Recent research indicates that siderophores, a class of biogenic ligands with known exceptional affinity for Fe(III), can also strongly complex Co(III), an element essential to normal metabolic function of microbes and animals. This study was conducted to examine the siderophore-promoted dissolution rates and mechanisms of Co from model synthetic Co-bearing minerals to elucidate the role of siderophores in biogeochemical processes of Co. Dissolution of heterogenite (CoOOH) and four Co-goethites (Co-FeOOH) with different levels of Co substitution were investigated in the presence of a trihydroxamate siderophore, desferrioxamine B (DFOB), using batch and flow-through experiments, respectively. By measuring the complex and total metal concentrations in dissolution products, dissolution rates via multiple pathways were measured as a function of pH. Results showed that DFOB promoted dissolution of Co from Co-bearing minerals via pH-dependent mechanisms. For heterogenite, ligand-promoted dissolution was the dominant pathway at neutral to alkaline pH, while reductive dissolution became dominant for pH < 6. Cobalt substitution in Co-goethite resulted in increased total dissolution rates of both Co and Fe, but ligand-promoted and reductive Co dissolution pathways were difficult to examine due to the slow dissolution rates. The fast dissolution rate of heterogenite, coupled with the high affinity of Co(III) for DFOB, suggests that siderophore-promoted dissolution of Co(III) oxides is a biogeochemically favorable process. Although the association of Co with Fe oxide mineral may limit the Co dissolution rate, siderophore-promoted Co dissolution may still be an effective enough way to increase Co bioavailability. The results also suggest the possibility of radionuclide 60Co by siderophores from recalcitrant Fe oxide phases, which may be important to the fate and transport of 60Co in contaminated environments.

Application of anaerobic swine (Sus scrofa domesticus) lagoon liquid onto cropland by irrigation is a common method of waste disposal and treatment. Currently, the application rate of swine lagoon liquid is based on the N concentration of the lagoon liqu id and the N required by the receiver crop to obtain a realistic yield. In North Carolina, only 50% of the total N in the swine lagoon liquid applied by irrigation is considered available for plant use during the first year after application. Uncertaint y exists as to whether this coefficient accurately predicts the amount of plant-available N. Therefore, research was conducted in the Coastal Plain of North Carolina to determine the efficiency of N uptake by corn (Zea mays L.) and soybean (Glycine max M errill) receiving swine lagoon liquid through irrigation. The line-source sprinkler irrigation method was used to provide a continuous variable N rate, ranging from 0 to 290 kg N/ha, across the field during 1999 and 2000. Ammonia volatilization losses r anged from 6 to 22% during irrigation. Crop yield and grain N recovered were affected more by the amount of liquid than N applied in 1999. Nitrogen recovered in grain in 1999 was <15% for both corn and soybean at 168 kg N/ha of either swine lagoon liqui d or ammonium nitrate. In 2000 at the 168 kg N/ha rate, grain N removal by corn, nonnodulating soybean, and nodulating soybean was 28, 25, and 39% from swine lagoon liquid and 45, 31, and 56% from ammonium nitrate. Based on yields and grain N removed by corn and nonnodulating soybean in 2000, N from applied swine lagoon liquid, accounting for N losses during irrigation, was about 70% as effective as ammonium nitrate. Symbiotic N2 fixation by the soybean was reduced by 60% when applied N reached 175 kg N/ha for both ammonium nitrate and swine lagoon liquid. While nodulating soybean removed more grain N than did either corn or nonnodulating soybean in 2000, soil inorganic N concentrations at the end of the growing season were higher for the nodulating s oybean. Therefore, it is not conclusive if soybean would be a better receiver crop than corn for swine lagoon liquid. Based on the results of this study, using the 50% available N coefficient of the lagoon liquid comes close to predicting plant-availabl e N when N losses during irrigation are around 25%. Nitrogen losses during irrigation can significantly affect plant-available N when applied N is based on the N concentrations of the lagoon liquid.

Antibiotics are used in livestock production for the treatment of diseases and for improvement of feed efficiency and growth. However, agricultural use of antibiotics may be partly responsible for the emergence of antibiotic-resistant organisms. Large amounts of managed manure are land applied, which opens the door for the spread of antibiotic resistance in the environment. Thus, the goal of this project was to evaluate the effects of lagoon treatment on the persistence of antibiotic resistant enteric bacteria isolated from swine feces. Both cool season and warm season samples were collected from a swine farm located in Sampson County, NC. Each season samples included three nursery swine fecal samples, three nursery swine lagoon liquid samples, four finishing swine fecal samples, three finishing swine lagoon liquid samples, and four soil samples from both nursery and finishing swine spray field. A total of 4032 E. coli isolates and 4896 Enterococcus isolates were obtained from the samples. The antibiotic resistance profiles of the isolates were determined using a set of antibiotics at various concentrations. The antibiotic cephalothin, erythromycin, oxytetracycline, tetracycline, streptomycin, and neomycin were tested for both bacterial species, but different concentrations were applied. For E. coli, rifampicin was also tested; for Enterococcus, chlortetracycline, vancomycin, and amoxicillin were also tested. After antibiotic resistance analysis was achieved, 25 isolates were randomly selected from each sample for further evaluation by polymerase chain reaction test. Soil samples were collected; however, fecal indicator bacteria were not recovered. Additionally, E. coli was not recovered from warm season nursery lagoon samples. All isolates displayed multiple antibiotic resistance, and for the isolates from the same source, the resistance patterns were similar for the antibiotics within the same antibiotic family. Percentages of resistant isolates were greater in nursery fecal samples than in finishing fecal samples for majority of antibiotic tests. For nursery samples, percentages of antibiotic resistant isolates decreased after lagoon treatment for majority of antibiotic tests. For finishing samples, no such trend was obvious. The results indicated that antibiotic resistant isolates still persist in the lagoon liquid, which may cause potential risk to human and environmental health. And because antibiotic resistance may affect later therapeutic and subtherapeutic value of these antibiotics, management strategies of agricultural antibiotic use may be improved. The antibiotic resistance patterns and molecular banding patterns of the isolates were not unique to a specific source. The results suggest that there is considerable overlap among nursery feces, nursery lagoon, finishing feces and finishing lagoon samples. However, if combine of the feces and the lagoon isolates together and only classify isolates from nursery to finishing swine, the percentages of correctly classified isolates became larger. The results suggest that ARA and PCR would best be used for identifying fecal contamination from swine sources based on broad categories (nursery versus finishing) instead of relying on these procedures for specific identification of lagoon and feces separately.

The restoration of drained agricultural soils to wetlands may result in the dissolution of P from reduced soils, causing the eutrophication of nearby surface waters. Therefore, continued improvements in the ability to predict P dissolution are necessary to minimize its potential environmental hazard. The objectives of this project were to determine if P dissolution would occur when soil material from a drained Carolina bay wetland was reduced, and to hypothesize explanations of differences in P dissolution between soils based on aqueous solution chemistry. Suspensions (15 g kg-1) of < 53 μm separates from surface samples (0-10 cm) of six poorly drained soils were subjected to microbial reduction for 25 d in a continuously stirred reactor. In a separate experiment, saturated whole soil samples (2.5 g H2O g-1 solids) were incubated under O2-free conditions for 62 d. In addition to total P, Fe, Mn, and Al; dissolved reactive phosphate (DRP), Fe(II), and dissolved organic carbon (DOC) were measured in filtrate samples from both experiments. A net increase in P dissolution (two-fold increase, up to 1.2 mg L-1) was observed for only one of six suspensions (Ponzer 1) in the continuously stirred reactor experiment. In that suspension the molar P:Fe(II) suggested that reductive dissolution of Fe(III)-bound P could not fully account for the P that dissolved, and DOC was highly correlated with P dissolution. For reactor suspensions in which no net P dissolution occurred, oxalate-extractable Al was negatively correlated (p < 0.05) with final [DRP], and DOC concentrations were approximately 2-fold lower than in the Ponzer 1 suspension. In the static incubation experiment, P dissolution occurred in all four samples, and the highest concentration was seen in the Ponzer 1 sample (three-fold increase, up to 2.2 mg DRP L-1). Dissolved organic carbon concentrations were between 2 and 4 fold higher in the static incubation experiment than the highest concentration observed in the stirred reactor experiment, and offer a qualitative explanation for the additional P dissolution that occurred in static incubation experiment. The results of these experiments suggest that P concentrations in soils of the restored wetland will increase upon reduction to levels that are environmentally threatening, and that interaction of DOC with PO4 or minerals that bind PO4 plays an important role in the release of P.

Understanding how management affects long-term site productivity will help sustain forest productivity. In 1991, the USDA Forest Service installed the Long-Term Soil Productivity study in the Croatan National Forest in Craven County, NC. The study objectives were to compare indices of plant-available inorganic N from ion-exchange resin (IER) in bead and membrane form and aerobic incubations in a 8-week study, and to analyze the effects of harvest intensity and site preparation on N availability and tree growth ten years after planting. Site treatments included three levels of organic matter removal and two levels of compaction arranged in a strip-plot design replicated in three blocks. Block 1 consisted primarily of Goldsboro soil, while Blocks 2 and 3 consisted of Lynchburg. The two-month study showed no correlation of the N availability among the three techniques. The short duration of the study and the low soil fertility at the site may have contributed to the lack of correlation, indicating that the two forms of IER may not be equally effective at low nutrient concentrations. Through the 2001 growing season, IER membranes were used to measure soil NO3 and NH4 biweekly. Non-linear analysis indicate that total inorganic N recovered from the IER membranes was significantly influenced by interactions between block, organic matter removal treatment and compaction level (p=0.005). Total basal area of loblolly pines was significantly impacted by block (p=0.015) and organic matter removal treatment (p=0.032). At year ten, treatment effects can still be seen on both soil processes and tree productivity.

An accurate soil nitrogen (N) test is needed to improve corn production, profitability, and reduce environmental concerns of increasing nitrate (NO₃) levels in groundwater. The objectives of this study were to (i) compare soil N tests: amino sugar N (ASN), gas pressure (GP), pre-plant NO₃ (PPNT), and incubation and residual N (IRN) for precision and ability to predict corn response parameters e.g., economic optimum N rates (EONR); and (ii) examine the spatial relationships of ASN with soil and landscape properties to develop a more efficient sampling strategy. Small-plot N-response trials (NRT) were conducted in 2001 to 2004 at 31 sites. Field scale (FS) ASN variability was measured in 2003 and 2004 at four sites located in the North Carolina Piedmont and Coastal Plain. The ASN test had lower coefficients of variation than the GP, PPNT, and IRN tests (10 versus 15, 30, 52%, respectively). Each tests was correlated with economic optimum N rates from NRT sites, but coefficients of determination were low for the PPNT, IRN, and GP tests. The ASN test had the strongest correlation with EONR, but only when sites were classified as well (r² = 0.85) or poorly (r² = 0.78) drained. A comparison of ASN and EONR regression models across years and cost ratios (different corn price and fertilizer cost) were not statistically different. Amino sugar N was positively correlated with humic matter (HM; r² = 0.25 to 0.71) at each FS sites. Elevation was negatively correlated with ASN at the Lower and Middle Coastal Plain (r² = 0.44 and 0.11, respectively). In the Piedmont, ASN was negatively correlated with slope (r² = 0.10 and 0.04). Amino sugar N was positively correlated with soil texture (percent clay) for the Middle Coastal Plain (r² = 0.56) but negatively correlated for a site in the Piedmont (r² = 0.04). Amino sugar N is spatially sensitive to changes in soil and landscape properties, and soil sampling zones may be created using HM, soil texture, and soil type to reduce sampling costs and time. These results show that the ASN test was the best test for predicting economical optimum N rates and could be used to develop a site specific soil test based fertilizer recommendation.

Decades of agricultural research have failed to determine the precise mechanisms of infliction caused by the conditions of boron deficiency and chilling injury. Both conditions affect the quality and marketability of tobacco transplants grown in the float system. Interestingly, boron deficiency and chilling injury produce strikingly similar symptoms in young tobacco transplants; so similar, in fact, that they are often confused for one another. This has lead to severe boron toxicity when growers treated chilling injury as boron deficiency by applying boron to non-deficient float beds. The observation of nearly identical symptoms suggests that boron deficiency and chilling injury have interdependent effects on cell physiology and/or metabolism. Because little research has been conducted on tobacco transplants in the float system, two studies were conducted to determine general parameters for the boron deficiency threshold and effect of non-optimal temperatures and large day/night temperature differentials in this system. The boron deficiency study established that the deficiency threshold for transplants growing at 26/22º C is 10-20 µg B g-1 dry matter. These tissue levels occurred with solution concentrations of 0.19-1.9 µM B. The chilling injury study determined that root and shoot growth of flue-cured cultivars is near maximum at a constant 26/26º C temperature regime. Burley cultivars display a wider range of temperature tolerance, but in general constant day/night temperatures seem to provide the greatest shoot tissue accumulation. A reduction in night temperature resulted in decreased shoot growth in all cultivars. The chilling injury study also examined the effect of boron deficient conditions at each temperature treatment. In general, boron uptake declined at sub-optimal temperature regimes when supplied at concentrations sufficient for near-optimal temperatures. Shoot growth of flue-cured varieties at transplant stage was near maximal at a constant optimal day/night temperature regime (26/26º C) and adequate B concentrations. Sub-optimal temperatures may alter the boron deficiency threshold such that it decreases with decreasing temperatures or with stressful temperature differentials. This may be summarized in the following way: Temperature is the immediate limiting factor in tobacco transplant growth in the float system under conditions of sub-optimal temperatures and low B concentration, and B deficiency is an additional potential limiting factor.

Aluminum tolerance of soybean [Glycine max (L.) Merr.] by citrate secretion from roots, leading to external complexation of toxic Al species in solution, is enhanced by addition of &mu;M Mg²⁺ to hydroponic solutions. The objectives of this dissertation were to assess ameliorative effects of &mu;M Mg additions on soybean root growth in acidic subsoils and to relate the soil solution ionic compositions to soybean root growth. Roots of soybean cultivar Plant Introduction 416937 extending from a limed surface soil compartment grew for 28 days into a subsurface compartment containing acid subsoils [Cecil (oxidic and kaolinitic), Creedmoor (montmorillonitic) and Norfolk (kaolinitic)]. The three Mg treatments consisted of the native equilibrium soil solution concentrations in each soil (50 or 100 &mu;M) and MgCl₂ additions to achieve 150 and 300 &mu;M Mg (Mg150, Mg300, respectively) in the soil solutions. Root elongations into Mg-treated subsoils were compared with a CaCO₃ treatment limed to achieve a soil pH value of 5.5. Subsoil root length for the treatments without added Mg or lime decreased in the order of the Cecil followed by Norfolk and Creedmoor subsoils, and corresponded to the increasing order of percent Al saturation (27, 61 and 83%, respectively). Subsoil root growth and dry matter responses to the Mg treatments were less than the lime treatments, and there were no differences for the Mg150 and Mg300 treatments as compared to the treatments without added Mg or lime. Citrate adsorption experiments found that over 66% citrate added in the subsoils were adsorbed and biodegraded, suggesting that root secreted citrate in the soil might readily be unavailable to complex Al for ameliorating its rhizotoxicity. Root length relative to the limed treatments for all subsoils (RRL) was poorly related to the activity of soil solution Al species (Al³⁺ and Al-hydroxyl species) and Mg²⁺. However, the RRL values were more closely related to the parameters associated with soil solution Ca activity including Ca²⁺, Al³⁺/Ca²⁺, and Al³⁺/(Ca²⁺ + Mg²⁺), suggesting that Ca could be a primary factor ameliorating Al and H⁺ rhizotoxicity in these subsoils. Increased tolerance to Al rhizotoxicity of soybean by &mu;M Mg additions to hydroponic solutions, inducing citrate secretion from roots to externally complex toxic Al species, may be less important in the acid subsoil with a poor native Ca available to root growth.

Runoff from agricultural fields amended with animal manure or fertilizer is a source of phosphorus (P) pollution to surface waters, which can have harmful effects such as eutrophication. The objectives of this study were to evaluate the impact of soil P status and the P composition of manure sources on P in runoff, characterize the effects of manure sources on mass loss of dissolved reactive P (DRP), total dissolved P (TDP), algal available P (AAP) and total P (TP) in runoff, and enhance the PLAT database with respect to soluble P attenuating factor (SPAF) and non-soluble P attenuating factor (NSPAF) values. Soil boxes set at 5% slopes received 7.5 cm hr-1 of simulated rainfall. Study soils included a Kenansville loamy sand (loamy siliceous subactive thermic Arenic Hapludults, a Coastal Plain soil) and a Davidson silt loam (kaolinitic thermic Rhodic Kandiudults, a Piedmont soil). Soil test P concentrations ranged from 16 to 283 mg P kg-1. Sources of P included broiler litter (BRL), breeder manure (BRD), breeder manure treated with three rates of alum (Al2(SO4)3) BRD0-0 kg m-2, BRDL-3.9 kg m-2, and BRDH-7.8 kg m-2 and DAP along with an unamended control. All manure sources were applied at 66 kg P ha-1. Water extractable P (WEP) represented an average of 10 ?b 6% total P in manure. Runoff samples were taken over a 30-min period. Piedmont soil contained greater amounts of clay, Al and Fe concentrations, and higher P sorption capacities that produced significantly lower DRP, TDP, AAP, and TP losses than the Coastal Plain soil. Runoff P loss did not differ for low and high STP soils of same taxonomy with the exception of AAP mass losses for Coastal Plain soil samples. Water extractable P in manures accounted for all DRP lost in runoff with DRP correlating strongly with WEP concentration (0.9961). A weak relationship between DRP in runoff and WEP applied to soil boxes was observed (R2=0.6547) and increased when a possible outlying manure treatment, BRL, was omitted from regression data (0.9927). Overall, manures containing the highest WEP concentrations supplied the largest losses of DRP in runoff. Manure treated with 3.9 and 7.8 kg m-2 of Al2(SO4)3 (alum) decreased DRP in runoff by 29%. Values calculated for PLAT SPAF and NSPAF coefficients were higher for Coastal Plain soil than Piedmont soil and overall higher than default values in PLAT. Management based on these results should help minimize harmful effects of P in runoff.

Understanding the carbon cycle is one of the most difficult challenges facing scientists studying the global environment.A series of studies were undertaken to explore a number of current issues that contribute to our inability to model SOC on a regional or landscape scale. Investigation into the spatial distribution of SOC occurred on a 32,500 ha forest ecosystem located entirely within the bounds of Hofmann Forest. LiDAR evaluations indicated that data reduction was possible while still maintaining DEM quality. Spatial modeling efforts proved troublesome for flat landscapes.