Biosolids effects on phosphorus retention and release in some sandy Florida soils

The soil solid phase components most responsible for P sorption in Florida soils are Fe and Al oxides. Thus, we hypothesized that land application of biosolids would significantly increase a soil's P retention by increasing its content of P-sorbing solids, especially when biosolids with high Fe and Al concentrations are applied to soils that sorb P poorly. Biosolids effects were quantified by a series of single-point isotherms on soils from two field studies sampled for up to 4 yr after initial biosolids application. Biosolids additions had little effect on P retention in a soil with abundant oxalate-extractable Fe and Al and a correspondingly large native P-sorbing capacity. However, biosolids significantly increased P retention in a soil with low oxalate-extractable Fe and Al content and low native P-sorbing capacity. Biosolids effects on P retention lasted 1 to 3 yr after application, depending on biosolids source and rate of application, and generally mimicked persistence of increased extractable Fe and Al concentrations in the poorly P-sorbing soil. Disappearance of added Fe and Al (and, hence, P retention capacity) from the surface horizons over time was relatively rapid, perhaps due to abundant organic acid production associated with biosolids degradation. Phosphorus in biosolids containing (or tailored to contain) abundant Fe and/or Al can be expected to behave as a slowly available P source, and to be less subject to leaching losses than completely soluble P sources.     

Soil profile distribution of phosphorus and other nutrients following wetland conversion to beef cattle pasture

Largely influenced by the passage of the Swamp Land Act of 1849, many wetlands were lost in the coastal plain region of the southeastern United States, primarily as a result of drainage for agricultural activities. To better understand the chemical response of soils during wetland conversion, soil core samples were collected from the converted beef cattle pastures and from the natural wetland at Plant City, FL in the summers of 2002 and 2003. Data collected from the natural wetland sites were used as reference data to detect potential changes in soil properties associated with the conversion of wetlands to improved beef cattle (Bos taurus) pastures from 1940 to 2003. The average concentration of total phosphorus (TP) in pasture soils (284 mg kg(-1)) was significantly (p 相似文献   

Results of a program to control phosphorus discharges from dairy operations in south-central Florida,USA

During 1987–1992, a mandatory program to control phosphorus discharges was implemented at dairy operations located to the north of Lake Okeechobee, Florida, USA. Thirty of 48 dairies participated in this program and implemented best management practices (BMPs), which included the construction of intensive animal waste management systems. Eighteen dairies closed their milkproducing operations under a government-funded buyout program. In this paper, we compare trends in runoff total phosphorus (TP) concentrations among the dairies that remained active and implemented BMPs. A central feature of the dairy waste management system is the high intensity area (HIA), defined as the milking barn and adjacent vegetation-free land, encircled by a drainage ditch and dike. Animal waste from the HIA is diverted into anaerobic lagoons and storage ponds, from which water is periodically removed and used for irrigation of field crops. The impacts of BMP construction on runoff TP concentrations were immediate and, in most cases, dramatic. Average TP concentrations declined significantly (P < 0.001), from 9.0 to 1.2 mg TP liter^–1 at dairies in one basin (Lower Kissimmee River), and from 2.6 to 1.0 mg TP liter^–1 in another (Taylor Creek/Nubbin Slough). Some sites experienced greater declines in TP than others. To elucidate possible causes for the difference in response, a multivariate statistical model was utilized. Independent variables included soil pH, soil drainage characteristics, spodic horizon depth, and the areas of different BMP components (pasture, HIA, spray fields). The analysis significantly separated dairies with the highest and lowest runoff TP concentrations. Lowest TP occurred at dairies having particular soil characteristic (shallow spodic horizon) and certain BMP features (large HIA and small heard pastures).     

Analysis of potentially mobile phosphorus in arable soils using solid state nuclear magnetic resonance

In many intensive agroecosystems continued inputs of phosphorus (P) over many years can significantly increase soil P concentrations and the risk of P loss to surface waters. For this study we used solid-state 31P nuclear magnetic resonance (NMR) spectroscopy, high-power decoupling with magic angle spinning (HPDec-MAS) NMR, and cross polarization with magic angle spinning (CP-MAS) NMR to determine the chemical nature of potentially mobile P associated with aluminum (Al) and calcium (Ca) in selected arable soils. Three soils with a range of bicarbonate-extractable Olsen P concentrations (40-102 mg P kg(-1)) were obtained from a long-term field experiment on continuous root crops at Rothamsted, UK, established in 1843 (sampled 1958). This soil has a threshold or change point at 59 mg Olsen P kg(-1), above which potentially mobile P (as determined by extraction with water or 0.01 M CaCl2) increases much more per unit increase in Olsen P than below this point. Results showed that CaCl2 and water preferentially extracted Al-P and Ca-P forms, respectively, from the soils. Comparison among the different soils also indicated that potentially mobile P above the threshold was largely present as a combination of soluble and loosely adsorbed (protonated-cross polarized) P forms largely associated with Ca, such as monetite (CaHPO4) and dicalcium phosphate dihydrate (CaHPO4-2H2O), and some Al-associated P as wavellite. The findings of this study demonstrate that solid-state NMR has the potential to provide accurate information on the chemical nature of soil P species and their potential mobility.     

Effects of organic matter on phosphorus release kinetics in different trophic lake sediments and application of transition state theory

Sediments have a significant influence on the overlying water, and phosphorus (P) release from sediments is an important source for the lake eutrophication, particularly in shallow ones. In this study, effects of organic matter on P release from sediments in different trophic lakes from the middle and lower reaches of Yangtze River, China, were investigated, and the release kinetics of different P fractions at different temperature were studied. The results show that the release kinetics of soluble reactive phosphorus (SRP), dissolved organic phosphorus (DOP) and dissolved total phosphorus (DTP) were similar for the studied sediments, the release rate increased rapidly in the initial hours, and it increased gradually after 10h. The release kinetics of SRP, DOP and DTP followed the Power Function model. SRP was the major fraction among the released DTP, while DOP was an important fraction in the heavily polluted sediments. Organic matter restricted the SRP and DTP release while it promoted the DOP release. Both DOP and SRP release processes were endothermic. The thermodynamic properties in the P release kinetics were calculated and discussed.     

Plant-available and water-soluble phosphorus in soils amended with separated manure solids

Physical, chemical, or biological treatment of animal liquid manure generally produces a dry-matter rich fraction (DMF) that contains most of the initial phosphorus (P). Our objective was to assess the solubility and plant availability of P from various DMFs as a function of soil P status. Eight different DMFs were obtained from liquid swine (LSM) and dairy cattle (LDC) manures treated by natural decantation, anaerobic digestion, chemical flocculation, composting, or mechanical separation. The DMFs were compared with mineral P fertilizer in a pot experiment with oat ( L.) grown in four soils with varied P-fixing capacities and P saturation levels. The DMFs were added at a rate of 50 mg P kg soil and incubated 14 d before seeding. Soil water-extractable P (P) at all water:soil extraction ratios (2:1, 20:1, and 200:1) was slightly higher when DMFs were derived from LDC rather than LSM. Soil P at the 2:1 ratio was lower with anaerobically digested LSM. At the 2:1 extraction ratio, DMF P was less soluble than mineral P as P saturation in soils increased. In soils with a lower P-fixing capacity, DMF P appeared less water soluble than mineral P under 20:1 and 200:1 extraction ratios. After 72 d of plant growth, DMFs produced yields comparable to mineral P fertilizer. Although the plant availability of P from DMFs was comparable to mineral P fertilizer, P from DMFs could be less vulnerable to leaching or runoff losses in soils with a high P saturation level or low P-fixing capacity.     

Phosphorus extractability of soils amended with stockpiled and composted cattle manure

Managing fertilizer applications to maintain soil P below environmentally unacceptable levels should consider the contribution of manure and synthetic fertilizer sources to soluble and extractable forms of P. Our objective was to evaluate soil and manure characteristics and application rates on P extractability in recently amended soils. Five soils of the U.S. southern High Plains were amended with beef cattle manures, composted beef manure, and inorganic fertilizers [Ca(H(2)PO(4))(2) or KH(2)PO(4)] at five rates and incubated under controlled conditions. Mehlich 3-, Olsen (NaHCO(3))-, Texas A&M extractant (TAM)-, and water-extractable P were determined for the soils after selected incubation periods. Except for TAM and some water extractions, P extractability as a function of total P applied was linear (P < 0.001) for a wide range of application rates. Mehlich-3, NaHCO(3), and water P extraction efficiencies of KH(2)PO(4)-amended soils averaged 22, 34, and 115% greater (P < or = 0.036), respectively, than efficiencies of soils amended with manures except for the Texline (calcareous) loam and Pullman clay loam soils. Phosphorus extraction efficiencies decreased with time for KH(2)PO(4)-amended soils (P < 0.05) but remained stable or increased for manure-amended soils during the 8-wk incubation period. Across all soils and manure sources, changes in water-extractable P per unit increase in Mehlich 3-, NaHCO(3)-, and TAM-extractable P averaged 100, 85, and 125% greater, respectively, for inorganic as compared with manure-amended soils. These source-dependent relationships limit the use of agronomic soil extractants to make correct inferences about water-extractable P and dissolved P in runoff.     

Chemical and physical changes following co-composting of beef cattle feedlot manure with phosphogypsum

Nitrogen (N) loss during beef cattle (Bos taurus) feedlot manure composting may contribute to greenhouse gas emissions and increase ammonia (NH(3)) in the atmosphere while decreasing the fertilizer value of the final compost. Phosphogypsum (PG) is an acidic by-product of phosphorus (P) fertilizer manufacture and large stockpiles currently exist in Alberta. This experiment examined co-composting of PG (at rates of 0, 40, 70, and 140 kg PG Mg(-1) manure plus PG dry weight) with manure from feedlot pens bedded with straw or wood chips. During the 99-d composting period, PG addition reduced total nitrogen (TN) loss by 0.11% for each 1 kg Mg(-1) increment in PG rate. Available N at the end of composting was significantly higher for wood chip-bedded (2180 mg kg(-1)) than straw-bedded manure treatments (1820 mg kg(-1)). Total sulfur (TS) concentration in the final compost increased by 0.19 g kg(-1) for each 1 kg Mg(-1) increment in PG rate from 5.2 g TS kg(-1) without PG addition. Phosphogypsum (1.6 g kg(-1) P) addition had no significant effect on total phosphorus (TP) concentration of the final composts. Results from this study demonstrate the potential of PG addition to reduce overall N losses during composting. The accompanying increase in TS content has implications for use of the end-product on sulfur-deficient soils. Co-composting feedlot manure with PG may provide an inexpensive and technologically straightforward solution for managing and improving the nutrient composition of composted cattle manure.     

Fate of coliform bacteria in composted beef cattle feedlot manure

The link between livestock production, manure management, and human health has received much public attention in recent years. Composting is often promoted as a means of sanitizing manure to ensure that pathogenic bacteria are not spread to a wider environment during land application. In a two-year study (1998 and 1999) in southern Alberta, we examined the fate of coliform bacteria during windrow composting of cattle (Bos taurus) manure from feedlot pens bedded with cereal straw or wood chips. Numbers of total coliforms (TC) and Escherichia coli declined as the composting period progressed. In 1998, TC levels (mean of both bedding types) were log10 7.86 cells g(-1) dry wt. for raw manure on Day 0, log10 3.38 cells g(-1) by Day 7, and log10 1.69 cells g(-1) by Day 14. More than 99.9% of TC and E. coli was eliminated in the first 7 d when average windrow temperatures ranged from 33.5 to 41.5 degrees C. The type of bedding did not influence the numbers of TC or E. coli. Dessication probably played a minor role in coliform elimination, since water loss was low (< 0.07 kg kg(-1)) in the first 7 d of composting. However, total aerobic heterotroph populations remained high (> 7.0 log10 CFU g(-1) dry wt., where CFU is colony forming units) throughout the composting period, possibly causing an antagonistic effect. Land application of compost, with its nondetectable levels of E. coli compared with raw manure, should minimize environmental risk in areas of intensive livestock production.     

Relationship of soil test phosphorus and sampling depth to runoff phosphorus in calcareous and noncalcareous soils

A study was initiated to investigate the relationship between soil test P and depth of soil sampling with runoff losses of dissolved molybdate reactive phosphorus (DMRP). Rainfall simulations were conducted on two noncalcareous soils, a Windthorst sandy loam (fine, mixed, thermic Udic Paleustalf) and a Blanket clay loam (fine, mixed, thermic Pachic Argiustoll), and two calcareous soils, a Purves clay (clayey, smectitic, thermic Lithic Calciustoll) and a Houston Black clay (fine, smectitic, thermic Udic Haplustert). Soil (0- to 2.5-, 0- to 5-, and 0- to 15-cm depths) and runoff samples were collected from each of the four soils in permanent pasture exhibiting a wide range in soil test P levels (as determined by Mehlich III and distilled water extraction) due to prior manure applications. Simulated rain was used to produce runoff, which was collected for 30 min. Good regression equations were derived relating soil test P level to runoff DMRP for all four soil types, as indicated by relatively high r2 values (0.715 to 0.961, 0- to 5-cm depth). Differences were observed for the depth of sampling, with the most consistent results observed with the 0- to 5-cm sampling depth. Runoff DMRP losses as a function of the concentration of P in soil were lower in calcareous soils (maximum of 0.74 mg L(-1)) compared with noncalcareous soils (maximum of 1.73 mg L(-1)). The results indicate that a soil test for environmental P could be developed, but it would require establishing different soil test P level criteria for different soils or classes of soils.     

Nitrogen and phosphorus budgets in experimental grasslands of variable diversity

Previous research has shown that plant diversity influences N and P cycles. However, the effect of plant diversity on complete ecosystem N and P budgets has not yet been assessed. For 20 plots of artificially established grassland mixtures differing in plant diversity, we determined N and P inputs by bulk and dry deposition and N and P losses by mowing (and subsequent removal of the biomass) and leaching from April 2003 to March 2004. Total deposition of N and P was 2.3 +/- 0.1 and 0.2 +/- 0.01 g m(-2) yr(-1), respectively. Mowing was the main N and P loss. The net N and P budgets were negative (-6.3 +/- 1.1 g N and -1.9 +/- 0.2 g P m(-2) yr(-1)). For N, this included a conservative estimate of atmospheric N(2) fixation. Nitrogen losses as N(2)O were expected to be small at our study site (<0.05 g m(-2) yr(-1)). Legumes increased the removal of N with the harvest and decreased leaching of NH(4)-N and dissolved organic nitrogen (DON) from the canopy. Reduced roughness of grass-containing mixtures decreased dry deposition of N and P. Total dissolved P and NO(3)-N leaching from the canopy increased in the presence of grasses attributable to the decreased N and P demand of grass-containing mixtures. Species richness did not have an effect on any of the studied fluxes. Our results demonstrate that the N and P fluxes in managed grassland are modified by the presence or absence of particular functional plant groups and are mainly driven by the management.     

Nitrogen and phosphorus availability in composted and uncomposted poultry litter

Poultry litter applications to land have been based on crop N requirements, resulting in application of P in excess of plant requirements, which may cause degradation of water quality in the Chesapeake Bay watershed. The effect of litter source (the Delmarva Peninsula and Moorefield, West Virginia) and composting of poultry litter on N mineralization and availability of P in two soil types (sandy loam and silt loam) was determined in a controlled environment for 120 d. Nitrogen mineralization (percent total organic N converted to inorganic nitrogen) rates were higher for fresh litter (range of 42 to 64%) than composted litter (range of 1 to 9%). The N mineralization rate of fresh litter from the Delmarva Peninsula was consistently lower than the fresh litter from Moorefield, WV. The N mineralization rate of composted litter from either source was not significantly different for each soil type (7 to 9% in sandy loam and 1 to 5% in silt loam) even though composting conditions were completely different at the two composting facilities. Litter source had a large effect on N mineralization rates of fresh but not composted poultry litter. Composting yielded a more predictable and reliable source of mineralizable N than fresh litter. Water-extractable phosphorus (WEP) was similar in soils amended with composted litter from WV and fresh litter from both sources (approximately 10 to 25 and 2 to 14 mg P kg(-1) for sandy loam and silt loam, respectively). Mehlich 1-extractable phosphorus (MEP) was similar in soils amended with WV fresh litter and composted litter from both sources (approximately 100 to 140 and 60 to 90 mg P kg(-1) for sandy loam and silt loam, respectively). These results suggest that the composting process did not consistently reduce WEP and MEP, and P can be as available in composted poultry litter as in fresh poultry litter.     

Quantity and quality of runoff from a beef cattle feedlot in southern Alberta

Southern Alberta, which has a cold climate dominated by strong chinook winds, has the highest density of feedlot cattle in Canada. However, the quantity and quality of runoff from beef cattle (Bos taurus) feedlots in this unique region has not been investigated. Our objectives were to compare runoff quantity (1998-2002) with catch-basin design criteria; determine concentrations of selected inorganic chemical parameters (1998-2000) in runoff in relation to water quality guidelines and the potential implications of irrigating adjacent crop-land; and determine if total heterotrophs, total coliforms, and Escherichia coli (1998-2000) persisted in the catch-basin water and soil. Runoff (< 0.1 to 42.5 mm) for a 24-h duration that included maximum peak discharge was less than the recommended design criteria of 90 mm based on runoff from 24 h of rainfall with a 30-yr return period. We found that curve numbers between 52 and 96 (mode of 90) were required to match the USDA Natural Resources Conservation Service predicted runoff and actual runoff volumes. Total P posed the greatest threat to water quality guidelines, and K posed the greatest threat for exceeding crop fertilizer requirements if catch-basin effluent was used as irrigation water. Water in the catch basin had continually high populations of E. coli throughout the study, with values ranging between log10 2 and log10 8 100 mL(-1). In contrast, soil in the catch basin generally had low populations of E. coli that were < log10 2 g(-1) wet wt., but at times higher populations between log10 2 and log10 6 g(-1) wet wt. were also found.     

Sorption kinetics and equilibria of organic pesticides in carbonatic soils from South Florida

A batch reactor was used to determine sorption kinetic parameters (k2, F, and K*) and the equilibrium sorption coefficient (K). The two-site nonequilibrium (TSNE) batch sorption kinetics model was used to calculate the kinetic parameters. Two probe organic pesticides, atrazine [2-chloro-4-ethylamino-6-isopropylamino-s-triazine] and diuron [3-(3,4-dichlorophenyl)-1,1-dimethylurea] were studied using three carbonatic soils from South Florida (Chekika, Perrine, and Krome), one noncarbonatic soil from Iowa (Webster), and one organic soil (Lauderhill) from South Florida. Carbonatic soils contained more than 600 g kg(-1) CaCO3. Sorption is initially very fast up to 3 h and then slowly reaches equilibrium. All soil-chemical combinations reached sorption equilibrium after about 24 h and all sorption isotherms were linear. The sorption kinetics data were well described by the TSNE model for all soil-chemical combinations except for the marl soil data (Perrine-Atrazine), which were better described by the one-site nonequilibrium (OSNE) model. Diuron, with higher K, undergoes slower sorption kinetics than atrazine. The Lauderhill soil containing organic carbon (OC) of 450 g kg(-1) exhibited slowest sorption kinetics for both pesticides. An inverse relationship between k3 and K was observed for atrazine and diuron separately in Chekika, Webster, and Lauderhill soils but not in Perrine and Krome soils. The sorption kinetic parameters were used to distinguish the sorption behavior between atrazine and diuron and to identify differences between soils. Normalizing the sorption coefficient (K) to OC showed that atrazine and diuron had K oc values in carbonatic soils that were a third of reported literature values for noncarbonatic soils. Using existing literature K oc values in solute transport models will most likely underestimate the mobility of atrazine, diuron, and other neutral organic chemicals in carbonatic soils.     

Surface runoff losses of phosphorus from Virginia soils amended with turkey manure using phytase and high available phosphorus corn diets

Many states have passed legislation that regulates agricultural P applications based on soil P levels and crop P uptake in an attempt to protect surface waters from nonpoint P inputs. Phytase enzyme and high available phosphorus (HAP) corn supplements to poultry feed are considered potential remedies to this problem because they can reduce total P concentrations in manure. However, less is known about their water solubility of P and potential nonpoint-source P losses when land-applied. This study was conducted to determine the effects of phytase enzyme and HAP corn supplemented diets on runoff P concentrations from pasture soils receiving surface applications of turkey manure. Manure from five poultry diets consisting of various combinations of phytase enzyme, HAP corn, and normal phytic acid (NPA) corn were surface-applied at 60 kg P ha(-1) to runoff boxes containing tall fescue (Festuca arundinacea Schreb.) and placed under a rainfall simulator for runoff collection. The alternative diets caused a decrease in manure total P and water soluble phosphorus (WSP) compared with the standard diet. Runoff dissolved reactive phosphorus (DRP) concentrations were significantly higher from HAP manure-amended soils while DRP losses from other manure treatments were not significantly different from each other. The DRP concentrations in runoff were not directly related to manure WSP. Instead, because the mass of manure applied varied for each treatment causing different amounts of manure particles lost in runoff, the runoff DRP concentrations were influenced by a combination of runoff sediment concentrations and manure WSP.     

Effect of poultry diet on phosphorus in runoff from soils amended with poultry manure and compost

Phosphorus in runoff from fields where poultry litter is surface-applied is an environmental concern. We investigated the effect of adding phytase and reducing supplemental P in poultry diets and composting poultry manures, with and without Fe and Al amendments, on P in manures, composts, and runoff. We used four diets: normal (no phytase) with 0.4% supplemental P, normal + phytase, phytase + 0.3% P, and phytase + 0.2% P. Adding phytase and decreasing supplemental P in diets reduced total P but increased water-extractable P in manure. Compared with manures, composting reduced both total P, due to dilution of manure with woodchips and straw, and water-extractable P, but beyond a dilution effect so that the ratio of water-extractable P to total P was less in compost than manure. Adding Fe and Al during composting did not consistently change total P or water-extractable P. Manures and composts were surface-applied to soil boxes at a rate of 50 kg total P ha(-1) and subjected to simulated rainfall, with runoff collected for 30 min. For manures, phytase and decreased P in diets had no significant effect on total P or molybdate-reactive P loads (kg ha(-1)) in runoff. Composting reduced total P and molybdate-reactive P loads in runoff, and adding Fe and Al to compost reduced total P but not molybdate-reactive P loads in runoff. Molybdate-reactive P in runoff (mg box(-1)) was well correlated to water-extractable P applied to boxes (mg box(-1)) in manures and composts. Therefore, the final environmental impact of dietary phytase will depend on the management of poultry diets, manure, and farm-scale P balances.     

Soil microbial communities associated with Bt and non-Bt corn in three soils

The effects of expression of Cry endotoxin by Bt corn (transgenic corn engineered to express Bacillus thuringiensis toxin) on soil microbial community structure were assessed in a growth chamber experiment. Two lines of transgenic corn expressing different Cry endotoxins were compared with their respective non-transgenic isolines in three soil types with differing textures. Phospholipid fatty acid (PLFA) profiles from bulk soil and community-level physiological profiles (CLPP) from the rhizosphere community were used to assess community structure. Differences in PLFA profiles due to soil type were significant, accounting for 73% of the total variability in the dataset. Differences in bacterial and fungal CLPP profiles due to soil type were statistically significant, but probably not biologically important, accounting for 6.3 and 3.8% of the total variability, respectively. Neither expression of Cry endotoxin nor corn line had a significant effect on microbial profiles, except in the high-clay soil where both factors significantly affected bacterial CLPP profiles (accounting for 6.6 and 6.1% of the variability in that soil, respectively). Expression of Cry endotoxin also significantly reduced the presence of eukaryotic PLFA biomarker in bulk soils, although it is unclear which groups of eukaryotes were affected. We conclude that the effects of transgenic Bt corn in this short-term experiment are small, and longer-term investigations are necessary.     

Distribution of phosphorus in manure slurry and its infiltration after application to soils

Computer models help identify agricultural areas where P transport potential is high, but commonly used models do not simulate surface application of manures and P transport from manures to runoff. As part of an effort to model such P transport, we conducted manure slurry separation and soil infiltration experiments to determine how much slurry P infiltrates into soil after application but before rain, thus becoming less available to runoff. We applied dairy and swine slurry to soil columns and after both 24 and 96 h analyzed solids remaining on the soil surface for dry matter, total phosphorus (TP), and water-extractable inorganic (WEIP) and organic (WEOP) phosphorus. We analyzed underlying soils for Mehlich-3 and water-extractable P. We also conducted slurry separation experiments by sieving, centrifuging, and suction-filtering to determine which method could easily estimate slurry P infiltration into soils. About 20% of slurry solids and 40 to 65% of slurry TP and WEIP infiltrated into soil after application, rendering this P less available to transport in runoff. Slurry separation by suction-filtering through a screen with 0.75-mm-diameter openings was the best method to estimate this slurry P infiltration. Measured quantities of manure WEOP changed too much during experiments to estimate WEOP infiltration into soil or what separation method can approximate infiltration. Applying slurries to soils always increased soil P in the top 0 to 1 cm of soil, frequently in the 1- to 2-cm depth of soil, but rarely below 2 cm. Future research should use soils with coarser texture or large macropores, and slurry with low dry matter content (1-2%).     

Occurrence of arsenic and phosphorus in ditch flow from litter-amended soils and barn areas

Little is known about the fate of arsenic (As) in land-applied litter from chickens that have been fed roxarsone, an organic feed additive containing As. This study seeks to elucidate the transfer of As in runoff from ditch-drained soils of the poultry-producing region of the Delmarva Peninsula by tracking As and phosphorus (P) export from seven drainage ditches over two water-years (1 July 2005 to 30 June 2007). Annual losses of As from ditches ranged from 0.004 to 0.071 kg ha(-1) while P losses ranged from 0.33 to 18.56 kg ha(-1), with the largest loads associated with a litter storage shed that served as a point source. Event-based As and P losses in ditch flow fluctuated by a factor of 162 and 1882, respectively. The two elements were correlated in flow from the ditch draining a litter storage shed (r = 0.99), and in sediment extracts in soils near the litter shed (r = 0.73), pointing to similar behavior under point source conditions. Indeed, As and P exhibited similar behavior within storms for all ditches, characterized by relatively high initial concentrations subject to rapid concentration declines before peak flow, consistent with dilution of a finite source. However, As and P concentrations varied significantly between ditches and showed considerable temporal variability within ditches, with no clear seasonal trends or associations with current management strategies. The results suggest that similar management strategies might be effective for As and P point sources, but that field management practices geared toward controlling nonpoint source P losses may not readily transfer to the control of As losses.     

Watershed scale assessment of nitrogen and phosphorus loadings in the Indian River Lagoon basin,Florida

There is a growing evidence that the ecological and biological integrity of the lagoon has declined during the last 50 years, probably due to the decline in water quality. Establishment of a watershed scale seagrass-based nutrient load assessment is the major aim of water quality management in the Indian River Lagoon (IRL). Best estimate loadings incorporate wet and dry deposition, surface water, groundwater, sediment nutrient flux, and point source effluent discharge data. On the average, the IRL is receiving annual external loadings of 832, 645 and 94,476kg of total nitrogen (TN) and total phosphorus (TP), respectively, from stormwater discharges and agricultural runoff. The average internal cycling of TN and TP from sediment deposits in the IRL was about 42,640kg TN and 1050kg TPyr(-1). Indirect evidence suggests that atmospheric deposition has played a role in the ongoing nutrient enrichment in the IRL. The estimated total atmospheric deposition of TN and TP was about 32,940 and 824kgyr(-1), while groundwater contribution was about 84,920 and 24,275kgyr(-1), respectively, to the surface waters of the IRL. The estimated annual contribution of point effluent discharge was about 60,408kg TN and 7248kg TP. In total, the IRL basin is receiving an annual loading of about 1,053,553kg TN and 127,873kg TP. With these results, it is clear that the current rate of nutrient loadings is causing a shift in the primary producers of the IRL from macrophyte to phytoplankton- or algal-based system. The goal is to reverse that shift, to attain and maintain a macrophyte-based estuarine system in the IRL.