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 μM Mg²⁺ to hydroponic solutions. The objectives of this dissertation were to assess ameliorative effects of μM 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 μM) and MgCl₂ additions to achieve 150 and 300 μM 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 μM 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.

Vegetable growers in the Southeast US have successfully used cultivation to grow pumpkins. Many growers, due to the lack of surface applied herbicides, no-till planting equipment, and knowledge of conservation tillage methods for vegetables, have not pursued no-till pumpkin production in this region. All of these production aides are now present for successful no-till plantings. Reasons to use no-till technology for pumpkins include soil moisture conservation, cleaner fruit and similar yields as conventional tillage, and long-term improvements of soil chemical, microbial, and physical properties of the soil. The objectives of the two experiments were to evaluate the influence of surface residue type and amount on yield and quality of no-till pumpkins, and to establish planting date and nitrogen (N) rate recommendations. Results suggest that a minimum amount of residue is required for good no-till pumpkin yields, but increasing residues beyond 5600-6720 kg ha-1 will not affect pumpkin yield. Although this range will vary with location, weather conditions, and soil type, a vegetable grower should expect to successfully grow no-till pumpkins at these residue rates. Planting date and N rate greatly influenced no-till pumpkin yields. Planting dates that were earlier than traditional planting dates increased yields at one location where cooler weather conditions persist, but had minimal affect at a second warmer mountain region location. The highest rate of 120 kg Nha-1 produced the greatest yields, suggesting that perhaps a greater N rate may have continued to increase yield.

One of the primary impediments to the implementation of bioremediation is uncertainty about success in the field. Soils and microbial populations are heterogeneous and it is difficult to extrapolate biodegradation rates from small samples to field scale. While biodegradation rates can be estimated from microcosm studies, in situ methods offer a more meaningful gauge of resident microbial activity. One method used to estimate biodegradation rates in the field is the newly developed Push-Pull technique. While this technique can be conducted on site, it is normally not possible to use target pollutants as the reactive substrates. Consequently, alternative, benign reactive tracers must be used. Ideally, these alternative, reactive tracers interrogate the same enzyme systems that are responsible for the biodegradation of the target pollutant. The objective of this study was to develop a reactive tracer system that could be used to assess toluene-dependent trichloroethylene (TCE) degradation. Our approach has been to determine whether a series of pure strains of toluene-oxidizing bacteria (Burkholderia cepacia G4, Pseudomonas putida F1, Pseudomonas putida mt2, Pseudomonas mendocina KR1), each with different toluene-oxidizing enzymes systems, are capable of cometabolically oxidizing a series of eleven potential alternative substrates. These substrates include simple alkenes, alkanes, and cyclic alkanes. The kinetics (Ks and Vmax) of the biotransformation of these compounds have been determined. While oxidation products were observed for a number of these substrates in connection with one or more of the test organisms, isobutylene was co-oxidized by all test organisms. Oxidation of isobutylene by each organism yielded kinetics constants comparable to the corresponding kinetics of TCE degradation. The enzyme system expressed by Burkholderia cepacia G4 catalyzed the epoxidation of isobutylene while the remaining enzyme systems catalyzed allylic alcohol formation. Isobutylene has potential in field scale Push-Pull studies as a tool for evaluating rates of aerobic toluene-dependent TCE degradation and of differentiating the relative contributions of the TCE-degrading population. A pilot study of this alternative substrate at Edwards Air Force Base will test whether it can be used successfully to estimate in situ degradation of TCE. Analysis of isobutylene oxidation products in toluene-enriched ground water may offer an inexpensive and effective method of measuring the degradation of TCE at contaminated sites nationwide.

The success of wetland restoration projects depends in part on the length of time that a soil is in a reduced redox state. The length of time that a soil is reduced depends on how quickly reduction occurs following saturation with water. The relationship between reduction rate and various soil chemical and mineralogical properties is poorly understood, but such properties might be manipulated to improve the success of wetland restoration projects. The goals of this research were to determine soil properties that predict the rate at which soils undergo reduction when saturated, and to determine the roles of electron donors and acceptors on reduction rates. Sixteen soil samples were collected at various depths from two wetland sites, a Carolina bay (Juniper Bay) and a wetland catena (Frog Level). Soils were incubated in specially designed redox incubators to monitor reduction rates, changes in soil properties, and soil solution chemistry. Soil samples were subjected to three cycles of oxidation and reduction during the course of 36 d. Soil reduction rates were determined from the slopes of linear regression models fit to data for redox potential (Eh) over time. Reduction rates varied among soils from 1.2 to 46.2 mV h-1, and were significantly greater (p-value < 0.05) for soils with total organic carbon (TOC) > 10 g kg-1 than in soils with TOC < 10 g kg-1. Increasing amounts of dissolved Fe(II) were found at Eh values below 500 mV for pH between 4.5 and 5.1. Mineral soils with total reduction rates > 10 mV h-1 released significantly more Fe(II) into solution than mineral soils with reduction rates < 10 mV h-1 (p-value < 0.05). Regression results indicated that organic carbon, an electron donor, was the dominant factor controlling reduction rates up to 10 mV h-1, and an electron acceptor Fe(III) was the dominant factor controlling reduction rates > 10 mV h-1. For wetland restoration purposes multiple linear regression models based on our results that include TOC concentration and pH can be used along with hydrologic data to predict reduction rates in saturated soils.

Realistic Yield Expectations (RYE) have been developed in North Carolina to assist in site-specific farming decisions that will improve N-use efficiency and reduce N contamination of ground- and surface water, especially in the Neuse River Basin. This study was conducted to determine whether correlations exist between soil chemical properties, actual yields, soil map units, zones, and RYEs. Soil surveys of the fields were completed at an approximate scale of 1:3500 in 2002 (remapped soil map units) and compared to existing county soil surveys (original soil map units). Samples from equilateral triangle grid soil sampling were analyzed and used to map the spatial distribution of soil pH, soil P, and soil K and lime requirement. Interpolated maps were created to display the spatial distribution of the investigated soil chemical properties. To represent zones (transition zone or map unit interior), 20 m buffers centered on map unit boundaries were created in order to investigate these highly unique and variable areas. Soybean (Glycine max [L.] Merr) and wheat (Triticum aestivum L.) yield data was collected for two site-years in one Piedmont field, while wheat and corn (Zea mays L.) were sampled for one site-year in the two remaining Piedmont fields. Soybean and wheat yield data was collected for three site-years in two Coastal Plain fields. Interpolated nutrient maps showed visual correlations between soil map units and soil K values in the Coastal Plain, but no other relationships between soil chemical properties and soil map units or zones were visually apparent for either location. Yield maps showed visual relationships with soil map units in the Coastal Plain but not in the Piedmont. Various statistical models were utilized to analyze the data and the spatial covariance model was determined to be more efficient than the independent and identically distributed fixed effects model in capturing a significant proportion of the variability for tested soil chemical properties and crop yield in both locations. Remapped and original soil map units were also studied to determine their effectiveness in capturing the variability of soil chemical properties and crop yield. The remapped soil map units were more effective than the original soil map units in capturing this variability in most cases. Soil K was highly significant among the remapped soil map units in the Field 7 in the Piedmont where r2=0.82. In all locations, other investigated parameters also displayed significance, but none as highly significant as soil K in Field 7. RYEs were found to be greater than actual yields for all crops harvested in both locations.

Nutrient availability from poultry manures can be affected by soil types and manure processing. Estimates of nutrient release from manures are important when recommending their use. Three separate laboratory experiments were conducted to evaluate N and P availability, and liming value of poultry layer manures (fresh, composted, and pelleted) with surfaces samples of three NC soils: Belhaven (loamy, mixed, dysic, thermic Terric Haplosaprists), Cecil (fine, kaolinitic, thermic Typic Kanhapludults), and Lynchburg (fine-loamy, siliceous, semiactive, thermic Aeric Paleaquults). The N incubation compared N mineralization from poultry manures and urea, applied at a rate of 133 µg N cm-3 soil (200 kg ha-1) and incubated for 90 days. Net N mineralized from the manures was described by a single pool first order kinetic model. Potential available N, estimated as the proportion of applied N, was greater for the fresh and composted manures than for the pelleted source in the three soils investigated. Nitrogen availability in fresh, composted, and pelleted manures for the Belhaven soil was 57, 53, and 46 % of total N applied, respectively; 83, 73, and 61 % of total N applied in the Lynchburg soil; and 41, 33, and 25 % for the same order of manure sources in the Cecil soil. The 21 day lime incubation compared poultry manure rates of 1333 and 2667 µg cm-3 of soil (2 and 4 t ha-1) with multiple rates of CaCO3. Liming materials in all the manures were just as effective in neutralizing soil acidity as equivalent amounts of CaCO3. Nitrification of manure N, however, can reduce the net liming effect by the release of H+. The 21 day P incubation experiment compared available P from the manures applied at rates of 1333 and 2667 µg cm-3 of soil (2 and 4 t ha-1) with multiple rates of Ca(H2PO4)2. A linear relationship across all P sources and rates was the best estimator of the increase in Mehlich-3 extractable P per unit of P added. These results suggested that P from the manures behaved similar to inorganic P fertilizer. Treatments in a subsequent greenhouse experiment were designed to evaluate millet [Urochloa ramosa (L.) T. Q. Nguyen] response to N, P and lime supplied in manures. Plant available N from the manures, estimated from the urea-N fertilizer equivalence of plant N accumulation, followed the decreasing order of fresh > composted > pelleted. This ranking among manures is similar to that obtained in the N incubation study. Millet dry matter and nutrient accumulation at targeted levels of N supply and soil values of Mehlich-3 P and pH were similar between treatments of manure supplemented with P fertilizer and lime, and treatments receiving only inorganic fertilizers and lime. These results indicate that optimum plant growth in manure amended systems requires the appropriate identification and correction of soil N, P and/or acidity constraints. Type of manure processing affects total N availability, and soil properties such as texture and buffer capacity can influence N mineralization and soil available P.