Runoff phosphorus losses from surface-applied biosolids

Runoff losses of dissolved and particulate phosphorus (P) may occur when rainfall interacts with manures and biosolids spread on the soil surface. This study compared P levels in runoff losses from soils amended with several P sources, including 10 different biosolids and dairy manure (untreated and treated with Fe or Al salts). Simulated rainfall (71 mm h(-1)) was applied until 30 min of runoff was collected from soil boxes (100 x 20 x 5 cm) to which the P sources were surfaced applied. Materials were applied to achieve a common plant available nitrogen (PAN) rate of 134 kg PAN ha(-1), resulting in total P loading rates from 122 (dairy manure) to 555 (Syracuse N-Viro biosolids) kg P ha(-1). Two biosolids produced via biological phosphorus removal (BPR) wastewater treatment resulted in the highest total dissolved phosphorus (13-21.5 mg TDP L(-1)) and total phosphorus (18-27.5 mg TP L(-1)) concentrations in runoff, followed by untreated dairy manure that had statistically (p = 0.05) higher TDP (8.5 mg L(-1)) and TP (10.9 mg L(-1)) than seven of the eight other biosolids. The TDP and TP in runoff from six biosolids did not differ significantly from unamended control (0.03 mg TDP L(-1); 0.95 mg TP L(-1)). Highest runoff TDP was associated with P sources low in Al and Fe. Amending dairy manure with Al and Fe salts at 1:1 metal-to-P molar ratio reduced runoff TP to control levels. Runoff TDP and TP were not positively correlated to TP application rate unless modified by a weighting factor reflecting the relative solubility of the P source. This suggests site assessment indices should account for the differential solubility of the applied P source to accurately predict the risk of P loss from the wide variety of biosolids materials routinely land applied.     

Phosphorus exchangeability and leaching losses from two grassland soils

Although phosphate phosphorus (P) is strongly sorbed in many soils, it may be quickly transported through the soil by preferential flow. Under flood irrigation, preferential flow is especially pronounced and associated solute losses may be important. Phosphorus losses induced by flood irrigation were investigated in a lysimeter study. Detailed soil chemical analyses revealed that P was very mobile in the topsoil, but the higher P-fixing capacity of the subsoil appeared to restrict P mobility. Application of a dye tracer enabled preferential flow pathways to be identified. Soil sampling according to dye staining patterns revealed that exchangeable P was significantly greater in preferential flow areas as compared with the unstained soil matrix. This could be partly attributed to the accumulation of organic carbon and P, together with enhanced leaching of Al- and Fe-oxides in the preferential flow areas, which resulted in reduced P sorption. The irrigation water caused a rapid hydrologic response by displacement of resident water from the subsoil. Despite the occurrence of preferential flow, most of the outflowing water was resident soil water and very low in P. In these soils the occurrence of preferential flow per se is not sufficient to cause large P losses even if the topsoil is rich in P. It appears that the P was retained in lower parts of the soil profile characterized by a very high P-fixing capacity. This study demonstrates the risks associated with assessing potential P losses on the basis of P mobility in the topsoil alone.     

Surface and subsurface phosphorus losses from fertilized pasture systems in Ohio

Phosphorus is an essential plant nutrient and critical to agricultural production, but it is also a problem when excessive amounts enter surface waters. Summer rotational grazing and winter feeding beef pasture systems at two fertility levels (56 and 28 kg available P ha(-1)) were studied to evaluate the P losses from these systems via surface runoff and subsurface flow using eight small (0.3-1.1 ha), instrumented watersheds and spring developments. Runoff events from a 14-yr period (1974-1988) were evaluated to determine the relationships between event size in mm, total dissolved reactive phosphorous (TDRP) concentration, and TDRP transport. Most of the TDRP transported was via surface runoff. There were strong correlations (r2 = 0.45-0.66) between TDRP transport and event size for all watersheds, but no significant (P = 0.05) correlations between TDRP concentration and event size. Flow-weighted average TDRP concentrations from the pasture watersheds for the 14-yr period ranged from 0.64 to 1.85 mg L(-1) with a few individual event concentrations as high as 85.7 mg L(-1). The highest concentrations were in events that occurred soon after P fertilizer application. Average seasonal flow-weighted TDRP concentrations for subsurface flow were < 0.05 mg L(-1). Applying P fertilizer to pastures in response to soil tests should keep TDRP concentrations in subsurface flow at environmentally acceptable levels. Management to reduce runoff and avoidance of P fertilizer application when runoff producing rainfall is anticipated in the next few days will help reduce the surface losses of P.     

Impact of soil amendments on reducing phosphorus losses from runoff in sod

Received for publication December 22, 2004. Research was initiated to study the interaction between soil amendments (lime, gypsum, and ferrous sulfate) and dissolved molybdate reactive phosphorus [RP(<0.45)] losses from manure applications from concentrated runoff flow through a sod surface. Four run-over boxes (2.2-m2 surface area) were prepared for each treatment with a bermudagrass [Cynodon dactylon (L.) Pers.] sod surface (using sod blocks) and composted dairy manure was surface-applied at rates of 0, 4.5, 9, or 13.5 Mg ha-1. The three soil amendments were then applied to the boxes. Two 30-min runoff events were conducted and runoff water was collected at 10-min intervals and analyzed for RP(<0.45). Results indicated that the addition of ferrous sulfate was very effective at reducing the level of RP(<0.45). in runoff water, reducing RP(<0.45) from 1.3 mg L(-1) for the highest compost rate with no amendment to 0.2 mg L(-1) for the ferrous sulfate in the first 10 min of runoff. Lime and gypsum showed a small impact on reducing RP(<0.45), with a reduction in the first 10 min to 0.9 and 0.8 mg L(-1), respectively. The ferrous sulfate reduced the RP(<0.45) in the tank at the end of the first runoff event by 66.3% compared with no amendment. In the second runoff event, the ferrous sulfate was very effective at reducing RP(<0.45) in runoff, with no significant differences in RP(<0.45) with application of 13.5 Mg ha(-1) compost compared with no manure application. The results indicate that the addition of ferrous sulfate may greatly reduce RP(<0.45) losses in runoff and has considerable potential to be used on pasture, turfgrass, and filter strips to reduce the initial RP(<0.45) losses from manure application to the environment.     

Estimating runoff phosphorus losses from calcareous soils in the Minnesota River basin

Bioavailable phosphorus (BAP) in stormwater runoff is a key issue for control of eutrophication in agriculturally impacted watersheds. Laboratory experiments were conducted in soil runoff boxes to determine BAP content in simulated storm runoff in 10 (mostly) calcareous soils from the Minnesota River basin in southern Minnesota. The soluble reactive phosphorus (SRP) portion of the runoff BAP was significantly correlated with soil Mehlich-III P, Olsen P, and water-extractable P (all r2 > 0.90 and p < 0.001). A linear relationship (r2 = 0.88, p < 0.001) also was obtained between SRP in runoff and the phosphorus saturation index based on sorptivity (PSIs) calculated with sorptivity as a measure of the inherent soil P sorption capacity. Runoff levels of BAP estimated with iron oxide-impregnated paper were predicted well by various soil test P methods and the PSI, of the soils, but correlation coefficients between these variables and runoff BAP were generally lower than those for runoff SRP. Using these relationships and critical BAP levels for stream eutrophication, we found corresponding critical levels of soil Mehlich-III P and Olsen P (which should not be exceeded) to be 65 to 85 and 40 to 55 mg kg(-1), respectively.     

Halting the upward trend in soluble phosphorus transported from a grassland catchment

An upward trend in soluble reactive phosphorus (SRP) concentrations in Northern Ireland rivers leading to increased eutrophication has been reported for the last two decades. To identify if a similar trend could be observed in land drainage waters SRP and other P fractions were measured weekly from 1989 to 1997 in land drainage from a 9-ha grassland catchment in Northern Ireland that had a mean P surplus applied of 23.4 kg P ha(-1) yr(-1). Regressions of annual median concentrations of P fractions in land drainage waters against time for 1989 through to 1997 showed significant increases of SRP and soluble unreactive phosphorus (SUP) of 2.4 and 1.2 microg P L(-1) yr(-1), respectively. However, the annual flow-weighted concentrations and loads of all P fractions did not show significant increases with time. During the period 1998-2000 a change of management was introduced when only maintenance dressings of P were applied to the catchment according to Ministry of Agriculture, Fisheries and Food guidelines. This resulted in significant reductions in SRP concentrations in 2000 compared with 1997.     

Influence of aeration implements, phosphorus fertilizers, and soil taxa on phosphorus losses from grasslands

Attenuation of rainfall within the solum may help to move contaminants and nutrients into the soil to be better sequestered or utilized by crops. Surface application of phosphorus (P) amendments to grasslands may lead to elevated concentrations of P in surface runoff and eutrophication of surface waters. Aeration of grasslands has been proposed as a treatment to reduce losses of applied P. Here, results from two small-plot aeration studies and two field-scale, paired-watershed studies are supplemented with previously unpublished soil P data and synthesized. The overall objective of these studies was to determine the impact of aeration on soil P, runoff volume, and runoff P losses from mixed tall fescue [Lolium arundinaceum (Schreb.) Darbysh.]-bermudagrass (Cynodon dactylon L.) grasslands fertilized with P. Small-scale rainfall simulations were conducted on two soil taxa using three types of aeration implements: spikes, disks, and cores. The-field scale study was conducted on four soil taxa with slit and knife aeration. Small-plot studies showed that core aeration reduced loads of total P and dissolved reactive P (DRP) in runoff from plots fertilized with broiler litter and that aeration was effective in reducing P export when it increased soil P in the upper 5 cm. In the field-scale study, slit aeration reduced DRP losses by 35% in fields with well-drained soils but not in poorly drained soils. Flow-weighted concentrations of DRP in aerated fields were related to water-soluble P applied in amendments and soil test P in the upper 5 cm. These studies show that the overall effectiveness of mechanical soil aeration on runoff volume and P losses is controlled by the interaction of soil characteristics such as internal drainage and compaction, soil P, type of surface-applied manure, and type of aeration implement.     

Economic analysis of best management practices to reduce watershed phosphorus losses

In phosphorus-limited freshwater systems, small increases in phosphorus (P) concentrations can lead to eutrophication. To reduce P inputs to these systems, various environmental and agricultural agencies provide producers with incentives to implement best management practices (BMPs). In this study, we examine both the water quality and economic consequences of systematically protecting saturated, runoff-generating areas from active agriculture with selected BMPs. We also examine the joint water quality/economic impacts of these BMPs-specifically BMPs focusing on barnyards and buffer areas. Using the Variable Source Loading Function model (a modified Generalized Watershed Loading Function model) and net present value analysis (NPV), the results indicate that converting runoff-prone agricultural land to buffers and installing barnyard BMPs are both highly effective in decreasing dissolved P loss from a single-farm watershed, but are also costly for the producer. On average, including barnyard BMPs decreases the nutrient loading by about 5.5% compared with only implementing buffers. The annualized NPV for installing both buffers on only the wettest areas of the landscape and implementing barnyard BMPs becomes positive only if the BMPs lifetime exceeds 15 yr. The spatial location of the BMPs in relation to runoff producing areas, the time frame over which the BMPs are implemented, and the marginal costs of increasing buffer size were found to be the most critical considerations for water quality and profitability. The framework presented here incorporates estimations of nutrient loading reductions in the economic analysis, and is applicable to farms facing BMP adoption decisions.     

Aerating grasslands: effects on runoff and phosphorus losses from applied broiler litter

Aeration has been promoted as improving infiltration of rainfall and extending grass or forage productivity, but research on the impact of this practice on P losses from grasslands has had mixed results. We designed a study to determine at the field scale, using a paired watershed approach, the impact of slit aeration on runoff volume and P losses in runoff from fescue (Festuca arundinacea Schreb.)/bermudagrass (Cynodon dactylon L.) hay fields fertilized with broiler litter. Three pairs of 0.8-ha fields, each with similar soils (Typic Kanhapludults, Aquic Hapludults, and Aquultic Hapludalfs), were fertilized with broiler litter and monitored under similar management from 1995 through 1998, then one field in each pair received aeration treatment from 2001 through 2003. In the field with mostly well-drained soils, grassland aeration reduced surface runoff volume and mass losses of dissolved reactive P (DRP) in runoff by approximately 35%. In contrast, when poorly drained soils dominated, grassland aeration increased runoff volume (4.8 mm/runoff event) and mass losses of DRP and total P (0.25 kg TP ha-1 per runoff event). This implies that aeration of well-drained soils in the top poultry-producing counties of Georgia (0.2 million ha) could decrease dissolved phosphorus losses by more than 500 Mg P each year. This is not the case if soils are poorly drained.     

Mathematical modeling of phosphorus losses from land application of hog and cattle manure

Mathematical models may provide a means to estimate phosphorus (P) losses from land application of manure. Phosphorus losses typically occur during brief episodes of runoff and erosion. Models must be able to simulate P losses during these episodes by representing the basic chemical, physical, and biological processes by which these losses occur. The mathematical model ecosys combines dynamic distributed flow of solutes and nonsolutes through runoff and erosion with convective-dispersive transport of solutes, and both biologically and thermodynamically driven transformations between solutes and nonsolutes. This model was tested against P lost in runoff, erosion, and leachate measured during 90 min of controlled rainfall at 65 mm h(-1) on soils from six sites at which different rates of manure had been applied over the previous 3 to 6 yr. Transport and transformation kinetics in the model enabled it to simulate changes of dissolved inorganic phosphorus (DIP) in runoff from >1.0 to <0.05 mg L(-1) and changes of total phosphorus (TP) in sediment from 15 to 3 mg L(-1) measured during controlled rainfall on soils with diverse P contents. Results from 60-yr model runs using these kinetics with different application rates of cattle manure indicated that (i) a positive interaction exists between annual rainfall and application rate on P losses and (ii) rates greater than 30 Mg ha(-1) yr(-1) would cause TP concentrations in water leaving the site to rise above acceptable limits. The interaction between rainfall and rate suggests that P losses from manure application at any site should be assessed under the upper range of likely rainfall intensities.     

Effects of tillage and phosphorus placement on phosphorus runoff losses in a grain sorghum-soybean rotation

Phosphorus enhances eutrophication of fresh water bodies. This study was conducted to determine the influence of tillage and P placement on P losses in runoff water from a somewhat poorly drained soil (Woodson silt loam [fine, smectitic, thermic Abruptic Argiaquoll], 1.0-1.5% slope) in a grain sorghum [Sorghum bicolor (L.) Moenchl-soybean [Glycine mar (L.) Merr] rotation. Chisel-disk-field cultivate (ChT), ridge-till (RT), and no-till (NT) in combination with 0 kg P ha(-1) or 24 kg P ha(-1) broadcast or knifed (applied prior to planting grain sorghum) were studied. Runoff volume and losses of sediment and P were summed over the growing season. Significant interactions between tillage and P placement for soluble P losses were found. For example, soluble P loss in 1999 for NT-broadcast in grain sorghum was 358 g ha(-1); significantly greater than 31 g ha(-1) for NT-knife or 23 g ha(-1) for NT-check. Similar results were found for RT but no such differences were found for ChT. Bioavailable P losses were generally highest with broadcast P placement and for NT and RT. Total P losses were significantly higher at 959 g ha(-1) with broadcast P on grain sorghum in 1998, compared with 521 g ha(-1) for the check and 659 g ha(-1) for the knifed P applications. Total P losses in 1999 for soybeans were only 18 g ha(-1) for NT, which was significantly lower than 75 g ha(-1) for ChT and 66 g ha(-1) for RT. The results indicate that broadcast P applications on RT and NT will increase P losses, but the influence of tillage was not consistent.     

Application of polyacrylamide to reduce phosphorus losses from a Chinese purple soil: A laboratory and field investigation

Use of anionic polyacrylamide (PAM) to control phosphorus (P) losses from a Chinese purple soil was studied in both a laboratory soil column experiment and a field plot experiment on a steep slope (27%). Treatments in the column study were a control, and PAM mixed uniformly into the soil at rates of 0.02, 0.05, 0.08, 0.10, and 0.20%. We found that PAM had an important inhibitory effect on vertical P transport in the soil columns, with the 0.20% PAM treatment having the greatest significant reduction in leachate soluble P concentrations and losses resulting from nine leaching periods. Field experiments were conducted on 5 m wide by 21 m long natural rainfall plots, that allowed collection of both surface runoff and subsurface drainage water. Wheat was planted and grown on all plots with typical fertilizer applied. Treatments included a control, dry PAM at 3.9 kg ha^?1, dry PAM at 3.9 kg ha^?1 applied together with lime (CaCO₃ at 4.9 t ha^?1), and dry PAM at 3.9 kg ha^?1 applied together with gypsum (CaSO₄·2H₂O at 4 t ha^?1). Results from the field plot experiment in which 5 rainfall events resulted in measurable runoff and leachate showed that all PAM treatments significantly reduced runoff volume and total P losses in surface runoff compared to the control. The PAM treatments also all significantly reduced water volume leached to the tile drain. However, total P losses in the leachate water were not significantly different due to the treatments, perhaps due to the low PAM soil surface application rate and/or high experimental variability. The PAM alone treatment resulted in the greatest wheat growth as indicated by the plant growth indexes of wheat plant height, leaf length, leaf width, grain number per head, and dried grain mass. Growth indexes of the PAM with Calcium treatments were significantly lesser. These results indicate that the selection and use of soil amendments need to be carefully determined based upon the most important management goal at a particular site (runoff/nutrient loss control, enhanced plant growth, or a combination).     

Decreasing phosphorus runoff losses from land-applied poultry litter with dietary modifications and alum addition

Phosphorus (P) losses from pastures fertilized with poultry litter contribute to the degradation of surface water quality in the United States. Dietary modification and manure amendments may reduce potential P runoff losses from pastures. In the current study, broilers were fed a normal diet, phytase diet, high available phosphorus (HAP) corn diet, or HAP corn + phytase diet. Litter treatments were untreated control and alum added at 10% by weight between flocks. Phytase and HAP corn diets reduced litter dissolved P content in poultry litter by 10 and 35%, respectively, compared with the normal diet (789 mg P kg(-1)). Alum treatment of poultry litter reduced the amount of dissolved P by 47%, while a 74% reduction was noted after alum treatment of litter from the HAP corn + phytase diet. The P concentrations in runoff water were highest from plots receiving poultry litter from the normal diet, whereas plots receiving poultry litter from phytase and HAP corn diets had reduced P concentrations. The addition of alum to the various poultry litters reduced P runoff by 52 to 69%; the greatest reduction occurred when alum was used in conjunction with HAP corn and phytase. This study demonstrates the potential added benefits of using dietary modification in conjunction with manure amendments in poultry operations. Integrators and producers should consider the use of phytase, HAP corn, and alum to reduce potential P losses associated with poultry litter application to pastures.     

Runoff losses of sediment and phosphorus from no-till and cultivated soils receiving dairy manure

Managing manure in no-till systems is a water quality concern because surface application of manure can enrich runoff with dissolved phosphorus (P), and incorporation by tillage increases particulate P loss. This study compared runoff from well-drained and somewhat poorly drained soils under corn (Zea mays, L.) production that had been in no-till for more than 10 yr. Dairy cattle (Bos taurus L.) manure was broadcast into a fall planted cover crop before no-till corn planting or incorporated by chisel/disk tillage in the absence of a cover crop. Rainfall simulations (60 mm h(-1)) were performed after planting, mid-season, and post-harvest in 2007 and 2008. In both years and on both soils, no-till yielded significantly less sediment than did chisel/disking. Relative effects of tillage on runoff and P loss differed with soil. On the well-drained soil, runoff depths from no-till were much lower than with chisel/disking, producing significantly lower total P loads (22-50% less). On the somewhat poorly drained soil, there was little to no reduction in runoff depth with no-till, and total P loads were significantly greater than with chisel/disking (40-47% greater). Particulate P losses outweighed dissolved P losses as the major concern on the well-drained soil, whereas dissolved P from surface applied manure was more important on the somewhat poorly drained soil. This study confirms the benefit of no-till to erosion and total P runoff control on well-drained soils but highlights trade-offs in no-till management on somewhat poorly drained soils where the absence of manure incorporation can exacerbate total P losses.     

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.     

Runoff phosphorus losses as related to phosphorus source, application method, and application rate on a Piedmont soil

Land application of animal manures and fertilizers has resulted in an increased potential for excessive P losses in runoff to nutrient-sensitive surface waters. The purpose of this research was to measure P losses in runoff from a bare Piedmont soil in the southeastern United States receiving broiler litter or inorganic P fertilizer either incorporated or surface-applied at varying P application rates (inorganic P, 0-110 kg P ha(-1); broiler litter, 0-82 kg P ha(-1)). Rainfall simulation was applied at a rate of 76 mm h(-1). Runoff samples were collected at 5-min intervals for 30 min and analyzed for reactive phosphorus (RP), algal-available phosphorus (AAP), and total phosphorus (TP). Incorporation of both P sources resulted in P losses not significantly different than the unfertilized control at all application rates. Incorporation of broiler litter decreased flow-weighted concentration of RP in runoff by 97% and mass loss of TP in runoff by 88% compared with surface application. Surface application of broiler litter resulted in runoff containing between 2.3 and 21.8 mg RP L(-1) for application rates of 8 to 82 kg P ha(-1), respectively. Mass loss of TP in runoff from surface-applied broiler litter ranged from 1.3 to 8.5 kg P ha(-1) over the same application rates. Flow-weighted concentrations of RP and mass losses of TP in runoff were not related to application rate when inorganic P fertilizer was applied to the soil surface. Results for this study can be used by P loss assessment tools to fine-tune P source, application rate, and application method site factors, and to estimate extreme-case P loss from cropland receiving broiler litter and inorganic P fertilizers.     

Management practice effects on phosphorus losses in runoff in corn production systems

Phosphorus losses in runoff from cropland can contribute to nonpoint-source pollution of surface waters. Management practices in corn (Zea mays L.) production systems may influence P losses. Field experiments with treatments including differing soil test P levels, tillage and manure application combinations, and manure and biosolids application histories were used to assess these management practice effects on P losses. Runoff from simulated rainfall (76 mm h(-1)) was collected from 0.83-m2 areas for 1 h after rainfall initiation and analyzed for dissolved reactive P (DRP), bioavailable P, total P (TP), and sediment. In no-till corn, both DRP concentration and load increased as Bray P1 soil test (STP) increased from 8 to 62 mg kg(-1). A 5-yr history of manure or biosolids application greatly increased STP and DRP concentrations in runoff. The 5-yr manure treatment had higher DRP concentration but lower DRP load than the 5-yr biosolids treatment, probably due to residue accumulation and lower runoff in the manure treatment. Studies of tillage and manure application effects on P losses showed that tillage to incorporate manure generally lowered runoff DRP concentration but increased TP concentration and loads due to increased sediment loss. Management practices have a major influence on P losses in runoff in corn production systems that may overshadow the effects of STP alone. Results from this work, showing that some practices may have opposite effects on DRP vs. TP losses, emphasize the need to design management recommendations to minimize losses of those P forms with the greatest pollution potential.     

Evaluating slurry broadcasting and injection to ley for phosphorus losses and fecal microorganisms in surface runoff

The recent growth in the size of dairy cattle farms and the concentration of farms into smaller areas in Finland may increase local water pollution due to increased manure production and slurry application to grass. Therefore, a field study was conducted to monitor losses of total phosphorus (TP), dissolved reactive phosphorus (DRP), and fecal microorganisms in surface runoff from a perennial ley. Cattle slurry was added once a year in June 1996-1997 (Study I) and biannually in June and October 1998-2000 (Study II). The slurry was surface broadcast or injected into the clay soil. The field had a slope of 0.9 to 1.7%. Mineral fertilizer was applied on control plots. Biannual slurry broadcasting increased DRP (p < 0.001) and TP losses (p < 0.001) and numbers of fecal microorganisms in surface runoff waters. The highest losses of TP (2.7 kg ha(-1) yr(-1)) and DRP (2.2 kg ha(-1) yr(-1)) and the highest numbers of fecal coliforms (880 colony-forming units [CFU] per 100 mL) and somatic coliphages (2700 plaque-forming units [PFU] per 100 mL) were measured after broadcasting slurry to wet soil followed by rainfall in fall 1998. Injection reduced the TP and DRP losses in surface runoff by 79 and 86%, respectively, compared with broadcasting (17 Oct. 1998-27 Oct. 1999). Corresponding numbers for fecal coliforms were 350 CFU (100 mL)(-1) and for somatic coliphages were 110 PFU (100 mL)(-1) in surface runoff after injection in October 1998. Slurry injection should be favored when spreading slurry amendments to grassland to avoid losses of P and fecal microorganisms in runoff to surface waters.     

Nitrate losses, nutrients and heavy metal accumulation from substrates assembled for urban soils reconstruction

Urban soils may suffer mild to severe degradation as a result of physical and chemical alterations. To reconstruct these soils, a new upper horizon must be created, usually through the application of organic matter, one source of which is biosolids. Different soil mixtures were evaluated with regard to loss of nitrates in percolates and the uptake and incorporation of nutrients and heavy metals into plant tissues. The experiment was conducted in trays; treatments were mixtures of biosolids and a coarse material (e.g., sand or pine wood sawdust), combined in different proportions. Randomized trays were seeded with a mix of tall fescue (Festuca arundinacea L.) and perennial ryegrass (Lolium perenne L.). Plant biomass was quantified. Nitrates in percolates were measured, as were nutrients and heavy metals in mixtures and plant tissues. Plants accumulated substantially more N, and biomass was 40% higher, in the treatments with higher levels of biosolids. The same treatments released more nitrogen and resulted in higher percolate nitrate levels. Plants had normal concentrations of all nutrients, except nitrogen, which was low. Heavy metal concentrations were not significantly different among treatments. Based on the analysis of these data, the proportion of biosolids appears to be the most important factor affecting the quality of reconstructed soil and the rate of improvement. The type of coarse material used did not significantly affect the outcome.     

Surface applied water treatment residuals affect bioavailable phosphorus losses in Florida sands

Water treatment residuals (WTR) can reduce runoff P loss and surface co-application of P-sources and WTR is a practical way of land applying the residuals. In a rainfall simulation study, we evaluated the effects of surface co-applied P-sources and an Al-WTR on runoff and leacheate bioavailable P (BAP) losses from a Florida sand. Four P-sources, namely poultry manure, Boca Raton biosolids (high water-soluble P), Pompano biosolids (moderate water-soluble P), and triple super phosphate (TSP) were surface applied at 56 and 224kgPha(-1) (by weight) to represent low and high soil P loads typical of P- and N-based amendments rates. The treatments further received surface applied WTR at 0 or 10gWTRkg(-1) soil. BAP loss masses were greater in leachate (16.4-536mg) than in runoff (0.91-46mg), but were reduced in runoff and leachate by surface applied WTR. Masses of total BAP lost in the presence of surface applied WTR were less than approximately 75% of BAP losses in the absence of WTR. Total BAP losses from each of the organic sources applied at N-based rates were not greater than P loss from TSP applied at a P-based rate. The BAP loss at the N-based rate of moderate water-soluble P-source (Pompano biosolids) was not greater than BAP losses at the P-based rates of other organic sources tested. The hazards of excess P from applying organic P-sources at N-based rates are not greater than observed at P-based rates of mineral fertilizer. Results suggest that management of the environmental P hazards associated with N-based rates of organic materials in Florida sands is possible by either applying P-sources with WTR or using a moderate water-soluble P-source.