PDF version
for printing

Impact
Statement

© 2007 Plant Management Network.
Accepted for publication 21 May 2007. Published 15 August 2007.

Soil Phosphorus Levels and Stratification as Affected by Fertilizer and Compost Applications

Douglas J. Soldat, Assistant Professor, Department of Soil Science, University of Wisconsin, Madison 53706; and A. Martin Petrovic, Professor, Department of Horticulture, Cornell University, Ithaca, NY 14853

Corresponding author: Douglas J. Soldat. djsoldat@wisc.edu

Soldat, D. J., and Petrovic, A. M. 2007. Soil phosphorus levels and stratification as affected by fertilizer and compost applications. Online. Applied Turfgrass Science doi:10.1094/ATS-2007-0815-01-RS.

Abstract

Little information exists that describes how soil P levels and vertical distribution throughout the soil profile are influenced by fertilization practices and the addition of composted manures. Two field studies were designed to provide more information on how adding P fertilizer or compost influences the concentration and distribution of P in turfgrass soils. Application of P fertilizer at rates of 19, 38, or 72 kg P₂O₅ per ha/year over a period of 4 or 5 years increased soil P in the upper 0 to 5 cm of soil by a factor of 2.7 to 3.3. Applying P at a rate of 10 kg P₂O₅ per ha did not increase soil P in the upper 0 to 5 cm of soil. With one exception, soil P levels at depths of 5 to 10 or 10 to 15 cm were not increased by fertilizer applications over a period of 4 or 5 years. In contrast, adding composted poultry or dairy manures to plots at rates of 12 to 24 mm/year resulted in 8 to 333-fold increases in soil P in the upper 5 cm of soil. Soil P levels also increased substantially in deeper layers as a result of poultry compost application, but not for dairy. These findings indicate that common fertilization practices have a much smaller influence on soil P levels compared to composted manures. The benefits of using composted manures must be weighed against the potentially negative environmental impacts that could result from a large increase in soil P layer where runoff occurs.

Introduction

Phosphorus can accumulate in the upper soil profile when continuous surface P fertilizer applications are made due to the relatively high P sorption capacity of most soils compared to P application rates. In conventionally tilled soils, P is usually evenly distributed throughout the plow layer. However, vertical soil P stratification is likely to occur in no-till systems (1) or in turfgrass areas where soil mixing is very infrequent. Howard et al. (10) found soil test P levels in the upper 8 cm of soil to be 1.6 to 4.5 times greater than P levels in the layer from 8 to 15 cm in no-till cotton soils. Similar differences in soil test P level with respect to depth have been reported in sand-based putting green root zones (3,8).

The spatial distribution of P in the soil can affect root distribution, as plant roots are known to proliferate in areas of high phosphorus concentration (6,9). Perhaps more importantly, knowledge of the extent of P stratification in soil may be important for protecting surface water quality. Excessive P loss in runoff from agricultural and urban areas is linked to the declining surface water quality in the US (4). Runoff interacts with and removes P from the upper few centimeters of the soil (14), and P in runoff has been shown to increase as soil P level increases in this upper soil layer (15). Traditional soil tests are taken from the soil surface to 10 to 15 cm and therefore might not adequately account for the high level of P in upper few cm of soil if significant vertical stratification exists.

Lawn maintenance practices of homeowners are known to vary widely (13) and no information can be found that describes the effect of various fertilization practices on soil P stratification in turfgrass areas on fine-textured soils. Therefore, one goal of this study is to examine how P stratification differs under a wide range of traditional homeowner fertilization practices.

Application of composted manures to turfgrass areas is a relatively new practice developed to reduce P inputs to soils associated with concentrated animal feeding operations, while attempting to improve the physical and chemical properties of urban soils (5,11,17). Emphasizing the positive public perception of composted materials, Dane Co., WI has specifically exempted compost from its ban on applying P-containing turfgrass fertilizer without a soil test showing an agronomic need (2). However, little attention is paid to the fact that composted manures contain significant amounts of P. In addition, typically suggested application rates of compost are high enough to suspect that soil P is inadvertently being elevated to potentially environmentally hazardous levels. Therefore, a second goal of this work is to examine the effect of various sources and rates of composted manure on the vertical stratification of soil P.

How Do Typical Fertilizer Practices Affect Extractable Soil P Levels?

The first study, hereafter referred to as the "fertilizer study," was designed to investigate differences in P stratification under typical homeowner fertilization regimes was conducted in Lake Placid, NY at the Lake Placid Resort Club and Farmingdale, NY at Bethpage State Park. Soil properties of each site are described in Table 1. The Lake Placid and Bethpage sites were slit seeded in August 2001 and September 2002, respectively, with a mixture (70:20:10 by weight): of Kentucky bluegrass (Poa pratensis L., 25% Midnight, 25% Total Eclipse, 20% Washington), fine fescue (Festuca longifolia Thuill, Attila Hard Fescue), and perennial ryegrass (Lolium perenne L., Manhattan III), at the rate of 196 kg/ha. The turfgrass at each site was mowed twice per week or as needed to a height of 5 cm by the golf course maintenance staff of the Lake Placid Resort and Bethpage State Park. The plots were not irrigated and received very little foot or vehicular traffic.

Table 1. Soil classifications and properties of study sites.

 ^x 1:1 in 0.01 M CaCl₂.

 ^y OM = organic matter by loss on ignition (16 h at 400°C).

Treatments at each site were identical and selected to encompass a wide range of soil P fertility representative of potential homeowner fertilizing practices. Treatments were replicated 3 times in a split plot design with fertilizer treatments as main plots and soil sampling depths as sub-plots and consisted of: (i) unfertilized control; (ii) P₂O₅ (as triple superphosphate) at 10 kg/ha/year; (iii) P₂O₅ (as triple superphosphate) at 19 kg/ha/year; (iv) P₂O₅ (as triple superphosphate) at 38 kg/ha/year; and (v) P₂O₅ (as 8-3-5 Nature Safe organic fertilizer) at 72 kg/ha/year. Each treatment received N at 192 kg/ha/year as sulfur coated urea (except the plots receiving the organic fertilizer). Potassium was only applied to plots receiving the organic fertilizer. The range of phosphorus application rates were half, equal to, double, and four times the amount recommended by the Cornell University Nutrient Analysis Laboratory in Ithaca, NY when soil test P is below optimum. Fertilizers were applied at a quarter of the annual rate in May, June, September, and October each year. At the time of soil sampling to determine vertical P stratification, treatments had been applied for 5 years (2002-2006) at the Lake Placid site and for 4 years (2003-2006) at the Farmingdale site.

Composite soil samples (six randomly chosen locations per plot, 25 mm in diameter) were taken in the fall of 2006. Each soil plug was separated into depths of 0 to 5 cm, 5 to 10 cm, and 10 to 15 cm. Soil samples were air-dried, ground and passed through a 2-mm sieve. Extractable soil P was measured for each depth using the Mehlich-3 extractant (12). Soil organic matter content was determined on 0- to 15-cm samples by loss on ignition for 16 h at 400°C. Soil particle size distribution was determined using the pipette method. (7)

For unfertilized plots, vertical soil P stratification was minor, and no statistical differences in soil P level existed among the three sampling depths (Table 2). In contrast to unfertilized plots, statistically significant differences in soil P level in the upper and middle soil layer existed for many fertilized plots at both sites (Table 2). Generally, greater P fertilization rates led to increased soil extractable P in the 0- to 5-cm layer. However, plots fertilized at the lowest rate (10 kg of P₂O₅ per ha/year) did not have greater soil P levels compared to the unfertilized control plots in the upper 5 cm of soil. Plots fertilized with P₂O₅ at 38 kg/ha/year had P levels 3.5 to 4.0 times greater in the upper 0 to 5 cm than at 5 to 10 cm. At depths of 5 to 10 cm and 10 to 15 cm, only one treatment difference existed suggesting that the movement of the P fertilizer was largely restricted to the upper 5 cm over the course of the study.

Table 2. Mehlich-3 soil P levels for 3 sampling depths at two sites where various rates of P fertilizer were applied for 4 and 5 years at Farmingdale and Lake Placid, respectively.

 ^x Treatments of 10, 19, and 38 kg P₂O₅ per ha/year were applied as triple superphosphate.

 ^y Treatment of 72 kg P₂O₅ per ha/year was applied as 8-3-5 organic fertilizer.

 ^z Column means followed by the same letters are not statistically different, alpha = 0.05.

The inclusion of the organic treatment (72 kg P₂O₅ per ha/year) was meant to assess how fertilization with an organic source to meet N needs of turfgrass (as is almost exclusively practiced) would affect soil P level and soil P stratification over time. Although the P application rate of the organic treatment was double that of the greatest inorganic P fertilization rate, soil P levels were not significantly different between those two treatments. Therefore, a larger amount of the organic source of P fertilizer was required to elevate soil P to a similar degree as a soluble inorganic source of P. At both sites the organic treatment had the greatest soil P level at the 10- to 15-cm depth, although not statistically significantly greater than any other treatments.

How Does Applying Compost Change Soil P Levels?

The second study, hereafter referred to as the "compost study," was designed to investigate the effect of applications of composted manure on vertical soil P stratification, was conducted on a soccer field in Genesee Park in Rochester, NY and on a youth baseball field in Clarence, NY. The turfgrass at these sites was predominantly Kentucky bluegrass and perennial ryegrass. The dates of establishment of these sites are unknown, but the turf at both sites was mature (> 3 years old). The sites were not irrigated, mowed to a height of 5 cm by the city maintenance workers once per week or as needed with clippings returned. Soil properties for these two sites are listed in Table 1. Treatments were replicated 3 times in a split plot design with compost treatments as main plots and soil sampling depths as sub-plots. The compost treatments consisted of: (i) un-amended control; (ii) composted dairy manure applied to a depth of 12 mm/year (31 Mg dry matter per ha, 1,063 kg P₂O₅ per ha/year); (iii) composted poultry manure applied to a depth of 12 mm/year (28 Mg dry matter per ha, 845 kg P₂O₅ per ha/year); (iv) composted dairy manure applied to a depth of 24 mm/year (62 Mg dry matter per ha, 2,136 kg P₂O₅ per ha/year); and (v) composted poultry manure applied to a depth of 24 mm/year (56 Mg dry matter per ha, 1,691 kg P₂O₅ per ha/year).

Compost treatments were applied twice each year at half the annual rate, plots were core cultivated prior to compost application. These P application rates may seem extraordinarily high; however, compost is almost exclusively used as a soil amendment and not thought of as a fertilizer, nor is it regulated as such. Also, compost has no guaranteed analysis with which a turfgrass manager could easily calculate a P application rate. These rates were chosen because they represent a typical application of compost that would be made by a turfgrass manager looking to modify soil physical properties. As a consequence of the large amount of material applied, a large amount of phosphorus is also applied. The rates used in this study are consistent with rates used by researchers in Colorado (11) who applied compost to established Kentucky bluegrass at rates of 6.6, 12.2, and 19.8 mm/year.

Properties of the composted dairy and poultry manure are listed in Table 3. At the time of soil sampling to determine vertical P stratification, treatments had been applied for 3 years (2003-2005). The methods of soil sampling and analysis were identical to those described in the fertilizer study.

Table 3. Properties of composted dairy and poultry manure used on
plots in Clarence and Rochester.

No statistically significant differences in soil P level existed among the three sampling depths for the un-amended control plots (Table 4). The plots receiving applications of compost showed greatly elevated soil P levels in the upper 5 cm of soil (Table 4). Soil P levels in the upper 5 cm of soil were elevated in the following order: composted poultry manure at the high rate (24 mm/year) > composted poultry manure at the low rate (12 mm/year) > composted dairy manure at the high rate > composted dairy manure at the low rate. These differences are not reflected in the total P content of the composts (Table 3), suggesting differences in P solubility or mineralization rate between may be responsible for the different rates at which soil P levels increased in response to the compost applications.

Table 4. Mehlich-3 soil P levels for 3 sampling depths at two sites where
composted dairy and poultry manure were surface applied at 2 rates for
3 years.

 ^x Column means followed by the same letters are not statistically
different, alpha = 0.05

The composted poultry manure at the high rate increased extractable soil P in the upper 5 cm approximately two orders of magnitude over the control plots. The compost treatment which increased soil P to the least extent (dairy, low rate) increased soil P levels by 8.1 times in Rochester, NY and 16.7 times in Clarence, NY. Significant P stratification was evident in plots receiving compost. Mehlich 3 soil P in the upper 0 to 5 cm was 2.7 to 7.4 times greater than in the 5- to 10-cm layer.

Discussion and Recommendations

Several years of fertilization at various rates with inorganic and organic sources of P increased soil P levels primarily in the upper 0 to 5 cm of soil. The highest rates of fertilizer application increased soil P levels in the upper layer of soil by approximately five times. In addition, fertilization at a rate of 10 kg P₂O₅  per ha over a period of 4 to 5 years did not change soil P compared to the unfertilized control over the course of the study. Fertilization at a rate of 19 kg P₂O₅  per ha resulted in a significant increase (factor of 2.3 to 3.3) in extractable soil P in the upper 5 cm. In a review of the literature Soldat (16) estimates that watershed scale inputs of P fertilizer to home lawns likely ranges from 6 to 22 kg of P₂O₅ per ha. According to the results of this study, fertilization at the low end of this range is unlikely to influence soil P levels in the upper 0 to 5 cm over a period of 4 to 5 years; while fertilization at the high end may result in significant soil P increases when clippings are returned.

In contrast to the fertilizer study, the use of composted dairy or poultry manure at two different rates resulted in a large increase in soil P level in the 0- to 5-cm depth. At this depth, compost elevated soil P to levels that would likely take decades or centuries to achieve through the "normal" fertilization practices as demonstrated by the fertilizer study. This is a result of the large P application that is made when composted manures are applied to amend soil physical properties. Based on the known relationship between soil P level and runoff P losses from turfgrass (16), it can be concluded that composted manures should not be applied at the rates used in this study in environmentally sensitive areas where runoff losses are likely to occur.

Acknowledgements

The authors thank two anonymous reviewers for their helpful comments which significantly improved the quality of this manuscript.

Literature Cited

1. Andraski, T. W., Bundy, L. G., and Kilian, K. C. 2003. Manure history and long-term tillage effects on soil properties and phosphorus losses in runoff. J. Environ. Qual. 32:1782-1789.

2. Anonymous. 2004. Chapter 80: Establishing regulations for lawn fertilizer and coal tar sealcoat products application and sale. Online. Ordinances 80.01-80.06(1). Dane County, WI.

3. Branham, B. E., Miltner, E. D., Rieke, P. E., Zabik, M. J., and Ellis, B. G. 2000. Groundwater contamination potential of pesticides and fertilizers used on golf courses. Fate and Management of Turfgrass Chemicals. J. M. Clark and M. P. Kenna, eds. Am. Chem. Soc., Washington, DC.

4. Carpenter, S. R., Caraco, N. F., Correll, D. L., Howarth, R. W., Sharpley, A. N., and Smith, V. H. 1998. Nonpoint pollution of surface waters with phosphorus and nitrogen. Ecolog. Applic. 8:559-568.

5. Cogger, C. G. 2005. Potential compost benefits for restoration of soils disturbed by urban development. Compost Sci. Util. 13:243-251.

6. Drew, M. C. 1975. Comparison of the effects of a localized supply of phosphate, nitrate, ammonium and potassium on the growth of the seminal root system, and the shoot, in barley. New Phytol. 75:479-490.

7. Gee, G. W., and Or, D. 2002. Particle-size analysis. Pages 272-278 in: Methods of Soil Analysis, Part 4. J. H. Dane and G. C. Topp, eds. ASA, CSSA, and SSSA, Madison, WI.

8. Guertal, E. A. 2006. Phosphorus movement and uptake in bermudagrass putting greens. Online. USGA Turfgrass Environ. Res. 5:1-7.

9. Hodge, A. 2004. The plastic plant: Root responses to heterogeneous supplies of nutrients. New Phytologist 162:9-24.

10. Howard, D. D., Essington, M. E., and Tyler, D. D. 1999. Vertical phosphorus and potassium stratification in no-till cotton soils. Agron. J. 91:266-269.

11. Johnson, G. A., Qian, Y. L., and Davis, J. G. 2006. Effects of compost topdressing on turf quality and growth of Kentucky bluegrass. Online. Applied Turfgrass Science doi:10.1094/ATS-2006-0113-01-RS.

12. Mehlich, A. 1984. Mehlich III soil test extractant: A modification of Mehlich II extractant. Commun. Soil Sci. Plant Anal. 15:1409-1416.

13. Osmond, D. L., and Hardy, D. H. 2004. Characterization of turf practices in five North Carolina communities. J. Environ. Qual. 33:565-575.

14. Sharpley, A. N. 1985. Depth of surface soil-runoff interaction as affected by rainfall, soil slope, and management. Soil Sci. Soc. Am. J. 49:1010-1015.

15. Sharpley, A. N. 1995. Dependence of runoff phosphorus on extractable soil phosphorus. J. Environ. Qual. 24:920-926.

16. Soldat, D. J. 2007. The contribution of soil phosphorus to phosphorus in runoff from turfgrass. Ph.D. diss. Cornell University, Ithaca, NY.

17. Vietor, D. M., Griffith, E. N., White, R. H., Provin, T. L., Muir, J. P., and Read, J. C. 2002. Export of manure phosphorus and nitrogen in turfgrass sod. J. Environ. Qual. 31:1731-1738.