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Published in J. Environ. Qual. 33:1424-1430 (2004).
© ASA, CSSA, SSSA
677 S. Segoe Rd., Madison, WI 53711 USA

TECHNICAL REPORTS

Surface Water Quality

Runoff Phosphorus Losses as Related to Phosphorus Source, Application Method, and Application Rate on a Piedmont Soil

David D. Tarkalsona,* and Robert L. Mikkelsenb

a Department of Agronomy and Horticulture, University of Nebraska–Lincoln, West Central Research and Extension Center, 461 West University Drive, North Platte, NE 69101
b Department of Soil Science, North Carolina State University, Campus Box 7619, Raleigh, NC 27695

* Corresponding author (dtarkalson2{at}unl.edu).

Received for publication May 20, 2003.

   ABSTRACT
TOP
 NOTES
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 
Land application of animal manures and fertilizers has resulted in an increased potential for excessive P losses in runoff to nutrient-sensitive surface waters. The purpose of this research was to measure P losses in runoff from a bare Piedmont soil in the southeastern United States receiving broiler litter or inorganic P fertilizer either incorporated or surface-applied at varying P application rates (inorganic P, 0–110 kg P ha–1; broiler litter, 0–82 kg P ha–1). Rainfall simulation was applied at a rate of 76 mm h–1. Runoff samples were collected at 5-min intervals for 30 min and analyzed for reactive phosphorus (RP), algal-available phosphorus (AAP), and total phosphorus (TP). Incorporation of both P sources resulted in P losses not significantly different than the unfertilized control at all application rates. Incorporation of broiler litter decreased flow-weighted concentration of RP in runoff by 97% and mass loss of TP in runoff by 88% compared with surface application. Surface application of broiler litter resulted in runoff containing between 2.3 and 21.8 mg RP L–1 for application rates of 8 to 82 kg P ha–1, respectively. Mass loss of TP in runoff from surface-applied broiler litter ranged from 1.3 to 8.5 kg P ha–1 over the same application rates. Flow-weighted concentrations of RP and mass losses of TP in runoff were not related to application rate when inorganic P fertilizer was applied to the soil surface. Results for this study can be used by P loss assessment tools to fine-tune P source, application rate, and application method site factors, and to estimate extreme-case P loss from cropland receiving broiler litter and inorganic P fertilizers.

Abbreviations: AAP, algal-available phosphorus • RP, reactive phosphorus • STP, soil test phosphorus • TP, total phosphorus


   INTRODUCTION
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 
PHOSPHORUS APPLIED in manures and inorganic fertilizer to agricultural land has the potential to be carried in runoff to surface water, resulting in eutrophication (Sharpley et al., 1993). Recent concerns regarding the effects of manure and inorganic fertilizer on water quality have led to the development of state-specific agricultural P management strategies and tools to identify sites vulnerable to losses.

Lemunyon and Gilbert (1993) first proposed the use of the P Index to assess potential P losses from agricultural land. Because field studies are expensive and time-consuming, and computer simulation models require detailed soil and management inputs that are frequently unavailable or difficult to obtain, a site-specific P Index can be used to identify sites vulnerable to P loss (Sharpley et al., 1993; Sharpley, 1995). The P Index uses site characteristics, including soil test phosphorus (STP), P application rate, application time and method, and P source, to predict P loss vulnerability from the land. The site-specific nature of P losses from agricultural land gives rise to the need for studies to more accurately determine potential P losses from a given location.

Several studies have been conducted to measure P in runoff following incorporation or surface application of various P sources. Incorporation of animal manure is generally the most efficient way of making nutrients from the manure available to plants; however, this is frequently not possible or desirable. Manure incorporation can also decrease P losses to surface waters (Mueller et al., 1984). Ginting et al. (1998) found that when cattle manure was incorporated into the soil, there was no difference in particulate phosphorus (PP) and total phosphorus (TP) losses in runoff compared with an unfertilized control. Similarly, Couillard and Li (1993) showed that algal growth in runoff water from plots with soil-incorporated swine manure was not significantly different than that in runoff from an unmanured soil. Yoon et al. (1994) found no difference in PP losses in runoff from plots receiving poultry litter applied at 399 kg P ha–1 or 796 kg P ha–1 when it was incorporated into the soil. However, Gascho et al. (1998) found that following the incorporation of inorganic P fertilizer, there were still significant losses of bioavailable phosphorus (BAP) and dissolved reactive phosphorus (DRP) compared with an unamended soil.

It is important to understand that excessive soil disturbance from tillage and manure incorporation, under certain circumstances, can increase soil erosion and have a negative effect on soil and water quality. However, manures and fertilizers applied to the soil surface without tillage are also susceptible to transport by runoff to surface waters (Edwards and Daniel, 1994; Nichols et al., 1994). Mostaghimi et al. (1989) found that TP in runoff from surface-applied fertilizer P was 65% higher than TP losses when the fertilizer P was injected beneath the soil surface at the same application rate.

There are conflicting reports concerning the differences in P loss in runoff between fertilized and manured agricultural fields. Yoon et al. (1994) found no difference in PP losses in runoff from soil-incorporated poultry litter (399 or 796 kg P ha–1) and an incorporated triple super-phosphate (TSP) treatment (222 kg P ha–1) from fields planted with a cover crop. Losses of DRP were significantly higher at the 796 kg P ha–1 rate than both the TSP treatment and the 399 kg P ha–1 litter treatment; however, there was no difference in TP losses between the three treatments. Edwards and Daniel (1994) showed that P fertilizer applied to the surface of pasture had higher DRP and TP in runoff from the first and second simulated rainfall event than broiler litter applied at the same P application rate. It was hypothesized that the difference in P loss was due to the higher solubility and mobility of P fertilizer. However, Nichols et al. (1994) found no difference in runoff P concentrations between poultry litter and fertilizer applied to the surface of a pasture. Gangbazo et al. (1997) found that there was no difference in runoff DRP and TP losses between incorporated hog manure and inorganic fertilizers from corn (Zea mays L.) plots in Quebec.

Concentration and mass loss of P in runoff following manure application to the soil surface have been found to increase as application rates increase (Edwards and Daniel, 1993; Nichols et al., 1994; Smith et al., 2001; Wood et al., 1999). However, Bengtson et al. (1998) measured no difference in TP losses in runoff from sugarcane (Saccharum spp.) plots in Louisiana on alluvial soil with 0, 20, and 39 kg P ha–1 applied to the soil surface. Variation in site-specific conditions and management (e.g., soils characteristics, rainfall, and cropping management) will influence the likelihood of P loss.

There is little information on P losses from soil when litter is applied to the soil surface or incorporated for row crop production in the southeastern United States. The objective of this research was to measure the effects of P source, application rate, and placement on P concentration and mass losses in runoff from a representative North Carolina Piedmont soil.


   MATERIALS AND METHODS
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 
Fifty-four 9-m2 plots (3 x 3 m) with a 1-m border were arranged on 0.12 ha located on the North Carolina State University Lake Wheeler Farm in Raleigh, NC. The area was selected for this study due to a uniform slope (2–3%) and surface soil texture (Cecil clay loam: fine, kaolinitic, thermic Typic Kanhapludults). The surface-2.5-cm soil contained 32% clay. The treatments consisted of six rates of broiler litter applied to the soil surface, four rates of broiler litter incorporated into the soil, four rates of inorganic P fertilizer (superphosphate, 8% P) applied to the soil surface, three rates of inorganic P fertilizer incorporated into the soil, and a control (Table 1). All treatments were replicated three times in a completely randomized design. The broiler litter had a percent dry matter of 76.8, total N content of 41.4 g kg–1, and a total P content of 16.5 g kg–1. The P sources were uniformly hand-applied to the 9-m2 plots on the day of rainfall simulation. Surface treatments remained undisturbed while incorporation to a depth of 13 cm was accomplished using a rototiller. The experimental design was originally a factorial with a single control. Deviating from the original design occurred due to two factors. First, limited plot space in experimental area limited the number of P rates for the incorporated treatments compared with the surface-applied treatments. Second, broiler litter P rates differed from inorganic P rates as a result of P rates from broiler litter being converted from a wet weight basis to a dry weight basis after application occurred. The control treatment did not receive tillage; therefore, it was similar to the surface-applied P treatments with respect to soil conditions.


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  		Table 1. Phosphorus sources, application rates, and placement of materials applied to plots, and mean total runoff volume for treatments collected over the 30-min rainfall event.

 
Before P application and rainfall simulation, eight, 2-cm-diameter soil cores were extracted to a depth of 2.5 cm outside each plot area. The individual cores were combined into one bulk sample per plot for analysis of Mehlich 3–extractable P (Mehlich, 1984). The Mehlich 3–extractable P results were used to estimate the soil P concentrations of the plots before addition of the treatments without disturbing the soil in the plot areas.

A variable rate rainfall simulator (Miller, 1987) was used to apply rainfall at a rate of 76 mm h–1 to a 4-m2 (2 x 2 m) plot area outlined by a steel frame inserted to a depth of 10 cm. This rainfall rate was based on the runoff simulation protocols of the National Phosphorus Research Project (North Carolina State University, 2004), and is 15.2% higher than the average 10-yr 1-h storm return period rainfall rate in the Piedmont region of North Carolina (66 mm h–1) (National Oceanic and Atmospheric Administration, 2004). Runoff was intercepted at the bottom of the plot with a plastic gutter buried in the ground and directed to a buried 19-L polycarbonate collection vessel. During the 30-min rainfall event, runoff water was collected at 5-min intervals after the start of runoff, the volume recorded, and subsampled for subsequent laboratory analysis. Water samples were refrigerated at 4°C while awaiting chemical analysis. Water samples were extracted for RP by filtration through a 0.45-µm filter (Haygarth and Sharpley, 2000). Algal-available phosphorus (AAP) was extracted from unfiltered samples using 0.11 M NaOH (Sharpley et al., 1991; Haygarth and Sharpley, 2000), and TP was extracted from unfiltered samples using a H2SO4 and (NH4)2S2O8 digestion (Greenberg et al., 1992, p. 112). Concentrations of RP, AAP, and TP in runoff were determined using a colorimetric procedure (Murphy and Riley, 1962). Mass losses of P were determined at each 5-min sampling interval by multiplying the measured concentration of P by the recorded runoff volume in the 5-min interval. Mass losses of P were summed over the six, 5-min intervals to give a total mass loss over the 30-min rainfall event. Measured concentrations of RP, AAP, and TP in runoff were flow-weighted by dividing the total 30-min mass losses of RP, AAP, and TP by the total runoff volume over the 30-min rainfall period. Because of the small size of the plots, very little runoff occurred after rainfall was stopped.

Statistical Analysis
Analysis of covariance was performed to determine if initial STP concentrations supplied statistically significant concentrations and masses of RP, AAP, and TP in runoff compared with added P sources. Regression analysis using the general linear model procedure (SAS Institute, 1998) was used to compare the 30-min concentration and mass loss of RP, AAP, and TP in runoff (dependent variables) with surface P application rates (independent variable) for the two P sources. Equality of slopes and intercepts was tested for the two P sources. A square root transformation was performed on runoff RP, AAP, and TP concentration and mass loss data before statistical analysis to achieve homogeneity of error variance. Mean separation using LSD analysis in SAS was used to separate runoff RP, AAP, and TP concentrations and mass losses in runoff for each P source separately at each 5-min sample time. All statistical analysis is based on transformed data, while nontransformed results are reported. All statistical comparisons were reported at P = 0.05.


   RESULTS AND DISCUSSION
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
CONCLUSIONS
 REFERENCES
 
Runoff
Runoff volumes from the treatment plots over the 30-min rainfall event ranged from 46.2 to 110.3 L (Table 1). Variability in hydrology of the experimental plots resulted in variability associated with runoff volumes among plots.

Initial Plot Soil Test Phosphorus and Runoff Phosphorus
Analysis of covariance with initial plot STP concentrations as the covariate showed that STP concentration significantly (P = 0.05) contributed to concentrations and mass losses of RP and AAP in runoff, and also to concentrations of TP in runoff for both incorporated P sources (Table 2). However, the same covariate analysis showed initial STP concentrations did not significantly contribute to runoff RP, AAP, and TP concentrations and mass losses in runoff for the two surface-applied P sources and incorporated mass losses of TP from both P sources (inorganic P and litter) (Table 2). Incorporation of broiler litter and inorganic P fertilizer into the soil reduced the P source contribution of P in runoff, and the initial STP concentration supplied significant amounts of P to runoff. However, if the broiler litter and inorganic P fertilizer were surface-applied, the STP contribution to runoff P was negligible in comparison with the runoff P from the applied P sources.


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  		Table 2. Significance of initial Mehlich 3–extractable P as a covariate in the analysis of runoff reactive phosphorus (RP), algal-available phosphorus (AAP), and total phosphorus (TP) concentration and mass losses allowing for effects of incorporated P sources (treatment) and application rate (rate).

 
Initial STP concentrations differed among the three untreated control plots (13.5, 16.9, and 58.9 mg P kg–1). This variability was due to different P fertilization practices from two different cropping systems that covered the current experimental area in the past. As initial STP increased, both the concentrations and mass losses of P in runoff from these plots also increased (Table 3). Soil P concentrations will greatly influence potential P movement from the field when broiler litter and inorganic P fertilizer are incorporated, and from fields not receiving recent surface P applications.


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  		Table 3. Initial soil test phosphorus (STP), runoff reactive phosphorus (RP), algal-available phosphorus (AAP), and total phosphorus (TP) flow-weighted concentration and mass losses, and runoff volumes from the replicate plots of the control treatment.

 
Losses of Phosphorus in Runoff after Incorporation of Phosphorus Sources
Concentrations of AAP and TP, and mass losses of RP, AAP, and TP in runoff from plots with incorporated broiler litter and inorganic P fertilizer were not significantly different from the control plots (Table 4). In this study, concentrations and mass losses of P in runoff after the incorporation of inorganic P and broiler litter at all rates were not related to the applied P. Initial soil P played an important role in runoff P losses from plots receiving incorporated P sources in this study. However, there was a significant rate effect for RP concentration in runoff (Table 4). As P application rates increase above those used in this study, the potential to increase runoff P losses may increase.


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  		Table 4. Flow-weighted concentration and mass losses of runoff reactive phosphorus (RP), algal-available phosphorus (AAP), and total phosphorus (TP) in runoff after incorporation of inorganic and P broiler litter at various P application rates. With the exception of RP concentration in runoff, phosphorus source main effects were not significantly different from the control at the 0.05 level.

 
Incorporation of the broiler litter into the soil decreased concentrations of RP, AAP, and TP in runoff compared with surface application by 97, 87, and 84% when averaged over all P application rates, respectively (Table 4 and Fig. 1). Incorporation of the inorganic P fertilizer into the soil decreased concentrations of RP, AAP, and TP in runoff compared with surface application by 94, 75, and 65% when averaged over all P application rates, respectively (Table 4 and Fig. 1). Incorporation of the broiler litter into the soil decreased mass losses of RP, AAP, and TP in runoff compared with surface application by 98, 90, and 88% when averaged over all P application rates, respectively (Table 4 and Fig. 2). Incorporation of the inorganic P fertilizer into the soil decreased mass losses of RP, AAP, and TP in runoff compared with surface application by 91, 85, and 72% when averaged over all P application rates, respectively (Table 4 and Fig. 2).



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  		Fig. 1. Relationship between surface P application rate of broiler litter and inorganic P fertilizer and the reactive phosphorus (RP), algal-available phosphorus (AAP), and total phosphorus (TP) flow-weighted concentrations in runoff from a Cecil clay loam. Each point is the average of three flow-weighted replications. Bars represent the standard errors for the treatment means.

 


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  		Fig. 2. Relationship between surface P application rate of broiler litter and inorganic P fertilizer and the reactive phosphorus (RP), algal-available phosphorus (AAP), and total phosphorus (TP) mass losses in runoff from a Cecil clay loam. Each point was summed over the six sampling times for 30 min and averaged over three replications. Bars represent the standard errors for the treatment means.

 
Losses of Phosphorus in Runoff after Surface Application of Phosphorus Sources
Concentrations and mass losses of RP, AAP, and TP in runoff from plots receiving surface applications of either broiler litter or inorganic P fertilizer were not significantly different at the lowest P application rates. However, as P application rate increased, both the concentration and mass loss of RP, AAP, and TP in runoff were greater from plots receiving broiler litter compared with inorganic P fertilizer (Fig. 1 and 2). The higher retention of inorganic P fertilizer in the plots compared with broiler litter was probably due to P sorption to the soil matrix because of the rapid dissolution of the fertilizer inorganic P from the rainfall before runoff and a relatively low average initial STP concentration of 43 mg P kg–1.

Higher runoff RP, AAP, and TP concentrations and mass losses in the broiler litter plots compared with inorganic P treatments at higher P application rates were potentially due to the greater ability of litter P to be carried in runoff as compared with the inorganic P. Wood shavings were the primary component of the broiler litter, and were easily transported in runoff. Conditions that vary from the experimental approach in this paper will probably influence the losses of P in runoff from land receiving broiler litter and inorganic P fertilizer applications. For example, a light rainfall event that does not result in runoff could possibly move P bound to wood shavings in broiler litter into the soil. Under this situation, P losses in runoff from these soils will possibly act more like inorganic P fertilizer applications when a runoff-producing rainfall event occurs. Another example is field border effects. Grass buffer strips have not been included in this study and will probably influence losses from the field edge. The experimental approach in this paper is based on in-field losses of P in runoff under worst-case conditions and the results should be interpreted accordingly.

High rates of surface-applied broiler litter (typical with N-based application rates) resulted in higher runoff P concentrations compared with inorganic P fertilizer. When broiler litter and inorganic P are added at rates to meet the crop P requirement, runoff P concentrations will be less compared with higher N-based application rates. In this study, the concentration of RP and mass loss of TP in runoff after surface application of 66 kg P ha–1 from broiler litter was 4.3 and 7.2 times higher than inorganic P fertilizer applied at the same rate, respectively (Fig. 1 and 2).

There was a significant linear relationship between RP, AAP, and TP concentrations and mass losses in runoff and application rate from plots receiving surface-applied broiler litter (Table 5). With the exception of RP, concentrations of P in runoff were related to P application rate from plots receiving inorganic P fertilizer. However, mass losses of RP, AAP, and TP in runoff were not related to P application rate from plots receiving inorganic P. Generally, concentrations of P in runoff significantly increased as application rates increased from plots receiving broiler litter and inorganic P fertilizer, and mass losses of P in runoff significantly increased as application rate increased from plots receiving broiler litter but not inorganic P fertilizer.


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  		Table 5. Linear regression correlation coefficients, slopes, and intercepts for the relationship between surface-applied broiler litter and inorganic P fertilizer rates correlated to square root–transformed{dagger} runoff reactive phosphorus (RP), algal-available phosphorus (AAP), and total phosphorus (TP) in runoff from a Cecil clay loam soil.

 
Concentrations of P in runoff from plots receiving broiler litter application rates of 8 to 82 kg P ha–1 ranged from 2.3 to 21.8 mg RP L–1, 4.3 to 24.4 mg AAP L–1, and 6.3 to 33.4 mg TP L–1 based on linear regression equations (Table 5, Fig. 1). Concentrations of runoff P from plots receiving surface-applied inorganic P application rates of 11 to 110 kg P ha–1 ranged from 3.7 to 11.9 mg AAP L–1 and 4.1 to 11.9 mg TP L–1 based on linear regression equations (Table 5, Fig. 1). Concentrations of RP in runoff were not significantly related to inorganic P application rate, but there was a trend for increasing concentrations in runoff of 1.9 to 6.6 mg RP L–1 as application rate increased from 11 to 110 kg P ha–1 (Table 5, Fig. 1). Variability between the three replications and adsorption of P to the soil matrix as previously discussed was probably the reason for the nonsignificant relationship between the concentration of RP in runoff and application rate.

Mass losses of P in runoff from plots receiving broiler litter were significantly correlated to broiler litter application rates of 8 to 82 kg P ha–1 (Table 5). Mass losses of P from these plots ranged from 0.5 to 5.5 kg RP ha–1, 1.0 to 6.7 kg AAP ha–1, and 1.3 to 8.5 kg TP ha–1 (Table 5, Fig. 2). Mass losses of P in runoff were not related to inorganic P application rate, but there was a trend for increasing mass losses of 0.33 to 0.77 kg RP ha–1, 0.66 to 1.7 kg AAP ha–1, and 0.65 and 1.5 kg TP ha–1 as application rates increased from 11 to 110 kg P ha–1 (Fig. 2). Nonsignificant relationships between mass loss of P in runoff and inorganic P application rate were probably due to P adsorption to the soil matrix as previously discussed.

The greater runoff losses of P at the application rate of 66 kg P ha–1 compared with 82 kg P ha–1 are not well understood. The runoff volume from the 66 kg P ha–1 treatment was 27.7% higher than from the 82 kg P ha–1 treatment. The higher flow of runoff water from the 66 kg P ha–1 treatment plots potentially carried a greater amount of P than from the 82 kg P ha–1 treatment. The quantity of litter and P remaining in the plots after the rainfall event was not assessed. Further studies focusing on the interaction of the soil and broiler litter chemical and physical properties would help clarify this observation.

Concentrations of RP in runoff from plots receiving broiler litter and inorganic P were 81 and 63% of the AAP losses and 64 and 60% of the TP losses, respectively, when averaged over all broiler litter P application rates, sampling times, and replications. The lower proportion of AAP and TP as RP from plots receiving inorganic P was potentially due to P being adsorbed to soil particles to a greater degree compared with soil receiving broiler litter. The solubility of the inorganic P and a relatively high P adsorption capacity of the soil may have been favorable to rapid adsorption of the P compared with the litter.

Mass loss of RP in runoff from plots receiving broiler litter and inorganic P were 64 and 48% of the AAP losses, respectively, when summed over sampling times, and averaged over application rates and replications. The higher proportion of AAP as RP from plots receiving broiler litters compared with inorganic P treatments may be a result of soluble P desorption from solid-phase litter in sample bottles after runoff left the plot before analysis.

Phosphorus Losses over Time
Assessing P losses in runoff as influenced by rainfall storm length can be an important factor in P loss management. At all application rates, the concentrations of RP in runoff decreased with time over the 30-min rainfall event after the surface application of broiler litter and inorganic P. However, as a result of increasing runoff volume over time, mass losses of TP in runoff showed a less consistent trend of decreasing P loss over time. Phosphorus losses in runoff at the 66 kg P ha–1 application rate are shown to illustrate this trend (Table 6). Plots receiving 66 kg P ha–1 in broiler litter had higher concentrations of RP and mass losses of TP in runoff than the plots receiving 66 kg P ha–1 as inorganic P fertilizer at all sampling times, with an exception of the 5-min sampling time. Runoff volumes from plots receiving 66 kg P ha–1 as inorganic P fertilizer, broiler litter, and the control over time are also shown in Table 6.


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  		Table 6. Flow-weighted concentrations of reactive phosphorus (RP) and mass losses of total phosphorus (TP) in runoff for surface-applied broiler litter and inorganic P fertilizer both applied at a rate of 65 kg P ha–1, and the unfertilized control over a 30-min rainfall event.{dagger}

 

   CONCLUSIONS
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
REFERENCES
 
Incorporation of broiler litter and inorganic P fertilizer into the soil resulted in P losses not significantly different than the unfertilized control. Surface application of broiler litter and inorganic P fertilizer resulted in significantly higher runoff P losses compared with the unfertilized control. As the P application rate increased, both concentration and mass of P in runoff were consistently greater from plots receiving broiler litter than from inorganic P fertilizer. This may be a result of inorganic P fertilizer being adsorbed to the soil matrix to a greater extent than the broiler litter, which due to its low density was carried readily from the plots in runoff.

The experimental approach used in this study represents an extreme-case scenario. The results from this study provide an estimation of the maximum potential losses of P in runoff from agricultural land with similar rainfall and soil characteristics. Implementation of selected best management practices can drastically reduce P losses in runoff compared with the losses reported from this study.

Evidence from this research shows that surface applications of broiler litter on bare soils with similar characteristics as the Cecil soil should be avoided before runoff events. Incorporation of broiler litter can help alleviate concentration and mass loss of P in runoff compared with surface application. However, since tillage associated with incorporation may increase erosion, best management practices such as vegetated buffers and contour planting should be implemented to minimize soil loss.

This study developed relationships between P source, application method, and application rate as related to runoff P losses from cropland. The relationships and data derived from this study can be used to help predict potential in-field P losses from agricultural land receiving P inputs in the Piedmont region of the southeastern United States.


   NOTES
TOP
 NOTES
ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 
A contribution of the University of Nebraska Agricultural Research Division, Lincoln, NE 68583. Journal Series no. 14122.


   REFERENCES
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 


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Vadose Zone Journal Journal of Plant Registrations
Journal of Natural Resources
and Life Sciences Education		 Soil Science Society of America Journal