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Tall fescue (Lolium arundinaceum [Schreb.] S.J. Darbysh.) is a widely adopted cool-season perennial forage in the southeastern United States. Historically, tall fescue contained a symbiotic fungal endophyte, Epichloe coenophiala, that produced an ergot alkaloid toxic to livestock. New fescue biotypes have been developed that are endophyte free or include endophytes that produce low-toxicity alkaloids. Ecological implications of these biotypes are not fully understood. We evaluated nutrient runoff quality for three tall fescue biotypes (common, high alkaloid endophyte [wild]; low alkaloid endophyte [novel]; and endophyte free [free]) under two fertilizer sources (broiler litter [BL] and inorganic fertilizer) in grazed systems and a hayed system with inorganic fertilization of endophyte free fescue. The seven treatments were replicated twice on 1 ha paddocks near Watkinsville, Georgia. Grazed paddocks were stocked in September each year with weaned Angus (Bos taurus) heifers (2002 to 2007) and steers (2008 to 2009) at rates of ~3 to 6 head paddock–1 adjusted every 28 days to maintain 1 to 3 Mg ha–1 of available forage. Weather conditions varied from very dry to very wet and allowed 15 grazing periods (50 to 198 days). Tall fescue with novel-endophyte association had lower or equal runoff concentrations and loads for inorganic nitrogen (N), total N (TN), ortho-phosphorus (ortho-P), and total P (TP) than fescue with wild- or free-endophyte association (fescue treatment mean concentrations [mg L–1]

Cereal rye (Secale cereale) cover crops supply many agroecosystem services in cropping systems including the provision of allelochemicals for weed suppression. Understanding the distinction between root and shoot relative contributions of these allelochemicals (such as phenolic acids) should provide better insight for residue management following termination of a cereal rye cover crop. A field experiment examining root and shoot contributions of phenolic acids to soil was conducted in 2015 at Beltsville, Maryland. Tissue and soil (0–10 cm) phenolic acid concentrations were analyzed over time using liquid chromatography–mass spectrometry. Cereal rye roots were found to be the primary contributor of phenolic acids to soil. Further, soil phenolic acid concentrations were unaffected by tillage or soil depth. Overall, the phenolic acid concentrations of coumaric > vanillic > 4-hydroxybenzoic acid increased in soils during the first 3–7 days after cereal rye termination and then decreased to initial concentrations after 56 days. Our research forms a basis for future allelopathy research. Specifically, there is a need to understand the contribution of roots to phenolic acid release in soils. Building this body of knowledge will improve our ability to employ allelopathy as part of a multi-tactic weed management system.

Tillage systems and fertilizer sources impact soil health and ecosystem services. Rainfall simulations can be used to evaluate tillage and fertilizer management effects on ecosystem services associated with runoff amount and quality. Fixed rate (FR; 57 mm h−1 for 60 minutes) and variable rate (VR; based on the pattern of the most frequent spring rain) simulations were conducted on corn (Zea mays L.) plots supplied with conventional fertilizer (CF; ammonium nitrate [NH4NO3]) or poultry litter (PL) and managed with conventional tillage (CT) or no-tillage (NT) on a Cecil soil (Ultisol) near Watkinsville, Georgia. Simulations were conducted in separate years (FR in 2004 and VR in 2005). Tillage and tillage × fertilizer interactions had significant effects on total runoff and sediment loss under FR but not VR. Under FR, 55.8% of the simulated rainfall was partitioned into runoff from CT compared with 9.7% from NT. Under VR, 42% to 60% was partitioned into runoff with no difference among treatments. Sediment loss was 11-fold greater from CT compared with NT under FR (919 g versus 82 g). Under VR, sediment loss varied between 755 g and 2,174 g with no difference among treatments. Tillage and tillage × fertilizer interactions had significant effects on total load for ammonium-nitrogen (NH4-N) and nitrate-nitrogen (NO3-N) in both methods and dissolved reactive and total phosphorus (DRP and TP) under VR. Fertilizer source affected loads of NH4-N under VR and NO3-N and TP under both methods. Our results confirm that 12 years of continuous NT on a Cecil soil, representative of much of the Southern Piedmont, is far superior to CT for reducing runoff and sediment loss. Larger and more intense storms predicted in future climate projections warrant greater adoption of reduced tillage systems to counteract potential runoff and sediment losses from CT systems.

Cereal rye (Secale cereale L.) is widely grown due to its winter hardiness and adaptability to varied soil and environmental conditions. Fall and spring climate and available soil N drive biomass production. However, there is limited empirical information on the effects of these factors on cover crop performance. Farmers need early spring indicators of cereal rye performance to guide management. A 3-yr experiment was initiated to test and model the effects of climate and soil N fertility on cereal rye growth and allometric relationships in Pennsylvania, Maryland, and North Carolina under five-six fall fertilizer rates. We hypothesized that allometric relationships between early spring growth indicators can guide management decisions. Measurements included tillering, biomass, tissue N, and normalized difference vegetation index (NDVI) at Zadoks growth stages (GS) 25, 30, and 60. Nitrogen application increased biomass: maximum average biomass was 2853, 4844, and 9739 kg ha–¹, respectively, at GS25, GS30, and GS60. At GS25, biomass accounted for the greatest amount of model variation and better predicted GS60 biomass than shoot density and NDVI. Variance attributed solely to GS25 and GS30 biomass constituted 38.5 to 65.2% of total model variance. Models accurately predicted biomass and N accumulation 34 to 60% of the time. This study illustrates the difficulty in predicting late season biomass and N content based on early measurements. One extension of this research would be the development of a simple protocol to accurately sample cereal rye biomass at GS25 to estimate potential N accumulation and biomass at GS60.

Soybean and sunflower are summer annuals that can be grown as an alternative to corn and may be particularly useful in organic production systems for forage in addition to their traditional use as protein and/or oil yielding crops. Rapid and low cost methods of analyzing plant forage quality would be helpful for nutrition management of livestock. We developed and validated calibration models using Near-infrared Reflectance Spectroscopic (NIRS) analysis for 27 different forage quality parameters of organically grown sunflower and soybean leaves or reproductive parts. Crops were managed under conventional tillage or no-till with a cover crop of wheat before soybean and rye-crimson clover before sunflower. From a population of 120 samples from both crops, covering multiple sampling dates within the treatments, calibration models were developed utilizing spectral information covering both visible and NIR region of 61 - 85 randomly chosen samples using modified partial least-squares (MPLS) regression with internal cross validation. Within MPLS protocol, we compared nine different math treatments on the quality of the calibration models. The math treatment “2,4,4,1” yielded the best quality models for all but starch and simple sugars (r2 = 0.699 - 0.999; where the 1st digit is the number of the derivative with 0 for raw spectra, 1 for first derivative, and 2 for second derivative, the 2nd digit is the gap over which the derivative is calculated, the 3rd digit is the number of data points in a running average or smoothing, and the 4th digit is the second smoothing). Prediction of an independent validation set of 28-35 samples with these models yielded excellent agreement between the NIRS predicted values and the reference values except for starch (r2 = 0.8260 - 0.9990). The results showed that the same model was able to adequately quantify a particular forage quality of both crops managed under different tillage treatments and at different stages of growth. Thus, these models can be reliably applied in the routine analysis of soybean and sunflower forage quality for the purposes of livestock nutrient management decisions.

Soil acidity is a constraint to global soil and food security, yet access to limestone to correct this problem is limited in many parts of the world. Research suggests that animal manures have a liming effect on acidified soils, representing a potential solution. This long-term (15 year) study used a split plot design to evaluate the effect of conventional tillage (CT) vs no-till (NT) (main plot) under conventional (CF) and poultry litter (PL) fertilizer source applications (sub-plots). A succession of three cropping systems consisting of cotton (Gossypium hirsutum L.) with a winter wheat (Triticum aestivum) cover crop, corn (Zea mays) with rye (Secale cereal), and millet (Panicum miliaceum) with rye was implemented. The soil is a Cecil sandy loam (1:1 kaolinitic). Changes in soil pH, soil organic carbon (SOC), and lime buffer capacity (LBC) were compared among the four treatments CTCF, CTPL, NTCF, and NTPL. The CTPL treatment had a 0.6 unit pH increase in the top 15 cm. However, cropping systems had more effect than tillage or fertilizer source on both soil pH and LBC. All treatments resulted in some increase in subsoil pH. Lime buffer capacity remained unchanged at all but the 76–91 cm depth, where all treatments exhibited a decrease ranging from 27 to 43 kg CaCO3 eq ha−1 pH unit−1 year−1. Our results suggest that previously reported liming effect of animal manures should be examined in the context of soil type and cropping system to better understand the true mechanism(s) of soil acidity amelioration.

Summary Megacopta cribraria (F.) (Hemiptera: Plataspidae) is a newly invasive, exotic pest of soybean (Glycine max [L.] Merr.; Fabales: Fabaceae) in the southeastern United States. In 2013, the exotic egg parasitoid Paratelenomus saccharalis (Dodd) (Hymenoptera: Platygastridae) was discovered parasitizing eggs of this pest in kudzu (Pueraria montana var. lobata [Willd.] Maesen & S. Almeida; Fabales: Fabaceae) and soybean in 3 states in this region of the United States. We evaluated parasitism of M. cribraria egg masses by P. saccharalis in conventional tillage and no-till organic soybean experimental plots in 2013. Density of M. cribraria egg masses was significantly higher in conventional tillage soybean than in no-till soybean in weeks 2 through 5 for the 7 wk period M. cribraria egg masses were detected on soybean. Percentage of parasitism of M. cribraria egg masses by P. saccharalis was significantly higher in conventional tillage soybean (58.4%) than in no-till soybean (44.9%). In general, parasitism...

Gypsum has been shown to reduce runoff on soils prone to crust formation in the southeastern United States. Increased infiltration from gypsum applications could therefore help reduce runoff P and other nutrient losses from application of broiler litter (BL), a nutrient-rich fertilizer. In rainfall simulation experiments in June 2009 and May 2011, runoff and nutrient (N, P, Ca, Mg) losses in runoff were compared among treatments consisting of 0, 2.2, 4.5, and 9.0 Mg ha⁻¹ flue gas desulfurization gypsum (FGDG) combined with 13.5 Mg ha⁻¹ of BL and two control treatments of (0–0) and (9.0–0.0) Mg ha⁻¹ (FGDG-BL). A randomized block design with three replications was set up on a Cecil (Typic Kanhapludult) soil growing Coastal bermudagrass (Cynodon dactylon L.) for hay near Watkinsville, Georgia. Amendments were applied each April from 2009 to 2011. A reduction in runoff of 30% each year from the (9.0–13.5) compared with the (0–0) treatment was not statistically significant. Gypsum was effective in reducing concentration and load in one of the two study years: P and NH₄–N in 2009 (up to 83%) and NO₃–N in 2011 (up to 73%). A combination of factors related to weather extremes, timing of FGDG and BL applications, and their implication on soil and vegetation responses at different landscape positions might have caused the different responses between years. Additional studies focused on isolating the impacts of such factors would be helpful to ascertain the effectiveness of multiyear applications of FGDG as a best management practice to reduce P and other nutrient losses in soils of the southeastern United States.

Sunnhemp (Crotalaria juncea L.) is a tropical legume that could be an important summer cover crop in the southeastern United States, but it has the potential for suppressing both crops and weeds. Allelopathic effects of sunnhemp on weeds, vegetable crops, and cover crops were evaluated in greenhouse and growth chamber experiments. In the greenhouse, ground dried sunnhemp residues (applied mixed with the soil at 1.6% w/w) reduced percent germination of lettuce (Lactuca sativa L.) and smooth pigweed (Amaranthus hybridus L.) to a similar degree as that caused by cereal rye (Secale cereale L. subsp. cereale) residues (applied at 1.5% w/w). The allelopathic activity of sunnhemp was greater in the leaves than in the roots or stems. In growth chamber studies, the mean reduction in germination (relative to the control) caused by sunnhemp leaf aqueous extracts was: bell pepper (100%), tomato (100%), onion (95%), turnip (69%), okra (49%), cowpea (39%), collard (34%), cereal rye (22%), sweet corn (14%), Austrian winter pea (10%), crimson clover (8%), cucumber (2%), and winter wheat (2%). In lettuce, carrot, smooth pigweed, and annual ryegrass, sunnhemp aqueous leaf extract reduced seedling length to a degree similar as that produced by rye aqueous leaf extract. Sicklepod [Senna obtusifolia (L.) H.S. Irwin & Barneby CA] germination was not inhibited by any of the sunnhemp or rye aqueous extracts. In conclusion, sunnhemp reduced the germination percentage and seedling growth of various crop species. The allelochemical activity in sunnhemp was primarily in the leaves and remained active at least 16 d after harvest under dry conditions. Sunnhemp's allelochemical effect may be a useful attribute for weed management in sustainable production systems. However, plant growth in the field in crops such as bell pepper, tomato, onion, and turnip may be impacted as a result of allelopathic activity of sunnhemp residues. Thus, weed management may be more effective when sunnhemp is grown in rotation with crops that tolerate the allelochemicals from sunnhemp, resulting in optimization of the rotation effects.

Poultry (Gallus gallus domesticus L.) litter (PL) is a readily available nutrient source for crop production in the Southeast USA. Long-term PL application may alter availability of N and the effect may be dependent on tillage practice. Tillage [no till (NT) vs. conventional (CT)] and N source (PL vs. commercial fertilizer CF) effects on N availability and plant uptake were evaluated in years 9, 10, and 11 of a long-term cropping systems study at the United States Department of Agriculture, Agricultural Research Service, J. Phil Campbell Sr. Natural Resource Conservation Center, Watkinsville, GA, USA. Mineral N in the top 10 cm, measured in situ, varied each year and was influenced by time, tillage, and N source. In 2003 (year 9), soil mineral N content was greater in CT–CF (100 kg ha−1) than in NT–PL (95 kg ha−1) but in 2004 (year 10) and 2005 (year 11) it was lower in CT–CF (93 and 60 kg ha−1) compared to NT–PL (140 and 71 kg ha−1). Nitrogen mineralization rates were generally greater for PL than for CF treatments with the difference being almost 1 kg ha−1 day−1 in 2003. Mineralization rates were greater for NT–PL compared to CT–CF in 2004 and 2005. Across the three growing seasons, corn (Zea mays L.) aboveground biomass was consistently greater in the NT–PL treatment than in the NT–CF and CT–CF treatments. Correlation between aboveground biomass and N mineralization was greater for PL than for CF (0.75 vs. 0.48). Patterns of N mineralization and total soil mineral N indicated that the distribution of N through the growing season more closely matched corn N demand in PL treatments. Results indicate that improved N availability through the growing season, by combining NT and PL, can result in more profitable corn production in the southeast.

Water-extractable organic matter (WEOM) contains labile organic carbon (C) and nitrogen (N) and is sensitive to soil management. The objective of this study was to determine the quantity and spectral properties of soil WEOM responding to types of nutrient addition and tillage managements. Soil samples were taken from treatments (con- ventional tillage, no-tillage, poultry litter, and NH4NO3 application) of a 10-year experiment in Watkinsville, Georgia, at different times and soil depths. Air-dried soil samples were extracted by deionized water followed by filtration (G0.45 Km), and soluble C and N, absorptivity at 254 nm, and fluorescence excitation/emission matrix in the extract were determined. Results showed that poultry litter application accumulated higher amounts of water-extractable organic C and N than NH4NO3 application. But no significant difference was found between tillage and no-tillage for both water-extractable C and N. Absorptivity at 254 nm decreased during cropping years for conventional tillage and NH4NO3 application, indicating accumulation of aliphatic organic compounds in WEOM, but the fluorescence-measured humification index showed an opposite trend. For no-tillage and poultry litter application treatments, there was no difference in absorptivity over the sampling time. Parallel factor analysis of excitation/emission matrix data showed that WEOM consisted of three fluorophore components: humic-, fulvic-, and tyrosine- like ''compounds,'' and relative distribution of these components differed among treatments and changed over soil depths. The tyrosine-like com- ponent tended to accumulate in the lower sampling depth (915 cm). Overall, the quantity and spectral properties of WEOM responded to the types of nutrient application and tillage practices.

Conservation tillage and judicious use of animal manures as fertilizers can make significant contributions for sustainable food production in the twenty-first century. Identifying and understanding the many interactions occurring within agricultural systems is fundamental for accomplishing this feat. This paper synthesizes 14 years of research results from a study that began in the early 1990s in which researchers from USDA-ARS and the University of Georgia investigated cropping system influences on nutrient management under natural rainfall. Increases in C and N with no-till resulted in improved soil structure that increased infiltration rate and soil water availability. Biological activity as indicated by earthworms was greater with no-till and poultry litter (PL). In all but the very driest year, yields of cotton and corn increased on average 10–27% with no-till and 32–42% with combination of no-till and PL. On the other hand soil nutrient accumulation, particularly P and Zn from long-term use of poultry litter in corn production, reached excessive levels and could present environmental risks. Drainage increased in no-till raising the risk of leaching of nutrients into the soil profile. However, runoff decreased in no-till and the presence of a rye cover crop during the winter reduced the leaching losses of N compared to no cover crop. During cotton production under relative drought, no-till and poultry litter led to somewhat elevated dissolved phosphorus concentration in runoff, and fluometuron was detected in runoff and drainage while pendimethalin was not. Fecal indicator bacteria (Escherichia coli and fecal enterococci), and the hormones estradiol and testosterone were observed in drainage and runoff but concentrations were similar across all treatments. By conducting the study for an extended period under natural environmental conditions, we were able to highlight real risks and potentials of the contrasting cropping systems. While 6 out of 14 years of relative drought might have limited the water quality response of treatments, such droughts are common features of the weather pattern in the region. Even then, use of no-till as the predominant tillage system was supported by improved yields. Fertilizer management, especially crop N need-based use of PL, requires closer monitoring to insure that production advantages of no-till and poultry litter are not offset by concerns with environmental risks. Long-term research requires sustained resource inputs to answer critical questions of environmental risk and emerging unknown issues.

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 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 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.

Corn (Zea mays L.) 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 cereale L.). 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.

The tropical legume sunn hemp (Crotalaria juncea L.) could be a valuable green manure/cover crop for vegetable producers in the southeastern USA because of its rapid growth and large N 2 fixing ability. Planting and termination date effects on biomass and N accumulation are relatively unknown for the region, but would help producers manage sunn hemp between summer and winter cash crops. We determined sunn hemp biomass and N content at 30, 60, 90, and 120 days after planting (DAP) for four planting dates (mid-April to mid-July) at a Piedmont and a Coastal Plain location in Georgia. Maximum biomass at a given DAP was produced from May and June plantings in the Piedmont and from April and May plantings in the Coastal Plains. Maximum biomass and N ranged from 8.9 to 13.0 Mg ha -1 and 135 to 285 kg ha -1 , respectively. An equation for estimating sunn hemp biomass as a linear function of cumulative degree days (CDD) and cumulative solar radiation (CSR) was verified with independent data from Alabama, Florida, and Virginia. A similar equation for estimating N content as a quadratic function of CSR was not as accurate but still might be useful. Sunn hemp can fit well into short-rotation sustainable vegetable production systems in the Southeast, and these equations can be used by producers to make reliable estimates of sunn hemp biomass production.

Cover crops may influence soil carbon (C) sequestration and microbial biomass and activities by providing additional residue C to soil. We examined the influence of legume [crimson clover (Trifolium incarnatum L.)], nonlegume [rye (Secale cereale L.)], blend [a mixture of legumes containing balansa clover (Trifolium michelianum Savi), hairy vetch (Vicia villosa Roth), and crimson clover], and rye + blend mixture cover cropson soil C fractions at the0‐150 mmdepth from 2001 to 2003. Active fractions of soil C includedpotentialCmineralization(PCM)andmicrobialbiomassC(MBC)andslowfraction assoilorganicC(SOC).Experiments were conducted in Dothan sandy loam (fine-loamy, kaolinitic, thermic, Plinthic Kandiudults) under dryland cotton (Gossypium hirsutum L.) in central Georgia and in Tifton loamy sand (fine-loamy, siliceous, thermic, Plinthic Kandiudults) under irrigated cotton in southern Georgia, USA. Both dryland and irrigated cotton were planted in strip tillage system where planting rows were

The type of conservation-tillage management employed could impact surface-soil properties, which could subsequently affect relationships between soil and water quality, as well as with soil C sequestration and greenhouse gas emissions. We determined soil bulk density, organic C and N fractions, plant-available N, and extractable P on Typic Kanhapludults throughout a 7-year period, in which four long-term (>10 years), no-tillage (NT) water catchments (1.3–2.7 ha each) were divided into two treatments: (1) continuation of NT and (2) paraplowing (PP) in autumn (a form of non-inversion deep ripping) with NT planting. Both summer [cotton (Gossypium hirsutum L.), maize (Zea mays L.), sorghum (Sorghum bicolor L. Moench), soybean (Glycine max L. Merr.)] and winter [wheat (Triticum aestivum L.), barley (Hordeum vulgare L.), rye (Secale cereale L.), crimson clover (Trifolium incarnatum L.)] crops were NT planted throughout the study under each management system. Soil bulk density was reduced with PP compared with NT by as much as 0.15 Mg m � 3 , but the extent of reduction was inversely related to the time lag between PP operation and sampling event. Soil organic C became significantly enriched with time during this study under NT (0.49 Mg C ha � 1 year � 1 ), but not under PP, in which poultry litter was applied equivalent to 5.7 Mg ha � 1 year � 1 to all water catchments. Soil maintained a highly stratified depth distribution of organic C and N fractions and extractable P under both NT and PP. Inability to perform the PP operation in the last year of this study resulted in rapid convergence of soil bulk density between tillage systems, suggesting that PP had

Understanding cover crop and tillage system interactions within specific environments can help maximize productivity and economic returns of cotton (Gossypium hirsutum L.) 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 sativum L. ssp. arvense (L.)], balansa clover (Trifolium michelianum Savi), crimson clover (Trifolium incarnatum L.), hairy vetch (Vicia villosa Roth subsp. villosa), oil seed radish (Raphanus sativus L.), black oat (Avena strigosa Schreb.), and rye (Secale cereale L.) and tillage (strip and none) influences on cotton grown on a Bonifay fine sand (loamy, siliceous, subactive, thermic Grossarenic PlinthicPaleudults)nearWaynesboro,GAfrom1999to2003.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 21 while other cover crops averaged ,40 kg N ha 21 . Cotton yields following black oat and rye had returns above variable costs ha 21 $461 and $406, respectively. Strip-tillage increased yields by 192 kg ha 21 and annual returns by $112 ha 21 over 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 21 compared to systems using rye on the 1.45 million ha of cotton where conservation systems have been adopted.

Reduced tillage and residue management can have significant impacts on soil and water quality, primarily through the accumulation of soil organic C. Yet, methods of tillage and residue cover assessment are time and resource intensive, and often do not yield spatially representative results. A major goal of this study was to compare new remote sensing (RS) indices with the current line-transect approach for differentiating between conventional (CT) and conservation tillage systems. Experimental plots were located in two physiographic regions in Georgia: the Southern Piedmont and Southern Coastal Plain. Treatments consisted of no tillage (NT) or CT at the Piedmont site, and strip-tillage (ST) or CT at the Coastal Plain site. Remotely sensed data were acquired three times prior to canopy closure, using a handheld multispectral radiometer (485-1650 nm) and thermal imager (7000-14 000 nm). Soil texture and soil water content were measured to assess the impact of changes in soil background reflectance on crop residue assessments. Results showed that differences in spectral response between CT and conservation tillage systems were best observed using a normalized difference ratio of near infrared (NIR) (1650 ± 100 nm) and blue (485 ± 45 nm) spectra under dry conditions and low canopy cover (

The application of poultry litter to agricultural fields can provide plant nutrients for crops and forage production, but fecal bacteria and the sex hormones estradiol and testosterone are components of litter that can be detrimental to the environment. Our objective was to determine if applications of poultry litter to small watersheds would contribute to the load of fecal bacteria and sex hormones to soil and runoff. We, therefore, investigated the fate and transport of fecal bacteria, estradiol and testosterone from surface applied poultry litter to four small watersheds. Poultry litter was applied to meet the nitrogen requirements of pearl millet (Pennisetum glaucum L.) in 2000 and grain sorghum [Sorgham bicolor (L.) Moench] in 2001. Neither Salmonella nor Campylobacter were detected in the litter but the fecal indicator bacteria were. The average load of total coliforms,Escherichia coli, and fecal enterococci applied with the litter was 12.2, 11.9, and 12.7 log10 cells ha(−1), respectively. The average load of estradiol and testosterone was 3.1 and 0.09 mg ha(-1), respectively.Runoff events first occurred seven months after the first litter application in 2000, and three weeks after the second application in 2001.Only for the 25 July 2001 runoff event three weeks after the second litter application, were the concentrations of total coliforms, E. coli,and fecal enterococci in runoff greater than background concentrations which were on average 5.2, 1.1, and 2.9 log10 MPN 100 ml(−1),respectively [corrected]. Average background levels of total coliforms, fecal enterococci,and E. coli in surface soil were 8.2, 7.9, and 3.5 log (10) cells kg(−1) soil. At the rate of litter application the concentrations of estradiol and testosterone in the litter did not appear to impact the background levels in the soil and runoff. Because concentrations of sex hormones in litter from other broiler operations are known to be greater than in the litter we applied, further study on the connection between concentrations of sex hormones in poultry litter and operational practices is recommended.

Calibration procedures and data used to parameterize a model, including model components that may or may not have been addressed, are generally not well documented in modeling studies. A comprehensive description of the process and parameters used for calibrating the Root Zone Water Quality Model, v. 1.3.2004.213, is presented in this article. The model was calibrated to simulate tile drainage and leached nitrate under conventional tillage management practices for maize (Zea mays L.) production followed by a rye (Secale cereale L.) cover crop in Cecil soils (kaolinitic, thermic, Typic Kanhapludults), and for cotton (Gossypium hirsutum L.) development in the Georgia Piedmont. Tile drainage and nitrate leaching were simulated within 15% of the observed values in the calibrated maize scenarios with and without the soil macroporosity option. Simulated and observed tile drainage and leached nitrate were not significantly different, and the simulated values were not significantly different with and without the macroporosity option. Simulated cotton biomass and leaf area index were well correlated with observed biomass and leaf area index until the last 21 d of the reproductive stage. Simulated and observed cotton water use were different by

Winter cover crops are essential in conservation tillage systems to protect soils from erosion and for improv- ing soil productivity. Black oat (Avena strigosa Schreb) and oilseed radish (Raphanus sativus L.) could be useful cover crops in the southeastern USA, but successful adop- tion requires understanding their influence on N availabil- ity in conservation tillage systems. Black oat and oilseed radish were compared to crimson clover (Trifolium incar- natum L.) and rye (Secale cereale L.) for biomass pro- duction and effects on N mineralization during the summer crop growing season from fall 1998 through summer 2002 near Watkinsville, GA. Rye produced 40 to 60% more biomass, although N contents were less than the other cover crops. Oilseed radish and black oat N contents were similar to crimson clover. Black oat, oilseed radish, and crimson clover C/N ratios were less than 30, whereas rye averaged 39. Amount of N mineralized in 90 days (Nmin90) measured with in situ soil cores was 1.3 to 2.2 times greater following black oat, crimson clover, and oilseed radish than following rye. No differences in Nmin90 were found between black oats, crimson clover, and oilseed radish in 1999 and 2000. The amount of potentially mineralizable N( N0) was not different due to cover crop, but was 1.5 times greater in 2000 and 2002 than in 1999. The rate of N mineralization (k) was 20 to 50% slower following rye than the other three cover crops. Black oat and oilseed radish biomass production and soil N mineralization dy- namics were more similar to crimson clover than to rye, which indicates that they could be used as cover crops in the southeast without significant changes in N recom- mendations for most crops.

Tillage to disrupt root-restricting, consolidated soil zones can improve rooting capacity and crop production, but costs increase with the need for more powerful tractors. Between 1992 and 1996, agronomic and economic consequences of annual or less frequent soil disruption treatments were evaluated for cotton (Gossypium hirsutum L.) on a Typic Kanhapludult. Two soil-disruptive treatments, fall paratillage (PT) and in-row chisel (IC) at planting (spring), were compared with two shallow-tillage treatments, coulter planting plus weed control with sweeps (ST) and conventional disk tillage (DT). The IC, PT, and ST treatments were applied annually or in Years 3, 4, and 5. Lint yield with annual IC was 15 to 20% greater than with DT each year. In 1994, yields ranged from 0.53 to 0.84 Mg ha -1 with annual IC and were better than with annual ST or PT. In 1995, yields ranged from 0.92 to 1.29 Mg ha -1 , with the top yield associated with current-year IC application. In 1996, no differences in yield were observed among tillages; however, yields of two IC treatments were among the top five. For Years 3, 4, and 5, cotton yields were numerically greater with annual IC than with annual PT and ST. Yields with PT, ST, and DT were not different. Average annual net returns from annual IC were $450, $403, and $287 ha -1 greater than those with annual DT, PT, and ST, respectively. In-row chisel appears to be a more economically viable production practice for heavy Piedmont soils compared with PT, ST, and DT.

Cotton has become a dominant crop in the southeastern USA, but only about 12% of the 620,000 ha of cotton ( Gossipium hirsutum L.) in Georgia, for example, is under conservation tillage. Georgia and bordering states produce about 42% of the poultry in the United States and in Georgia alone, this results in over 1.6 million Mg of poultry litter (PL) annually. The fertilizer value of PL is well-recognized but much of it is applied to pastures and only a small percentage is applied to crop land. Limited information is available on the response of cotton to PL as fertilizer in conservation tillage systems in the Southeast. The performance of cotton under two tillage and two fertilizer treatments was evaluated from 1996 to 1999 to highlight management options for increased adoption of conservation tillage and PL use. Cotton, followed by a rye ( Secale cereale L.) cover crop, was grown under a factorial arrangement of tillage (no-till (NT) vs conventional tillage (CT)) and fertilizer (ammonium nitrate, as conventional fertilizer (CF) vs PL) on a Cecil sandy loam (clayey, kaolinitic thermic Typic Kanhapludult; Chromi-Alumic Acrisol) near Watkinsville, Georgia. Average lint yield from 1996 to 1999 was in the sequence no - till poultry litter ( NTPL )> no - till conventional fertilizer ( NTCF )> conventional tillage poultry litter ( CTPL )> conventional tillage and fertilizer ( CTCF ) . Differences were significant at P ≤0.05 for NTPL vs CTPL, NTPL vs CTCF, and NTCF vs CTCF. Average yield differences were also significant between NT and CT but not PL and CF. PL yielded more than CF only in 1997. NT generally had a more favorable soil water regime than CT. Yield differences among treatments occurred during the first 3 years only. Drought in the fourth year reduced yield across all treatments and negated treatment effects. Lint yield would increase in the southeastern USA and an additional outlet for the PL would be created by adopting NT and fertilizing with PL in cotton production.

Knowing the amount of N available from crop residues and soil is important for determining the amount of fertilizer N needed by a crop. Nitrogen availability in conservation tillage systems is often difficult to assess because of uncertain interactions of surface residues with N mineralization processes. Estimates of residual N availability in cotton systems are more critical because both over- and underfertilization can reduce lint yields. The CERES plant growth models use a moderately complex N submodel to simulate many interacting factors influencing net N mineralization and could be useful as a tool to estimate N needs. Simulations of in situ net N mineralization under two cotton (Gossypium hirsutum L.) cover crop systems were conducted with the original N submodel (CERES-N) and a version modified to allow user input of soluble carbohydrate, cellulose, and lignin pool sizes (CERES-NP) and were then compared to field data. Both model versions indicated greater in situ net N mineralization following crimson clover (Trifolium incarnatum L.) than following rye (Secale cereale L.) cover crops. This agreed with results measured in a field study during 1997 and 1998. Simulations of in situ N mineralization were better with CERES-NP than for CERES-N and were improved for both versions when using decomposition parameters determined from data of a previous field study. Simulations of residue biomass and N loss from bagged residues in 1998 indicate that the original model tends to overpredict in situ net N mineralization which is most likely related to the overestimation of soil organic matter N mineralization. Results with CERES-NP indicate that it can be a better tool for estimating N needs for cotton in conservation tillage cover crop systems than the original CERES-N.

Maintaining residue cover provides diverse conservation benefits. Exponential relationships have been developed to estimate cover from biomass of randomly distributed, flat residues, but a large portion of crop biomass remains standing after harvest. Our objective was to determine how relationships between biomass and soil cover change in no-tillage small grain fields as residues decompose and shift from standing to flat. Winter and spring wheat (Triticum aestivum L.), winter barley (Hordeum vulgare L.), and spring oat (Avena sativa L.) were grown at Bushland, TX, on Pullman clay loam (fine, mixed thermic Torrertic Paleustoll) in 12 field plots in three randomized complete blocks. For each crop, differential seeding rate, fertilization, and irrigation produced a range of biomass. During decomposition, differential irrigation increased environmental variability (13, 5, and 0 applications to sub-sub-plots). Ash-free residue biomass was measured seven times in 14 mo, after taking photographs to determine soil cover of 1-m 2 sites. For crop-date combinations, coefficients were determined from total (k t , m 2 g -1 ) or flat (k f , m 2 g -1 ) biomass. Regression indicated k t increased with time (P < 0.0001 for all crops, except spring wheat with P < 0.0(141). Across crops, the relationship k t = 0.0037 + 0.000047.DAH (r 2 = 0.54, P < 0.0001) indicated that decomposition affects cover provided by total biomass. Across crops, the weak relationship k f = 0.0136 + 0.000023 DAH (r 2 = 0.17, P < 0.016) indicated that cover could be estimated from flat biomass with k f 0.0175 for extended periods. These findings can improve estimation of residue cover for no-tillage fields and indicate that residue orientation should be considered in biomass-to-cover relationships.

Animals influence nutrient cycling within grazed systems, and the effect may be greater with tall fescue (Festuca arundinacea Schreb.) because of endophyte-produced alkaloids that cause fescue toxicosis and alter animal behavior. Twelve grazed tall fescue pastures, established in a Cecil sandy loam (fine, kaolinitic, thermic Typic Kanhapludult) soil near Watkinsville, GA were used to measure fertility (134-15-56 and 336-37-139 kg N-P-K ha -1 yr -1 ) and endophyte (low, 0 to 29% and high, 65 to 94%) effects on P and K distribution. Soil samples were collected in winter 1997 at distances of 1, 10, 30, 50, and 80 m from permanently located shade and water sources at eight depth increments down to 1.5 m. Nutrient accumulation was greatest 1 m from shade and water sources where P, K, and Mg concentrations were 1.7 to 8, 2.5 to 15, and 1.1 to L5 times greater than average concentrations at the remaining distances, depending on depth and fertility level. Accumulation of P, K, and Mg in the area 10 to 80 m from shade and water was limited. When summed for the 0- to 300-mm depth and estimated on a per hectare basis, extractable P was 64% greater in high than in low endophyte-infected tall fescue pastures at 1 m from shade and water sources (703 vs. 428 kg ha -1 , LSD = 93) and averaged 252 kg ha -1 for remaining distances. Endophyte levels did not affect K distribution and only affected Mg distribution under the low-fertility treatment. Endophyte effects accrued over a long time period, which would indicate that altering grazing and pasture management (movement of animals, fertilizer and lime applications, and location of shade and water sources) to reduce these effects would be needed only occasionally to reduce potential environmental risks.

Soil organic matter pools under contrasting long-term management systems provide insight into potentials for sequestering soil C, sustaining soil fertility and functioning of the soil‐atmospheric interface. We compared soil C and N pools (total, particulate and microbial) under pastures (1) varying due to harvest technique (grazing or haying), species composition (cool- or warm-season), stand age and previous land use and (2) in comparison with other land uses. Grazed tall fescue-common bermudagrass pasture (20 yr old) had greater soil organic C (31%), total N (34%), particulate organic C (66%), particulate organic N (2.4 fold) and soil microbial biomass C (28%) at a depth of 0‐200 mm than adjacent land in conservation-tillage cropland (24 yr old). Soil organic C and total N at a depth of 0‐200 mm averaged 3800 and 294 g m ˇ2 , respectively, under grazed bermudagrass and 3112 and 219 g m ˇ2 , respectively, under hayed bermudagrass. A chronosequence of grazed tall fescue suggested soil organic N sequestration rates of 7.3, 4.4 and 0.6 g m ˇ2 yr ˇ1 to a depth of 200 mm during 0‐10, 10‐30 and 30‐50 yr, respectively. Soil C storage under long-term grazed tall fescue was 85 to 88% of that under forest, whereas soil N storage was 77 to 90% greater under grazed tall fescue than under forest. Properly grazed pastures in the Southern Piedmont USA have great potential to restore natural soil fertility, sequester soil organic C and N and increase soil biological activity. Published by Elsevier Science Ltd.

Cattle (Bos taurus) behavior may be an important variable controlling the spatial distribution of soil C and N pools in long-term, grazed pastures. Shade and water sources are more frequented areas of a pasture that can also serve as camping areas where excreta are deposited. We sampled a Cecil sandy loam (fine, kaolinitic, thermie Typic Kanhapludult) under tall fescue (Festuca arundinacea Schreb.) at distances of 1, 10, 30, 50, and 80 m from permanent shade or water sources at the end of 8 and 15 yr of grazing. To a depth of 75 mm. soil bulk density was 1.15 Mg m -3 at 1 m and averaged 1.00 Mg m -3 at other distances from shade or water. To a depth of 300 mm, soil organic C was 4.6 kg m -2 at 1 m, 4.3 kg m -2 at 10 m, and = 4.0 kg m 2 at distances of 30, 50, and 80 m from shade or water. Particulate organic C averaged 1.53 kg m 2 at distances of I, 10, and 30 m and 1.30 kg m -2 at distances of 50 and 80 m from shade or water. Soil microbial biomass C, basal soil respiration, and net potential N mineralization were also greater nearer shade or water than farther away. Although lateral distribution effects were most dramatic at a depth of 0 to 25 mm, similar effects were observed even at a depth of 150 to 300 mm. Long-term cattle grazing in relatively small paddocks (0.7-0.8 ha) with permanent shade and water sources resulted in significant lateral and vertical changes in soil organic C and N pools.

Tall fescue (Festuca arundinacea Schreb.) is an important cool-season perennial forage for cattle production in the humid regions of the USA and throughout the world. While endophyte (Neotyphodium coenophialum Glenn, Bacon, & Hanlin) infection of tall fescue has many benefits, it also results in accumulation of toxic alkaloids in leaf tissue known to cause animal health disorders when ingested. We hypothesized that pastures containing these alkaloids may alter soil organic matter dynamics. A set of three grazed field experiments representing low (0-29%) and high (65-94%) endophyte infection of tall fescue was evaluated at the end of either 8 or 15 yr. Soil samples from 12 paddocks (0.7-0.8 ha) were collected at depths of 0 to 25, 25 to 75, 75 to 150, and 150 to 300 mm. Soil under tall fescue with high endophyte infection had 13 ± 8% greater concentrations of soil organic C and N and particulate organic N to a depth of 150 mm than with low endophyte infection. However, with high endophyte infection, microbial biomass and basal soil respiration per unit of soil organic C or particulate organic C were 86 ± 5% of those with low endophyte infection. Only small differences in soil microbial community structure, estimated via fatty acid methyl ester profiles, were observed between soils under fescue with 0 and 100% endophyte infection. Endophyte infection of tall fescue may perform an important ecological function, allowing more soil organic C and N to accumulate, perhaps because of reduced soil microbial activity on plant residues containing endophyte byproducts.

Conservation practices retain crop residues on the soil surface that affect nutrient distribution in time and space. We hypothesized that nutrient mineralization from surface residues may not be correlated to mass loss but may depend on crop type and water availability. Frequent, moderate, and no irrigation were used to evaluate water effects on N, P, K, and mass dynamics of alfalfa (Medicago sativa L.), corn (Zea mays L.), grain sorghum [Sorghum bicolor (L.) Moench], spring and winter wheat (Triticum aestivum L.). Residues (20 g) in 10 by 10 cm, 1-mm mesh bags were placed on a Pullman clay loam (fine, mixed, thermic Torrertic Paleustolls) at Bushland, TX, in August 1991 and collected monthly until August 1992. Water regime did not influence mass, N, or P dynamics but did affect K. Mass declined exponentially with decomposition coefficients (-r) of 4.4, 1.5, 2.0, 1.7, and 1.1 g kg -1 d -1 for the five crop residues listed above, respectively. Potassium loss was first order with -r ranging from 29.3 to 4.4 g kg -1 initial K d -1 , depending on crop and water. Averaged across water regimes, -r equaled 25, 9, 8, 12, and 7 g kg ' initial K d -1 for the respective crops. The water effect indicated 150-mm water removed 500 g kg -1 initial K from residues. Residue N declined from 38.7 to 16.0, 10.9 to 5.1, 12.2 to 6.4, 9.5 to 4.5, and from 7.6 to 3.4 g kg during the first 34 d for the respective crop residues, after which nonlegume residues accumulated N (0.21 to 0.96 g kg ' initial N d '), while alfalfa lost N (-0.37 g kg ' initial N d 1 ). Corn and winter wheat residue P increased from 0.7 to 1.2 and 0.5 to 1.0 g P kg ', respectively, during the first 34 d, after which all residues lost P(-1.4, -2.1, -1.3, -2.0, and -2.8 g kg -1 initial P d -1 , respectively). Nutrient dynamics were not directly related to mass loss. Water regime effects were small, so nutrient availability from residues should be similar in irrigated and dryland systems in the southern High Plains.

Little information exists on the biogeochemical effects of combining no-tillage planting with paraplowing (to improve deep water penetration) or with secondary tillage (to control weeds). We determined surface residue and soil C and N pools (total, particulate, microbial biomass, and mineralizable) and water-stable aggregation at depths of 0 to 25, 25 to 75, and 75 to 150 mm from a Cecil sandy loam (fine, kaolinitic, thermic Typic Kanhapludults) in Georgia, Soil tillage treatments were a factorial arrangement of tillage type [(i) minimal disturbance with in-row chisel at planting, (ii) no-tillage planting with autumn paraplow, and (iii) no-tillage planting with secondary tillage during the summer] and tillage frequency [(i) every year, (ii) every second year, and (iii) every fourth year I. No-tillage planting without further disturbance occurred in remaining years. At a depth of 0 to 25 mm, basal soil respiration averaged 9 mg kg -1 d -1 with conventional tillage, 27 mg kg -1 d -1 with no-tillage planting and soil disturbance every year, and 36 mg kg -1 d -1 with no-tillage planting and soil disturbance every fourth year. At a depth of 0 to 150 mm, mean-weight diameter averaged 1.03 mm with conventional tillage, 1.12 mm with paraplow, 1.17 mm with secondary tillage, and 1.23 mm with in-row chisel. No-tillage planting with alternative tillage types and frequencies not only improved surface soil properties compared with conventional tillage, but also improved seed cotton yield an average of 19%, Biophysical improvement of surface soil structure would presumably lead to greater water infiltration and improved water use efficiency in the long term.

Crop residues protect soil from water and wind erosion. How long the residues remain effective depends on their decomposition rate. The crop residue decomposition submodels developed for the Revised Wind Erosion Equation (RWEQ) and Revised Universal Soil Loss Equation (RUSLE), which are used to determine the effectiveness of conservation practices, use different approaches to account for water and temperature effects on decomposition. Because of these differences, residue losses may not agree between the two models for a given location. We compared the climatic indices used in RWEQ and RUSLE to determine the similarity of results for simulated climatic scenarios, as well as for field data. Simulated climatic regimes were used to evaluate the relative responsiveness of the temperature and water functions. The two models estimated different numbers of decomposition days (DD) when water and temperature were not limiting. RUSLE usually predicted more DDs than RWEQ. Underwaterlimiting conditions, the estimation of DD was similar for the two models. In comparisons with field decomposition data, mass loss predictions by RWEQ were as good as or better than those by RUSLE for locations in Texas, Oregon, and Georgia. RUSLE overpredicted decomposition by 20 to 50% when residues were irrigated. RWEQ underpredicted decomposition by 20 to 50% in the Pacific Northwest. Interactions between the climatic indices (CF) and decomposition coefficients influenced the differences between measured and predicted values. Differences in the CF were related to the method of calculating the water coefficient (WC) and interpretation of the interaction between the temperature coefficient and WC. The models could be improved by developing water and temperature functions that give results closer to those produced with daily time-step functions.

As sustainable crop management systems are developed, an assessement of the effects of these practices on the soil microflora is essential to ensure maximum productivity. A 3-year field study was established to determine the effects of crop residue burning, no-till management and four preemergence herbicides on soil microorganisms. Numbers of actinomycetes, algae, bacteria, fungi and nitrifiers were evaluated during the soybean [ Glycine max (L.) Merrill] growing season in a wheat ( Triticum aestivum L.)-soybean double-cropping system. Residue burning and tillage had no effect on numbers of bacteria and nitrifiers. Non-disturbed (non-burned or no-till) plots had greater numbers of actinomycetes, algae and fungi 7 days after herbicide application each year, but the increases generally did not persist through the season. Herbicide application had no effect on microbial numbers. This is particularly important with recent increased emphasis on protection of soil and water resources from pesticide contamination. As new management systems are developed, their effects on biological properties must be carefully assessed, since the soil microflora play such a vital role.

Interest in the use of biochar from pyrolysis of biomass to sequester C and improve soil productivity has increased; however, variability in physical and chemical characteristics raises concerns about effects on soil processes. Of particular concern is the effect of biochar on soil N dynamics. The effect of biochar on N dynamics was evaluated in a Norfolk loamy sand with and without NHNO. High-temperature (HT) (≥500°C) and low-temperature (LT) (≤400°C) biochars from peanut hull ( L.), pecan shell ( Wangenh. K. Koch), poultry litter (), and switchgrass ( L.) and a fast pyrolysis hardwood biochar (450-600°C) were evaluated. Changes in inorganic, mineralizable, resistant, and recalcitrant N fractions were determined after a 127-d incubation that included four leaching events. After 127 d, little evidence of increased inorganic N retention was found for any biochar treatments. The mineralizable N fraction did not increase, indicating that biochar addition did not stimulate microbial biomass. Decreases in the resistant N fraction were associated with the high pH and high ash biochars. Unidentified losses of N were observed with HT pecan shell, HT peanut hull, and HT and LT poultry litter biochars that had high pH and ash contents. Volatilization of N as NH in the presence of these biochars was confirmed in a separate short-term laboratory experiment. The observed responses to different biochars illustrate the need to characterize biochar quality and match it to soil type and land use.

Understanding environmental and residue influences on decomposition and nutrient dynamics under diverse conditions is critical for efficient resource management. Our objective was to evaluate the influence of water on decomposition and N dynamics for surface and buried residues. Decomposition of alfalfa (Medicago sativa L.), grain sorghum (Sorghum bicolor [L.] Moench), and winter wheat (Triticum aestivum L. emend. Thell.) residues in fiberglass bags on the surface or buried at 120 mm in Pullman soil (fine, mixed, thermic Torrertic Paleustoll) at Bushland, TX, was measured from May 1990 to May 1991. A line-source sprinkler provided five water regimes (336, 287, 166, 60, and 5 mm) while precipitation provided 305 mm water. Decomposition coefficients (k) were greater for alfalfa than for wheat or grain sorghum and were greater for buried than for surface residues. Rate coefficients increased linearly with water applied. The increase was greater for alfalfa than for sorghum and wheat. Net N mineralization occurred from alfalfa residues throughout the study. Net N immobilization was longer than 1 yr for surface wheat and sorghum and about 0.33 yr for buried residues. Both Nₘₐₓ (grams N immobilized per kilogram of original biomass) and Nₑqᵥ (grams N immobilized per kilogram of biomass loss) were influenced by crop and placement but not water regime. The Nₘₐₓ value was similar for surface wheat and sorghum residues but was 50% lower for buried wheat than for sorghum. The Nₑqᵥ indicated the N requirement of microorganisms was less for buried than for surface residues. Water and residue quality interactions affecting decomposition and N dynamics should be considered in residue management strategies for soil protection and nutrient cycling.

Approximately 11% of the Southern Piedmont (1.8 million ha) is used for pasture and hay production, mostly under low-input management. Few studies have investigated in the region long-term nitrogen and carbon losses in surface runoff, which can be significant. We present 1999 to 2009 hydrologic and water quality data from a rotationally grazed, 7.8-ha, zero-order pasture (W1) near Watkinsville in the Georgia Piedmont. Annual rainfall was 176 to 463 mm below the long-term average (1240 mm) in 7 of the 11 yr. There were 20 runoff events during 86 mo of below-average rainfall (deficit period), compared with 54 events during 46 mo of nondeficit period. Mean event flow-weighted concentration (in mg L) was 0.96 for nitrate-nitrogen (NO-N), 0.97 for ammonium-nitrogen (NH-N), 3.70 for total nitrogen (TN), and 9.12 for total organic carbon (TOC) ( = 43-47; limited due to instrument problem). Nutrient loads (in kg ha per event) averaged 0.04 for NO-N, 0.03 for NH-N, 0.19 for TN, and 0.54 for TOC. Total loads for N and TOC were 6 to 11 times greater from nondeficit than from deficit periods. The observed N concentrations, while well below maximum drinking water standard limits, could pose risk for eutrophication, which can be stimulated at lower concentrations. However, the ability of headwater streams, such as the one downstream of W1, to reduce nutrient concentrations might partially alleviate this concern. The results of this study point to the need to use a long-term dataset that includes measurements made in drought and wet years when evaluating the efficacy of water quality standards.

Nitrogen availability is important for rapid establishment of small seeded legumes and is influenced by soil N status and rapid development of N 2 fixation activity. Seedlings of arrowleaf clover (Trifolium vesiculosum L. Savi) are exposed to soil temperatures (10-35°C) during the fall which can reduce seedling vigor by influencing N nutrition. Root temperature (18, 25, or 32°C) effects on N nutrition of arrowleaf clover receiving starter N was evaluated in two controlled experiments. Temperature influenced the N status of inoculated plants through an effect on N 2 fixation but not on starter N uptake []

(...) Three experiments were conducted using a growth chamber and a glasshouse to determine the influence of starter mineral N and strains of Rhizobium leguminosarum biovar trifolii on dry matter production and N 2 fixation on arrowleaf clover. In one experiment, seeds were planted in a N-deficient medium, inoculated with two strains of rhizobia and provided with five levels of mineral N. The lowest level of mineral N doubled seedling dry weights and the amount of biologically fixed N in 40-d-old seedlings. Rhizobial strain interacted with mineral N in influencing dry matter production and N 2 fixation (...)

Land application of poultry litter can provide essential plant nutrients for crop production, but ammonia (NH(3)) volatilization from the litter can be detrimental to the environment. A multiseason study was conducted to quantify NH(3) volatilization rates from surface-applied poultry litter under no-till and paraplowed conservation tillage managements. Litter was applied to supply 90 to 140 kg N ha(-1). Evaluation of NH(3) volatilization was determined using gas concentrations and the flux-gradient gas transport technique using the momentum balance transport coefficient. Ammonia fluxes ranged from 3.3 to 24% of the total N applied during the winter and summer, respectively. Ammonia volatilization was rapid immediately after litter application and stopped within 7 to 8 d. Precipitation of 17 mm essentially halted volatilization, probably by transporting litter N into the soil matrix. Application of poultry to conservation-tilled cropland immediately before rainfall events would reduce N losses to the atmosphere but could also increase NO(3) leaching and runoff to streams and rivers.

Understanding cover crop influences on N availability is important for developing N management strategies in conservation tillage systems. Two cover crops, cereal rye (Secale cereale L.) and crimson clover (Trifolium incarnatum L.), were evaluated for effects on N availability to cotton (Gossypium hirsutum L.) in a Typic Kanhapludult soil at Watkinsville, Ga. Seed cotton yields following clover and rye were 882 kg ha−1 and 1,205 kg ha−1, respectively, in 1997 and were 1,561 kg ha−1 and 2,352 kg ha−1, respectively, in 1998. In 1997, cotton biomass, leaf area index, and N were greater on some dates following crimson clover than following rye but not in 1998. During 1997, net soil N mineralized increased with time in both systems, but a similar response was not observed in 1998. Net soil N mineralization rates following crimson clover and rye averaged, respectively, 0.58 kg and 0.34 kg N ha−1 day−1 in 1997 and 0.58 kg and 0.23 kg N ha−1 day−1 in 1998. Total soil N mineralized during the cotton growing season ranged from 60 kg ha−1 to 80 kg ha−1 following crimson clover and from 30 kg ha−1 to 50 kg ha−1 following rye. Soil N mineralization correlated positively with heat units and cumulative heat units. Net soil N mineralization rates were 0.023 kg ha−1 heat unit−1 once net mineralization began. Soil heat units appeared to be a useful tool for evaluating N mineralization potential. Nearly 40% of the rye and 60% of the clover biomass decomposed during the 6 weeks prior to cotton planting, with nearly 35 kg N ha−1 mineralized from clover.

The authors regret that in the Abstract the order of background concentrations of total coliforms, E. coli, and fecal enterococci in runoff is incorrect. The corrected Abstract is presented below. The application of poultry litter to agricultural fields can provide plant nutrients for crops and forage production, but fecal bacteria and the sex hormones estradiol and testosterone are components of litter that can be detrimental to the environment. Our objective was to determine if applications of poultry litter to small watersheds would contribute to the load of fecal bacteria and sex hormones to soil and runoff. We, therefore, investigated the fate and transport of fecal bacteria, estradiol and testosterone from surface applied poultry litter to four small watersheds. Poultry litter was applied to meet the nitrogen requirements of pearl millet (Pennisetum glaucum L.) in 2000 and grain sorghum [Sorgham bicolor (L.) Moench] in 2001. Neither Salmonella nor Campylobacter were detected in the litter but the fecal indicator bacteria were. The average load of total coliforms, Escherichia coli, and fecal enterococci applied with the litter was