Water-extractable P Research Articles

Winter Phosphorus Release from Cover Crops and Linkages with Runoff Chemistry.

Cover crops (CC) have both agronomic and environmental benefits but also have the potential to increase losses of dissolved reactive P after freeze-thaw cycles (FTC). This field study, conducted over one nongrowing season (NGS) in Ontario, Canada, characterized water-extractable P (WEP) content in different CC species and compared observed changes in plant WEP content with changes in P content in soil, surface runoff, and shallow groundwater (5-25 cm). Five plots (0.4 ha) of cereal rye ( L.), oilseed radish ( L. var. Metzg Stokes), oat ( L.), and hairy vetch ( Roth) were established after winter wheat ( L.) harvest. Throughout the NGS (October-April), CC shoot tissues and surface soil were routinely sampled for WEP analyses, and groundwater and runoff water samples were collected after rain and snowmelt. Responses to FTC varied among CC species, with P released from frost-intolerant species but not frost-tolerant species. Although CC released P, the top 5 cm of soil contained greater WEP than plants at all times, and the changing WEP content in CC over the NGS was not reflected in soil or water P concentrations. These results suggest that the degree of frost exposure should be considered in the selection of CC species in cold regions; however, in temperate regions with snow cover that insulates the soil surface from heavy frost, P release from vegetation may not lead to increased P loss in runoff.

Impacts of Cover Crops and Crop Residues on Phosphorus Losses in Cold Climates: A Review.

The use of cover crops and crop residues is a common strategy to mitigate sediment and nutrient losses from land to water. In cold climates, elevated dissolved P losses can occur associated with freeze-thaw of plant materials. Here, we review the impacts of cover crops and crop residues on dissolved P and total P loss in cold climates across ∼41 studies, exploring linkages between water-extractable P (WEP) in plant materials and P loss in surface runoff and subsurface drainage. Water-extractable P concentrations are influenced by plant type and freezing regimes. For example, WEP was greater in brassica cover crops than in non-brassicas, and increased with repeated freeze-thaw cycles. However, total P losses in surface runoff and subsurface drainage from cropped fields under cold climates were much lower than plant WEP, owing to retention of 45 to >99% of released P by soil. In cold climatic regions, cover crops and crop residues generally prevented soil erosion and loss of particle-bound P during nongrowing seasons in erodible landscapes but tended to elevate dissolved P loss in nonerodible soils. Their impact on total P loss was inconsistent across studies and complicated by soil, climate, and management factors. More research is needed to understand interactions between these factors and plant type that influence P loss, and to improve the assessment of crop contributions to P loss in field settings in cold climates. Further, tradeoffs between P loss and the control of sediment loss and N leaching by plants should be acknowledged.

Phosphorus sorption characteristics and related properties in urban soils in southeast China

Phosphorus (P) is usually enriched in urban soils but the environmental consequences of this P enrichment are not well understood. The objective of this study was to investigate P sorption characteristics as a measure of potential P loss from urban soils due to P enrichment via runoff and leaching. We collected soil samples at 0–5 and 5–15 cm soil depths from urban park areas in Nanchang, China, a rapidly expanding city with low P contents in its natural soils. Soil P sorption indices were characterized by a multiple-point isotherm batch experiment. The 0–5 cm layer had lower Langmuir P sorption maximum (Smax) than the 5–15 cm layer, probably because of its lower amorphous Al oxide (Alox) content and higher soil organic carbon (SOC) content. Stepwise multiple regression showed that the combination of Alox and SOC were the two most important soil properties related to Smax of the studied soils. A two-piece segmented linear regression was fitted to the relationships between labile P fractions (i.e., water extractable-P and anion exchange resin-extractable P) and binding energies (k) and the change point values were identified for k below which labile P decreased linearly. Soils below the change point had greater contents of SOC and exchangeable Ca and Mg and higher pH than those above the change point. These results suggest that parent materials played a major role in regulating P sorption capacities of the urban soils, particularly for the soils in urban green spaces. However, the enrichment of Ca and Mg derived from dissolution of calcareous materials in urban areas could significantly influence P bonding strength and saturation ratio of urban soils.

Phosphorus release from shoots of Phleum pretense L. after repeated freeze-thaw cycles and harvests

Vegetated buffer strips (VBS) are a common best management practice used in agricultural landscapes because of their possible effectiveness to reduce loadings of sediments and nutrients, including phosphorus (P), to adjacent surface waters. In cold climates, buffer vegetation is prone to numerous freeze-thaw cycles (FTCs). The freezing may cause plant cells to lyse and release P, which would reduce buffer effectiveness. Greenhouse experiments were conducted to investigate if P fertilization of soils growing timothy grass (Phleum pretense L.) and the number of FTCs affect the type and concentrations of P released from the above-ground biomass. Timothy grass was grown in a greenhouse with and without P fertilizer application. Above-ground biomass was harvested twice: after 65 days of growth and again 37 days later, and these samples were subjected to zero, three, or six FTCs. Water extractions of the above-ground biomass were analysed for water extractable P (WEP) and alkali P with an oxidative agent (P-OH). Above-ground biomass was additionally analysed for nitric acid digested P (P-HNO3). Results from both harvests showed no significant difference in WEP or P-OH concentrations between soil fertilizer treatments, but there was a significant difference in WEP concentrations with increased FTCs. Combined data from both harvests showed that after six FTCs, 65–100% of P-OH was released as WEP, and 19–55% of P-HNO3 was released as WEP. These results indicate that timothy grass undergoing multiple FTCs can become a source of highly bioavailable P and that, as previous work has showed, harvesting vegetation is a potentially useful management practice in order to reduce P losses to surface waters.

Phosphorus leaching through column study to evaluate P movement and vertical distribution in black, red and alluvial soils of India

Abstract Phosphorus leaching from soils is a major environmental concern leading to eutrophication of water bodies. Three different soil types namely black, red and alluvial soils from Nagpur, Raipur and Kanpur were taken for the study. Soil column leaching experiment was conducted during 2014–15 with different levels of P (0, 50, 100, 150, 300, 600 mg L−1) application with the objective to evaluate P buildup and vertical distribution in different soil types. Soluble reactive P (RP) content in three soils increased slowly with P application rates and decreased with increase in number of leaching events. Total P in leachate followed the similar trend. Phosphorus leaching mainly occurred during the initial seven leaching events accounting to 50–60% of total P leached over whole period. Among the various soil types RP content in leachate followed the order alluvial (0.01–0.23 mg l−1) followed by red (0.01–0.17 mg l−1), and black (0–0.1 mg l−1) soil. Soluble reactive P (RP) accounting for 75–80% leaching mainly during initial 10 leaching events with alluvial soil leached highest P followed by red and black soils. Vertical distribution and movement of Olsen and bray P content in all the soils were higher beneath 0–10 cm depth and increased with P application and decreased in untreated column section. Environmental test like water extractable P (WEP) and CaCl2 P content were higher in alluvial soil, suggesting the greater potential of P leaching loss under chemical P fertilization. The result of the study can further be extended at field level for efficient P management in various soil types and thus could quantify the contribution of P from different sources to P leaching in agricultural land.

Water-Extractable Phosphorus in Animal Manure and Manure Compost: Quantities, Characteristics, and Temporal Changes.

Water-extractable P (WEP) in manure and manure compost is widely used as an indicator of P release to runoff from manure and compost that are land applied. A survey of 600 manures and composts was conducted to assess trends in WEP (dry weight equivalent) related to manure and compost types from sources in the Mid-Atlantic region. Manure and compost WEP ranged from 0.2 to 20.8 g kg. Mean WEP was highest in turkey and swine manures (manure: 4.1-5.6 g kg; no composts tested), followed by layer and broiler chicken manures (manure: 3.0-3.5 g kg; compost: 4.6-5.1 g kg), cattle manure (dairy and beef manure: 2.1-2.8 g kg; compost: 1.1-2.7 g kg), and horse manure (manure: 2.7 g kg; compost: 1.9 g kg). Across all manures and composts, WEP was negatively correlated with manure dry matter content ( = 0.42, < 0.001). Moreover, WEP was strongly correlated ( = 0.66, < 0.001) to degree of P saturation expressed as a molar ratio of total P to total metals (Ca, Mg, Fe, Al, and Mn). Although WEP levels of beef, broiler chicken, and turkey manures from this survey are similar to those from a decade ago, WEP is now significantly lower for dairy (30%, < 0.001), swine (46%, < 0.001), and layer chickens (39%, < 0.05). Lower WEP resulted from decreasing total P and/or increasing P sorption capacity, combined with increasing dry matter content. Results highlight the potential to use degree of P saturation to predict WEP and suggest an opportunity to reduce WEP by managing manure handling, storage, and chemistry.

Nutrient Release from Living and Terminated Cover Crops Under Variable Freeze–Thaw Cycles

Core Ideas Light frosts did not increase phosphorus release from cover crops.Heavy frosts released more water‐extractable phosphorus than light frosts.Herbicide induced termination increased phosphorus and ammonium losses.Frost tolerant species released less phosphorus than frost‐intolerant species.Cover crops remain a suitable management practice in temperate regions. Cover crops (CC) are planted into fields during the non‐growing season as a best management practice (BMP) for agronomic and environmental benefits. However, freeze–thaw cycles (FTC) may increase the availability of water extractable P (WEP) from damaged plant tissues, leading some to question their efficacy as a nutrient BMP due to their potential to release P during snowmelt. The objectives of this study were to experimentally determine the influence of: (1) FTC magnitude (4°C, −4 to 4°C, –18 to 4°C, and –18 to 10°C), (2) CC species [cereal rye (Secale cereale L.), oilseed radish (Raphanus sativus L. var. oleoferus Metzg Stokes), red clover (Trifolium pratense L.), oat (Avena sativa L.), and hairy vetch (Vicia villosa Roth)], and (3) termination using herbicide on the magnitude of WEP, NH4+, and NO3− release. Shoot tissue clippings underwent five FTC followed by extraction. Large magnitude FTC from –18 to 4 and –18 to 10°C (heavy frost) elevated WEP release, whereas the −4 to 4°C (light frost) treatment did not. Responses varied with plant type, where frost‐intolerant species released more WEP than frost‐tolerant species. In contrast, NH4+, and NO3− release did not increase following FTC. Termination elevated WEP and NH4+ release across all temperature treatments. The use of CC as a nutrient BMP should be used with caution in some regions, but in areas with mild winter climates, growing frost tolerant species without termination may reduce the risk of P leaching from vegetation in winter and early spring.

Use of Penicillium bilaiae to improve phosphorus bioavailability of thermally treated sewage sludge – A potential novel type biofertiliser

This study explored the potential of different phosphorus (P)-rich sewage sludge biochars and ashes to be colonised and be used as a P sources for the phosphate-solubilising fungus, Penicillium bilaiae. P. bilaiae was inoculated on five different biochars and ashes supplemented with nutrient solution. Fungal colonisation, pH and water-extractable P (WEP) in the materials were determined after incubation. P. bilaiae colonised at similar rates on all materials tested, but colonisation was affected by glucose level, pH and total N content in the material. A pH decline, accompanied by an increase in WEP concentration, was observed in three materials. The amount of soluble P was significantly greater at the high glucose level and showed the largest relative increase in incineration ash (>100-fold after 10 days). The results show a potential to use P-solubilising microorganisms to solubilise P from thermally converted sewage sludge, but the approach has to be further investigated regarding its effects in a soil/plant system.

Mobility of phosphorus from organic and inorganic source materials in a sandy soil

PurposeThe long-term use of manure as a source of nutrients can promote phosphorus (P) leaching, especially in sandy soils. The aim was to evaluate P mobility from organic and mineral sources in columns, linked with the Dystric Xeropsamments adsorption characteristics with long-term organic fertilization regime.MethodsThe mineral, chemical, and physical properties of the samples were characterized, including Langmuir adsorption and desorption kinetics. The P mobility was determined in one leaching experiment, in 20 cm soil columns. The topsoil (0–10 cm) layer was treated with organic (cattle, swine, goat, and hen manure) and inorganic fertilizers. Leaching was corresponding to 10 pore volumes (PV), 1 PV day−1. Aliquots of the leachate were collected to analyze P concentrations. After the leaching, the columns were sliced into 5-cm sections for the analysis of water-extractable P (WEP).ResultsThe mineral source obtained higher leaching of P and between the organic sources the bovine and swine manure. The latter were the ones that had higher value of Pw in the soil after the leaching. Due to the increase of the adsorption capacity of P with depth, there was a reduction in the mobility of P, and an unbalance of Pw in the soil was found.ConclusionsThe mobility of P depends on the concentration of the soluble P soil or added material; moreover, the presence of Fe and Al oxides, even in small amounts, reduces the mobility of P in sandy soil.

Organic Phosphorus Can Make an Important Contribution to Phosphorus Loss from Riparian Buffers

Core Ideas Forested and vegetative buffers can retain P runoff from adjacent fields. High concentrations of molybdate unreactive P were detected in soil water extracts. With time, these buffer soils can be a source of soluble inorganic and organic P. High microbial activity in buffer soils suggests biologically mediated P release. Vegetative buffer strips (VBS) and managed or unmanaged riparian zones between the edge of field and receiving watercourse are widely adopted conservation practices aimed at reducing nonpoint nutrient pollution. However, their effectiveness at decreasing phosphorus (P) loss has been mixed. This study investigated the effectiveness of a VBS and a forested riparian zone (FRZ) in decreasing P loss from pasture soils receiving swine manure and aimed to determine the potential factors controlling P release, using water extractable P (WEP) as a proxy for P loss. The inorganic WEP concentrations were significantly greater in the fertilized pasture zone soils than the VBS or FRZ soils. However, there was no significant difference between the field and riparian soils for total WEP due to increased contribution from organic WEP in these soils. Degree of P saturation, which is a function of soil test P, was a good predictor of inorganic WEP, but not organic WEP, where the variation in concentrations was better explained by variables involved in biotic P release.

Assessing Intra-Event Phosphorus Dynamics in Drainage Water Using Phosphate Stable Oxygen Isotopes

Abstract. Quantifying fluxes and pathways of dissolved reactive phosphorus (DRP) in tile-drained landscapes has been hampered by a lack of measurements that are sensitive to P fate and transport processes. One potential tool to help understand these dynamics is the oxygen isotope signature of phosphate (d18OPO4); however, its potential benefits and limitations are not well understood for intra-event dynamics at the field scale. The objectives of this study were to quantify intra-event variability of d18OPO4 signatures in tile drainage water and assess the efficacy of d18OPO4 to elucidate mechanisms and flow pathways controlling DRP transport to tile drains. We collected water samples during a summer storm event from a subsurface (tile)-drained field located in west-central Ohio and analyzed for d18OPO4 of DRP. Supplementary water quality measurements, hydrologic modeling, and soil temperature data were used to help understand intra-event d18OPO4 dynamics. Results of the soil extraction analysis from our study site highlight that the soil water-extractable P (WEP) pool was not in equilibrium with long-term, temperature-dependent water isotope values. This result suggests that P-rich soils may, at least partially, retain their original source signature, which has significant implications for identifying hotspots of P delivery in watershed-scale applications. Results of the storm event analysis highlight that equilibration of leached DRP in soil water creates a gradient between isotopic compositions of pre-event shallow subsurface sources, pre-event deep subsurface sources, and the WEP tied up in surface soils. The current study represents the first intra-event analysis of d18OPO4 and highlights the potential for phosphate oxygen isotopes as a novel tool to improve understanding of P fate and transport in artificially drained agroecosystems. Keywords: Agriculture, Edge-of-field, Macropores, Phosphate oxygen isotopes, Tile-drainage.

Plant availability of phosphorus from dewatered sewage sludge, untreated incineration ashes, and other products recovered from a wastewater treatment system

AbstractThe objective of the present study was to evaluate the plant phosphorus (P) availability of products derived from new P‐recovery technologies deployed in wastewater treatment systems against sewage sludge and untreated sewage sludge ashes. Eight P sources were evaluated in a six‐week pot experiment with spring barley (Hordeum vulgare L.) and a soil incubation experiment with anaerobically digested and dewatered sewage sludge (Sludge), sewage sludge ash (Ash), thermochemically treated sewage sludge ash (TrAsh), struvite (Struv), concentrate (Conc), and centrifuged concentrate (Prec) from evaporated reject water, with triple super phosphate (TSP), and composted organic household waste (Comp) as references. All sludge‐related materials except struvite came from the same wastewater treatment plant in Denmark. The apparent plant P use efficiency (PUE) of the treatments in the pot experiments was in the following order: Prec (17.0%) &gt; TSP (12.8%) ≥ Conc (12.7%) &gt; Sludge (8.8%) ≥ TrAsh (6.9%) ≥ Struv (6.0%) ≥ Comp (5.8%) &gt; Ash (3.4%). The water‐extractable P (WEP) in the incubation experiment largely supported this order and there was a strong correlation between WEP in the incubation experiment and plant P uptake in the pot experiment. Overall, the results of this study demonstrate that it should not automatically be assumed that products recovered with new treatment technologies for P recovery are more effective P fertilizers than the sewage sludge from which they originate. Furthermore, these results indicate that the measurement of water‐extractable P after soil incubation could be a suitable proxy for plant P availability.

Effects of thermal drying on phosphorus availability from iron‐precipitated sewage sludge

AbstractThermal drying of sewage sludge implies sanitation and improves practical handling options of the sludge prior to land application. However, it may also affect its value as a fertilizer. The objective of this study was to assess whether thermal drying of sewage sludge, as well as drying temperature, affects plant P availability after application to soil. The experiment included dewatered sewage sludge (20% DM) and thermally dried sewage sludge (95% DM) collected at a Danish wastewater treatment plant, as well as laboratory oven‐dried (70, 130, 190, and 250°C; DM &gt; 95%) subsamples of the dewatered sludge, and a triple superphosphate as a reference. Plant P availability was studied in a 197 d soil incubation experiment, with sampling for Diffusive Gradients in Thin films (DGT) and water extractable P (WEP) analyses over time, and in a pot experiment with spring barley (Hordeum vulgare L.). In both experiments, thermal drying reduced P availability, as shown by 37 and 23% lower DGT and WEP values, respectively, and a 16% lower P uptake by barley in the pot experiment. The specific drying temperature did not appear to have much effect. Overall, our results suggest that thermal drying of iron‐precipitated sewage sludge is not an optimal treatment option if the aim is to optimize plant P availability.

Potential phosphorus mobilization from above-soil winter vegetation assessed from laboratory water extractions following freeze–thaw cycles

Maintaining crop residue or cover crops on fields during winter is a recommended beneficial management practice (BMP). However, losses of dissolved reactive phosphorus (DRP) to runoff have been attributed to vegetation following freeze–thaw cycles (FTC). Using a factorial design in the laboratory, this study investigated the potential influence of four FTC types at −4 to +4°C (frozen, frozen and thawed 1×, frozen and thawed 5×, frozen and thawed 5× with extraction after each thaw) and one control (never frozen) on DRP loss from the residue of Triticum aestivum (winter wheat) and from two cover crops, Trifolium pretense (red clover) and Avena sativa (oat). DRP losses were measured using three different water extraction techniques: a traditional laboratory determination of water extractable P (WEP), a modified water extraction intended to simulate a rainfall event, and a modified water extraction intended to simulate surface ponding. Both cover crops released more DRP than winter wheat residue did under all treatments, suggesting that winter wheat residues pose little risk for DRP release during the non-growing season (NGS). Of the two cover crops studied, oat was more sensitive to FTC and may therefore pose a greater risk of late autumn/winter DRP loss in comparison to red clover, which is often terminated in early fall. Water extraction technique was also found to be important, as simulated surface ponding extracted more DRP than simulated rainfall did for all three plant types. These results suggest that both cover crop species and placement in the landscape can be optimized to reduce P release from above-ground vegetation in winter. The use of cover crops in sections of fields that are prone to flooding following large events such as snowmelt should be avoided. Field studies are needed to further examine the rates and timing of potential and actual losses of DRP from above-ground vegetation in winter.

Assessment risk of phosphorus leaching from calcareous soils using soil test phosphorus

Accurate estimation of phosphorus (P) leaching is important because excess P may reduce surface and ground water quality. Little attention has been paid to estimate P leaching from soil tests in calcareous soils. The relation between different soil tests P (STP), P sorption index (PSI) and degree of P saturation (DPS) and leaching of P were examined for assessing the risk of P loss from calcareous soils. Columns leaching repacked with native soils were leached with either distilled water or 10 mM CaCl2 solutions, separately. Four leaching events were performed at four days, and 28.7 mm of distilled water or 10 mM CaCl2 solutions was applied at each leaching events. Compared with distilled water, CaCl2 had a small ability to solubilize P from soils. Concentration of P in leachate in both leaching solutions was exceeding 0.1 mg l−1 associated with eutrophication. Cumulative P leached P was ranged from 0.17 to 18.59 mg P kg−1 and 0.21–8.16 mg P kg−1, when distilled water and 10 mM CaCl2 solutions were applied, respectively and it was higher in sandy clay loam soils compared with clay soils. Among evaluated environmental soil P tests, PCaCl2-3h (P extracted by 10 mM CaCl2 for 3 h), PCaCl2-1h (P extracted by 10 mM CaCl2 for 1 h) were more accurate than other soil P tests for predicting P concentration in the leachates in both leaching solutions and accounting for 83% and 72% of variation of P concentration, respectively. The water extractable P (WEP) (r = 0.771) and Olsen-P (POls)(r = 0.739) were significantly related to the leached P concentration using distilled water solution in a split line model, with a change point of 27.4 mg P kg−1 and 61.5 mg P kg−1, respectively. Various DPS were calculated and related to the leached P concentration. Based on P extracted by Mehlich-3 (PM3) and HCl (PHCl) and PSI, the change point of the relationship between leached P concentration and DPSM3-3 (PM3(PM3+PSI)×100) and DPSHCl-2 (PHCl(PHCl+PSI)×100) for both leaching solutions was approximately the same, thus a mean value of 49% for DPSM3-3 and 73% for DPSHCl-2 was obtained. Soils were grouped into four categories of increasing P leaching potential based on WEP, POls, and DPSM3-3. The results indicated that 8.00%–25.50% of the soil grouped in no risk category whereas 8.00%–13.70% of the soils fell into the high risk category.

Soil Testing Indices for Phosphorus Leaching in Selected Vertisol and Inceptisol of India

Little information is available on P leaching potential of Indian soils. The degree of P saturation (DPS) relating the extractable P to the P sorption capacity governed by soil constituents (Al, Fe, Ca) has been widely used to predict the potential to adsorb or release P. The aim of the present study was to determine DPS in two major cultivable soils of India and to evaluate routine agronomic and environmental soil test P as indicators of P leaching through column leaching experiment with different levels of P fertilization. The results of the study showed the variation in leachate reactive P (RP) content which was significantly affected by P rates and increased significantly above threshold DPS values. For vertisol and inceptisol, threshold DPS Ol was 25.07 and 12.43%, DPSA.O. was 7.87 and 3.76%, and DPSM3 was 18.66 and 6.79%, respectively. The RP concentration showed a strong correlation with DPS and environmental soil test like 0.01 M CaCl2 and water extractable P (WEP) suggesting that soil 0.01 M CaCl2 and WEP can be used as surrogate for RP concentration for risk of P loss via leaching. Thus, the use of Olsen P, Mehlich 3 and ammonium oxalate P for calculating DPS provides reliable criteria for identifying soils having high risk of P loss to surface water bodies and works well in all soil types.

Degree of phosphorus saturation threshold for minimizing P losses by runoff in cropland soils of Southern Brazil

Abstract The objective of this work was to assess the risk of phosphorus losses by runoff through an index based on the degree of P saturation (DPS), in cropland soils of Southern Brazil. Sixty-five highly representative cropland soils from the region were evaluated. Three labile P forms were measured (Mehlich-1, Mehlich-3, and ammonium oxalate), and four P sorption indexes were tested (phosphorus single sorption point and Fe+Al determined with the three extractors). Water-extractable P (WEP) was used as an index of P susceptibility to losses by surface runoff. The DPS was determined from the ratio between labile P and each sorption index. DPS values obtained from the ratio between Mehlich-1 P and the single P sorption point ranged from 1 to 25%, whereas those from Mehlich-1 P and Fe+Al (ammonium oxalate) ranged from 1 to 55%. All DPS types were highly correlated with WEP. From a practical stand point, the DPS obtained with both P and Fe+Al extracted with Mehlich-1 can be used to estimate the risk of P losses by runoff in soils of Southern Brazil.

Determination of Biosolids Phosphorus Solubility and Its Relationship to Wastewater Treatment.

In North Carolina (NC), biosolids land application rates governed by crop nitrogen (N) requirements typically surpass crop phosphorus (P) needs, increasing surface water pollution potential. The NC Department of Environmental Quality (NCDEQ) is considering P-based biosolids application guidelines for some nutrient-impaired watersheds using the P Loss Assessment Tool (PLAT), but important biosolids information is lacking: total P (TP), water-extractable P (WEP), and percent water-extractable P (PWEP). In each of three seasons, we sampled 28 biosolids from 26 participating water resource recovery facilities (WRRFs) and analyzed for TP, WEP, and percent dry matter (DM), from which PWEP and nonsoluble P were calculated. Based on descriptive statistics and an online survey of treatment processes, biosolids were divided into Class A-alkaline, Class A-heat, Class B-slurry, and Class B-cake. The average TP in Class A alkaline stabilized biosolids was more than five times less than the average of the other biosolids, 5.0 vs. 26.6 g/kg, respectively. Averaged over biosolids, WEP and PWEP were 1.4 g/kg and 5.0%, respectively. Stabilization processes appeared to reduce WEP substantially, so biosolids potential soluble-P loss is low. Our data will allow PLAT to be used for biosolids P-loss risk assessments.

Predicting Phosphorus Release from Anaerobic, Alkaline, Flooded Soils.

Anaerobic conditions induced by prolonged flooding often lead to an enhanced release of phosphorus (P) to floodwater; however, this effect is not consistent across soils. This study aimed to develop an index to predict P release potential from alkaline soils under simulated flooded conditions. Twelve unamended or manure-amended surface soils from Manitoba were analyzed for basic soil properties, Olsen P (Ols-P), Mehlich-3 extractable total P (M3P), Mehlich-3 extractable molybdate-reactive P (M3P), water extractable P (WEP), soil P fractions, single-point P sorption capacity (P), and Mehlich-3 extractable Ca (M3Ca), and Mg (M3Mg). Degree of P saturation (DPS) was calculated using Ols-P, M3P or M3P as the intensity factor, and an estimated adsorption maximum based on either P or M3Ca + M3Mg as the capacity factor. To develop the model, we used the previously reported floodwater dissolved reactive P (DRP) concentration changes during 8 wk of flooding for the same unamended and manured soils. Relative changes in floodwater DRP concentration (DRP), calculated as the ratio of maximum to initial DRP concentration, ranged from 2 to 15 across ten of the soils, but were ≤1.5 in the two soils with the greatest clay content. Partial least squares analysis indicated that DPS3 calculated using M3P as the intensity factor and (2 × P) + M3P as the capacity factor with clay percentage can effectively predict DRP ( = 0.74). Results suggest that P release from a soil to floodwater may be predicted using simple and easily measurable soil properties measured before flooding, but validation with more soils is needed.

Development of a New Manure Amendment for Reducing Ammonia Volatilization and Phosphorus Runoff from Poultry Litter.

Treating poultry litter with alum is a best management practice that reduces phosphorus (P) runoff and ammonia (NH) emissions. However, alum prices have increased substantially during the past decade. The goal of this research was to develop inexpensive manure amendments that are as effective as alum in reducing NH volatilization and P runoff. Sixteen amendments were developed using mixtures of alum mud, bauxite ore, sulfuric acid, liquid alum, and water. Alum mud is the residual left over from alum manufacture when produced by reacting bauxite with sulfuric acid. A laboratory NH volatilization study was conducted using 11 treatments: untreated poultry litter, poultry litter treated with liquid or dry alum, or eight new mixtures. All of the litter amendments tested resulted in significantly lower NH volatilization than untreated litter. Dry and liquid alum reduced NH losses by 86 and 75%, respectively. The eight new litter amendments reduced NH losses from 62 to 73% compared with untreated litter, which was not significantly different from liquid alum; the three most effective mixtures were not significantly different from dry alum. Water-extractable P (WEP) was significantly reduced by all of the amendments, three of which resulted in significantly lower WEP than dry alum. The most promising new amendments were mixtures of alum mud, bauxite, and sulfuric acid. The potential impact of these amendments could be enormous because they could be produced for less than half the price of alum while being as effective in reducing NH emissions and P runoff.