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.

The National Technical Committee for Hydric Soils developed the Hydric Soil Technical Standard (HSTS) to identify a functioning wetland (hydric) soil using quantitative measurements of saturation and anaerobic conditions. We used the HSTS to assess wetland restoration success and to compare surface treatments designed to replicate microtopographic relief found in forested wetlands. Experiments were conducted on a wetland restored from agricultural fields in eastern NC where monitoring stations were installed across three surface treatments in the restored wetland: 1) a microtopography (MT) treatment created by roughing the soil surface to mimic the uneven surface of forested wetlands, 2) a crown removal treatment imposed by grading the field flat, and 3) a control treatment that had no surface alteration. Monitoring stations were also installed in a nearby nonriverine swamp forest as a reference wetland. Weekly measurements of water table depth and redox potential were collected for 15 months. Soil at all monitoring stations met the HSTS, indicating that functioning hydric soils were restored. Although a significant difference between surface treatments was not detected, the MT treatment resulted in anaerobic conditions most similar to the reference wetland, signifying that this type of surface treatment should be considered for wetland restoration of areas with smooth surfaces. The HSTS proved to be a useful tool in evaluating wetland restoration success and microtopographic effects. Microtopographic relief did not create nonhydric areas as measured by HSTS; however, microtopographic relief is likely to influence plant establishment.

Agricultural management decisions that influence biological activity and diversity include tillage, fertilizer and pest-control inputs, and crop rotations. Our research objective was to characterize relationships between biological and physical properties resulting from long-term agricultural management decisions. A nine-year old factorially-designed field experiment was used to examine the effects of tillage (moldboard plow or strip-tillage), input (synthetic fertilizers and pesticides or inputs approved for organic certification programs), and crop rotation (continuous staked tomatoes or 3-year vegetable rotation) on a suite of biological and physical soil parameters. Biological measurements included microbial, nematode, and earthworm community composition, soil respiration and N mineralization potential, enzyme activity, and microbial biomass. Physical property measurements included aggregate stability, bulk density, and pore-size distribution. Biological properties generally responded to all treatment combinations, but tillage provided the strongest treatment effect in most cases. Compared to strip-tillage, tillage consistently yielded significantly lower values for the following biological measurements: total C and N, above-ground biomass, microbial biomass, enzyme activity, soil respiration, N mineralization, some nematode trophic groups, and earthworms. Compared with organic inputs, synthetic inputs consistently induced significantly lower values for the following biological measurements: microbial biomass, enzyme activity, some nematode trophic groups, and soil respiration. An examination of relationships between biological and physical parameters using redundancy analysis revealed that microporosity was the physical property that was most strongly correlated with most biological parameters. Soil organisms responded to our treatments in the following order: tillage > input > rotation.

Residential lawn management practices (mowing, fertilizer, irrigation, reseeding, and aeration) result in aesthetically appealing landscapes, but can result in nutrient losses via overland flow or gaseous losses to the atmosphere (e.g. nitrous oxide - N2O). The overall objective of this study was to determine the effect of lawn management on nutrient losses from residential lawns. The specific objectives were: modify a passive sampling system to determine nutrient loads due to overland flow from lawns; evaluate differences in overland flow frequency, volumes, and nutrient losses during rainfall events (⥠2.54 cm); and compare N2O losses following rainfall events. Three lawn schemes were studied: a high maintenance fescue (Festuca arundinacea) lawn (HMFL), a low maintenance fescue lawn (LMFL), and a mixed forested residential landscape (RFL). The modified passive sampling system allowed 100% recovery of overland flow and demonstrated that differences in maintenance influenced the overland flow frequency, volumes, and nutrient losses. The LMFL had the greatest overland flow volumes and nutrient unit area loads, although N and P concentrations in overland flow exceeded USEPA recommendations from all three lawns. Nutrient losses (g ha-1 yr-1) from all three residential landscapes were 1000 times less than fertilizer (kg ha-1 yr-1) and throughfall (kg ha-1 yr-1) inputs, due in part to the presence of well-structured soils (low bulk densities and high infiltration rates). Irrigation practices between the HMFL and LMFL explained the differences in overland flow volumes and nutrient loads, especially during the first half of the study when drought conditions existed at the study site (Cary, North Carolina). Lack of irrigation in the LMFL resulted in early dormancy, a minimal thatch layer and lower plant density, resulting in higher volumes of overland flow. Trends in the N2O losses from the HMFL and LMFL were associated with timing of fertilizer applications, presence or absence of irrigation, and seasonal growth patterns of the fescue. For the RFL, the presence of a decomposing litter layer limited N2O production. Well-maintained residential lawns, receiving recommended fertilizer N applications and frequent irrigation, reduce nutrient losses via overland flow but may provide optimum conditions for greater N2O fluxes.

Subsurface solute transport is a major mechanism that contributes to the contaminant load in both surface and ground waters. Among these contaminants are plant nutrients that if transported in excessive amounts to surface waters can cause adverse effects on humans and animals, as well as negative impacts on aquatic life. The general objective of this study was to conduct a field evaluation of subsurface solute transport in the capillary fringe (CF) and shallow ground water (SGW) and their contribution to nutrient load in the ditches prior to restoration of a Carolina Bay. Specifically, this study was aimed at evaluating: a) the horizontal flow of bromide (Br-) in the CF and SGW under field conditions, b) the fate of nitrate (NO3-) in the CF and SGW in a sandy field site drained by ditches, and c) the possible contribution of subsurface flow to the increased nutrient load in drainage ditches at a drained Carolina Bay following storm events. The study was conducted in Juniper Bay, a drained Carolina Bay in Robeson County, NC. A solute transport experiment was conducted at a sandy site in the Bay where a solution containing Br- and NO3- was applied into an auger hole dug to about 10 cm above the CF during the time of application. The transport of Br- and NO3- in the CF and SGW was monitored by frequently collecting soil water samples using tension lysimeters installed at depths of 45, 60, 75, 90 and 105 cm at lateral distances of 20, 60, 120, 220 and 320 cm from the auger hole along the general direction of the ground water flow. A representative monitoring site from each of the Bay?s mineral and organic soil areas was also chosen for a year-long monitoring of fluctuations in nutrient concentrations in water samples from the Bay?s main ditch exit as well as from the vadose zone, ground water and lateral ditches. Soil solution from the vadose zone and ground water samples were collected using tension lysimeters installed at 15-cm depth intervals from 15 to 120, and 30 to 180 cm depths at the mineral and organic soil sites, respectively. Ground water samples were collected from three fully perforated wells. Seven piezometers installed at each site also allowed collection of ground water samples from different depth intervals below the water table The direction and magnitude of the subsurface hydraulic gradient at the monitored sites were also determined using the three-point technique. Lateral transport of Br- in the CF was observed in the direction of ground water movement up to 320 cm from the auger hole where solutes were applied. The Br- plume from the unsaturated zone that entered into the CF tended to stay and move horizontally in the CF until it was partially moved into the ground water by the fluctuating WT following rain events. The normalized concentrations (concentration in soil solution/concentration in the applied solution) of both NO3- and Br- in water samples collected from CF were comparable for all distances from the application spot. However, in the groundwater, the normalized concentration of NO3- was substantially lower than the normalized Br- concentrations. We believe the reduction in NO3- concentration in the ground water was due to denitrification. Results from the nutrient monitoring experiment reveal that the sample taken from the main ditch exit following a 5 cm d-1 storm event had higher concentrations of total organic carbon (TOC), phosphates (PO4-P), calcium (Ca) and magnesium (Mg) compared to the average of samples collected during baseflow conditions. The same was also observed for samples collected from the vadose zone especially at depths closer to the soil surface where organic carbon and extractable Ca, Mg and PO4-P contents were higher. Higher concentrations of these solutes in the ditches and vadose zone coincided with observed increase in the magnitude of the groundwater hydraulic gradient. In addition, it was observed that following the storm events, the direction of the ground water hydraulic gradient tended to become more perpendicular to the nearby lateral ditch suggesting that the route taken by the water as it moves in the subsurface towards the ditch is shortened. We believe that the increase in concentration of PO4-P, Ca, Mg and TOC in the soil solution at certain depths in the soil profile coupled with their higher rate of movement in the subsurface towards the ditch following the storm event should have contributed to the increase in concentration of such nutrients in the ditches.

Knowledge of the effect of reduced soil redox conditions on P dissolution is needed to better assess P mobility to surface or ground water. The objectives of our study were to determine the effect of microbial reduction on P dissolution and determine mechanisms of P release in a reduced soil. Duplicate suspensions of silt+clay from a Cape Fear sandy clay loam were reduced in a continuously-stirred redox reactor for 40 d. We studied the effects of three treatments on P dissolution: (i) 2 g dextrose kg-1 solids added as a microbial carbon source at time 0 d; (ii) 2 g dextrose kg-1 solids split into three additions at 0, 12, and 26 d; and (iii) no added dextrose. Regardless of treatment or variation in the intensity of reduction rates, dissolved reactive P (DRP) increased up to 7-fold from 1.5 to 10 mg L-1 and was linearly related (R2 = 0.79) with dissolved organic C. Dissolved Fe and Al and pH also increased, suggesting the formation of aqueous Fe- and Al-dissolved organic matter (DOM) complexes. Separate batch experiments were performed to study the effects of increasing pH and citrate additions on PO4 dissolution under aerobic conditions. Increasing additions of citrate increased concentrations of DRP, Fe, and Al, while increasing pH had no effect. Results indicated that increased DOM during soil reduction contributed to the increase in DRP, perhaps by competitive adsorption or by formation of aqueous ternary PO4-Fe-DOM or PO4-Al-DOM complexes.