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.

The interaction of phosphate with Fe(III) and Al(III) is important in soils, wastes and other systems of environmental significance. The goal of this research was to characterize phosphate sorption in single- and mixed Fe- and Al-oxide systems using XANES (X-ray absorption near edge structure spectroscopy). The specific objectives of this research were: 1) To determine the quantitative distribution of phosphate between Fe-and Al-oxide minerals in mixtures containing these minerals; 2) To assign XANES spectral features for phosphate associated with Fe(III) or Al(III) to specific electronic transitions; and 3) To characterize adsorption versus surface precipitation in single- and binary mixtures of Fe- and Al-oxide minerals. Phosphate was sorbed in single-mineral aqueous suspensions of ferrihydrite (ferric hydroxide), boehmite (aluminum oxyhydroxide), goethite (iron oxyhydroxide), or non-crystalline (non-xl) Al-hydroxide, and mixtures of ferrihydrite/boehmite, goethite/boehmite, and ferrihydrite/non-xl Al-hydroxide at pH 6. Samples were reacted at 22 degrees Celsius for 42 h. Phosphate sorption isotherm trends for mixed-mineral systems were L-curves and were intermediate to those of the respective minerals in the mixture. Phosphorus K-XANES spectra for phosphate on Fe- vs. Al-oxide minerals differed in that a weak doublet peak was observed for Fe-oxides on the low-energy side of the P K-edge, i.e., in the pre-edge region. The quantitative distribution of phosphate between ferrihydrite and boehmite in mixtures of these minerals was determined using linear combination fitting (LCF) analysis of the XANES pre-edge region. Results showed that phosphate essentially distributed itself in proportion to the maximum phosphate sorption capacity of each of these minerals. Using a XANES fitting procedure, phosphate was found to show a greater apparent preference for boehmite and non-xl Al-hydroxide minerals in goethite/boehmite and ferrihydrite/non-xl Al-hydroxide mixtures, respectively. To interpret XANES spectra based on molecular bonding configuration, spectral features were assigned to specific electronic transitions using bonding arguments supported by extended Huckel (EH) model computations of molecular orbital energies (projected density of states-PDOS). Experimental evidence (both XANES and UV-visible spectroscopy) was given for the white-line peak in Fe(III)/phosphate systems being caused by a dipole allowed transition of a P 1s electron to a P(3p)-O(2p) antibonding molecular orbital. Similarly, the white-line peak in Al-phosphate systems was assigned to a dipole allowed transition into a Al(3p)-O(2p)-P(3p) antibonding molecular orbital. The pre-edge feature in XANES spectra was assigned to a dipole allowed transition into a Fe(4p)-O(2p) antibonding molecular orbital. Using these XANES spectral assignments, the increase in FWHM (full width at half maximum height) of the white-line peak in XANES spectra indicated precipitation. Based on a linear increase in FWHM with increasing sorbed phosphate concentration, Al-phosphate surface precipitation occurred in boehmite and non-xl Al-hydroxide systems. On the contrary, no evidence was found for Fe-phosphate precipitation in single-mineral systems of goethite and ferrihydrite. Surface precipitation occurred in goethite/boehmite mixtures following similar trends as in boehmite, but no evidence for surface precipitation was found in ferrihydrite/non-xl Al-hydroxide mixtures over the range of phosphate studied (up to 1230 mmol/ kg). In these mixtures, mineral interactive effects apparently inhibited Al-phosphate precipitation as occurred when phosphate was reacted with non-xl Al-hydroxide alone. Furthermore, phosphate showed a trend of affinity preference for non-xl Al-hydroxide with increasing adsorbed P concentrations in the ferrihydrite/non-xl Al-hydroxide mixtures.

The potential for improved fertilizer nitrogen (N) use efficiency (NUE) and yield in winter wheat (Triticum aestivum L.) and maize (Zea mays L.) was tested using a new, controlled release urea formaldehyde polymer (UFP). This polymer was compared with conventional aqueous urea-ammonium nitrate (UAN) [(NH2)2CO?NH4NO3] fertilizer during a two-year field experiment in North Carolina from 2004 to 2006. The crops were grown on three soils: Candor (sandy, siliceous, thermic Grossarenic Kandiudult), Portsmouth (fine-loamy over sandy or sandy-skeletal, mixed, semiactive, thermic Typic Umbraquult) and Cape Fear (fine, mixed, semiactive, thermic Typic Umbraquult). The sandy soil was irrigated as needed to avoid drought stress. Treatments were N source (UAN and UFP) and N rate (0, 50, 78, 106, 134, 162, and 190 kg N ha-1 or 0, 45, 70, 95, 120, 145, and 170 lb ac-1 for wheat and 0, 39, 78, 118, 157, 196, and 235 kg N ha-1 or 0, 35, 70, 105, 140, 175, and 210 lb ac-1 for maize) arranged as randomized complete blocks with four replications. The UAN and UFP were applied as a split application for wheat, while maize received UFP at planting and split UAN. Timing of the materials was determined either by label (UFP) or prior experimental experience (UAN). Harvest biomass, grain, and mid-season soil sampling were performed to assess N availability. For both crops, UAN performed statistically similar to or better than UFP at both sites with regards to yields and NUE. Also, soil sampling and incubation results showed no consistent difference between N sources, implying the slow release properties of the UFP were not seen under the site and laboratory conditions. The release time for both sources at both sites was approximately 14 days (2 weeks). Since the cost of UFP is substantially greater than UAN and form did not significantly affect yield, UFP may not be as economical as UAN, depending on pricing of the different fertilizers.

With increasing pressure to regulate land application of animal manure, North Carolina faces a difficult dilemma, given the number of large-scale animal production facilities currently in operation. Poultry and swine industries in the state generate large volumes of animal manure that must be properly managed in order to avoid loss of N to ground water and surface water bodies. Using swine manure as an N source for soybean production is not commonly practiced due to soybean¡¦s ability to fix N, but recent research suggests that soybean may be a suitable receiver crop of anaerobic swine lagoon effluent. The objectives of this research were twofold: (1) determine the quantity of swine effluent-derived N taken up by soybean and estimate the degree of inhibition of symbiotic N-fixation and (2) determine how soil pH affects N mineralization, nitrification and immobilization when soil is amended with broiler litter. Swine effluent was spiked with (15NH4)2SO4 in order to attain a mean final 15N enrichment of 5.765 atom % 15N. The enriched effluent was applied 6 times at weekly intervals to nodulating and nonnodulating soybean growing in one-meter deep lysimeters at a rate of 185 kg PAN ha-1. Additional lysimeters with nodulating and nonnodulating soybean received no applications of effluent. Leachate was collected on a weekly basis and analyzed for 15N and total N. Soybean were harvested near maturity and analyzed for 15N and total N. Biological N-fixation in soybean was not completely inhibited when swine effluent was added and accounted for 55% of the total N in the shoot. Nodulated and nonnodulated soybean shoots recovered similar amounts of effluent N (36.6% and 33.4%, respectively). The addition of effluent and nodulation were both important sources of N for soybean growth, although the results suggest that nodulating and nonnodulating soybean behaved differently when they received effluent additions, as indicated by significant interactions. The experimental data showed that less than 1% of the added effluent N was accounted for in the leachate. An N budget of the plant-soil-water system showed that, of the effluent N added to nodulated soybean, 37% remained in the soil after the soybean were harvested, while 33% remained in the effluent-treated nonnodulated soybean. These results suggest that soybean can serve as an N receiver crop when swine effluent is the N source. To determine the effects of soil pH on N transformations in broiler litter amended soils, Wagram loamy sand with a pH of 4.4 was collected from a forested area near Clayton, NC, and sub-samples were limed to pH 4.8, 5.3, 5.8, 6.4, and 7.0. Broiler litter was added at a rate of 155 kg PAN ha-1 to the limed soils and incubated at 25?ßC and 60% of field capacity for 112 d. Total inorganic N was measured at 0, 7, 14, 28, 56, 77, and 112 d. Cumulative net N mineralized was fitted to a first order model to determine potentially mineralizable N. Although nitrification rates increased as soil pH increased, there were significant inverse relationships between soil pH and net N mineralized, as well as soil pH and potentially mineralizable N. Isotope dilution measurements showed that gross and net mineralization rates were equivalent, refuting the notion that relatively more NH4 immobilization had occurred in the high pH soils. The results indicate that N mineralization was enhanced at low soil pH, a phenomenon that presently is not fully understood.

In-season, site-specific (SS) N management based on remote sensing (RS) has been suggested as a way of reducing groundwater NO3-N contamination. In-season N management seeks to match the temporal variability of crop N needs by applying appropriate amounts of N at critical crop growth stages. Site-specific N management attempts to match the spatial variability of crop N requirements by applying appropriate, spatially variable N rates within fields. We evaluated the environmental and agronomic benefits of two in-season, RS-informed N management strategies applied on a uniform field-average (FA) or SS basis. We compared these to current uniform N recommendations based on "Realistic Yield Expectations" (RYE) in a typical coastal plain cropping system. We also sought to understand the spatial and temporal dynamics of shallow groundwater NO3-N. An additional objective was to develop a statistical procedure for the analysis of spatially dense, georeferenced subsample data in randomized complete block designs, a common characteristic of precision agriculture research. The experiment was established in a 12-ha North Carolina field with a 2-yr winter wheat double-crop soybean-corn rotation. The three N management treatments were applied to 0.37 ha plots in a randomized complete block design with 10 replications. Groundwater NO3-N and water table depth were measured every two weeks at 60 well nests (two per plot) sampling 0.9- to 1.8-, 1.8- to 2.7-, and 2.7- to 3.7-m depths from 2001 to 2003. We developed a statistical procedure for selecting an appropriate covariance model in randomized complete block analyses in the presence of spatial correlation. When warranted, incorporating spatial covariance in the statistical analysis provides greater efficiency in estimating treatment effects. Elevations, soil organic matter (SOM), and water table elevations (WTE) were spatial covariates used for explaining NO3-N spatial correlation. Compared to RYE, SS achieved: (i) less groundwater NO3-N by reducing fertilizer N and increasing the harvest N ratio (the ratio of N harvested in grain or forage to the total fertilizer N applied) for wheat in 2001; (ii) increased yield associated with higher N applied and decreased harvest N ratio for corn in 2002; and (iii) increased yield associated with similar fertilizer N and increased harvest N ratio for wheat in 2003. Overall, FA performed similarly to SS for wheat, but differed greatly for corn due to an overapplication of N at tasselling. These results indicate that RS-informed SS and FA might improve groundwater quality with no sacrifice in yield, or increase grain yield with similar fertilizer N compared to RYE-based N recommendations in the Coastal Plain. Mean NO3-N concentrations averaged over sampling depth at each well nest showed clear temporal fluctuations and were positively correlated with WTE. Groundwater NO3-N was frequently spatially correlated and spatial covariance structure changed periodically. The spatial correlation range varied over time from 46 to 551 m, and appeared to follow the trend of the mean water table depth. Blocking alone or together with elevation, SOM, and WTE frequently explained NO3-N spatial correlation. Our data suggest that to assess the environmental efficacy of N management, frequent and periodic monitoring of groundwater NO3-N, especially after significant rainfall, is essential to capture in-season treatment effects. Simultaneous measurement of precipitation and water table depth facilitate understanding of these effects. The traditional sampling of NO3-N only at or after harvest is likely to be insufficient to capture the entirety of treatment effects throughout the growing season. This is especially true in coastal plain and other coarse-textured soils where in-season NO3-N leaching may be pronounced. Our data also suggest that residual effects of differential N management may appear long after N application, even on these coarse-textured soils, indicating a need for longitudinal sampling.

Phosphorus (P) runoff and leaching from agricultural fields have been identified as major environmental concerns for the health of aquatic ecosystems. North Carolina has responded by implementing the Phosphorus Loss Assessment Tool (PLAT). The goal of the PLAT is to determine relative P losses from agricultural fields based on several site factors and characteristics, including Mehlich-3 P (M3P) soil test values. Based on previous research, the current version of PLAT is programmed to predict greater soluble P losses from organic soils than from mineral soils with the same M3P values. However, recent research specific to North Carolina?s organic soils has indicated decreased soluble P release in the presence of high Al concentrations. Our objectives were to determine (i) the Al content of Typic Haplosaprists and Terric Haplosaprists of North Carolina?s Lower Coastal Plain, and (ii) how the Al in these soils affects P retention. We sampled four organic soil series and determined M3P, Mehlich-3 Al (M3Al), Mehlich-3 Fe (M3Fe), water-soluble P (WSP), total P, pH, particle size distribution, and the organic matter content (OM). Water-soluble P and M3P were also measured in a 21-d incubation study in which P was added at a rate equivalent to 150 kg P ha-1. Total CuCl2 extractable Al and inorganic soil P fractions were identified in an Al and inorganic P fractionation study, respectively. According to the results of the incubation, multiple regression, and fractionation studies, Al was the main cation responsible for P retention; the mean topsoil M3Al concentrations (1926 mg kg-1) in these organic soils were much higher than those observed in another study of mostly mineral NC soils. The concentration of M3Fe was low in every series and was not correlated to any P characteristics. Mehlich-3 P was not consistently correlated to P retention and WSP; however, OM, M3Al, and total CuCl2 extractable Al were correlated with P retention. In the incubation study, the percentage of applied P that was adsorbed was greater in soils with lower OM and/or higher M3Al. Increased OM was associated with increased WSP and lower total P, as well as decreased P retention. The opposite effect was observed with increasing M3Al concentrations; however, the ratio of OM to M3Al showed increased correlation to P retention and WSP than when OM and Al were used alone. These results indicate that soils with higher OM and lower Al did not retain P as well as soils with lower OM and higher Al contents. Furthermore, as more Al bound P was extracted by M3P (causing higher M3P/Al-P %), WSP increased, and coincided with decreased total CuCl2 Al. The results from this study show that in high OM soils, the concentration of extractable Al controlled the solubility of P. North Carolina?s PLAT could be modified to include M3Al concentrations to more accurately predict P losses in the organic soils of the lower coastal plain, thus potentially reducing P runoff and leaching into our aquatic ecosystems.