Evaluation of phosphorus transport in surface runoff from packed soil boxes

Evaluation of phosphorus (P) management strategies to protect water quality has largely relied on research using simulated rainfall to generate runoff from either field plots or shallow boxes packed with soil. Runoff from unmanured, grassed field plots (1 m wide x 2 m long, 3-8% slope) and bare soil boxes (0.2 m wide and 1 m long, 3% slope) was compared using rainfall simulation (75 mm h(-1)) standardized by 30-min runoff duration (rainfall averaged 55 mm for field plots and 41 mm for packed boxes). Packed boxes had lower infiltration (1.2 cm) and greater runoff (2.9 cm) and erosion (542 kg ha(-1)) than field plots (3.7 cm infiltration; 1.8 cm runoff; 149 kg ha(-1) erosion), yielding greater total phosphorus (TP) losses in runoff. Despite these differences, regressions of dissolved reactive phosphorus (DRP) in runoff and Mehlich-3 soil P were consistent between field plots and packed boxes reflecting similar buffering by soils and sediments. A second experiment compared manured boxes of 5- and 25-cm depths to determine if variable hydrology based on box depth influenced P transport. Runoff properties did not differ significantly between box depths before or after broadcasting dairy, poultry, or swine manure (100 kg TP ha(-1)). Water-extractable phosphorus (WEP) from manures dominated runoff P, and translocation of manure P into soil was consistent between box types. This study reveals the practical, but limited, comparability of field plot and soil box data, highlighting soil and sediment buffering in unamended soils and manure WEP in amended soils as dominant controls of DRP transport.     

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.     

Effect of mineral and manure phosphorus sources on runoff phosphorus

Concern over nonpoint-source phosphorus (P) losses from agricultural lands to surface waters has resulted in scrutiny of factors affecting P loss potential. A rainfall simulation study was conducted to quantify the effects of alternative P sources (dairy manure, poultry manure, swine slurry, and diammonium phosphate), application methods, and initial soil P concentrations on runoff P losses from three acidic soils (Buchanan-Hartleton, Hagerstown, and Lewbeach). Low P (12 to 26 mg kg(-1) Mehlich-3 P) and high P (396 to 415 mg kg(-1) Mehlich-3 P) members of each soil were amended with 100 kg total P ha(-1) from each of the four P sources either by surface application or mixing, and subjected to simulated rainfall (70 mm h(-1) to produce 30 min runoff). Phosphorus losses from fertilizer and manure applied to the soil surface differed significantly by source, with dissolved reactive phosphorus (DRP) accounting for 64% of total phosphorus (TP) (versus 9% for the unamended soils). For manure amended soils, these losses were linearly related to water-soluble P concentration of manure (r2 = 0.86 for DRP, r2 = 0.78 for TP). Mixing the P sources into the soil significantly decreased P losses relative to surface P application, such that DRP losses from amended, mixed soils were not significantly different from the unamended soil. Results of this study can be applied to site assessment indices to quantify the potential for P loss from recently manured soils.     

Effect of methodology in estimating and interpreting water-extractable phosphorus in animal manures

Manure water-extractable phosphorus (WEP) data are used in indices and models to assess P transport in runoff. Methods to measure WEP vary widely, often without understanding the effect on how much P is extracted. We conducted water extractions on five dairy, swine, and poultry manures to assess single and sequential extractions, drying manures, solution to solid (cm3 g(-1)) extraction ratios, and P determination method. We found little difference in WEP of single or sequential extractions. Increasing extraction ratio from 10:1 to 250:1 resulted in more WEP recovered, but in a diminishing fashion so that ratios of 200:1 and 250:1 were not significantly different. Patterns of increased WEP with extraction ratio varied with manure type, presence of bedding material, and drying treatment. Fresh and air-dried manures had similar patterns, but differed substantially from oven-dried (90 degrees C) manures. The differential effect of oven-drying on WEP was greatest for dairy and poultry manure, and less for swine manure. We analyzed water extracts colorimetrically before and after digestion, to examine the potential effect of P determination by inductively coupled plasma (ICP) spectroscopy. Digested extracts always contained more P. For manures with bedding, drying decreased the difference in P measured before and after digestion. The opposite was true for manures without bedding. Results highlight the influence of methodology on manure WEP measurement and caution needed when comparing data across studies using different WEP methods. Overall, our results point to a need for a standard manure water extraction method.     

Freeze-thaw effects on phosphorus loss in runoff from manured and catch-cropped soils

Concern over nonpoint source P losses from agricultural lands to surface waters in frigid climates has focused attention on the role of freezing and thawing on P loss from catch crops (cover crops). This study evaluated the effect of freezing and thawing on the fate of P in bare soils, soils mixed with dairy manure, and soils with an established catch crop of annual ryegrass (Lolium multiflorum L.). Experiments were conducted to evaluate changes in P runoff from packed soil boxes (100 by 20 by 5 cm) and P leaching from intact soil columns (30 cm deep). Before freezing and thawing, total P (TP) in runoff from catch-cropped soils was lower than from manured and bare soils due to lower erosion. Repeated freezing and thawing significantly increased water-extractable P (WEP) from catch crop biomass and resulted in significantly elevated concentrations of dissolved P in runoff (9.7 mg L(-1)) compared with manured (0.18 mg L(-1)) and bare soils (0.14 mg L(-1)). Catch crop WEP was strongly correlated with the number of freeze-thaw cycles. Freezing and thawing did not change the WEP of soils mixed with manures, nor were differences observed in subsurface losses of P between catch-cropped and bare soils before or after manure application. This study illustrates the trade-offs of establishing catch crops in frigid climates, which can enhance P uptake by biomass and reduce erosion potential but increase dissolved P runoff.     

A simple method to predict dissolved phosphorus in runoff from surface-applied manures

Computer models are a rapid, inexpensive way to identify agricultural areas with a high potential for P loss, but most models poorly simulate dissolved P release from surface-applied manures to runoff. We developed a simple approach to predict dissolved P release from manures based on observed trends in laboratory extraction of P in dairy, poultry, and swine manures with water over different water to manure ratios. The approach predicted well dissolved inorganic (R2 = 0.70) and organic (R2 = 0.73) P release from manures and composts for data from leaching experiments with simulated rainfall. However, it predicted poorly (R2 = 0.18) dissolved inorganic P concentrations in runoff from soil boxes where dairy, poultry, and swine manures had been surface-applied and subjected to simulated rainfall. Multiplying predicted runoff P concentrations by the ratio of runoff to rainfall improved the relationship between measured and predicted runoff P concentrations, but runoff P was still overpredicted for dairy and swine manures. We attributed this overprediction to immediate infiltration of dissolved P in the freely draining water of dairy and swine manure slurries upon their application to soils. Further multiplying predicted runoff dissolved inorganic P concentrations by 0.35 for dairy and 0.60 for swine manures resulted in an accurate prediction of dissolved P in runoff (R2 = 0.71). The ability of our relatively simple approach to predict dissolved inorganic P concentrations in runoff from surface-applied manures indicates its potential to improve water quality models, but field testing of the approach is necessary first.     

Source-related transport of phosphorus in surface runoff

Continual application of mineral fertilizer and manures to meet crop production goals has resulted in the buildup of soil P concentrations in many areas. A rainfall simulation study was conducted to evaluate the effect of the application of P sources differing in water-soluble P (WSP) concentration on P transport in runoff from two grassed and one no-till soil (2 m(2) plots). Triple superphosphate (TSP)-79% WSP, low-grade single superphosphate (LGSSP)-50% WSP, North Carolina rock phosphate (NCRP)-0.5% WSP, and swine manure (SM)-30% WSP, were broadcast (100 kg total P ha(-1)) and simulated rainfall (50 mm h(-1) for 30 min of runoff) applied 1, 7, 21, and 42 d after P source application. In the first rainfall event one d after fertilizer application, dissolved reactive P (DRP) and total P (TP) concentrations of runoff increased (P < 0.05) for all soils with an increase of source WSP; with DRP averaging 0.27, 0.50, 14.66, 41.69, and 90.47 mg L(-1); and total P averaging 0.34, 0.61, 19.05, 43.10, and 98.06 mg L(-1) for the control, NCRP, SM, LGSSP, and TSP, respectively. The loss of P in runoff decreased with time for TSP and SM, such that after 42 d, losses from TSP, SM, and LGSSP did not differ. These results support that P water solubility in P sources may be considered as an indicator of P loss potential.     

Phosphorus runoff from incorporated and surface-applied liquid swine manure and phosphorus fertilizer

Excessive fertilization with organic and/or inorganic P amendments to cropland increases the potential risk of P loss to surface waters. The objective of this study was to evaluate the effects of soil test P level, source, and application method of P amendments on P in runoff following soybean [Glycine max (L.) Merr.]. The treatments consisted of two rates of swine (Sus scrofa domestica) liquid manure surface-applied and injected, 54 kg P ha(-1) triple superphosphate (TSP) surface-applied and incorporated, and a control with and without chisel-plowing. Rainfall simulations were conducted one month (1MO) and six months (6MO) after P amendment application for 2 yr. Soil injection of swine manure compared with surface application resulted in runoff P concentration decreases of 93, 82, and 94%, and P load decreases of 99, 94, and 99% for dissolved reactive phosphorus (DRP), total phosphorus (TP), and algal-available phosphorus (AAP), respectively. Incorporation of TSP also reduced P concentration in runoff significantly. Runoff P concentration and load from incorporated amendments did not differ from the control. Factors most strongly related to P in runoff from the incorporated treatments included Bray P1 soil extraction value for DRP concentration, and Bray P1 and sediment content in runoff for AAP and TP concentration and load. Injecting manure and chisel-plowing inorganic fertilizer reduced runoff P losses, decreased runoff volumes, and increased the time to runoff, thus minimizing the potential risk of surface water contamination. After incorporating the P amendments, controlling erosion is the main target to minimize TP losses from agricultural soils.     

Phosphorus and nitrogen in rainfall simulation runoff after fresh and composted beef cattle manure application

Fresh beef cattle (Bos taurus) manure has traditionally been applied to cropland in southern Alberta, but there has been an increase in application of composted manure to cropland in this region. However, the quality of runoff under fresh manure (FM) versus composted manure (CM) has not been investigated. Our objective was to compare runoff quality under increasing rates (0, 13, 42, 83 Mg ha(-1) dry wt.) of FM and CM applied for two consecutive years to a clay loam soil cropped to irrigated barley (Hordeum vulgare L.). We determined total phosphorus (TP), particulate phosphorus (PP), dissolved reactive phosphorus (DRP), total nitrogen (TN), NH4-N, and NO3-N concentrations and loads in runoff after one (1999) and two (2000) applications of FM and CM. We found significantly (P < or = 0.05) higher TP, DRP, and NH4-N concentrations, and higher DRP and TN loads under FM than CM after 2 yr of manure application. The TP loads were also higher under FM than CM at the 83 Mg ha(-1) rate in 2000, and DRP loads were higher for FM than CM at this high rate when averaged over both years. Application rate had a significant effect on TP and DRP concentrations in runoff. In addition, the slope values of the regressions between TP and DRP in runoff versus application rate were considerably higher for FM in 2000 than for FM in 1999, and CM in both 1999 and 2000. Significant positive relationships were found for TP and DRP in runoff versus soil Kelowna-extractable P and soil water-extractable P for FM and CM in 2000, indicating that interaction of runoff with the soil controlled the release of P. Total P and DRP were the variables most affected by the treatments. Overall, our study found that application of CM rather than FM to cropland may lower certain forms of P and N in surface runoff, but this is dependent on the interaction with year, application rate, or both.     

Effect of liquid swine manure rate, incorporation, and timing of rainfall on phosphorus loss with surface runoff

Excessive manure phosphorus (P) application increases risk of P loss from fields. This study assessed total runoff P (TPR), bioavailable P (BAP), and dissolved reactive P (DRP) concentrations and loads in surface runoff after liquid swine (Sus scrofa domesticus) manure application with or without incorporation into soil and different timing of rainfall. Four replicated manure P treatments were applied in 2002 and in 2003 to two Iowa soils testing low in P managed with corn (Zea mays L.)-soybean [Glycine max (L.) Merr.] rotations. Total P applied each time was 0 to 80 kg P ha(-1) at one site and 0 to 108 kg P ha(-1) at the other. Simulated rainfall was applied within 24 h of P application or after 10 to 16 d and 5 to 6 mo. Nonincorporated manure P increased DRP, BAP, and TPR concentrations and loads linearly or exponentially for 24-h and 10- to 16-d runoff events. On average for the 24-h events, DRP, BAP, and TPR concentrations were 5.4, 4.7, and 2.2 times higher, respectively, for nonincorporated manure than for incorporated manure; P loads were 3.8, 7.7, and 3.6 times higher; and DRP and BAP concentrations were 54% of TPR for nonincorporated manure and 22 to 25% for incorporated manure. A 10- to 16-d rainfall delay resulted in DRP, BAP, and TPR concentrations that were 3.1, 2.7, and 1.1 times lower, respectively, than for 24-h events across all nonincorporated P rates, sites, and years, whereas runoff P loads were 3.8, 3.6, and 1.6 times lower, respectively. A 5- to 6-mo simulated rainfall delay reduced runoff P to levels similar to control plots. Incorporating swine manure when the probability of immediate rainfall is high reduces the risk of P loss in surface runoff; however, this benefit sharply decreases with time.     

Phosphorus losses in simulated rainfall runoff from manured soils of Alberta

Manure applied to agricultural land at rates that exceed annual crop nutrient requirements can be a source of phosphorus in runoff. Manure incorporation is often recommended to reduce phosphorus losses in runoff. A small plot rainfall simulation study was conducted at three sites in Alberta to evaluate the effects of manure rate and incorporation on phosphorus losses. Treatments consisted of three solid beef cattle manure application rates (50, 100, and 200 kg ha(-1) total phosphorus), an unmanured control, and two incorporation methods (nonincorporated and incorporated with one pass of a double disk). Simulated rain was applied to soils with freshly applied and residual (1 yr after application) manure at 70 mm h(-1) to produce 30 min of runoff. Soil test phosphorus (STP), total phosphorus (TP), and dissolved reactive phosphorus (DRP) concentrations in runoff increased with manure rate for fresh and residual manure. Initial abstraction and runoff volumes did not change with manure rate. Initial abstraction, runoff volumes, and phosphorus concentrations did not change with manure incorporation at Lacombe and Wilson, but initial abstraction volumes increased and runoff volumes and phosphorus concentrations decreased with incorporation of fresh manure at Beaverlodge. Phosphorus losses in runoff were directly related to phosphorus additions. Extraction coefficients (slopes of the regression lines) for the linear relationships between residual manure STP and phosphorus in runoff were 0.007 to 0.015 for runoff TP and 0.006 to 0.013 for runoff DRP. While incorporation of manure with a double disk had no significant effect on phosphorus losses in runoff from manure-amended soils 1 yr after application, incorporation of manure is still recommended to control nitrogen losses, improve crop nutrient uptake, and potentially reduce odor concerns.     

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.     

Corn residue level and manure application timing effects on phosphorus losses in runoff

Growing interest in corn (Zea mays L.) silage utilization on Wisconsin dairy farms may have implications for nutrient losses from agricultural lands. Increasing the silage cutting height will increase residue cover and could reduce off-site migration of sediments and associated constituents compared with conventional silage harvesting. We examined the effects of residue level and manure application timing on phosphorus (P) losses in runoff from no-till corn. Treatments included conventional corn grain (G) and silage (SL; 10- to 15-cm cutting height) and nonconventional, high-cut (60-65 cm) silage (SH) subjected to different manure application regimes: no manure (N) or surface application in fall (F) or spring (S). Simulated rainfall (76 mm h(-1); 1 h) was applied in spring and fall for two years (2002-2003), runoff from 2.0- x 1.5-m plots was collected, and subsamples were analyzed for dissolved reactive phosphorus (DRP), total phosphorus (TP), and P mass distribution in four particle size classes. Total P and DRP loads were inversely related to percent residue cover, but both TP and DRP concentrations were unaffected by residue level. Manure application increased DRP concentrations in spring runoff by two to five times but did not significantly affect DRP loads, since higher concentrations were offset by lower runoff volumes. Spring manure application reduced TP loads in spring runoff by 77 to 90% compared with plots receiving no manure, with the extent of reductions being greatest at the lower residue levels (<24%). The TP concentration in sediments increased as particle size decreased. Manure application increased the TP concentration of the 0- to 2-microm fraction by 79 to 125%, but elevated the 2- to 10- and 10- to 50-microm fractions to a lesser extent. Recent manure additions were most influential in enriching transported sediments with P. By itself, higher residue cover achieved by high-cutting silage was often insufficient to lower P losses; however, the combination of manure application and higher residue levels significantly reduced P losses from corn fields harvested for silage.     

Degree of phosphorus saturation thresholds in manure-amended soils of alberta

The risk of P losses from agricultural land to surface and ground water generally increases as the degree of soil P saturation increases. A single-point soil P sorption index (PSI) was validated with adsorption isotherm data for determination of the P sorption status of Alberta soils. Soil P thresholds (change points) were then examined for two agricultural soils after eight annual applications of different rates of cattle manure and for three agricultural soils after one application of different rates of cattle manure. Linear relationships were found between soil-test P (STP) levels up to 1000 mg kg(-1) and desorbed P in the five Alberta soils. Weak linear relationships were also found between STP and runoff dissolved reactive phosphorus (DRP) in three of these soils. Change points for the degree of P saturation (DPS) were detected in four of the five soils at 3 to 44% for water-extractable P (WEP) and at 11 to 51% for CaCl(2)-extractable P (CaCl(2)-P). Change points were not found for DPS or runoff DRP. Overall DPS thresholds for the five soils combined were 27% for WEP and 44% for CaCl(2)-P at a critical desorbable-P value of 1 mg L(-1). The corresponding STP levels (44 mg kg(-1) for WEP and 71 mg kg(-1) for CaCl(2)-P) are similar to agronomic thresholds for crops grown on Alberta soils. Soluble P losses in overland flow and leaching may be greater in soils with DPS values that exceed these thresholds than in soils with lower DPS values.     

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

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

Nutrient transport from livestock manure applied to pastureland using phosphorus-based management strategies

Land applications of manure from confined animal systems and direct deposit by grazing animals are both major sources of nutrients in streams. The objectives of this study were to determine the effects of P-based manure applications on total suspended solids (TSS) and nutrient losses from dairy manures and poultry litter surface applied to pasturelands and to compare the nutrient losses transported to the edge of the field during overland flow events. Two sets of plots were established: one set for the study of in-field release and another set for the study of edge-of-the-field nutrient transport. Release plots were constructed at three pastureland sites (previous poultry litter applications, previous liquid dairy manure application, and no prior manure application) and received four manure treatments (turkey [Meleagris gallopavo] litter, liquid dairy manure, standard cowpies, and none). Pasture plots with a history of previous manure applications released higher concentrations of TSS and higher percentages of total P (TP) in the particulate form. Transport plots were developed on pasture with no prior manure application. The average flow-weighted TP concentrations were highest in runoff samples from the plots treated with cowpies (1.57 mg L(-1)). Reducing excess P in dairy cow diets and surface applying manure to the land using P-based management practices did not increase N concentrations in runoff. This study found that nutrients are most transportable from cowpies; thus a buffer zone between pastureland and streams or other appropriate management practices are necessary to reduce nutrient losses to waterbodies.     

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.     

Phosphorus runoff: effect of tillage and soil phosphorus levels

Continued inputs of fertilizer and manure in excess of crop requirements have led to a build-up of soil phosphorus (P) levels and increased P runoff from agricultural soils. The objectives of this study were to determine the effects of two tillage practices (no-till and chisel plow) and a range of soil P levels on the concentration and loads of dissolved reactive phosphorus (DRP), algal-available phosphorus (AAP), and total phosphorus (TP) losses in runoff, and to evaluate the P loss immediately following tillage in the fall, and after six months, in the spring. Rain simulations were conducted on a Typic Argiudoll under a corn (Zea mays L.)-soybean [Glycine max (L.) Merr.] rotation. Elapsed time after tillage (fall vs. spring) was not related to any form of P in runoff. No-till runoff averaged 0.40 mg L(-1) and 0.05 kg ha(-1) DRP and chisel-plow plots averaged 0.24 mg L(-1) and 0.02 kg ha(-1) DRP concentration and loads, respectively. The relationship between DRP and Bray P1 extraction values was approximated by a logistic function (S-shaped curve) for no-till plots and by a linear function for tilled plots. No significant differences were observed between tillage systems for TP and AAP in runoff. Bray P1 soil extraction values and sediment concentration in runoff were significantly related to the concentrations and amounts of AAP and TP in runoff. These results suggest that soil Bray P1 extraction values and runoff sediment concentration are two easily measured variables for adequate prediction of P runoff from agricultural fields.     

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.     

Efficacy of alum and coal combustion by-products in stabilizing manure phosphorus

Animal manures contain large amounts of soluble phosphorus (P), which is prone to runoff losses when manure is surface-applied. Here we report the efficacy of alum and three coal combustion by-products in reducing P solubility when added to dairy, swine, or broiler litter manures in a laboratory incubation study. Compared with unamended controls, alum effectively reduced readily soluble P, determined in water extracts of moist manure samples with 1 h of shaking, for all three manures. The reduction ranged from 80 to 99% at treatment rates of 100 to 250 g alum kg(-1) manure dry matter. The fluidized bed combustion fly ash (FBC) reduced readily soluble P by 50 to 60% at a rate of 400 g kg(-1) for all three manures. Flue gas desulfurization by-product (FGD) reduced readily soluble P by nearly 80% when added to swine manure and broiler litter at 150 and 250 g kg(-1). Another by-product, anthracite refuse fly ash (ANT), was ineffective for all three manures. In all cases, reduction in readily soluble P is primarily associated with inorganic phosphorus (P(i)) with little change in organic phosphorus (P(o)). Sequential extraction results indicate that the by-product treatments shifted manure P from H2O-P into a less vulnerable fraction, NaHCO3 - P, while the alum treatment shifted the P into even more stable forms, mostly NaOH-P. Such shifts in P fractions would have little influence on P availability for crops over the long-term but would retard and reduce potential losses of P following manure applications.