Soluble P Research Articles

Using artificial neural networks to improve phosphorus indices

The phosphorus index (PI) was developed as a field-scale assessment tool used to identify critical source areas of phosphorus (P) loss, thus most US states have adopted the PI as their strategy for targeted management and conservation practices for effective mitigation of P loss from agricultural landscapes to surface waters. Recent studies have focused on evaluating and updating PI weighting factors (WFs) to ensure agreement between PI values and measured losses of P. Given that the WF of each site characteristic is usually determined individually without considering possible interactions, the goal of this study was to demonstrate how artificial neural networks (ANNs) that consider real-world interdependence can be used to determine WFs. Our specific objectives were to evaluate ANN performance for predicting soluble P (SP) concentrations in tile effluent using site characteristics as predictor variables, and to evaluate whether ANN-generated WFs can be used to improve PI performance. Garson’s algorithm was used to determine the relative importance of each site characteristic to SP loss. Data from a monitored in-field laboratory were used to evaluate the ability of a PI with no WFs (PI_NO), a PI with WFs as proposed in the original Lemunyon and Gilbert PI (PI_LG), and a PI with ANN-generated WFs (PI_ANN), to estimate SP loss potential in tile discharge. Simulation results showed that the ANN model provided reliable estimates of SP in tile effluent (<i>R²</i> = 0.99; RMSE = 0.0024). The relative importance analysis underscored the value of routine soil P testing for agronomic sufficiency for environmental stewardship, and highlighted the necessity of prioritizing both contemporary and legacy P sources during P loss risk assessments. Unlike the other PIs, PI_ANN was able to provide reasonable estimates of SP loss potential as illustrated with significant exponential relationships (<i>R²</i> = 0.60; <i>p</i> &lt; 0.001) between PI_ANN values and measured mean annual SP concentrations in tile effluent. These findings demonstrate that ANNs can be used to develop PIs with a strong correlation to measured SP.

Effects of particulate fractions on critical slope and critical rainfall intensity for runoff phosphorus from bare loessial soil

Slope and rainfall intensity are important factors affecting runoff phosphorus (P), but the dynamic mechanism of their coupled influence on P fractions in loessial bare sloping lands is not completely understood. The critical slope and critical rainfall intensity are thresholds associated with significant changes in runoff, erosion, and/or nutrient loss. In this study, 30 rainfall events (45, 60, 75, 90, 105 and 120 mm/h; 5°, 10°, 15°, 20° and 25°) were simulated to estimate the contribution of particulate P (PP) and soluble P (SP) fractions to P loss from bare loessial soils and identify the critical slope and critical rainfall intensity for different P forms and TP fluxes. The results indicate that: (i) total phosphorus (TP) and PP loss concentrations are significantly correlated to sediment yield and slope gradient, although there were close relationships between the average TP loss concentration and rainfall intensity at slopes of 20° and 25°; (ii) P in runoff from bare loessial soil consists almost entirely of the reactive PP form (96.6%), regardless of rainfall intensity and slope. The average PP fraction for different rainfall intensities increases with increasing slope, from 94.6% at a 5° slope to 98.0% at a 25° slope; and (iii) PP and TP have the same critical slope and critical rainfall intensity for bare loessial soil because of the dominance of PP in runoff P. The critical slope for the sharp increases in PP and TP was found to be in the range of 15–20° because the average losses at 20–25° increased about 1.67 times compared to 5–15°, and the critical rainfall intensity for significant increases in PP and TP was found to be in the range of 90–105 mm/h. The hydrological pathways transporting the various P fractions under storms may help to provide new insights needed to guide sloping farmland management in rainfed land agroecosystems of loess hilly regions.

Adsorption Media for the Removal of Soluble Phosphorus from Subsurface Drainage Water.

Phosphorus (P) is a valuable, nonrenewable resource in agriculture promoting crop growth. P losses through surface runoff and subsurface drainage discharge beneath the root zone is a loss of investment. P entering surface water contributes to eutrophication of freshwater environments, impacting tourism, human health, environmental safety, and property values. Soluble P (SP) from subsurface drainage is nearly all bioavailable and is a significant contributor to freshwater eutrophication. The research objective was to select phosphorus sorbing media (PSM) best suited for removing SP from subsurface drainage discharge. From the preliminary research and literature, PSM with this potential were steel furnace slag (SFS) and a nano-engineered media (NEM). The PSM were evaluated using typical subsurface drainage P concentrations in column experiments, then with an economic analysis for a study site in Michigan. Both the SFS and generalized NEM (GNEM) removed soluble reactive phosphorus from 0.50 to below 0.05 mg/L in laboratory column experiments. The most cost-effective option from the study site was the use of the SFS, then disposing it each year, costing $906/hectare/year for the case study. GNEM that was regenerated onsite had a very similar cost. The most expensive option was the use of GNEM to remove P, including regeneration at the manufacturer, costing $1641/hectare/year. This study suggests that both SFS and NEM are both suited for treating drainage discharge. The use of SFS was more economical for the study site, but each site needs to be individually considered.

Phosphorus loss index for conservation agriculture systems in Southern Brazil: A new approach to environmental risk assessment

The transport of phosphorus (P) from agricultural fields to watercourses is a worldwide concern. Development of tools to evaluate the environmental P risk is required to assist farmers and field technicians to recommend best management practices. The objective of this work was to develop and test a new approach to assess P loss vulnerability for agricultural conservationist systems in southern Brazil using easily obtainable soil attributes: cover crop residue (CCR), soil organic carbon (OC), visual evaluation of soil structure (VESS), soil test P (STP) and clay content. For that, the principal component analysis was applied, and simulated rainfall was conducted in ten agricultural fields with three replicates under Oxisol, with slopes from 7% to 12%. The database was separated into main and test groups. Significant principal components were correlated with runoff coefficient (RC), final infiltration rate (FIR), total sediment (TS), total P (TP), particulate P (PP), soluble P (SP) and bioavailable P (BAP). Component 1, interpreted as ‘increased risk of PP transport’, explained 49% of the variation with a strong dependence on CCR, OC, STP and VESS, and correlated with decreased FIR, and increased RC, TS, PP and TP. Component 2, interpreted as ‘increased risk of SP transport’, explained 21% of the variation with a strong dependence on OC, STP and clay content, and correlated with decreased TS, and increased SP and BAP. The P-index scores from components 1 and 2 were divided into four classes of P loss vulnerability (low, medium, high and very high) considering the first, median and third quartile. The Euclidean distances demonstrated a high similarity of the P-index scores obtained for the main and test groups. Therefore, the developed model can estimate the risk of P loss in agricultural fields with conservative management and moderate slope in conditions similar to the database.

Effects of drought-flood abrupt alternation on phosphorus in summer maize farmland systems

Phosphorus (P) is well known as a vital nutrient required for plant growth and a critical factor often causing eutrophication in water bodies. However, few studies have focused on the effects of drought-flood abrupt alternation (DFAA), a new type of extreme climate event, on the transformation of P in farmland systems. In this study, we, therefore, focused on DFAA effects on available P (AP) in topsoil, soluble P (SP) and total P (TP) in surface runoff, as well as plant P contents and P uptake in summer maize farmland systems. Field control experiments (sheltered under a ventilated shed with an artificial rainfall device) were conducted to simulate two levels of DFAA (i.e., light drought-light flood and moderate drought-light flood) during parts of two summer maize growing seasons (i.e., seeding-jointing stage and tasseling-grain filling stage). Results showed that DFAA increased AP concentration in topsoil, which was probably induced by the accumulation of the phyla Proteobacteria and Actinobacteria under moderate drought and by an increase in phosphate-solubilizing bacteria (PSB), especially the genera Bacillus and Bradyrhizobium. In addition, broken soil aggregates and increasing soil porosity caused by DFAA could also cause an increase of AP in topsoil. Soluble P and TP in surface runoff showed a decreasing trend with moderate drought in DFAA. The higher AP increased the root P uptake, while P in stems and leaves could be transported to fruits under DFAA with moderate drought. The results could provide some references for the study of the effects and adaptation-strategies related to extreme climate events and their effects on P in farmland systems.

Effect of phosphate releasing in activated sludge on phosphorus removal from municipal wastewater

Aluminum and ferric salts are commonly used in municipal wastewater treatment plants (WWPTs) for phosphorus (P) removal. In this study, on-site jar tests were conducted to determine the removal of different P species from the fresh samples in the presence and absence of activated sludge (AS) with different doses of alum, poly-aluminum chloride, and ferric chloride at different pH. The soluble P (SP) concentration in the samples was about 0.63mg/L. When the mixed liquor containing AS was treated with 8mg/L of Al, SP could be reduced to 0.13mg/L, while it was reduced to 0.16mg/L with only 1mg/L of Al after sedimentation removal of AS from sample. Chemical analysis determined that AS contained 59.8mg-P/g-TSS and 43.8mg-Al/g-TSS and most of the P was associated with the aluminum hydroxide. We discovered that the phosphate in the AS could readily be released from it, which was mainly responsible for ineffective removal of P to low levels in mixed liquor even with very high alum dose. This study provides new insight into the behavior and fate of P in the wastewater treatment plants that use alum to enhance P removal in the final effluent.

Phosphorus fertilization, soil stratification, and potential water quality impacts

Water quality experts have suggested that no-till induces phosphorus (P) stratification, which may exacerbate soluble P (SP) runoff from agricultural fields, contributing to eutrophication. Conservationists have been concerned about increased SP loading to Lake Erie, which has been partially blamed on adoption of no-till and the concomitant P stratification of no-till soils. This study was conducted to provide better insight into the potential link between P stratification from no-till soils and P losses via runoff with the objective of exploring P fertilization strategies on P stratification and P runoff from a corn (<i>Zea mays</i> L.)–soybean (<i>Glycine max</i> L.) rotation. Plots were established with nine treatments, including unfertilized, diammonium phosphate (DAP) applications, monoammonium phosphate (MAP) applications, surface applied, injecting fertilizer or tilling fertilizer in, and the use of cover crops. Fertilizer applications were made at 24.4 kg P ha⁻¹ (21.8 lb P ac⁻¹) every other year or at 9.6 kg P ha⁻¹ (8.7 lb P ac⁻¹) every year. Disking, which was intended to minimize P stratification, resulted in the greatest stratification, with significantly higher water SP and Mehlich 3 P in the 0 to 5 cm (0 to 2 in) soil layer compared to the other treatments. There were no differences in SP or total P (TP) runoff from rainfall simulations between fertilizer source (MAP versus DAP) or fertilizer rate (annual versus biennial). The highest SP concentrations observed were from DAP applied to cover crops at the high application rate (24.4 kg P ha⁻¹ applied every other year). This may suggest cover crops are not the ideal practice to decrease SP losses from agricultural fields. Incorporation of fertilizer reduced SP but increased erosion and could potentially increase TP loss. Injecting liquid fertilizer (polyphosphate [Poly]) at the time of planting resulted in lower SP and TP loads than surface applied fertilizers. We encourage other researchers to confirm these results at the field-to-watershed scale to ensure there are not unintended consequences of adopting this fertilization strategy. Further, fertilizer dealers, crop consultants, and farmers should be encouraged to consider liquid fertilizer applications as one option to minimize P losses.

Managing acute phosphorus loss with fertilizer source and placement

Surface water eutrophication is a pervasive global problem, with P losses from agriculture often identified as a significant contributor. This study was conducted to evaluate the implications of fertilizer source and placement on soluble P (SP) losses in runoff. Earn 0.5 CEUs in Soil &amp; Water Management by reading this article and taking the quiz at www.certifiedcropadviser.org/certifications/self‐study/797.

Managing Acute Phosphorus Loss with Fertilizer Source and Placement: Proof of Concept

Core Ideas Up to 19% of common commercial P fertilizer applied to soil can be lost via runoff. Liquid fertilizers or banding fertilizers 1 cm below the surface can reduce P loss. Inherent fertility inefficiencies must be balanced with water quality concerns. Surface water eutrophication is a pervasive global problem, with P losses from agriculture often identified as a significant contributor. This study was conducted to evaluate the implications of fertilizer source and placement on soluble P (SP) losses in runoff. Using the National P Runoff Project protocol, SP losses in runoff from eight P fertilizers broadcast on the soil surface and three P fertilizers banded 1 cm below the surface were compared with a nonfertilized control. Results showed that 16 to 19% of the surface‐applied inorganic P fertilizers was lost in one rainstorm, except for liquid polyphosphate, which lost less than 0.2% of the applied P. Banding monoammonium phosphate and poultry litter below the surface decreased SP loading by 98 and 84%, respectively. These results indicate that critical examination of current fertilizer management may be needed to diminish eutrophication while ensuring sufficient P for crop uptake.

The relationship between operational and bioavailable phosphorus fractions in effluents from advanced nutrient removal systems

Because different phosphorus (P) forms vary greatly in their bioavailability, total phosphorus concentrations are a problematic predictor of the eutrophication potential of natural surface waters and wastewater treatment facility effluents. It is currently not known which operational P characterizations (i.e., dissolved/particulate and reactive/non-reactive) best predict effluent P bioavailability. We characterized the P speciation and directly measured the bioavailability of P (BAP) using algal bioassays for 14 full-scale advanced nutrient removal wastewater treatment plants representing a wide range of P removal technologies. A strong statistical relationship was observed between the effluent total BAP (tBAP) and total reactive P (TRP) (r 2 ≈ 0.81), with a tBAP/TRP ratio of 0.61 ± 0.24, indicating that TRP can be used as a conservative surrogate predictor of tBAP. A comparison of different operational categories for phosphorus indicated that sBAP is consistently lower than both soluble P (SP) and soluble reactive P (SRP) with average ratios of 0.34 ± 0.19 and 0.62 ± 0.27, respectively. This shows a large fraction of the dissolved non-reactive P (i.e., SP−SRP), and ≥40 % of the P classified as SRP was not bioavailable. Total BAP concentrations were on average 30 % higher than soluble BAP (sBAP) concentrations, indicating that the particulate P fraction was an important component of the BAP for the tested effluents. Comparisons between different P removal technologies suggest the bioavailability, and P species composition varies with the nutrient removal process, and that in many cases, a large portion (>60 %) of the effluent P is recalcitrant to algal growth.

Phosphorus losses from monitored fields with conservation practices in the Lake Erie Basin, USA

Conservation practices are implemented on farm fields in the USA through Farm Bill programs; however, there is a need for greater verification that these practices provide environmental benefits (e.g., water quality). This study was conducted to assess the impact of Farm Bill eligible conservation practices on soluble P (SP) and total P (TP) losses from four fields that were monitored between 2004 and 2013. No-tillage doubled SP loading compared to rotational tillage (e.g., tilled only before planting corn); however, no-tillage decreased TP loading by 69 % compared to rotational tillage. Similarly, grassed waterways were shown to increase SP loads, but not TP loads. A corn–soybean–wheat–oat rotation reduced SP loads by 85 % and TP loads by 83 % compared to the standard corn–soybean rotation in the region. We can potentially attain TP water quality goals using these Farm Bill practices; however, additional strategies must be employed to meet these goals for SP.

Simulating phosphorus removal from a vertical-flow constructed wetland grown with C. alternifolius species

Vertical flow constructed wetland (VFCW) is a promising technique for removal of excess nutrients and certain pollutants from wastewaters. The aim of this study was to develop a STELLA (structural thinking, experiential learning laboratory with animation) model for estimating phosphorus (P) removal in an artificial VFCW (i.e., a substrate column with six zones) grown with umbrella papyrus (Cyperus alternifolius) species under a wetting-to-drying cycle. Simulations showed that rate of soluble P (SP) leaching was highest at the top zone (i.e., Zone 1) and decreased gradually with increasing zone number due to the adsorption, clogging, and plant uptake when the SP flowed through the zones. Our simulations further revealed that the best time for an optimal removal of SP from the wastewater was within the first week because the adsorption capacity of the substrate in the VFCW was highest at this time period. In general, the cumulative amounts of total P (TP) were in the following order: adsorption (53.3%)>leaching (13.5%)>uptake (0.49%). Adsorption of P was a major mechanism for P removal from the VFCW system. This study suggested that the STELLA model developed is a useful tool for estimating P removal from wastewater in VFCWs.

Coal fly ash enhanced planted-floating bed performance in phosphorus-contaminated water treatment

Despite the ability of fly ash (FA) to remove phosphorus (P) from water via sorption and precipitation, its use as a bedding material for planted floats has never been evaluated. This study was conducted to investigate the effects of FA on P removal and chlorophyll-a (an indicator of algal growth) reduction in P-contaminated water. Six different FA rates (0, 2.5, 5, 10, 25, and 50w/w%; codes are FA0, FA2.5, FA5, FA10, FA25, and FA50, respectively) and two rice (Oryza sativa L.) treatments (unplanted and planted) were investigated. The floats containing FA were placed on P-enriched (4mgPL−1) baths. Water samples were collected periodically and analyzed for the concentrations of total P (TP), soluble P (SP), and chlorophyll-a. Both SP and TP decreased (P<0.05) as FA rate increased, and rice planting further enhanced (P<0.05) P removal. The first-order rate constants of TP decrease in FA50 (0.143 and 0.192 day−1 for rice unplanted and planted, respectively) were two-fold greater than those (0.072 and 0.090 day−1, respectively) in FA0. Regardless of rice planting, chlorophyll-a concentration in the treatments with FA at 0–10% increased rapidly up to 0.65mgL−1 within 10 days after treatment; however, those in FA25 and FA50 were consistently lower than 0.05mgL−1, indicating suppression of algal growth, probably due to enhanced P removal by FA. However, increased salinity by FA mixing might further contribute to the suppression of algal growth.

Study on phosphorus loadings in ten natural and agricultural watersheds in subtropical region of China

Water eutrophication in subtropical regions of southern China threatens watershed health and is of major concern. However, annual phosphorus (P) loading and its dominant causes are still unclear, especially at the watershed scale. In this study, we investigated dynamic P loadings and associated factors (e.g., land use, livestock production, and runoff depth) in ten watersheds that varied in area from 9 to 5,212 ha in a hilly area of Hunan Province, China. A flowmeter was installed at the outlet of each watershed, and total P (TP) and soluble P (SP) concentrations were monitored periodically from June 2010 to October 2012. The results showed that annual P loadings (APLs) in the ten watersheds ranged from 22.8 to 247.8 kg P/km(2) and that P loss primarily occurred from April to June of each year during the main rainfall season in the study area. In addition, the average eutrophication (>0.05 mg P/L) ratio for stream waters was 86.7 % during the study period, which was indicative of a potentially serious condition for the local water environments. Annual P loadings were linearly related to livestock density (LD; R = 0.92, p < 0.01), whereas the eutrophication ratio of stream water was significantly (p < 0.05) correlated with LD (R = 0.61), percentage cropland (R = 0.71), and percentage forest cover (R = -0.68). Thus, it is concluded that the control of livestock production has the greatest potential for reducing P loadings in watersheds in this subtropical area. This will be beneficial to the amelioration and protection of local environment.

Nitrate in shallow fluctuating groundwater under sugarcane: Quantifying the lateral export quantities to surface waters

The contribution of groundwater (GW) pollutants, exported from via base-flow discharge, towards the loads in surface waters (SW) has been poorly characterised. This characterisation is needed for intensively cultivated agricultural catchments in which the base-flow discharges are substantial. In this study the flux theory based solute transport equations were used to clarify the issue of lateral transport of the nitrate in GW to SW and the contribution that it made towards the total load, in runoff plus base-flow, in the nearby creek. Water table levels under sugarcane and the concentrations of nitrate-N, ammonium-N (AN), and soluble P (SP), in six piezometers (10m deep) installed along a 1.1km transect perpendicularly crossing a creek were monitored over a period of two rainy seasons in paddocks in the northeast humid tropics of Queensland, Australia. Nitrate-N, AN, and SP concentrations in the GW increased with rising water table, decreased with receding levels, and varied spatiotemporally from 23 to 1500μgL−1 for nitrate-N, 4–332μgL−1 for AN, and 1–51μgL−1 for SP. Nitrate was transported at rates ranging from 0.008gm−2d−1 to 0.012gm−2d−1 in base-flow discharge towards the creek. Based on a hypothetical equivalent surface land area vs. 1m×1m sub-surface soil matrix area, we show that approximately 52% of the total anthropogenic loading in the creek was from GW. This suggested a need for the adoption of N-fertiliser management practices that will reduce or minimise nitrate leaching to GW.

Chemical phosphorus removal: a clean strategy for piggery wastewater management in Brazil

The intensive production of animal protein is known to be an environmental polluting activity, especially if the wastewater produced is not managed properly. Swine production in Brazil is growing, and technologies to manage all pollutants present in the wastewater effluent are needed. This work presents a case of study of phosphorus (P) removal from piggery wastewater using Ca(OH)2, and demonstrates the feasibility of this strategy for P management. The effluent of a swine manure treatment plant was treated with Ca(OH)2. According to the addition of Ca(OH)2 the pH of the effluent ranged from 8.0 to 10.0. Different conditions of sludge dewatering were evaluated, and the chemical composition of sludge was investigated. Ion chromatography analysis of effluent samples showed that 92% of total P (TP) was present as soluble P (SP) whereas 75% of SP species were present as phosphate. The efficiency of P removal was typically 90% at pH 8.5 and higher than 98% at pH 10.5. The sludge was separated by sedimentation, centrifugation or filtration and dried. The TP content of dried sludge was 9.3% (w/w). X-ray diffraction analysis of the dry sludge showed the presence of amorphous compounds of Ca and P, which is an indication that the sludge obtained from the swine manure treatment has a potential for application as biofertilizer.

Assessment of in-stream phosphorus dynamics in agricultural drainage ditches

The intensive agricultural systems in the Midwestern United States can enrich surface waters with nutrients. Agricultural drainage ditches serve as the first and second order streams throughout much of this region, as well as other highly productive agricultural areas in humid regions throughout the world. This project was conducted to evaluate in-stream processing of soluble P (SP) in agricultural drainage ditches. Soluble P injection studies were conducted at seven sites along three drainage ditches (298 to 4300 ha drainage area), and one site on a third-order stream that receives the discharge from the agricultural ditches (19,000 ha drainage area) by increasing the SP concentration in the ditch water by approximately 0.25 mg L − 1 . Sediments collected from smaller watersheds contained greater amounts of Mehlich 3 and exchangeable P (ExP), silt and clay size particles, and organic matter. Phosphorus uptake lengths ( S net) ranged from 40 to 1900 m, and SP uptake rates ( U) ranged from 0.4 to 52 mg m − 2 h − 1 . Phosphorus S net was correlated with ditch geomorphological (i.e. width) and sediment properties (i.e. organic matter, ExP, and equilibrium P concentration; r 2 = 1.00, P < 0.001), indirect drainage in the watershed ( r 2 = 0.92, P < 0.001), and the amount of small grains, forest, urban area, alfalfa and corn ( r 2 = 1.00, P < 0.0001). Agricultural drainage ditches actively process nutrients and could potentially be managed to optimize this processing to minimize SP export from these landscapes.

The Effect of Dietary Phosphorus Level and Phytase Supplementation on Growth Performance, Bone-Breaking Strength, and Litter Phosphorus Concentration in Broilers

This research was conducted to determine the effects of feeding different P levels with and without phytase supplementation on broiler growth performance, bone-breaking strength (BBS), and litter P concentration. An experiment with 4 trials was conducted with 7,840 Ross x Ross straight-run broilers. For each trial, 1,960 broilers were allotted on d 0 to treatments, with 7 replications each and with 70 broilers per replication. The broilers were fed a 4-period feeding program consisting of starter (0 to 14 d), grower (14 to 32 d), finisher (32 to 41 d), and withdrawal (41 to 50 d) periods. For each trial, the same pen was used continuously for each treatment-replication combination, and the litter was not removed between trials. Broilers were fed a control diet [0.43, 0.40, 0.36, or 0.32% nonphytate P (nPP)] in the starter, grower, finisher, and withdrawal periods, respectively, a low Ca and P (LCaP) diet with a 0.05% reduction in nPP in each period, and these 2 diets supplemented with phytase at 600 phytase units/kg (nPP and Ca were reduced by 0.094% in diets with phytase). Diet did not affect (P > 0.10) broiler performance in the starter or withdrawal periods. Generally, both phytase addition and the LCaP diet decreased some aspects of growth performance during the grower and finisher periods. There was no main effect of phytase on BBS, but BBS was decreased in the broilers fed the LCaP diet with phytase addition (nPP x phytase, P < 0.01) in the grower period, and BBS was decreased in the finisher (P < 0.02) and withdrawal (P < 0.01) periods for broilers fed the LCaP diet. Total P, soluble P (SP), and reactive soluble P (RSP) were decreased (P < 0.04) in the litter of broilers fed the LCaP diets. Total P, SP, and RSP were decreased (P < 0.01) in the litter of broilers fed phytase. These data indicate that phytase supplementation at 600 phytase units/kg reduces growth in some periods, has no effect on BBS, and reduces total P, SP, and RSP in the litter.

Soluble Phosphorus Released by Poultry Wastes in Acidified Aqueous Extracts

Research has shown that measured water‐soluble phosphorus (WSP) from poultry litter might have been less than that released in the field. The effects of acidified extractions on soluble P (SP) concentrations were studied, and a buffer was selected to measure SP at pH 6.0, which is a target value for soil management in Georgia. Soluble P concentrations were extracted from poultry wastes at three pHs: 1) at natural pH, using deionized water (DIw); 2) after titrating DIw suspensions with 0.5N hydrochloric acid (HCl) to pH end‐points 3.0, 4.0, and 6.0; and 3) at pH 6.0 with buffers of sodium (Na) acetate, potassium hydrogen phthalate (KHP), 2‐(N‐morpholino) ethanesulphonic acid (MES), Na cacodylate, imidazole, N‐(2‐acetamido)‐2‐aminoethansulphonic acid (ACES), N‐(carbamoyl‐methyl) iminodiacetic acid (ADA), bis‐(2‐hydroxyethyl) imino]‐tris‐[(hydroxymethyl) methane (Bistris), and 1,4 piperazine‐bis‐(ethane sulphonic acid) (PIPES). Total SP increased 60% to 140% in suspensions acidified with HCl to pH 6.0 compared to suspensions at pH≥8. Dissolved unreactive P responded more (2× to 30×) than molybdate reactive P (20–100%). Buffers extracted more soluble minerals than suspensions acidified with HCl, probably because of their complexation ability. The most effective buffer was MES, because its effects seemed mainly due to acidification.

Bioavailable Phosphorus Export by Surface Runoff from Agricultural Field Plots in Guanting Watershed,Beijing

Bioavailable P (BAP) in agricultural runoff represents P potentially available for algal uptake and consists of soluble P (SP) and a variable portion of particulate P (PP). Runoff and soil losses from agricultural fields were investigated as major nonpoint sources of phosphorus(P) entering Guanting Reservoir, Beijing. There is relatively little information on bioavailable P transport from cropland of Guanting watershed. Soil and bioavailable P in surface runoff from a series of plots in the waershed were evaluated under simulated rainfall conditions. The objectives of this study were to evaluate the effects of rainfall intensity, slope, crop cover, and fertilizer application on bioavailable P concentrations in surface runoff and eroded soil. Accumulated sediment yields varied from 305.1 to 24933.4g/10m2, depending on rainfall intensity, slope, crop cover, and fertilizer application. Weighted average concentrations of soluble P(SP) and particulate bioavailable P (BPP) were much higher than 0.02mg/L,the limiting concentration for lake (reservoir) water. This result showed the potential contamination of reservoir water from agricultural surface runoff. Accumulated BAP losses were 0.08-4.804g/10m2 for croplands. The estimated annual loss of BAP was more than 0.49kg/hm2 per year for croplands in Guanting watershed. Most of BAP loss was in the PP form, which accounted for more 79.7% of BAP loss from cropland. The large amount of BPP may constitute a long-term source of potentially bioavailable P in Guanting Reservoir.