| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
|
|
|
|||||||
|
|||||||||
USDA-ARS, Northwest Irrigation and Soils Research Lab., 3793 N. 3600 E., Kimberly, ID 83341
* Corresponding author (dtw{at}kimberly.ars.pn.usbr.gov)
Received for publication September 8, 2000.
 |
ABSTRACT |
|---|
 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
|---|
Abbreviations: DRP, dissolved reactive phosphorus • EC, electrical conductivity • FeO-Ps, iron-oxide impregnated paper–extractable phosphorus in soil • FeO-Pw, iron-oxide impregnated paper–extractable phosphorus in runoff water • Pi, Olsen P (inorganic phosphorus) • PSI, phosphorus sorption index • Pws, water-soluble phosphorus • RO, reverse osmosis • RO/Tap, 50:50 mix of RO and well water • SAR, sodium adsorption ratio
|
INTRODUCTION |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
|---|
Dissolved reactive phosphorus (DRP) concentrations in soil solution required for plant growth are in the range of 0.2 to 0.3 mg L-1. Total P concentrations as low as 0.02 mg L-1 may cause eutrophication of lakes and streams (USEPA, 1996). The USEPA (1986) recommended a limit of 0.05 mg total P L-1 in streams flowing into lakes, and 0.1 mg total P L-1 in other waters. Therefore, P entering lakes and streams from agricultural runoff could seriously affect growth of algae and other aquatic plants. Research is under way to identify and develop management practices that will minimize potential P effect on water bodies (Sharpley et al., 2000; Tunney et al., 1997).
Generally, total P losses leaving agricultural fields are not large and depend greatly on sediment amounts carried off the fields (Berg and Carter, 1980). In irrigated agriculture, most erosion occurs from surface irrigation. However, depending on field slopes and water application rates, runoff and erosion also occur from overhead sprinkler irrigation systems. Some of this runoff may reach water bodies. Therefore, development of management practices to minimize potential runoff and concomitant P loss is also germane where sprinkler irrigation is practiced.
Soil tests are available relating soil P concentrations to crop needs. Whether or not the same soil tests are related to P in runoff remains uncertain (Sibbesen and Sharpley, 1997). Pote et al. (1996) found on fescue (Festuca arundinacea Schreb.)-covered acid soil that dissolved reactive P and biologically available P in runoff were better related to soil P extracted by distilled water, iron-oxide impregnated paper strip (Sharpley, 1993), or acidified ammonium oxalate than to soil P extracted by Mehlich III (Mehlich, 1984), Bray–Kurtz P1 (Bray and Kurtz, 1945), and Olsen (Olsen et al., 1954) methods. In a subsequent simulated rainfall field study on three Ultisols, Pote et al. (1999) considered site hydrology by dividing runoff DRP concentrations by runoff volume and found that runoff P from each soil had statistically (P = 0.05) the same correlations to water-extractable soil P.
Water quality available for runoff studies varies depending on source and may differ from rain water quality (Lentz et al., 1996). Therefore, a postulate is that water from various sources may influence runoff and P losses. Soil surface conditions, whether a loose dry seedbed, a wet surface following a rain, or a dry crust, may also influence runoff and P loss. Thus, our objectives were, on a calcareous soil in a laboratory sprinkler study, to evaluate effects of water from two sources on runoff, soil loss, and phosphorus forms in runoff from soil with different surface conditions and P concentrations.
|
MATERIALS AND METHODS |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
|---|
The soil was a Portneuf silt loam. Topsoil was removed from some plots in 1991 to create a pattern of topsoil and exposed subsoil. Conventional subsoil plots were fertilized according to soil test with monocalcium phosphate in 1991. Subsoil whey plots received acid cheese whey (with H3PO4) in the spring and fall of 1991, and sweet cheese whey in the fall of 1994. Subsoil manure 1994 plots received acid whey in the spring and fall of 1991, and an application of fresh dairy manure in the fall of 1994. Subsoil manure 1991 received fresh dairy manure in the spring and fall of 1991. Topsoil manure 1994 received fresh dairy manure in the fall of 1994, and topsoil whey received sweet whey in the fall of 1994. Conventional topsoil plots received no fertilizer or amendments. General background soil test concentrations are listed in Table 1. Average Olsen P concentrations ranged from 21 mg kg-1 in the subsoil to 107 mg kg-1 in the topsoil. Topsoil plots averaged 9.2 g kg-1 organic carbon, nonmanured subsoil plots averaged 5.6 g kg-1, and manured subsoil plots, 9.0 g kg-1. Lime content for the topsoil averaged 108 g kg-1, and for the subsoil, 243 g kg-1.
|
To minimize the soil requirement for each test we placed a dry substrate of leveled clay loam in each box. Each test soil was friable and no screening or mixing was done prior to placing it on top of the substrate at about a 5-cm depth. We smoothed the soil surface by screeding (moving a flat wood board edgewise back and forth across the soil surface), leaving the surface crumbly and loose. Bulk density was about 1 Mg m-3 in all tests.
There was a total of 32 complete runoff tests: two each of four topsoil and four subsoil samples and two water sources. Each test soil was irrigated sequentially three times with either reverse osmosis (RO) water or a mix of half RO water and half well water (RO/Tap). The first irrigation was when the soil surface was air-dry and crumbly, followed by a second irrigation 2 d later when the soil surface was still visibly wet. The third irrigation followed about 7 to 10 d later when the soil surface had dried and formed a crust with resultant shallow 1- to 2-mm-wide cracks. Each irrigation was restricted to 15 min. Following three irrigation runs with either RO water or RO/Tap water, the soil was allowed to dry. The surface soil was then removed and replaced with the next set of sample soils and irrigated. To maintain similar conditions for each irrigation series, the moist substrate was loosened prior to adding new test soil. Soil water content, by oven-dry weight, in the surface 2.5 cm ranged from 9 to 13% for the first, 22 to 27% for the second, and 10 to 13% for the third irrigation. These soil water contents compare to about 24% at field capacity, and about 12% at the permanent wilting point for this soil (Robbins, 1977).
We used the RO/Tap water to simulate surface irrigation water. The RO/Tap water had pH = 7.5, electrical conductivity (EC) = 0.4 dS m-1, sodium adsorption ratio (SAR) = 1.3, total P < 0.02 mg L-1, and DRP < 0.01 mg L-1. The RO water had pH = 5.3, EC = 0.02 dS m-1, total P < 0.02 mg L-1, and DRP < 0.002 mg L-1; SAR was nonapplicable. For comparisons, Snake River source-irrigation water for the area averages pH = 8.2, EC = 0.5 dS m-1, SAR = 0.7, and total P and DRP 
0.07 mg L-1 (Carter et al., 1973, 1974). Average reported rainwater analysis for Idaho locations is pH 
5.4, EC 5.7 x 10-3 dS m-1, and SAR 0.8 (National Atmospheric Deposition Program, National Trends Network, 2000).
Water was pumped from 210-L mixing barrels and applied through an oscillating sprinkler similar to one described by Meyer and Harmon (1979). A Veejet nozzle (8070; Spraying Systems Co., Wheaton, IL) was mounted 3 m above the soil surface and water was applied at 80 mm h-1 with a nozzle pressure of 76 kPa, providing a 1.2-mm diam. median drop size and a 20-mm water depth per irrigation. The resultant Christiansen's uniformity coefficient was 88% (Cuenca, 1989). Droplet energy striking the soil surface was about 25 J kg-1 (Kincaid, 1996). The configuration was chosen to simulate water application rates at the outer end of center pivot irrigation systems.
Runoff was determined following each irrigation run by weighing the gross runoff and subtracting the weight of the filtered and dried sediment. Filtration was done by using Whatman (Maidstone, UK) No. 5 filter paper placed in a buchner funnel subjected to house vacuum. Sediment and filter paper were oven-dried at 105°C and weighed; filter paper weight was subtracted to obtain sediment weight. We took two 60-mL water samples for phosphorus analyses as soon as each irrigation run was completed. One sample was filtered through a 0.45-µm filter and stabilized with 0.6 mL saturated boric acid for later DRP analysis. The second, unfiltered sample was used to determine total P after persulfate digestion (American Public Health Association, 1992) and biologically available P by the iron-oxide impregnated filter paper strip method (Sharpley, 1993).
Prior to the first irrigation, four surface (ca. 2 cm) soil samples from each soil box were collected, composited, and analyzed for inorganic Olsen P (Pi) (Olsen et al., 1954), organic Olsen P following digestion with persulfate, iron-oxide impregnated paper–extractable phosphorus in soil (FeO-Ps), and water-soluble phosphorus (Pws) (Pote et al., 1996). We determined a single-point phosphorus sorption index (PSI) based on the procedure developed by Bache and Williams (1971). All phosphorus concentrations were determined using the molybdenum-blue method (Murphy and Riley, 1962). We also determined acid equivalent lime (Allison and Moodie, 1965) and organic carbon (Nelson and Sommers, 1982) on each soil sample.
The data were analyzed with statistical regression techniques using a general linear test approach described by Neter and Wasserman (1974) and by stepwise regression. All statistical comparisons are reported at P 0.05.
|
RESULTS AND DISCUSSION |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
|---|
0.05) linear relationships among soil test P concentrations. The strongest relationship was between FeO-Ps and Pi, described by FeO-Ps = 0.72 x Pi + 27.13, r2 = 0.89. The relationship between Pws and Pi was the weakest with r2 = 0.49. The relationship between Pws and FeO-Ps was intermediate with r2 = 0.57. Whether the soil surface was initially loose and dry (first irrigation), wet (second irrigation), or dry and crusted (third irrigation) made no difference on any of the relationships developed except for differences in runoff quantities (Fig. 1A). These differences were statistically significant with the order of runoff from wet surface > dry crusted > dry loose. Comparisons of soil loss and sediment concentration between the two water sources were essentially random with r2 values less than 0.1. Therefore, although irrigation sequences are identified when data are presented in figure form, no consideration will be given to soil surface conditions when reporting or discussing results.
|
|
0.05) between RO and RO/Tap water for soil Pi and FeO-Ps concentrations, indicating that the respective relationships belong to the same population. The relation between DRP and Pws was significantly different (r2 and slope) between the two water sources, having a much stronger predictive value for RO than for RO/Tap water, and was the best of any calculated. By adding lime, organic carbon, and runoff in a stepwise regression analysis for RO water there was a slight improvement to R2 = 0.93 from r2 = 0.90; by reducing the added independent variables to only lime, R2 became 0.91. Thus, there was not much to be gained by adding variables. For RO/Tap water nothing was gained through stepwise regression.
|
|
|
|
In none of the stepwise regression analyses was soil NaHCO3–extractable organic P selected as contributing to the regression expressions, contrary to findings from a furrow erosion field study on the same plots from which soil was taken for our laboratory study (Westermann et al., 2001). The possibility exists, during the time we stored the soil, that some oxidation of organic matter took place, accounting for the difference.
Soluble P in runoff is related to P saturation of the sorption complex (Pote et al., 1999; Tunney et al., 1997). The sorption maximum may be estimated from the single-point phosphorus sorption index, PSI (Bache and Williams, 1971). We used stepwise regression to obtain the following significant relationships among PSI and other soil variables: for RO water PSI = 5.74 x lime - 2.13 x Pws + 147, R2 = 0.82; and for RO/Tap water PSI = 6.26 x lime - 0.818 x FeO-Ps + 158, R2 = 0.88.
We calculated ratios between soil test P concentrations and the PSI, similar to the approach used by Pote et al. (1999), except that we did not adjust PSI for maximum sorption. We used these ratios as estimates of P saturation in regressing DRP against them. For illustration, with RO water we obtained the following statistically significant relationships with Pi: DRP = 0.648 x (Pi/PSI) + 0.00036, r2 = 0.71, and with FeO-Ps: DRP = 0.755 x (FeO-Ps/PSI) - 0.066, r2 = 0.84, improving the regression relationships from r2 = 0.40 and r2 = 0.53, respectively, when only soil test P concentrations were used in the regression calculations (Fig. 2).
Using RO/Tap water, corresponding relationships were: DRP = 0.384 x (Pi/PSI) + 0.0213, r2 = 0.54, and DRP = 0.489 x (FeO-Ps/PSI) - 0.023, r2 = 0.54. These regression relationships were worse than for RO water and were similar to those when only soil test P concentration was used in the regression calculation (Fig. 2).
We divided each runoff DRP and FeO-Pw concentration by its corresponding runoff volume (or depth of runoff). By so doing, in every case in our experiment, relationships between P concentration in runoff versus soil P tests deteriorated contrary to results obtained by Pote et al. (1999). Their field study was done on different soils and with different ranges of runoff and infiltration conditions compared with our box study. Their study would be affected by site hydraulic factors whereas an attempt was made to minimize hydraulic factors in our laboratory study.
We also related P mass loss in runoff to soil P test concentrations, with mixed results. Relationships (r2) for RO water were about the same as for DRP and FeO-Pw concentrations versus soil tests shown in Fig. 2 and 3. However, for RO/Tap water, P mass versus soil P test concentration relationships were worse than even those for normalized P concentration relationships (data not shown). The simple regression relationships displayed in our paper, therefore, generally stand as the best manner in which to report our results.
A moderate EC (ca. 2 dS m-1) and low SAR are preferable in irrigation water to prevent soil dispersion, reduce soil erosion, and increase infiltration because of strengthened soil bonds and heightened retention of soil aggregates (Lentz et al., 1996). There was a trace of Na+ (0.6 mg L-1) in the RO water and no evidence of Ca++ and Mg++, and therefore a low EC (0.02 dS m-1) and an undefined SAR. By mixing RO and well water we added all three ions, with a resultant EC of 0.4 dS m-1, a 20-fold increase compared with RO water, but nevertheless a low EC for irrigation water. By adding the divalent Ca++ (55 mg L-1) and Mg++ (33 mg L-1) ions contained in the well water, we obtained a SAR of 1.3. These numbers compare with a Snake River irrigation water EC of about 0.5 dS m-1 and a SAR of about 0.9. (Suitable irrigation water should have a SAR no higher than about 5.)
It appears that RO water caused greater soil dispersion than RO/Tap water since average soil loss and sediment concentration in runoff were greater in RO than in RO/Tap water runoff (P = 0.05), and average runoff across all three irrigations did not differ. This is indicated by the greater number of points falling above the 1:1 lines in the sediment relationships (Fig. 1B,C). Overall average runoff sediment concentrations for RO and RO/Tap runoff were 6.33 and 5.01 g L-1, respectively.
The dispersive action on soil aggregates by RO water may affect particle size distribution in runoff sediment (Kim and Miller, 1996). We did not measure particle size distribution in runoff; however, it is conceivable that finer particle-size fractions were more prominent in RO runoff than in RO/Tap runoff. More divalent cations in RO/Tap than in RO water would encourage larger aggregates in the runoff. If this occurred, P losses could be potentially greater in RO than in RO/Tap water since finer soil particles and aggregates have higher P concentrations than larger soil particles and aggregates in sediments from Snake River irrigation water (Carter et al., 1974). Average total P was greater (P = 0.05) in RO than in RO/Tap water runoff, largely because of greater sediment concentration in RO runoff, because the sediment's total P concentration was the same for both water sources (data not shown). There were also no differences in sediment total P concentrations between subsequent irrigations for either RO or RO/Tap water (Fig. 4), implying that sufficient particle size sorting with repeated irrigations did not occur as reported in other studies (Sharpley et al., 1981). Droplet energy striking the soil surface was also the same for both water sources and irrigations because experimental conditions were identical. The better simple linear regression relationship between average total P and sediment concentration in runoff for RO/Tap than for RO water (Fig. 4) could imply that the soil in RO/Tap runoff was similar to the bulk soil.
Increasing ionic strength increases solubility of a slightly soluble salt via reduction in ion activity coefficients for a system at chemical equilibrium. However, the desorption and/or dissolution of P in soil–solution systems is considered to be predominantly controlled by kinetics rather than driven by chemical equilibria (Sharpley, 1983). Dissolved reactive P concentrations in runoff for both RO and RO/Tap water (Fig. 2) were much higher than those obtained from the furrow irrigation runoff study (0.007 to 0.045 mg P L-1) on plots where soil for the laboratory study was taken (Westermann et al., 2001). Soil–water contact time in the laboratory study was limited to application duration (15 min) plus a few minutes to complete runoff and filtering (<5 min), suggesting that dissolution and/or desorption is very rapid. Exploratory laboratory studies showed that about 70% of the final DRP concentration was achieved in the first 15 min of soil–water contact (Westermann and Aase, unpublished data, 2000).
Increasing the EC (ionic strength) of the extracting solution decreases P desorption (Barrow and Shaw, 1979; Lehr and van Wesemael, 1952; Yli-Halla et al., 1995), particularly in acid soils. Increasing cation charge decreases desorption whereas increasing hydrated radii increases desorption (Barrow and Shaw, 1979). Based on chemical differences between RO and RO/Tap water, larger DRP concentrations in RO runoff might be expected. Even though the average DRP concentrations in RO and RO/Tap runoff were 0.149 and 0.129 mg L-1, respectively, they were equivalent (P = 0.05). The saturated paste extract from the soil used in our study had an EC of 0.5 to 0.9 dS m-1 (Table 1). This is slightly higher than that of RO/Tap water (i.e., 0.4 dS m-1). The dissolution of soluble Ca and Mg salts when RO water was added to the soil probably increased the EC of the applied RO water to approach that of RO/Tap water. These properties would tend to negate potential DRP runoff differences caused by initial ionic differences between RO and RO/Tap water. This implies that the specific response to water source depends on amount and kind of soluble salts present in the soil as well as on chemical characteristics of the applied water.
The best regression between average runoff DRP concentration and water soluble soil P (Fig. 2) probably occurred because the soil extractant (RO water) better simulated soil surface conditions during RO water application and runoff. Applying RO irrigation water would be similar to extracting the soil with RO water but at a higher solution to soil ratio. Substituting the ratio of soil test P concentration divided by PSI for the soil test concentration improved the regression relationships for RO runoff because the ratio does not depend on chemical properties of the soil extractant and because RO water is relatively free of soluble ions. Conversely, using the ratio in the DRP relationship for RO/Tap runoff did not improve the relationships because it does not account for possible chemical interactions of the RO/Tap water with the soils.
We compared extractable soil P from the test soils with either RO/Tap or RO water using the procedure given by Pote et al. (1996). The extractable P concentrations from the topsoil samples were similar (one-to-one) with both extractants; however, the extractable P was consistently greater (2 to 5 mg L-1) with the RO/Tap extractant for the subsoil samples (data not shown). Runoff DRP in RO/Tap water was slightly less than or equivalent to runoff DRP in RO water (Fig. 2) in opposition to that found in our laboratory extraction test for the subsoils. We also could not successfully separate our runoff data (Fig. 2 and 3) into topsoil and subsoil, or into manure, whey, and conventional data groups. Both RO and RO/TAP water had similar effects on visible soil dispersion. This illustrates the difficulty of relating P extracted by laboratory procedures to P in runoff and emphasizes the need for further studies to resolve this predicament.
|
CONCLUSIONS |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
|---|
All relationships between runoff P concentrations and soil test P concentrations appear linear in our study. Dissolved reactive P concentrations at the lowest soil test P concentration were nearly 0.1 mg P L-1 for RO runoff and 0.05 mg P L-1 for RO/Tap runoff. These concentrations are considered sufficient to affect the eutrophication of receiving waters. Average FeO-Pw runoff concentrations generally exceeded 0.4 mg P L-1, regardless of water source. Total P concentrations were all above 1 mg P L-1 in the runoff.
Water source and antecedent soil surface condition in our study had little effect on P in runoff from a calcareous soil. Water quality (chemistry) and possibly soil particle dispersion should be determined and considered before a decision is made about what water source to use in field studies of P runoff relationships. It may be impractical and expensive to use RO or distilled water as a source of water for field determinations of P relationships to runoff and erosion. Therefore, if reasonably clean, acceptable water is available it may be used because it appears that a water source with similar chemical constituents to that of the soil will yield equivalent, reliable, and comparable results with that of RO water. Whether this conclusion holds for a wider range of soil and water conditions remains to be determined.
|
ACKNOWLEDGMENTS |
|---|
|
REFERENCES |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
|---|
This article has been cited by other articles:
|
|
 |
|
  D. L. Bjorneberg, D. T. Westermann, J. K. Aase, A. J. Clemmens, and T. S. Strelkoff Sediment and Phosphorus Transport in Irrigation Furrows J. Environ. Qual., April 3, 2006; 35(3): 786 - 794. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
J. L. Little, D. R. Bennett, and J. J. Miller Nutrient and Sediment Losses Under Simulated Rainfall Following Manure Incorporation by Different Methods J. Environ. Qual., September 8, 2005; 34(5): 1883 - 1895. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
P. A. Vadas, P. J. A. Kleinman, A. N. Sharpley, and B. L. Turner Relating Soil Phosphorus to Dissolved Phosphorus in Runoff: A Single Extraction Coefficient for Water Quality Modeling J. Environ. Qual., March 1, 2005; 34(2): 572 - 580. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
R. P. Udawatta, P. P. Motavalli, and H. E. Garrett Phosphorus Loss and Runoff Characteristics in Three Adjacent Agricultural Watersheds with Claypan Soils J. Environ. Qual., September 1, 2004; 33(5): 1709 - 1719. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
B. L. Turner, M. A. Kay, and D. T. Westermann Phosphorus in Surface Runoff from Calcareous Arable Soils of the Semiarid Western United States J. Environ. Qual., September 1, 2004; 33(5): 1814 - 1821. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
I. C. Daverede, A. N. Kravchenko, R. G. Hoeft, E. D. Nafziger, D. G. Bullock, J. J. Warren, and L. C. Gonzini Phosphorus Runoff from Incorporated and Surface-Applied Liquid Swine Manure and Phosphorus Fertilizer J. Environ. Qual., July 1, 2004; 33(4): 1535 - 1544. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
I. C. Daverede, A. N. Kravchenko, R. G. Hoeft, E. D. Nafziger, D. G. Bullock, J. J. Warren, and L. C. Gonzini Phosphorus Runoff: Effect of Tillage and Soil Phosphorus Levels J. Environ. Qual., July 1, 2003; 32(4): 1436 - 1444. [Abstract] [Full Text] [PDF]
|
|
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
| The SCI Journals | Agronomy Journal | Crop Science | |||
| Journal of Natural Resources and Life Sciences Education |
Vadose Zone Journal | ||||
| Soil Science Society of America Journal | Journal of Plant Registrations | The Plant Genome | |||
