures were applied at a target rate of 30 kg P ha−1, and simulated rainfall was applied at a rate of 85 mm h−1Although the impact of aeration type on P export varied before and after simulated compaction, overall results indicated that core aeration has the greatest potential for reducing P losses. Export of TKP was reduced by 55%, TDP by 62%, DRP by 61%, total BAP by 54%, and dissolved BAP by 57% on core‐aerated plots with applied broiler litter as compared with the control (p< 0.05). Core and no‐till disk aeration also showed potential for reducing P export from applied dairy slurry (p< 0.10). Given that Cecil soil is common in pastures receiving broiler litter in the Southern Piedmont, our results indicate that pairing core aeration of these pastures with litter application could have a widespread impact on surface water quality.

Understanding cover crop and tillage system interactions within specific environments can help maximize productivity and economic returns of cotton (Gossypium hirsutumL.) produced on sandy coastal plain soils of the southeastern USA. A strip‐plot design with three replications was used to evaluate the cover crops Austrian winter pea [Pisum sativumL. ssp. arvense(L.)], balansa clover (Trifolium michelianumSavi), crimson clover (Trifolium incarnatumL.), hairy vetch (Vicia villosaRoth subsp. villosa), oil seed radish (Raphanus sativusL.), black oat (Avena strigosaSchreb.), and rye (Secale cerealeL.) and tillage (strip and none) influences on cotton grown on a Bonifay fine sand (loamy, siliceous, subactive, thermic Grossarenic Plinthic Paleudults) near Waynesboro, GA from 1999 to 2003. Drought influenced production 3 of 4 yr. Cover crop biomass was greatest from rye, intermediate from black oat, oilseed radish, hairy vetch, and Austrian winter pea. Hairy vetch and Austrian winter pea contained more than 80 kg N ha−1while other cover crops averaged <40 kg N ha−1. Cotton yields following black oat and rye had returns above variable costs ha−1$461 and $406, respectively. Strip‐tillage increased yields by 192 kg ha−1and annual returns by $112 ha−1over no‐tillage, most likely due to improved available water. Combining strip‐tillage with black oat was the best combination for maximizing profit. Using black oat with strip‐tillage could increase cotton profit by $50 to $75 ha−1compared to systems using rye on the 1.45 million ha of cotton where conservation systems have been adopted.

Previous work showed that simulated rainfall applied immediately after urea application to a pine forest floor decreased NH3losses 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 NH3losses. This study evaluated the effects of diurnal humidity cycles and rainfall amounts on the proportion of urea leached from loblolly pine (Pinus taedaL.) 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−1were 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, NH3losses 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

Phosphorus loss in runoff from agricultural fields has been identified as an important contributor to eutrophication. The objective of this research was to determine the relationship between phosphorus (P) in runoff from a benchmark soil (Cecil sandy loam; fine, kaolinitic, thermic Typic Kanhapludult) and Mehlich III–, deionized water–, and Fe2O3–extractable soil P, and degree of phosphorus saturation (DPS). Additionally, the value of including other soil properties in P loss prediction equations was evaluated. Simulated rainfall was applied (75 mm h−1) to 54 1‐m2plots installed on six fields with different soil test phosphorus (STP) levels. Runoff was collected in its entirety for 30 min and analyzed for total P and dissolved reactive phosphorus (DRP). Soil samples were collected from 0‐ to 2‐, 0‐ to 5‐, and 0‐ to 10‐cm depths. The strongest correlation for total P and DRP occurred with DPS (r2= 0.72). Normalizing DRP by runoff depth resulted in improved correlation with deionized water–extractable P for the 0‐ to 10‐cm sampling depth (r2= 0.81). The STP levels were not different among sampling depths and analysis of the regression equations revealed that soil sampling depth had no effect on the relationship between STP and P in runoff. For all forms of P in runoff and STP measures, the relationship between STP and runoff P was much stronger when the data were split into groups based on the ratio of oxalate‐extractable Fe to Al. For all forms of P in runoff and all STP methods, R2increased with the inclusion of oxalate‐extractable Al and Fe in the regression equation. The results of this study indicate that inclusion of site‐specific information about soil Al and Fe content can improve the relationship between STP and runoff P.

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−1yr−1N on the three upland landscape positions and averaged 38 kg ha−1yr−1N 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 r2of 0.18. Overall, on a landscape position weighted basis, only 2.4% of the wastewater‐applied N was lost through denitrification.

Nitrate leached from soils can contaminate drinking water and pose a health risk at concentrations > 10 mg N L−1. Computer models may be useful management tools for estimating NO3leaching, but they need to be calibrated and validated before use. The objective of this work was to calibrate and validate LEACHN to simulate soil NO3, soil NH4, water drainage, and NO3leaching in a Cecil sandy loam (fine, kaolinitic, thermic Typic Kanhapludults). The calibration was done by determining rate constants and parameters under laboratory conditions. The validation data was obtained from a two‐year study with conventionally tilled corn (Zea maysL.) during summer and either a rye (Secale cerealeL.) cover crop or fallow conditions during winter. Water drainage collected by tiles was automatically measured, subsampled, and analyzed for inorganic N concentrations. During the cold season, LEACHN underestimated soil NH4and NO3in at least half of the cases. During the warm season, the model correctly estimated soil NO375% of the time, but it overestimated soil NH4in an equal 75% of the cases. Also, LEACHN overestimated cumulative drainage and leached NO3at least 50% of the time during both cold‐ and warm‐season periods. These results suggest that the soil hydraulic properties and N mineralization rate constants determined under laboratory conditions did not apply to field conditions. Also, results obtained by changing rate constants for N transformations indicate that LEACHN was not properly simulating N immobilization from fertilizer N, or nitrification under dry conditions.

Pearl millet [Pennisetum glaucum(R.) Br.] is a high‐quality grain crop that can that can be grown without irrigation during hot, dry summers in the southeastern United States. The N rate required for optimum pearl millet grain yield varies widely in published studies, possibly because of variability in residual soil N from the subsoil. Field studies were conducted in the southern Coastal Plain at Tifton, GA, on a Tifton loamy sand (fine‐loamy, siliceous, thermic Plinthic Kandiudult) with nitrate accumulations near subsoil plinthite. The objective was to determine if pearl millet can extract N from acidic, relatively impermeable subsoils. Nitrate N (1 MKCl‐extractable) was 4 mg kg−1in the surface 0.6 m, 1 mg kg−1in the next 0.6 m, and 6 mg kg−1from 1.2 to 1.5 m. We fertilized pearl millet field plots with two levels of N (0 and 168 kg ha−1) and studied root development during the growing seasons in 1993 and 1994. Soil cores were taken 40 d after planting to a depth of 1.2 m, separated into 0.3‐m depth segments, and root length density was measured. Roots were found in the deepest segments. Nitrogen fertilization increased the proportion of the root length density found in the surface soil in one year. We also injected 15N as 60% atom l5N‐enriched KNO3at a depth of 1 m at 30 and 40 d after planting. At physiological maturity, atom % 15N abundance in the plants ranged from 10.1 to 12.0 where 15N was injected and was near natural abundance where no 15N was injected. These results indicate that pearl millet can extract N from 1 to 1.2 m in an acidic and impermeable subsoil.

Further improvement of residue decomposition models may help to optimize the use of N released from cover crop residues. CERES models are widely used to simulate crop‐soil systems and have a common subroutine that describes N dynamics (CERES‐N). In this work, we tested CERES‐N with results from a litterbag study over 120 d in which crimson clover (Trifolium incarnatum (L.), rye (Secale cereale(L.), wheat (Triticum aestivum(L.), and oat (Avena sativaL.) residues were allowed to decompose on the soil surface. The field data were used to (i) evaluate the original CERES‐N and a modification of CERES‐N that allows users to enter actual sizes for the carbohydrates, cellulose, and lignin pools and (ii) determine the best‐fitting rate constants for decomposition of the carbohydrates and cellulose pools in the original CERES‐N and in CERES‐N with user‐supplied pool sizes. CERES‐N with the original rate constants or with rate constants and parameters proposed by other workers either underestimated (root mean square error RMSE = 1.23 g N m−2) or overestimated (RMSE = 2.18 g N m−2) N remaining in the crop residues after 120 d of decomposition. CERES‐N with user‐supplied pool sizes improved the simulation of N remaining after 120 d (RMSE = 0.69 g N m−2), but the simulated values generally tended to overestimate the field data. The best‐fitting rate constants for carbohydrates and cellulose pools were 0.67 and 0.021 d−1, respectively, for the original CERES‐N (RMSE = 0.77 g N m−2), and 0.17 and 0.011 d−1for CERES‐N with user‐supplied pool sizes (RMSE = 0.55 g N m−2). Future work should further evaluate these fitted rate constants under field conditions.

A careful study of the output of simulation models can help students understand concepts of crop production and soil management. Very often, graphical representation of the simulated data allows faster and easier understanding of the different processes occurring in a particular system. N-Show is an educational computer program that produces a dynamic, graphical representation of results generated by CERES—Maize, a simulation model of corn (Zea maysL.) growth and development. The program allows the user to observe and compare the results of several runs of CERES—Maize, which were selected to demonstrate the effect of soil type and N rate on nitrate leaching. N-Show displays dynamic graphs of water and inorganic N contents in the soil, N in the plant, and N leached out of the soil profile. The unique feature of N-Show is that it allows the user to move the graphical display back and forth in time, thereby allowing careful study of the events that occur at specific times. N-Show could be used in undergraduate crop and soil courses and in training sessions for extension workers and farmers.

Poultry litter is a mixture of broiler (chicken, Gallus gallus domesticus) excreta and bedding material. The broiler industry may produce more litter than can be locally land-applied without causing environmental degradation. Passing whole litter through 0.83- and 3.33-mm sieves separates a fine fraction that can be land-applied as fertilizer and a coarse fraction that can be mixed with bedding and re-utilized in broiler houses. A study was conducted to determine whether the coarse litter fraction could be re-utilized as a supplement for bedding in broiler houses without significant accumulation of heavy metals and other elements. Wood shavings supplemented with either stored or fresh coarse litter and a treatment of unsupplemented wood shavings were used as bedding material during a 40-day broiler growth period. Initial and final litter samples were collected and analyzed for Al, As, B, Ba, Ca, Cd, Co, Cr, Cu, Fe, K, Mg, Mn, N, Na, Ni, P, Pb, Si, Sr, and Zn. Results indicated that element concentrations in wood shavings bedding supplemented with litter did not increase significantly during the final 30 days of a 40-day growth period. However, significant accumulation of several litter elements in unsupplemented wood shavings bedding during the entire 40-day growth period indicated that repeated recycling of litter as a bedding supplement may lead to significant accumulation of elements in litter.

A study of broiler litter re-utilization potential was conducted with a goal of determining if a coarse litter fraction could be safely re-utilized as a supplement for wood shavings bedding without significant pathogen accumulation. Pathogenic and indicator bacteria were monitored in three litter types (coarse fractions of fresh or stored litter supplemented with wood shavings, or wood shavings alone) during a 40-day growth period in broiler house pens. Initial microbial concentrations were higher in fresh litter than in stored litter or wood shavings. Significant increases in microbial concentrations occurred during 40 days of re-utilization in fresh/stored/shavings litter. No consistent significant differences were found among concentrations of microorganisms in fresh/stored/shavings litter during re-utilization.

Broiler (poultry) litter consists of excreta, bedding material (used to cover floor of broiler houses and absorb excreta), soil, feathers, and other components generated during broiler production. The objective of this study was to determine concentrations of 20 elements in whole litter and coarse and fine size fractions of whole litter exposed to single flocks and multiple flocks of broilers as well as to determine any significant differences or changes in concentrations of these elements during 4 months of litter storage. During storage for up to 4 months, whole litter and its fractions were analyzed for concentrations of Al, As, B, Ba, Ca, Cd, Co, Cr, Cu, Fe, Hg, K, Mg, Mn, Ni, P, Pb, Si, Sr, and Zn. No consistent significant differences in litter elemental concentrations were found among samples taken at 0, 2, 4, 8, and 16 wk. Significantly higher concentrations of several elements were found in multi-flock litter than in single-flock litter. No consistent significant differences in elemental concentrations were found among whole litter and coarse and fine whole litter fractions. This research shows that while size fractionation of litter facilitates re-use of litter, litter exposed to multiple flocks of broilers contains significantly higher concentrations of several elements, so recycling of multi-flock litter may be limited.

A study of broiler litter re-utilization potential was conducted with the goal of determining if storage of litter significantly reduced potential pathogens to levels safe for re-utilization. Litter from four broiler houses was separated into a fine fraction for fertilizer use and a coarse fraction for use as a supplement to wood shavings in growing subsequent flocks of birds. Fractions and whole litter were stored in indoor piles for four months with periodic analysis for culturable pathogenic and indicator bacteria. Significant reductions in microbial concentrations occurred in a majority of samples tested during four months of storage (in most cases to below detection limits of approximately 30 CFU/g dry weight). Poultry feed was found to be one possible source of litter contamination.