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.     

Bioavailable phosphorus in runoff from alfalfa, smooth bromegrass, and alfalfa-smooth bromegrass

Runoff from sloping landscapes cropped with established alfalfa (Medicago sativa L.) may contain bioavailable P (BAP) which accelerates eutrophication of surface water bodies. Such BAP exists as either dissolved reactive P (DRP) or bioavailable reactive particulate P (BPP). We hypothesized that before and after harvest, sod-forming smooth bromegrass (Bromus inermis Leyss.) or alfalfa-smooth bromegrass mixtures would have less BAP, DRP, and BPP runoff losses than taprooted alfalfa. Swards established in 1992 near Lancaster, WI were subjected to a 72 mm simulated rainfall applied for 1 h in 1993 and 1994 to forage regrowth at 4 and 6 wk after first harvest and immediately (0 wk) after second harvest. Hourly BAP losses for all sward types were 82% less when 1.5 Mg ha(-1) of forage dry matter was present. High DRP losses (>0.050 kg ha(-1)) were associated with high DRP concentrations (>7.1 micromol L(-1)) and high surface soil P concentrations (>59 mg kg(-1)) resulting from broadcast maintenance P fertilizer. High BPP losses (>0.035 kg ha(-1)) were associated with high runoff volumes (>24 mm) and sediment concentrations (>2 g L(-1)). Summed over all 6 rainfall simulations, total BAP loss was only 0.07 kg ha(-1) at the 6 wk stage of regrowth compared with 0.35 at 4 wk, and 0.41 at 0 wk. Moreover, there was no significant difference between sward types for DRP concentration, DRP loss, or BAP loss. We conclude that avoiding excessive defoliation was more effective at reducing BAP losses than specific forage species selection.     

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.     

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.     

Effect of broadcast manure on runoff phosphorus concentrations over successive rainfall events

Concern over eutrophication has directed attention to manure management effects on phosphorus (P) loss in runoff. This study evaluates the effects of manure application rate and type on runoff P concentrations from two, acidic agricultural soils over successive runoff events. Soils were packed into 100- x 20- x 5-cm runoff boxes and broadcast with three manures (dairy, Bos taurus, layer poultry, Gallus gallus; swine, Sus scrofa) at six rates, from 0 to 150 kg total phosphorus (TP) ha(-1). Simulated rainfall (70 mm h(-1)) was applied until 30 min of runoff was collected 3, 10, and 24 d after manure application. Application rate was related to runoff P (r2 = 0.50-0.98), due to increased concentrations of dissolved reactive phosphorus (DRP) in runoff; as application rate increased, so did the contribution of DRP to runoff TP. Varied concentrations of water-extractable phosphorus (WEP) in manures (2-8 g WEP kg(-1)) resulted in significantly lower DRP concentrations in runoff from dairy manure treatments (0.4-2.2 mg DRP L(-1)) than from poultry (0.3-32.5 mg DRP L(-1)) and swine manure treatments (0.3-22.7 mg DRP L(-1)). Differences in runoff DRP concentrations related to manure type and application rate were diminished by repeated rainfall events, probably as a result of manure P translocation into the soil and removal of applied P by runoff. Differential erosion of broadcast manure caused significant differences in runoff TP concentrations between soils. Results highlight the important, but transient, role of soluble P in manure on runoff P, and point to the interactive effects of management and soils on runoff P losses.     

Subsurface application of poultry litter and its influence on nutrient losses in runoff water from permanent pastures

Environmental pressure to reduce nutrient losses from agricultural fields has increased in recent years. To abate this nutrient loss to the environment, better management practices and new technologies need to be developed. Thus, research was conducted to evaluate if subsurface banding poultry litter (PL) would reduce nitrogen (N) and phosphorus (P) loss in surface water runoff using a four-row prototype implement. Rainfall simulations were conducted to create a 40-min runoff event in an established bermudagrass (Cynodon dactylon L.) pasture on soil types common to the Coastal Plain and Piedmont regions. The Coastal Plain soil type was a Marvyn loamy sand (fine-loamy, kaolinitic, thermic Typic Kanhapludults) and the Piedmont soil type was a Hard Labor loamy sand (fine, kaolinitic, thermic Oxyaquic Kanhapludults). Treatments consisted of surface- and subsurface-applied PL at a rate of 9 Mg ha(-1), surface broadcast-applied commercial fertilizer (CF; urea and triple superphosphate blend) at the equivalent N (330 kg N ha(-1)) and P (315 kg N ha(-1)) content of PL, and a nonfertilized control. The greatest loss for inorganic N, total N, dissolved reactive P (DRP), and total P occurred with the surface broadcast treatments, with CF contributing to the greatest loss. Nutrient losses from the subsurface banded treatment reduced N and P in surface water runoff to levels of the control. Subsurface banding of PL reduced concentrations of inorganic N 91%, total N 90%, DRP 86%, and total P 86% in runoff water compared with surface broadcasted PL. These results show that subsurface band-applied PL can greatly reduce the impact of N and P loss to the environment compared with conventional surface-applied PL and CF practices.     

Nitrogen and phosphorus runoff losses from variable and constant intensity rainfall simulations on loamy sand under conventional and strip tillage systems

Further studies on the quality of runoff from tillage and cropping systems in the southeastern USA are needed to refine current risk assessment tools for nutrient contamination. Our objective was to quantify and compare effects of constant (Ic) and variable (Iv) rainfall intensity patterns on inorganic nitrogen (N) and phosphorus (P) losses from a Tifton loamy sand (Plinthic Kandiudult) cropped to cotton (Gossypium hirsutum L.) and managed under conventional (CT) or strip-till (ST) systems. We simulated rainfall at a constant intensity and a variable intensity pattern (57 mm h(-1)) and collected runoff continuously at 5-min intervals for 70 min. For cumulative runoff at 50 min, the Iv pattern lost significantly greater amounts (p < 0.05) of total Kjeldahl N (TKN) and P (TKP) (849 g N ha(-1) and 266 g P ha(-1) for Iv; 623 g N ha(-1) and 192 g P ha(-1) for Ic) than did the Ic pattern. However, at 70 min, no significant differences in total losses were evident for TKN or TKP from either rainfall intensity pattern. In contrast, total cumulative losses of dissolved reactive P (DRP) and NO3-N were greatest for ST-Ic, followed by ST-Iv, CT-Ic, and CT-Iv in diminishing order (69 g DRP ha(-1) and 361 g NO3-N ha(-1); 37 g DRP ha(-1) and 133 g NO3-N ha(-1); 3 g DRP ha(-1) and 58 g NO3-N ha(-1); 1 g DRP ha(-1) and 49 g NO3-N ha(-1)). Results indicate that constant-rate rainfall simulations may overestimate the amount of dissolved nutrients lost to the environment in overland flow from cropping systems in loamy sand soils. We also found that CT treatments lost significantly greater amounts of TKN and TKP than ST treatments and in contrast, ST treatments lost significantly greater amounts of DRP and NO3-N than CT treatments. These results indicate that ST systems may be losing more soluble fractions than CT systems, but only a fraction the total N (33%) and total P (11%) lost through overland flow from CT systems.     

Contribution of particulate phosphorus to runoff phosphorus bioavailability

Runoff P associated with eroded soil is partly solubilized in receiving waters and contributes to eutrophication, but the significance of particulate phosphorus (PP) in the eutrophying P load is debatable. We assessed losses of bioavailable P fractions in field runoff from fine-textured soils (Cryaquepts). Surface runoff at four sites and drain-flow at two of them was sampled. In addition to dissolved molybdate-reactive phosphorus (DRP) losses, two estimates of bioavailable PP losses were made: (i) desorbable PP, assessed by anion exchange resin-extraction (AER-PP) and (ii) redox-sensitive PP, assessed by extraction with bicarbonate and dithionite (BD-PP). Annual losses of BD-PP and AER-PP were derived from the relationships (R2 = 0.77-0.96) between PP and these P forms. Losses of BD-PP in surface runoff (94-1340 g ha(-1)) were typically threefold to fivefold those of DRP (29-510 kg ha(-1)) or AER-PP (13-270 g ha(-1)). Where monitored, drainflow P losses were substantial, at one of the sites even far greater than those via the surface pathway. Typical runoff DRP concentration at the site with the highest Olsen-P status (69-82 mg kg(-1)) was about 10-fold that at the site with the lowest Olsen P (31-45 mg kg(-1)), whereas the difference in AER-PP per mass unit of sediment was only threefold, and that of BD-PP 2.5-fold. Bioavailable P losses were greatly influenced by PP runoff, especially so on soils with a moderate P status that produced runoff with a relatively low DRP concentration.     

Phosphorus runoff losses from subsurface-applied poultry litter on coastal plain soils

The application of poultry litter to soils is a water quality concern on the Delmarva Peninsula, as runoff contributes P to the eutrophic Chesapeake Bay. This study compared a new subsurface applicator for poultry litter with conventional surface application and tillage incorporation of litter on a Coastal Plain soil under no-till management. Monolith lysimeters (61 cm by 61 cm by 61 cm) were collected immediately after litter application and subjected to rainfall simulation (61 mm h(-1) 1 h) 15 and 42 d later. In the first rainfall event, subsurface application of litter significantly lowered total P losses in runoff (1.90 kg ha(-1)) compared with surface application (4.78 kg ha(-1)). Losses of P with subsurface application were not significantly different from disked litter or an unamended control. By the second event, total P losses did not differ significantly between surface and subsurface litter treatments but were at least twofold greater than losses from the disked and control treatments. A rising water table in the second event likely mobilized dissolved forms of P in subsurface-applied litter to the soil surface, enriching runoff water with P. Across both events, subsurface application of litter did not significantly decrease cumulative losses of P relative to surface-applied litter, whereas disking the litter into the soil did. Results confirm the short-term reduction of runoff P losses with subsurface litter application observed elsewhere but highlight the modifying effect of soil hydrology on this technology's ability to minimize P loss in runoff.     

Water quality impacts of converting to a poultry litter fertilization strategy

When improperly managed, land application of animal manures can harm the environment; however, limited watershed-scale runoff water quality data are available to research and address this issue. The water quality impacts of conversion to poultry litter fertilization on cultivated and pasture watersheds in the Texas Blackland Prairie were evaluated in this three-year study. Edge-of-field N and P concentrations and loads in surface runoff from new litter application sites were compared with losses under inorganic fertilization. The impact on downstream nutrient loss was also examined. In the fallow year with no fertilizer application, nutrient losses averaged 3 kg N ha(-1) and 0.9 kg P ha(-1) for the cultivated watersheds and were below 0.1 kg ha(-1) for the pasture watersheds. Following litter application, PO(4)-P concentrations in runoff were positively correlated to litter application rate and Mehlich-3 soil P levels. Following litter application, NO(3)-N and NH(4)-N concentrations in runoff were typically greater from cultivated watersheds, but PO(4)-P concentrations were greater for the pasture watersheds. Total N and P loads from the pasture watersheds (0.2 kg N ha(-1) and 0.7 kg P ha(-1)) were significantly lower than from the cultivated watersheds (32 kg N ha(-1) and 5 kg P ha(-1)) partly due to lower runoff volumes from the pasture watersheds. Downstream N and P concentrations and per-area loads were much lower than from edge-of-field watersheds. Results demonstrate that a properly managed annual litter application (4.5 Mg ha(-1) or less depending on litter N and P content) with supplemental N should supply necessary nutrients without detrimental water quality impacts.     

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.     

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.     

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 forms in biosolids-amended soils and losses in runoff: effects of wastewater treatment process

Continuous addition of municipal biosolids to soils based on plant nitrogen (N) requirements can cause buildup of soil phosphorus (P) in excess of crop requirements; runoff from these soils can potentially contribute to nonpoint P pollution of surface waters. However, because biosolids are often produced using lime and/or metal salts, the potential for biosolids P to cause runoff P losses can vary with wastewater treatment plant (WWTP) process. This study was conducted to determine the effect of wastewater treatment process on the forms and amounts of P in biosolids, biosolids-amended soils, and in runoff from biosolids-amended soils. We amended two soil types with eight biosolids and a poultry litter (PL) at equal rates of total P (200 kg ha(-1); unamended soils were used as controls. All biosolids and amended soils were analyzed for various types of extractable P, inorganic P fractions, and the degree of P saturation (acid ammonium oxalate method). Amended soils were placed under a simulated rainfall and all runoff was collected and analyzed for dissolved reactive phosphorus (DRP), iron-oxide-coated filter paper strip-extractable phosphorus (FeO-P), and total phosphorus (EPA3050 P). Results showed that biosolids produced with a biological nutrient removal (BNR) process caused the highest increases in extractable soil P and runoff DRP. Alternatively, biosolids produced with iron only consistently had the lowest extractable P and caused the lowest increases in extractable soil P and runoff DRP when added to soils. Differences in soil and biosolids extractable P levels as well as P runoff losses were related to the inorganic P forms of the biosolids.     

Relationships between soil and runoff phosphorus in small Alberta watersheds

Field-scale relationships between soil test phosphorus (STP) and flow-weighted mean concentrations (FWMCs) of dissolved reactive phosphorus (DRP) and total phosphorus (TP) in runoff are essential for modeling phosphorus losses, but are lacking. The objectives of this study were (i) to determine the relationships between soil phosphorus (STP and degree of phosphorus saturation (DPS)) and runoff phosphorus (TP and DRP) from field-sized catchments under spring snowmelt and summer rainfall conditions, and (ii) to determine whether a variety of depths and spatial representations of STP improved the prediction of phosphorus losses. Runoff was monitored from eight field-scale microwatersheds (2 to 248 ha) for 3 yr. Soil test phosphorus was determined for three layers (0 to 2.5 cm, 0 to 5 cm, and 0 to 15 cm) in spring and fall and the DPS was determined for the surface layer. Average STP (0 to 15 cm) ranged from 3 to 512 mg kg(-1), and DPS (0 to 2.5 cm) ranged from 5 to 91%. Seasonal FWMCs ranged from 0.01 to 7.4 mg L(-1) DRP and from 0.1 to 8.0 mg L(-1) TP. Strong linear relationships (r2=0.87 to 0.89) were found between the site mean STP and the FWMCs of DRP and TP. The relationships had similar extraction coefficients, intercepts, and predictive power among all three soil layers. Extraction coefficients (0.013 to 0.014) were similar to those reported for other Alberta studies, but were greater than those reported for rainfall simulation studies. The curvilinear DPS relationship showed similar predictive ability to STP. The field-scale STP relationships derived from natural conditions in this study should provide the basis for modeling phosphorus in Alberta.     

Response of turf and quality of water runoff to manure and fertilizer

Manure applications can benefit turfgrass production and unused nutrients in manure residues can be exported through sod harvests. Yet, nutrients near the soil surface could be transported in surface runoff. Our research objective was to evaluate responses of bermudagrass [Cynodon dactylon (L.) Pers. var. Guymon] turf and volumes and P and N concentrations of surface runoff after fertilizer or composted manure applications. Three replications of five treatments were established on a Boonville fine sandy loam (fine, smectitic, thermic Vertic Albaqualf) that was excavated to create an 8.5% slope. Manure rates of 50 and 100 kg P ha(-1) at the start of two monitoring periods were compared with P fertilizer rates of 25 and 50 kg ha(-1) and an unfertilized control. Compared with initial soil tests, nitrate concentrations decreased and P concentrations increased after two manure or fertilizer applications and eight rain events over the two monitoring periods. The fertilizer sources of P and N produced 19% more dry weight and 21% larger N concentrations in grass clippings than manure sources. Yet, runoff volumes were similar between manure and fertilizer sources of P. Dissolved P concentration (30 mg L(-1)) in runoff during a rain event 3 d after application of 50 kg P ha(-1) was five times greater for fertilizer than for manure P. Observations during both monitoring periods indicated that total P and N losses in runoff were no greater for composted manure than for fertilizer sources of P at relatively large P rates on a steep slope of turfgrass.     

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.     

Runoff losses of phosphorus and nitrogen imported in sod or composted manure for turf establishment

Nutrient loading on impaired watersheds can be reduced through export of sod grown with manure and export of composted manure for turf production on other watersheds. Effects of the sod and manure exports on receiving watersheds were evaluated through monitoring of total dissolved phosphorus (TDP) and N concentrations and losses in runoff from establishing turf. Three replications of seven treatments were established on an 8.5% slope of a Booneville soil (loamy-skeletal, mixed, superactive Pachic Argicryolls). Three treatments comprised imported 'Tifway' bermudagrass [Cynodon dactylon (L.) Pers. x C. transvaalensis Burtt-Davy) sod grown with composted dairy manure (382 or 191 kg P ha(-1)) or fertilizer (50 kg P ha(-1)). Three treatments were sprigged with Tifway and top-dressed with either composted manure (92 or 184 kg P ha(-1)) or fertilizer (100 kg P ha(-1)). The control was established bermudagrass [Cynodon dactylon (L.) Pers. var. Guymon]. During eight fall rain events, mean TDP concentration in runoff (7.8 mg L(-1)) from sprigged Tifway top-dressed with manure (84 kg P ha(-1)) was 1.6 times greater than sod imported with 129 kg manure P ha(-1). During the first fall event, mass losses of TDP (232 mg m(-2)) and total Kjeldahl nitrogen (TKN) (317 mg m(-2)) from sprigged treatments top-dressed with manure or fertilizer were nearly three times greater than manure-grown sod. Percentages of manure P lost as TDP in runoff from imported sod were 33% of percentages lost from sprigged treatments top-dressed with manure. Sod grown with manure P rates of 190 kg P ha(-1) can be imported without increasing runoff losses of TDP compared with conventional fertilization of establishing turfgrass.     

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

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

Effect of 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.