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TECHNICAL REPORTS

Surface Water Quality

Phosphorus Losses in Simulated Rainfall Runoff from Manured Soils of Alberta

^a Alberta Agriculture, Food and Rural Development, 100, 5401 1st Ave. South, Lethbridge, AB, Canada T1J 4V6
^b Univ. of Alberta, 751 General Services Bldg., Edmonton, AB, Canada T6G 2H1
^c Agriculture and Agri-Food Canada, Lethbridge Research Centre, 5403 1st Ave. South, Lethbridge, AB, Canada T1J 4B1

^* Corresponding author (gerald.ontkean{at}gov.ab.ca)

Received for publication July 10, 2006.

	ABSTRACT

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
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.

Abbreviations: DRP, dissolved reactive phosphorus • FWMC, flow-weighted mean concentration • STP, soil test phosphorus • TP, total phosphorus • WEP, water-extractable phosphorus

	INTRODUCTION

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
PHOSPHORUS is an essential nutrient for agricultural crop and livestock production. However, excessive amounts of phosphorus in agricultural soils can contribute to accelerated eutrophication of surface waters when transported and delivered by runoff (Campbell and Edwards, 2001). Livestock production trends in Alberta show a movement toward larger operations that are concentrated in certain areas of the province (Alberta Agriculture, Food, and Rural Development, 2005). The increased amount of manure in these areas can result in application of manure to surrounding agricultural land at rates that exceed crop nutrient requirements. This leads to a buildup of phosphorus in soil (Whalen and Chang, 2001) and a greater risk of impairment to surrounding surface waters (Carpenter et al., 1998).

Recent studies have linked increasing soil test phosphorus (STP) with increasing phosphorus concentrations in runoff (Pote et al., 1996; Pote et al., 1999; Schroeder et al., 2004b; Turner et al., 2004; Vadas et al., 2005). Similarly, other studies have found a positive relationship between manure application rate and phosphorus in runoff (Edwards and Daniel, 1993; Kleinman and Sharpley, 2003; Tarkalson and Mikkelsen, 2004). Kleinman and Sharpley (2003) also reported that phosphorus concentrations in runoff decreased with repeated rainfall events during the month following manure application. Schroeder et al. (2004a) observed a similar trend with exponential decline in P during a period of 5 mo following manure application.

Pote et al. (1996) and Schroeder et al. (2004b) found that many variables can affect the relationship between STP and phosphorus in runoff, including: variability in soil properties, phosphorus adsorption, calcium carbonate content of the soil, hydrology, antecedent moisture conditions, and management practices. While the recent addition of phosphorus to soils can overshadow the relationship between STP and phosphorus in runoff, this effect decreases with time as equilibrium is reached (Vadas et al., 2005).

Manure application methods can affect the relationship between phosphorus in soil and in runoff. Relative to surface-applied manure, incorporation of manure has been associated with decreased dissolved reactive phosphorus (DRP) concentrations in runoff (Mueller et al., 1984a; Eghball and Gilley, 1999; Bundy et al., 2001; Kleinman et al., 2002a; Little et al., 2005). Kleinman et al. (2002a) attributed this decline in DRP with manure incorporation to a decrease of phosphorus concentrations at the soil surface and greater sorption of phosphorus in manure to soil. In most cases, tillage for manure incorporation increases particulate phosphorus and consequently total phosphorus (TP) concentrations in runoff due to increased soil erosion (Mueller et al., 1984a; Eghball and Gilley, 1999; Bundy et al., 2001; Kleinman et al., 2002a).

The objective of this study was to determine the effects of beef cattle manure application rate and incorporation by a double disk on phosphorus concentrations in runoff from agricultural land under cereal crop production in Alberta, Canada. These effects were studied immediately after manure application and incorporation treatments were applied as well as 1 yr later, allowing phosphorus from the manure to equilibrate with the soil.

	MATERIALS AND METHODS

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
Study Sites
Two study sites were established in 2003 near Lacombe and Beaverlodge, Alberta. A third site, Wilson, was selected in 2004 near Lethbridge, Alberta (Fig. 1). The three sites represent a range of soils in various natural regions of the province associated with agriculture (Table 1). A randomized complete block design was used with four replicates of eight treatments (four manure levels and two tillage levels). Each treatment plot measured 7 by 10 m. A 5-m buffer was left between each replicate and a minimum 3-m buffer was provided around the plot area. During the study, land managers performed their management practices as previously planned. Oat (Avena sativa L.) was produced at Beaverlodge and barley (Hordeum vulgare L.) was grown at Lacombe under a conventional tillage regime, while hard red spring wheat (Triticum aestivum L.) was produced under a no-till system at Wilson.

View larger version (28K): [in this window] [in a new window]   Fig. 1. Rainfall simulation sites in Alberta, Canada.

Manure Analysis
Manure was obtained from the outdoor storage piles of straw-bedded, unpaved feedlots near each site. Ten samples of fresh manure from the manure source for each site were analyzed for moisture content and TP (Peters, 2003) within 10 d of application. The manure was removed from the storage piles and stored on-site. Land application of manure was performed one replicate at a time for four consecutive days. Manure application rates (wet weight basis) were determined according to the TP content of the manure. Manure samples collected from each plot at the time of application were analyzed for TP (Peters, 2003) and water-extractable P (WEP) (Kleinman et al., 2002b) to calculate actual rates of manure TP and WEP applied. The WEP in the manure was determined by shaking 1 g of manure in 200 mL of distilled water for 1 h in an end-over-end shaker, followed by centrifugation (30 min at 1900 x g) and filtration through Whatman 1 filter paper (Kleinman et al., 2002b).

Soil Sampling and Analysis
Before manure application at each site, baseline soil samples were collected to a depth of 2.5 cm from the 32 plots at each site using a frame-excavation method (Nolan et al., 2006). A 50 cm long by 19 cm wide by 2.5 cm deep metal frame was inserted level with the soil surface. Soil was collected from within the frame to the 2.5-cm depth at two locations within the plot and composited for analysis. Following manure application and incorporation, and before each set of rainfall simulations, post-treatment soil samples were also collected from each treatment plot using the frame-excavation method. These samples included the soil, manure, and crop residue associated with the upper 2.5 cm of the soil profile. Soil samples were air-dried, ground (2-mm sieve) and analyzed for STP content using the modified Kelowna extraction method (Qian et al., 1991). The modified Kelowna extractant consists of 0.25 M HOAc, 0.25 M NH₄OAc, and 0.015 M NH₄F with a pH of 4.9.

Soils were classified at each of the study sites according to the Canadian and U.S. systems of classification. Four (Lacombe and Wilson) or five (Beaverlodge) cores to a depth of 2 m were sampled and classified at each site in areas without manure. Soils cores were sampled individually by horizon. Samples were air-dried, ground (<2 mm), and analyzed from a saturated paste extract for pH, electrical conductivity, and soluble cations (Rhoades, 1982), and sodium adsorption ratios were calculated. Samples were also analyzed for particle size distribution (Gee and Bauder, 1986). Characteristics of representative soil cores from each site are presented in Table 2.

The rainfall simulators were constructed using the specifications defined for rain simulation experiments of the United States National Phosphorus Project (Humphry et al., 2002). Four rainfall simulators were used simultaneously on four adjacent plots. Each simulator was fitted with a single Fulljet 1/2 HH-SS50WSQ nozzle centered 3 m above the soil surface over the runoff frame. Simulators were operated at a nozzle pressure of approximately 28 kPa to generate continuous flow at an intensity of 70 mm h^–1 on the framed area. This intensity for the 30-min collection period equated to approximately a 25 to 50 yr return period storm at Beaverlodge, a greater than 50 yr return period storm at Lacombe, and a 15 yr return period storm at Lethbridge (Tauchin et al., 1991).

Treated water from the municipal supplies of Beaverlodge, Lacombe, and Raymond was used for this study. Source water was sampled at the municipal outlet and at each site before the rainfall simulation tests. Concentrations were low for both TP (Beaverlodge <0.002 to 0.017 mg L^–1; Lacombe <0.002 to 0.09 mg L^–1; Wilson 0.007 to 0.04 mg L^–1) and DRP (Beaverlodge <0.002 to 0.01 mg L^–1; Lacombe <0.002 to 0.09 mg L^–1; Wilson <0.002 to 0.02 mg L^–1).

Runoff water was collected from a triangular metal tray attached to the front plate of the runoff frame. The collection end of the tray was positioned lower than the soil surface above a 0.3 m deep hole to allow collection of the runoff water. The collection tray was covered with a 1.2 by 1.8 m sheet of clear plexiglass that prevented simulated rain from falling directly onto the collection tray.

Water Sampling and Analysis
Composite samples of runoff water were collected during consecutive intervals ending 5, 10, 20, and 30 min after the commencement of continuous runoff. Runoff was considered to have commenced when 200 mL min^–1 of water was measured. The total volume of water collected during each time interval was recorded. A 1-L sample of water from the total volume collected from each time interval was transported to the lab in a cooler with ice packs. After agitation, approximately 200 mL of unfiltered water was poured from the 1-L bottles and refrigerated at 4°C. An additional 200 mL was collected after filtration using a Nalgene membrane 0.45-µm filter unit or a Gelman 0.45-µm high-capacity filter within 24 h of sampling. Samples were preserved with 5% sulfuric acid. Filtered water samples were analyzed for DRP, and unfiltered water samples were analyzed for TP (Greenberg et al., 1995).

Data Analysis
Mean initial abstraction, or the amount of rainfall required to fill the surface soils to saturation before runoff begins, and runoff volumes were calculated for each treatment at each site from the fresh and residual manure rainfall simulations. Initial abstraction is a reflection of the soil's infiltration capacity and moisture content.

The DRP and TP flow-weighted mean concentration (FWMC) values were determined by dividing the total DRP or TP mass load for the 30-min interval by total flow volume for the same period. Total DRP and TP mass loads for the 30-min runoff period were the sum of the mass loads from the four runoff intervals, which were calculated by multiplying the DRP or TP concentration and the runoff volume for the specified interval.

A few of the 32 plots at each site were excluded from analysis due to hydrologic or chemical inconsistencies between replicates. The twelve plots at Wilson that received natural precipitation between the time of manure application and initial simulations were excluded from analysis. These plots generated notably lower concentrations of P than plots that received no rain after manure application.

Statistically significant differences were determined at the P < 0.05 level. Analytical results for TP and DRP reported as below detection limits were adjusted to zero. Significant differences among pre- and post-treatment STP values for different manure TP rates and incorporation treatments were determined using Tukey's adjustment for multiple comparisons.

Analysis of covariance (ANCOVA), using the mixed-model procedure in SAS (Littell et al., 1996; SAS Institute Inc., 2000), was applied to comparisons of STP to TP FWMC and DRP FWMC measured immediately after manure application and 1 yr later. Additionally, the mixed-model ANCOVA method was used to assess the relationships of total and water-extractable phosphorus in manure, and combinations of pretreatment STP and manure parameters in predicting DRP and TP FWMC measured immediately after manure application and incorporation. Incorporated and nonincorporated data were combined or analyzed separately, depending on results of the mixed-model analysis. A paired t test was used to compare mean runoff volumes from incorporated and nonincorporated treatments after ANCOVA results indicated no manure rate effect or treatment interaction. Regression analyses were also performed to obtain the r² values of significant relationships determined from the mixed-model analysis (SAS Institute Inc., 2000). The mixed-model procedure was chosen because it accounts for the random variation between replicates.

	RESULTS AND DISCUSSION

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
Manure and Soil Characteristics
Manure applied at Wilson had the greatest TP and WEP concentrations and the lowest moisture content, while Beaverlodge manure had the lowest TP and WEP concentrations, and Lacombe had the highest moisture content of the three sites (Table 3). Despite the variable nature of manure and changes in moisture content with time, the actual rates of TP applied to the Lacombe and Beaverlodge plots were close to the target rates (Table 4). At the Wilson site, rates calculated from the source manure samples resulted in over-application of TP on the plots by approximately two times target rates due to a reduction in moisture content between the time of source pile sampling and land application.

Mean post-treatment STP concentrations from samples collected during the fresh and residual manure rainfall simulations at all three sites had a positive relationship with target manure rate (Table 4), but with no significant differences between the incorporated and nonincorporated treatments. This suggests that the majority of phosphorus applied with manure remained in the upper 2.5 cm of the soil profile after a single incorporation. In a similar study in Alberta, Little et al. (2005) sampled soils following beef cattle manure application and incorporation by different tillage methods within a few days before rainfall simulation tests, and observed no significant difference in nutrient concentrations of the upper 2.5-cm soil profile between manured double disk and manured nonincorporated treatments in 2 yr of a 3-yr study.

For both the fresh and residual manure rainfall simulations, the lowest post-treatment STP concentrations were observed at the Beaverlodge site and the greatest values were observed at the Wilson site, a direct reflection of the amounts of phosphorus added with manure (Table 4). There were very few differences in STP concentrations between unmanured treatments. The mean STP concentrations of manured treatments 1 yr after application were generally lower and less variable than STP concentrations immediately after manure application. Similarly, Gaston et al. (2003) observed decreased levels of phosphorus in soils 2 yr after the cessation of poultry manure application to sites with short- and long-term manure histories.

Hydrology
No significant manure rate effect was observed for initial abstraction or runoff volumes, thus mean values were calculated for incorporation treatments, disregarding manure rate, at each site (Table 5). Daverede et al. (2004) and Michaud and Laverdière (2004) also reported no manure effects on the time required to produce runoff and runoff volume, though these studies involved liquid swine manure. Alternatively, studies involving solid manure (Mueller et al., 1984b; Ginting et al., 1998; Bundy et al., 2001; Little et al., 2005) reported greater runoff from unmanured than manured soils of various rates. Little et al. (2005) also recorded lower times to produce runoff from unmanured than manured soils.

In contrast, the Beaverlodge fresh manure rainfall simulations produced a mean initial abstraction from the incorporated treatment that was significantly greater than the mean initial abstraction from the nonincorporated treatment (Table 5). Inversely, mean runoff depth decreased with incorporation. A similar observation was reported by Daverede et al. (2003), who found that tilling with a chisel plow increased surface retention and infiltration rate of water in soils containing 25% clay on slopes of 6%. Soil texture at the Beaverlodge site was finer than these soils (Table 2), with a similar hill slope of 5%. Other studies that found less runoff from various types of tilled treatments compared with untilled treatments include Laflen and Tabatabai (1984), Mueller et al. (1984b), Freese et al. (1993), Myers and Wagger (1996), Gupta et al. (1997), Tabbara (2003), and Little et al. (2005).

Mean runoff depths from the nonincorporated Beaverlodge fresh manure simulations were similar to runoff depths from both incorporation treatments of the residual manure simulations, likely due to similar surface conditions (Table 5). These elevated volumes and lower initial abstraction of the Beaverlodge treatments not recently tilled, indicate impeded infiltration with several possible causes. Based on texture, lower infiltration rates could be expected from the fine-textured soils at Beaverlodge compared with the coarse-textured soils at Lacombe (Table 2). Though the Beaverlodge and Wilson soil textures were similar in the A horizon, Beaverlodge had finer B horizon textures due to translocated clay, which is characteristic of Luvisolic soils. This translocated clay may have impeded percolation below the A horizon. Additionally, Beaverlodge has been managed with conventional tillage practices, while Wilson has a history of no-till management that is known to enhance macropore development and infiltration (Edwards et al., 1988). The Lacombe and Wilson soils were also classified as Chernozems that typically contain greater amounts of organic matter than Luvisols (Agriculture Canada, 1987), which can improve soil tilth and infiltration (Tisdale et al., 1985). Finally, greater amounts of sodium in the Beaverlodge soil, compared with Lacombe and Wilson soils, increased the potential for soil dispersion that could have reduced infiltration (Table 2). While tillage may affect the volume of a runoff event, preexisting soil conditions appeared to dictate the degree and nature of these effects relative to untilled soil.

Relationships between Phosphorus in Manure and Runoff Phosphorus
Positive relationships between manure TP application rate and TP and DRP FWMC in runoff were observed from the fresh manure rainfall simulations at the three study sites (Table 6). Several other studies have also observed increased phosphorus in runoff with increasing manure application rates and various tillage practices and manure sources (Edwards and Daniel, 1993; Eghball and Gilley, 1999; Pote et al., 2001; Kleinman and Sharpley, 2003; Tabbara, 2003; Schroeder et al., 2004a; Tarkalson and Mikkelsen, 2004).

Dissolved reactive phosphorus FWMC in runoff was poorly related to manure WEP application rate and pretreatment STP plus manure WEP (data not shown). Contrary to these findings, similar studies have found a strong relationship between water-extractable phosphorus concentrations in manure and DRP concentrations in runoff (Kleinman et al., 2002a; Kleinman and Sharpley, 2003; DeLaune et al., 2004).

Effect of Incorporation on Runoff Phosphorus
Incorporation did not have a significant effect on TP and DRP FWMCs in runoff at the Lacombe and Wilson sites for either set of rainfall simulations (Fig. 2 and 3). Similarly, there was no significant incorporation effect on phosphorus in runoff from the Beaverlodge residual manure simulations (Fig. 2f and 3f). However, the Beaverlodge STP to TP and DRP FWMC relationships of the fresh manure simulations had significantly greater extraction coefficients for the nonincorporated than the incorporated data as a result of greater phosphorus concentrations in runoff (Fig. 2e and 3e). Similar studies have reported a variety of runoff phosphorus responses to manure incorporation. Withers et al. (2001), Kleinman et al. (2002a), Tabbara (2003), and Daverede et al. (2004) observed decreased runoff TP and DRP concentrations with manure incorporation. Tarkalson and Mikkelsen (2004) also reported this difference in TP but did not measure DRP concentrations. Mueller et al. (1984a) and Eghball and Gilley (1999) found decreases in DRP with incorporation, but observed increases in TP due to greater soil erosion.

View larger version (23K): [in this window] [in a new window]   Fig. 2. Relationships between soil test phosphorus (STP) and total phosphorus (TP) flow-weighted mean concentration (FWMC) for fresh (a, c, e) and residual (b, d, f) rainfall simulations.

View larger version (23K): [in this window] [in a new window]   Fig. 3. Relationships between soil test phosphorus (STP) and dissolved reactive phosphorus (DRP) flow-weighted mean concentration (FWMC) for fresh (a, c, e) and residual (b, d, f) rainfall simulations.

While P concentration in runoff in this study was not significantly different between incorporated and nonincorporated treatments on residual manure, incorporation of freshly applied manure is still recommended. Incorporation has been shown to reduce nitrogen losses by volatilization, increase crop nutrient recovery, and has the potential to reduce odor (Schoenau and Davis, 2006).

Relationships between Soil Test Phosphorus and Runoff Phosphorus
Similar to the effects of manure TP rate, TP and DRP FWMCs in runoff also increased with increasing post-treatment STP values (Fig. 2 and 3) at all three sites immediately after manure application, as well as 1 yr later. Relationships between STP and TP or DRP FWMC in runoff were strongest at Lacombe and Wilson, while the weakest relationships were observed at Beaverlodge from the fresh manure and residual manure rainfall simulations. Phosphorus concentrations decreased between the fresh and residual manure rainfall simulations relative to STP as shown by the 40% or more reduction in extraction coefficients between simulations. Kleinman and Sharpley (2003) found a decrease in DRP and TP concentrations with successive rainfall events on manured soil. They noted that loss of phosphorus with runoff was not the sole cause of the decrease, but that sorption of applied phosphorus by the soil may also have been a factor. Crop uptake will also have accounted for loss of P in the system.

Generally, phosphorus concentrations in runoff from the fresh manure simulations were similar in magnitude between Lacombe and Wilson at a given STP level. At the Beaverlodge site, P concentrations in runoff were much greater for the nonincorporated treatments compared with Lacombe and Wilson and notably less for the incorporated treatments (Fig. 2 and 3). Likewise, 1 yr later, concentrations from the residual manure simulations were similar between Lacombe and Wilson at a given STP level, but were notably less from Beaverlodge. The lower manure TP application rates at Beaverlodge, coupled with differences in the degree of soil phosphorus saturation as described by Casson et al. (2006), may explain the low phosphorus concentrations in runoff relative to the other sites from the residual manure simulations. Soil samples collected at Beaverlodge from our study had considerably higher phosphorus sorption index (PSI) values and lower degree of soil phosphorus saturation (DPS) values than the other two sites. With a greater capacity to tightly bind phosphorus to soil and lower phosphorus additions with manure, the Beaverlodge soils were less vulnerable to phosphorus losses in runoff than the other sites.

Dissolved reactive phosphorus concentrations accounted for 60 to 92% of TP in runoff from manured treatments at all three sites, except for the Beaverlodge fresh manure simulations where DRP ranged from 13 to 42% of TP in runoff. The high percentage of DRP in TP is similar to other studies conducted in Alberta (Ontkean et al., 2003; Ontkean et al., 2005). The proportion of DRP to TP concentrations in runoff varied little between incorporated and nonincorporated treatments, but was generally greater from manured than unmanured treatments. The DRP proportions of TP in runoff from unmanured treatments were 34 to 78% for all sites except Beaverlodge, which ranged from 10 to 12%. Similar experiments involving recently applied manure revealed much variation of DRP/TP ratios in runoff. Schroeder et al. (2004a) reported DRP fractions greater than half of TP in runoff from broadcast poultry manured soils. Kleinman et al. (2002a) also reported DRP concentrations greater than half of TP from broadcast and incorporated dairy, poultry, and swine manured soils, but DRP concentrations less than half of TP from unmanured soils. Kleinman and Sharpley (2003) found DRP concentrations generally greater than half of TP from broadcast dairy, poultry, and swine manured and unmanured coarse-loamy soil, but found DRP concentrations less than half of TP from a fine-loamy soil. These variable results were most likely caused by a number of factors that influenced erosivity of the soils, the forms of phosphorus in each experiment, and the ability of the individual soils to bind P.

Comparison of Extraction Coefficients with Other Studies
Relationships from this study involving STP as the independent variable in relation to TP and DRP FWMC in runoff were compared with similar published studies (Tables 7 and 8). Few studies have reported STP relationships with TP FWMC (Table 7). A number of studies have reported STP relationships with DRP FWMC (Table 8); however, variations in soil type, analytical and rain simulation methods, and management practices make comparisons difficult. In contrast, Vadas et al. (2005) concluded that a single extraction coefficient can be used across a wide range of conditions.

For the STP to DRP FWMC relationship, extraction coefficients for the Lacombe, Wilson, and Beaverlodge residual manure equations were two to six times greater than most of the other studies (Table 8). These larger DRP coefficients in this study may be due to differences in the amount of manure at or near the surface of the soil as compared with other studies. However, the Lacombe and Wilson residual manure equations had similar extraction coefficients to those reported by Sharpley et al. (2002) from lab simulations on cultivated soils of a historically manured Pennsylvania watershed. The Beaverlodge residual manure equation had a similar extraction coefficient to the coefficient from the 30-min equation reported by Wright et al. (2006), but was slightly greater than their coefficient for the equilibrated runoff rate equation.

Mass Load of Phosphorus in Runoff
Mass load removal of TP and DRP at all three sites was similar to changes in phosphorus concentrations with respect to manure rate and incorporation treatments (Table 9). Similar observations were reported by Pote et al. (1996) and Daverede et al. (2003, 2004). Mueller et al. (1984a) and Schroeder et al. (2004a) also observed phosphorus loads that differed from phosphorus concentrations in runoff due to treatment or extraneous effects on runoff volume and rate.

	CONCLUSIONS

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
Positive relationships were observed between phosphorus in soil or manure and phosphorus in runoff from incorporated and surface-applied freshly manured soil as well as for residual manured soil, 1 yr after application. Soil test phosphorus measured on fresh and residual manured soils increased with manure rate, but was lower for the residual manured soils at all sites. Similarly, concentrations of TP and DRP in runoff increased with manure rate and STP from freshly manured soil, as well as from residual manured soil, though at a lower rate. Manure rate had no significant effect on initial abstraction or runoff volumes from either fresh or residual manured soils.

Soil test phosphorus concentrations were similar between incorporated and nonincorporated fresh and residual manured treatments, indicating an insignificant amount of phosphorus was incorporated below the 0- to 2.5-cm depth interval. Incorporation had no significant effect on initial abstraction, runoff depths, or concentrations of TP and DRP in runoff, except for the fresh manure rainfall simulations at Beaverlodge. For the fresh manure simulations at Beaverlodge, initial abstraction volumes increased, while runoff depths and phosphorus concentrations decreased with manure incorporation. These effects at Beaverlodge were likely due to impeded infiltration of the nonincorporated treatments.

Overall, concentrations of phosphorus in runoff were lower from the residual manured soils than from the freshly manured soils. This decrease with time was likely due to increased soil/manure interaction that enhanced phosphorus sorption to soil.

Extraction coefficients (slopes) for the relationships between STP and phosphorus in runoff decreased from simulations conducted on freshly manured soils (0.013 to 0.11) to those on residual manured soils (0.006 to 0.015). However, extraction coefficients for residual manured soils were two to six times greater than those found in most other studies, possibly due to greater amounts of manure at or near the surface of the soil.

Phosphorus loads in runoff from rainfall simulations conducted on fresh and residual manured soils exhibited similar trends to phosphorus concentrations with respect to manure application rates and incorporation treatments. Incorporation with the double disk had no significant effect on phosphorus loads in runoff from manure-amended soils 1 yr after application compared with the nonincorporated manure-amended soils. While incorporation of fresh manure in this study showed only limited effectiveness in reducing P in runoff, incorporation of manure is still recommended to reduce nitrogen losses, improve nutrient uptake by crops, and potentially reduce odor concerns.

A relatively small portion (less than 2%) of the phosphorus applied with manure was removed in runoff from the freshly manured soils and even less (less than 1%) was removed 1 yr after manure application. Hence, a large amount of phosphorus from the manure application remained in the soil after 1 yr, some of which was available for transport to surface water during subsequent runoff events.

	ACKNOWLEDGMENTS

 
Special thanks to those who helped carry out this project from Alberta Agriculture, Food, and Rural Development (AAFRD) and 5th on 5th Youth Services from Lethbridge, Alberta. Many thanks also go to Toby Entz (Agriculture and Agri-Food Canada, Lethbridge, Alberta) for his statistical wisdom and Ray Taylor of Darray Farms, as well as Raman Azooz and Dave Young and their staff from the Agriculture and Agri-Food Canada Research Centres at Beaverlodge and Lacombe respectively, for sharing their time, equipment, land, and historical records. Partial funding for this study was provided by the Agricultural Funding Consortium. Contributors included the Alberta Livestock Industry Development Fund, the Alberta Crop Industry Development Fund, and the Alberta Agricultural Research Institute.

	REFERENCES

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 

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