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Published in J. Environ. Qual. 33:2296-2305 (2004).
© ASA, CSSA, SSSA
677 S. Segoe Rd., Madison, WI 53711 USA

TECHNICAL REPORTS

Waste Management

Phosphorus Dynamics in Soils Receiving Chemically Treated Dairy Manure

M. Kalbasi and K. G. Karthikeyan*

Biological Systems Engineering Department, 460 Henry Mall, University of Wisconsin, Madison, WI 53706

* Corresponding author (kkarthikeyan{at}wisc.edu)

Received for publication November 25, 2003.

   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 
Chemical treatment of animal manure with Al, Fe, and Ca salts appears capable of concentrating P in a smaller volume, thereby providing increased manure management options. However, little information is available on the fate of nutrients in soils receiving chemically treated manure. An incubation study (1 d to 2 yr) was conducted with three soils (Soils I, II, and III with 12, 66, and 94 mg kg–1 Bray-1 P, respectively) and four manure treatments (one untreated and three chemical including Al-, Fe-, and Ca-treated) at two rates (12.5 and 25 mg P kg–1), and a control (no manure). Subsamples were analyzed for Bray-1 P and water-extractable phosphorus (WEP) after eight incubation time periods. Phosphorus distribution among different fractions (soluble and loosely bound; Al-, Fe-, and Ca-bound; organic P; and residual) was also determined after 1 d and 1 yr. Water-extractable P increased when soils received untreated or Ca-treated manure in proportion to P application rate. Water-extractable P, however, decreased (compared with control) for Soils II and III or slightly increased for Soil I with addition of Al- or Fe-treated manure. Water-extractable P decreased sharply between 1 d and 1 to 2 wk and then remained relatively constant or increased slightly up to 2 yr depending on treatment and soil type. Bray-1 P increased for all treatment types and soils in the following order: Ca-treated > Al-treated ≥ untreated > Fe-treated > control. Within each treatment, Bray-1 P decreased between 1 d and 1 to 2 wk and then gradually increased for up to 3 mo (Soils II and III) or 6 mo (Soil I). Application of Al- or Fe-treated manure decreased P solubility with the effect being more pronounced in soils with high background P. Since the application of Ca-treated manure increased both WEP and Bray-1 P, it should be recommended for soils where the objective is to increase P availability. Several years of P input through fertilizer and manure contributed mainly to aluminum-bound phosphorus (Al-P) and to a lesser degree to other fractions. Only soluble and loosely bound P (all soils) and Al-P (Soil I) exhibited treatment-type effects after receiving chemically treated manure. The study results will help bridge the gap between our knowledge of chemical treatment systems for animal manure and the ultimate fate of P when the treated manure is land-applied.

Abbreviations: Al-P, aluminum-bound phosphorus • Ca-P, calcium-bound phosphorus • DRP, dissolved reactive phosphorus • Fe-P, iron-bound phosphorus • PBray-1, fraction of applied phosphorus released as Bray-1 phosphorus • WEP, water-extractable phosphorus


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 
DETERIORATION OF WATER QUALITY of streams and lakes in the United States and worldwide through nonpoint sources of pollution is a growing environmental concern (Sharpley et al., 1999). Runoff from agricultural lands is rich in nutrients (N and P), and hence contributes significantly to nonpoint-source pollution. While N is a major cause of eutrophication in coastal ecosystems, lakes and other freshwater bodies are most directly affected by inputs of P (Schindler, 1977; USEPA, 1990; National Research Council, 1992). Currently, the focus is specifically on P additions through runoff from agricultural lands and urban areas (Moore and Miller, 1994; Sims et al., 2000). There is a greater concern in regions where sensitive water resources are located near concentrated livestock operations (Daniel et al., 1994; Sharpley et al., 1997). Concentrated livestock operations are very efficient producers of protein, but produce a large volume of manure that is being distributed on less land, leading to a surplus of on-farm nutrients. This situation is especially true for P (Beegle and Lanyon, 1994). Numerous reports indicate a buildup of soil bioavailable and WEP as a result of manure or poultry litter application (Sharpley et al., 1993; Lucero et al., 1995). Future existence and expansion of these livestock operations may depend on efficient recycling of nutrients generated on the farm. Due to changes in animal farm dynamics and impending P-based regulations, available land resources for manure management, particularly near the farms, are going to be seriously stressed (Converse et al., 2000). Therefore, it is imperative to develop and implement practices that will help minimize nutrient loading in areas near the farm (with high P levels) and export the excess nutrients off-farm.

Chemical treatment of animal manure with salts of Al, Fe, and Ca and polyacrylamide (PAM) polymers appears capable of providing efficient separation of solids and concentration of nutrients, especially dissolved P (Moore and Miller, 1994; Zhang and Lei, 1998; Vanotti and Hunt, 1999; Sherman et al., 2000), thereby creating more options to manage P distribution over the landscape. Phosphorus is known to interact strongly with the above chemicals and, as a result, it is likely to be converted into less water-soluble and bioavailable forms. However, there have been limited attempts to bridge the gap between our knowledge of chemical treatment systems and the ultimate fate of nutrients when the treated manure is land-applied. With a few notable exceptions (e.g., Shreve et al., 1996; Moore et al., 1999), most of the earlier investigations on chemical treatment have largely overlooked the interaction of treated manure with soils and the long-term stability of applied nutrients.

Limited evidence available in the literature suggests that land application of chemically treated manure can reduce runoff P losses. Gallimore et al. (1999) observed a 43% reduction in dissolved reactive phosphorus (DRP) in runoff from a field where poultry litter (applied at 6.72 Mg ha–1) amended with water treatment residual rich in Al (1.2–5% as Al oxide) was applied. Similarly, Shreve et al. (1995) reported a significant decrease in both dissolved and total P from a field receiving alum- and ferrous sulfate–amended poultry litter. Smith et al. (2001) reported a substantial decrease in DRP in runoff from fields fertilized with swine manure treated with alum or aluminum chloride. In a short-term (1-wk) incubation study, application of Al- and Fe-treated dairy manure to a silt loam soil lowered WEP compared with that obtained after the addition of untreated manure (Dao and Daniel, 2002). Soon et al. (1978) and Soon and Bates (1982) studied the effect of land application of sewage sludge treated with Ca(OH)2, Al2(SO4)3, or FeCl3 on P extractability from different soils. They observed an increase in both NaHCO3–extractable P and soluble P in soils amended with chemically treated sewage sludge. Since untreated sludge was not included in their investigation, the effectiveness of chemical treatment in lowering P extractability cannot be directly determined. The above studies employed relatively short (up to 3 wk) contact times and except for Dao and Daniel (2002) the focus was not on dairy manure. Most of these investigations were performed at a field scale and do not provide information on other P forms (e.g., Bray-1 P) and P distribution among different fractions. In addition, effectiveness as a function of background soil P levels was not investigated.

Therefore, the present study was conducted to systematically evaluate the short- and long-term (from 1 d to 2 yr) nutrient dynamics on soils with different background soil P receiving both untreated and chemically treated dairy manure. Specific objectives are to (i) evaluate the effect of chemical treatment type (treatment with alum, FeCl3, or lime) on water-extractable and Bray-1 P levels as a function of incubation time, manure (i.e., P) application rate, and background soil P level and (ii) determine changes in P distribution among six different fractions (soluble and loosely bound; Al-, Fe-, and Ca-bound; organic P; and residual) obtained by using sequential extraction techniques.


   MATERIALS AND METHODS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 
An incubation study was conducted with three soils (I, II, and III with 12 [low], 66 [high], and 94 [excessive] mg kg–1 Bray-1 P, respectively) and four manure treatments (one untreated; three chemically treated with Al [alum]; Fe [FeCl3], and Ca [lime]) at two application rates (low equivalent to 25 kg P ha–1 or 12.5 mg P kg–1 soil and high equivalent to 50 kg P ha–1 or 25 mg P kg–1), and a control (no manure application) at constant moisture (50% water-holding capacity [WHC]; WHC was determined to be 55.6, 53.1, and 55.4% w/w for Soils I, II, and III, respectively) and temperature (25°C). At 50% WHC, the moisture content of these soils was close to the level at field capacity. Triplicate samples were incubated for eight different time periods (1 d, 1 and 2 wk, 1, 3, and 6 mo, and 1 and 2 yr). Three surface (0–15 cm) Plano silt loam soils (fine-silty, mixed, superactive, mesic Typic Argiudoll) varying in Bray-1 P were collected from three different fields at the University of Wisconsin (UW) Arlington Agricultural Research Station, Arlington, WI. Soil samples were air-dried and then gently crushed to pass a 2-mm sieve. Selected physicochemical characteristics of the soils, determined by analyses performed by the UW Soil and Plant Analysis Laboratory, Madison, WI, are shown in Table 1.


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  		Table 1. Selected physicochemical characteristics of soils used in this study.

 
Chemically Treated Manure Preparation
Chemically treated manure samples were prepared using solution conditions and optimum dosage as determined in our previous study (Karthikeyan et al., 2002). Diluted liquid dairy manure (total solids = 0.8%) was treated with alum [Al2(SO4)3·18H2O], ferric chloride (FeCl3), or lime (CaO) using a PB-900 programmable jar tester (Phipps & Bird, Richmond, VA) with 2-min rapid mixing at 100 rpm followed by 15 min slow mixing at 30 rpm and finally a settling period for 30 min. Chemical dosages applied were 8 mM Al from alum, 8 mM Fe from FeCl3, and 20 mM Ca from CaO, which correspond to optimal dosage rates (defined as the rate above which further chemical addition produced a negligible increase in P removal) as determined in our previous study (Karthikeyan et al., 2002). After sedimentation, the clear supernatant was siphoned out and the sludge was transferred into a 1-L beaker and stored in a refrigerator at 4°C. After 24 h the clear solution on top of the beaker was siphoned out again and the resultant sludge was stored at 4°C for further analysis and for use in the incubation experiment. Treated and untreated manure samples were analyzed for total solids, total organic C, total N, total Kjeldahl N, total P, and DRP following standard procedures (American Public Health Association, 1992). Phosphorus analysis was performed in our laboratory with a Lachat autoanalyzer (Zellweger Analytics, Milwaukee, WI) by following the standard molybdate-based colorimetric methods at a wavelength of 880 nm (Murphy and Riley, 1962). Electrical conductivity and pH of treated or untreated manure were measured using an Accumet AR-50 pH meter (Fisher Scientific, Hampton, NH). Measurements of pH and electrical conductivity for treated and untreated manure were performed on the forms that were added to the soils, namely, the sludge and manure slurry, respectively. Total elemental analysis was performed using inductively coupled plasma spectrometry (after HNO3–HClO4 acid digestion) at the UW Soil and Plant Analysis Laboratory. Important characteristics of treated and untreated manure are listed in Table 2.


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  		Table 2. Physicochemical characteristics{dagger} of untreated and chemically treated manure.

 
Incubation Experiments
Soil for each treatment (75 g) and all incubation times (75 g x seven time periods x triplicates = 1575 g) was transferred into a large plastic bowl. Two-thirds of the water required to obtain 50% water-holding capacity was initially added to the soil with a water dispenser and mixed thoroughly to form a uniform soil-water mixture. Appropriate amounts of untreated or treated manure, determined based on P content (Table 2), to obtain 12.5 and 25 mg P kg–1 soil for low and high manure application rates, were diluted with the remaining portion (one-third) of water and spread uniformly on the soil and then thoroughly mixed. Treated soil mixtures were then transferred into 125-mL polypropylene jars. Weight of the jar plus treated soil was recorded for moisture control for the duration of experiments. Jars were covered with para-film, perforated for air circulation, and incubated in a constant temperature chamber at 25°C. Moisture content of the soil was kept constant during incubation by periodically weighing the jars and adding deionized water to compensate for evaporative losses. Due to the slow rate of evaporative losses (<0.5 mL per wk), adjustment for moisture content was done once a month. After each incubation period, corresponding soil samples were air-dried, gently crushed to pass a 2-mm sieve, and stored for further analysis.

Phosphorus Extraction and Determination
Water-Extractable Phosphorus
Two grams of soil were extracted with 20 mL of deionized water. The suspension was shaken for 1 h in 40-mL centrifuge tubes (Self-Davis et al., 2000). At the end of shaking period, pH was measured and the suspension was centrifuged for 10 min at 10000 rpm and passed through a 0.45-µm filter. Phosphorus concentration was measured in the filtrate using the methods described earlier.

Bray-1 Phosphorus
One and a half grams of soil were extracted with 15 mL of extracting solution (0.025 M HCl + 0.03 M NH4F) (Bray and Kurtz, 1945). The suspension was shaken for 5 min in a 40-mL centrifuge tube, after which it was centrifuged for 10 min at 10000 rpm and passed through a 0.45-µm filter. Filtrate P concentration was determined using the methods described earlier.

Sequential Extraction of Phosphorus
A modification of the fractionation scheme used by Nair et al. (1995) was followed to determine P distribution in different pools for each soil as a function of treatment types. Two grams of air-dried soil sample were sequentially extracted with 20 mL of 1 M NH4Cl (adjusted to pH of 7.0) with 2 h of shaking, 20 mL of NH4F (pH = 8.2) for 1 h, 0.1 M NaOH with 17 h of shaking, and 0.5 M HCl with 24 h of shaking. The corresponding P fractions extracted by NH4Cl, NH4F, NaOH, and HCl have been operationally defined as soluble and loosely bound P (Psenner and Pucsko, 1988), Al-bound, Fe-bound, and Ca-bound, respectively. Residual P represents the fraction that is not readily removed by the above chemical extractants and is considered recalcitrant and primarily organic in nature. After each extraction, the suspensions were centrifuged for 15 min at 15000 rpm and filtered through a 0.45-µm filter. Residual P was determined by ashing 0.5 g of the previously extracted soil for 2 h and then solubilizing it with 6 M HCl (Anderson, 1976). Inorganic P (orthophosphate) in the various extracts was determined using the methods described earlier. A portion of the NaOH extract was also digested using HNO3–H2SO4 (American Public Health Association, 1992) to determine the total NaOH-soluble P, which is the sum of NaOH-soluble inorganic and organic P. Sequential extraction was performed on all soils incubated for 1 d and 1 yr and only for Soil III after a 2-yr time period.


   RESULTS AND DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
CONCLUSIONS
 REFERENCES
 
Water-Extractable Phosphorus
All the experimental factors affected WEP levels. Figures 1 and 2 show the effect of treatment type and incubation time on WEP for Soils I, II, and III for high (Fig. 1) and low (Fig. 2) P application rates, respectively. For illustrative purposes, the experimental data in Fig. 1, 2, 4, and 5 are plotted based on category (i.e., incubation time) rather than the time scale. Use of time scale for the wide range of incubation periods (1 d to 2 yr) used in our study would obscure trends at shorter contact times. Despite the differences induced by the above variables, a common overall trend with incubation time can be observed. Water-extractable P decreased sharply between 1 d and 1 to 2 wk and then remained relatively constant or increased gradually up to 2 yr. For Soil I, WEP decreased sharply between 1 and 2 yr of incubation. The extent of initial reduction in WEP was controlled by treatment type and application rate with maximum values obtained for the higher rate of untreated manure for all the soils. The initial reduction can be attributed to the reaction of soluble P in untreated or Ca-treated manure with the mineral components in soils or to the interaction between free Al or Fe in Al- and Fe-treated manure (molar ratio of Al to P and Fe to P in Al- and Fe-treated manure is 4.01 and 3.55, respectively; Table 2) with soil P via adsorption and/or precipitation. The gradual increase in WEP with increasing reaction times could be due to mineralization of organic P and desorption and/or dissolution from soil colloids and solid phases induced by changes in soil pH. Soil pH varied between pH 6.85 and 7.65 depending on the treatment type and incubation time. Within each treatment type, soil pH did not vary significantly with contact time (Table 3). Treatment effects can also be illustrated by comparing the fraction of applied P (in treated or untreated manure) that was released as WEP. This fraction, termed as percent WEP released, was calculated using:

[1]
where sample WEP is the WEP from soils receiving treated or untreated manure and control WEP is the WEP for the corresponding controls. To highlight overall trends in percent WEP released, values averaged over all the time periods (1 d to 2 yr) for different treatments and soils are shown in Fig. 3 . In all instances, the observed time dependence (data not shown) was such that percent WEP released decreased between 1 d and 2 wk of incubation and then gradually increased for up to 2 yr.



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  		Fig. 1. Effect of treatment type and incubation time on water-extractable phosphorus (WEP) for (a) Soil I, (b) Soil II, and (c) Soil III at the high (25 mg P kg–1) manure application rate. Cont., control; M-H, manure with high P application rate; ATM-H, Al-treated manure with high P application rate; ITM-H, Fe-treated manure with high P application rate; LTM-H, Ca-treated manure with high P application rate. Error bars show plus and minus one standard deviation.

 


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  		Fig. 2. Effect of treatment type and incubation time on water-extractable phosphorus (WEP) for (a) Soil I, (b) Soil II, and (c) Soil III at the low (12.5 mg P kg–1) manure application rate. Cont., control; M-L, manure with low P application rate; ATM-L, Al-treated manure with low P application rate; ITM-L, Fe-treated manure with low P application rate; LTM-L, Ca-treated manure with low P application rate. Error bars show plus and minus one standard deviation.

 

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  		Table 3. Soil pH for treated and untreated manure.{dagger}

 


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  		Fig. 3. Effect of treatment type on the fraction of applied P released as water-extractable phosphorus (WEP), termed as percent WEP released. M-L, manure with low P application rate; M-H, manure with high P application rate; ATM-L, Al-treated manure with low P application rate; ATM-H, Al-treated manure with high P application rate; ITM-L, Fe-treated manure with low P application rate; ITM-H, Fe-treated manure with high P application rate; LTM-L, Ca-treated manure with low P application rate; LTM-H, Ca-treated manure with high P application rate.

 
Chemical treatment effects are manifested differently in Soil I (low Bray-1 P) as compared with Soils II and III (high and excessive Bray-1 P). Application of untreated and treated manure increased WEP (as compared with "control," which had no manure application and, hence, no fresh P input) from Soil I (Fig. 1a, 2a, and 3). The magnitude of increase was proportional to P application rate, but was smaller with the application of Fe- and Al-treated manure (percent WEP released < 0.5%) than those in soils receiving Ca-treated and untreated manure (percent WEP released = 0.94–2.64%). The WEP levels and, hence percent WEP released, for both application rates followed the order: Ca-treated >> untreated > Al-treated > Fe-treated > control. Increase in WEP due to manure addition to soils has been reported elsewhere (Vivekanandan and Fixen, 1990; Graetz et al., 1999). Soon et al. (1978) and Soon and Bates (1982) showed that the application of sewage sludge at rates varying from 200 to 1600 kg as N ha–1 treated with Ca(OH)2, alum, or FeCl3 to a near-neutral loamy sand, a loam, or a clay loam soil increased water-soluble P in the order of Ca-treated sludge >> Fe-treated sludge ≥ Al-treated sludge.

For Soils II and III (high and excessive background P), only application of Ca-treated and untreated manure increased WEP (Fig. 1b, 1c, 2a, 2c, and 3). Addition of Al- and Fe-treated manure decreased WEP levels below those obtained in control samples, thereby producing negative values of percent WEP released (–1.7 to –6.5%), and was especially effective at the higher application rate. Interestingly, percent WEP released is inversely related to the initial P content in soils receiving Al- and Fe-treated manure. The converse is true for the application of untreated and Ca-treated manure with Soil III and Soil I having the highest and lowest percent WEP released, respectively. Our results indicate that treatment with FeCl3 is more effective than with alum in lowering P solubility. This is in agreement with results reported by Dao and Daniel (2002) from a short-term (1 wk) incubation of untreated, Al (alum)-, Fe (FeCl3)-, and fly ash–treated dairy manure with a silt loam soil. Other researchers using field-scale observations have shown that application of Al- or Fe-treated manure can lower water-soluble P levels in runoff compared with those from soils receiving untreated manure (Shreve et al., 1995; Peters and Basta, 1996; Dao, 1999; Codling et al., 2000; Moore et al., 1999, 2000; Smith et al., 2001). However, an important finding obtained in our study is that the addition of Al- and Fe-treated manure can, in fact, decrease WEP below the level extracted from soils that did not receive any P input (i.e., control).

Our findings highlight the potential of chemical treatment of manure with Al and Fe salts to stabilize P in soils, especially those with high or excessive background levels. Water-extractable P from Soils II and III is about 1 to 1.5 orders of magnitude larger than that in Soil I ("control" values in Fig. 1b, 1c, 2b, and 2c versus those in Fig. 1a and 2a). Consequently, application of Al- or Fe-treated manure is more effective in lowering WEP from soils high in background P. Application of Ca-treated manure, on the other hand, increased WEP in all three soils, which is not surprising since the DRP content of Ca-treated manure was significantly higher than that in untreated or Al- or Fe-treated manure (Table 2). A very high Ca to P ratio of 10.11 in Ca-treated manure could have promoted the formation of amorphous calcium phosphate mineral phases, which are usually more soluble in neutral to slightly acidic soils as compared with Fe and Al phosphates (Lindsay, 1979). In addition, the high organic acid content in manure may have inhibited the crystallization of freshly precipitated Ca-P solids (Grossl and Inskeep, 1991; Harris et al., 1994), thereby increasing P solubility. Grossl and Inskeep (1991) reported that dicalcium phosphate dihydrate (DCPD) precipitation is inhibited by the presence of organic acids such as humic, fulvic, citric, and tannic acids. They postulate that organic acid molecules are adsorbed onto the DCPD surface blocking sites for crystal growth. Harris et al. (1994) studied surface horizons in areas with intense dairy operations and suggested that manure components, specifically organic acids, Mg, and Si, can inhibit crystallization of stable Ca-P minerals, resulting in high P solubility in these soils. Lime treatment of liquid dairy manure is, therefore, a suitable management option for manure application only on soils low in plant-available P. It can be seen from Fig. 1 and 2 that the relative difference in WEP between untreated and Ca-treated manure application is greater for the soil with low initial total and Bray-1 P (Soil I) compared with the other two soils.

Bray-1 Phosphorus
Effect of treatment type and incubation time on Bray-1 P of the three soils is indicated in Fig. 4 and 5 for high and low manure (P) application rates, respectively. Application of untreated and treated manure increased Bray-1 P concentration of all soils for almost all incubation times. This increase was proportional to the application rate for all treatments except for the addition of Fe-treated manure to soils with high initial soil P (i.e., Soils II and III). The magnitude of increase at each application rate was in the order of: Ca-treated > Al-treated ≥ untreated > Fe-treated ≥ control. Interestingly, when Soil II received Fe-treated manure at the higher application rate, its Bray-1 P was lower than that in control (no P input) after 3 and 6 mo incubation. Higher Bray-1 P level in soils receiving Ca- or Al-treated manure as compared with those applied with untreated or Fe-treated manure can be attributed to the aggressive P dissolution nature of the extractants used. Bray-1 P extracting solution (0.03 M NH4F + 0.025 M HCl) reacts more strongly with Ca-P and Al-P.



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  		Fig. 4. Effect of treatment type and incubation time on Bray-1 P for (a) Soil I, (b) Soil II, and (c) Soil III at the high (25 mg P kg–1) manure application rate. Cont., control; M-H, manure with high P application rate; ATM-H, Al-treated manure with high P application rate; ITM-H, Fe-treated manure with high P application rate; LTM-H, Ca-treated manure with high P application rate. Error bars show plus and minus one standard deviation.

 


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  		Fig. 5. Effect of treatment type and incubation time on Bray-1 P for (a) Soil I, (b) Soil II, and (c) Soil III at the low (12.5 mg P kg–1) manure application rate. Cont., control; M-L, manure with low P application rate; ATM-L, Al-treated manure with low P application rate; ITM-L, Fe-treated manure with low P application rate; LTM-L, Ca-treated manure with low P application rate. Error bars show plus and minus one standard deviation.

 
Changes in plant-available P (e.g., Bray, Mehlich, or Olsen P) in soils receiving untreated or treated manure have been previously reported. Sharpley et al. (1993) reported a substantial increase in Bray-1 P of soils receiving poultry litter for up to 35 yr. An increase in NaHCO3–extractable P was observed by Soon et al. (1978) in soils mixed with Ca-amended sewage sludge. Soon and Bates (1982) reported similar results when near-neutral pH soils were reacted with sewage sludge treated with Ca(OH)2, Al2(SO4)3, or FeCl3. The NaHCO3–extractable P from treated soils followed the order of Ca-treated >> Fe-treated ≥ Al-treated. When amendments (water treatment residuals, WTR) containing very high levels of Al, Fe, or Ca were applied to soils containing excess plant-available P, a decrease in Mehlich-III P was noticed after short-term (<9 wk) incubation (Peters and Basta, 1996). Codling et al. (2000) found that Al-rich WTR were more effective than Fe-rich WTR in reducing Bray-1 P from amended soils collected from areas under intensive poultry operations. Dao (1999) and Dao and Daniel (2002), on the other hand, found no effect on plant-available P of soils amended with alum- and FeCl3–treated dairy manure. Dao (1999) reported little or no decrease in Bray-1 or Mehlich-III P when two soils were amended for 1 wk with alum or fly ash–treated dairy manure. These results are consistent with our observations for Al-treated manure (Fig. 4, 5, and 6) but differ from our findings for Fe-treated manure. It should be noted that Al or Fe content in treated manure used in our study was 10 to 100 times higher than those used by Dao and Daniel (2002).



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  		Fig. 6. Effect of treatment type on the fraction of applied phosphorus released as Bray-1 phosphorus (PBray-1). M-L, manure with low P application rate; M-H, manure with high P application rate; ATM-L, Al-treated manure with low P application rate; ATM-H, Al-treated manure with high P application rate; ITM-L, Fe-treated manure with low P application rate; ITM-H, Fe-treated manure with high P application rate; LTM-L, Ca-treated manure with low P application rate; LTM-H, Ca-treated manure with high P application rate.

 
Bray-1 P decreased between 1 d and 1 to 2 wk for all the treatments and soils. It then increased gradually for up to 3 or 6 mo for Soils II and III or 2 yr for Soil I. A significant increase in Bray-1 P was observed for Soils II and III between 1 and 2 yr. The initial decrease is due to the interaction of P in untreated or treated manure with the mineral components in soils or between soil P and applied Al, Fe, and Ca. The subsequent increase could have been caused by the mineralization of organic P and/or desorption or dissolution of inorganic P influenced by changes in soil pH and as the system attains a new equilibrium condition. In fact, data obtained from sequential extraction experiments (discussed below) revealed an increase in Al-P, iron-bound phosphorus (Fe-P), Ca-P, and organic P between 1 d and 2 yr of incubation. For example, Al-P of Soil III after 1 d, 1 yr, and 2 yr is 10.97 ± 1.45, 11.85 ± 1.76, and 16.86 ± 1.62% of total P, respectively, which corresponds to 66.3, 76.2, and 117.1 mg P kg–1.

Figure 6 shows the fraction of applied phosphorus that was released as Bray-1 phosphorus (PBray-1) calculated and plotted by the same procedures used for percent WEP released (Eq. [1] and Fig. 3). To highlight overall trends in PBray-1, values averaged over all the time periods (1 d to 2 yr) for different treatments and soils are shown in Fig. 6. For Soil I, the observed time dependence (data not shown) was such that PBray-1 decreased between 1 d and 2 wk of incubation and then gradually increased for up to 1 yr. For Soil II, the initial decline in PBray-1 continued for up to 3 or 6 mo after which it increased for longer contact periods. For Soil III, however, the time-dependent trend in PBray-1 was different from the other two soils, with PBray-1 being the lowest after 1 d, after which it continued to increase with increasing contact times.

Similar to percent WEP released, fractional conversion of applied P to a plant-available form was greatly influenced by the treatment type. The PBray-1 values were highest for samples receiving Ca-treated manure and lowest for Fe-treated manure (Fig. 6). While almost all the applied P was converted to a plant-available form after 2 yr of application of Ca-treated manure (PBray-1 for Soils II and III after 2 yr is 76 and 90.1%, respectively), PBray-1 was <18% in soils receiving Fe-treated manure. The PBray-1 values were sensitive to P application rate only for soils receiving Fe-treated manure. In general, higher PBray-1 was obtained for Soils II and III than Soil I, attributable to their initial Bray-1 P levels, with the trend reversed for Fe-treated manure (Fig. 6). An important finding is the disproportionate increase in Bray-1 P after the addition of Fe-treated manure to soils with high to excessive Bray-1 P. For example, 2 yr incubation of Soil III (initial Bray-1 P = 94 mg kg–1) with 25 mg P kg–1 of untreated, Ca-treated, Al-treated, and Fe-treated manure resulted in final Bray-1 P of 124.1, 132.7, 124.4, and 113.9 mg kg–1, respectively. The corresponding PBray-1 values are 55.8, 90.1, 56.7, and 14.7, respectively. Unlike application of Al-treated manure, which is effective only to reduce WEP, Fe-treated manure is highly effective in decreasing both WEP and Bray-1 P levels. On the other hand, soils receiving Ca-treated manure had elevated levels of both WEP and Bray-1 P.

Water-extractable P increased with an increase in Bray-1 P content for all soils (Table 4). The equations shown in Table 4 were obtained by combining data for all treatment types and incubation periods. Separating the data based on treatment variables did not improve the fit. Both the slope and y intercept increased with an increase in background soil P, indicating that a unit change in Bray-1 P for Soil III (with the application of either untreated or treated manure) is likely to influence WEP more than a corresponding change for Soil I.


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  		Table 4. Relationship between Bray-1 P and water-extractable phosphorus (WEP) for the three soils.

 
Phosphorus Fractionation
Distribution of soil P among various fractions as influenced by treatment type after 1 d and 1 yr of incubation is shown in Table 5. For all soils, irrespective of treatment type, residual P was the dominant fraction. Although the concentration (mg P kg–1) in the residual fraction was comparable for the three soils (data not shown), a significantly higher percentage of P could not be extracted from Soil I (lowest total P content, Table 1) compared with Soils II and III. For example, the residual P concentration averaged over all treatments after 1 d of incubation for Soils I, II, and III is 259.1, 245.3, and 260.9 mg kg–1, respectively, representing 66.8, 45.4, and 43.1% of total P. Corresponding numbers after 1 yr of incubation for Soils I, II, and III are 244.4, 255.1, and 262.2 mg kg–1, respectively, accounting for 63.4, 48.9, and 40.8% of total P. These soils were obtained from the same farm, and as shown in Table 1, possess similar textural properties, N and organic carbon content, and pH, but have different background P levels. Manure and fertilizer application during several years of agricultural production activities has not only elevated total P content of Soils II and III, but also increased P concentration and relative percent distribution in other fractions. On a concentration basis, the soluble and loosely bound P, Al-P, Fe-P, organic P, and Ca-P of Soil III is 5, 7.4, 2.9, 1.6, and 2.8 times higher, respectively, than in Soil I with the corresponding increase in percent distribution (relative to total P) being 3.3, 4.7, 1.9, 1.01, and 1.8 times. Since there is no increase in residual P despite additional nutrient inputs to fields from where Soils II and III were collected, this fraction likely contains the native form of P, and subsequent addition through various sources contributed mostly to Al-P and soluble and loosely bound P and to a lesser degree to Fe-P, Ca-P, and organic P.


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  		Table 5. Phosphorus distribution among different fractions after 1 d and 1 yr of incubation.

 
Tran and N'dayegamiye (1995) reported similar results from a long-term (9 yr) trial of dairy manure application at 20 Mg ha–1 yr–1 on an eastern Quebec silt loam soil. They observed that manure application significantly increased resin exchangeable P (resin Pi), NaHCO3–extractable inorganic P (NaHCO3–Pi), NaOH-extractable inorganic P (Fe-P + Al-P), and total P. The levels in Ca-P (HCl-extractable), organic P, and residual P pools, however, did not change or the extent of increase was not significant. Lyamuremye et al. (1996) conducted a short-term (4 wk) incubation study to determine the effect of manure addition on P distribution in five acidic soils. Using manure application rates of 1 to 5%, which were much higher than those used in our study, they reported an increase in resin Pi, NaHCO3–Pi, and NaHCO3–extractable organic P. Maguire et al. (2000) found that application of biosolids rich in Al and Fe for 2 to 14 yr (with a mean equivalent rate of 185 kg P ha–1 yr–1) increased, on an average, Fe-P (from 137 to 311 mg kg–1), Al-P (from 166 to 342 mg kg–1), and total P (from 403 to 738 mg kg–1) in the soil. The increases were much greater compared with what we observed and could be attributed to the significantly higher P application rates for a longer time period.

The amount of P added to soils in our incubation experiments (12.5–25 mg kg–1) constitutes a small portion when compared with background total P content (422.5–697.2 mg kg–1). Therefore, the effect of treatment type on soil total P or its distribution among different fractions will not be significant, and in some cases can be expected to be masked by the experimental error. Application of manure or treated manure had a statistically significant effect (compared with control) only for the soluble and loosely bound P fraction in all soils and the Al-P content of Soil I (Table 5). The soluble and loosely bound P fraction (0.2–1.8% of total P) increased with manure application, but only the addition of untreated or Ca-treated manure resulted in a proportional increase with application rate. The overall increase followed this particular order: Ca-treated > untreated > Al-treated ≥ Fe-treated. Compared with control, the Al-P fraction of Soil I exhibited a slight increase for high rates of untreated, Al-treated, and Ca-treated manure addition. Soils II and III initially have a much higher fraction of Al-P and, therefore, an appreciable increase was not obtained with manure addition.

Incubation period (1 yr vs. 1 d) had a relatively minor effect on P distribution among various fractions and affected the three soils differently. Only Al-P of Soil I increased marginally with longer incubation. For Soil II, on the other hand, a significant decrease in organic P (from 17.5 to 8.6%) resulted in a slight increase in the other P fractions. Soil III exhibited similar trends in relative distributions as Soil II, but the magnitude of increase or decrease was smaller. Mineralization of organic P may be responsible for the observed decrease in this fraction and a corresponding increase in the other inorganic P fractions. Since Soil III produced the greatest change (concentration-wise) in Bray-1 P and WEP between 1 and 2 yr, the sequential extraction experiments were extended to this soil alone for 2 yr incubation. Even after 2 yr statistically significant treatment type differences did not emerge for P distribution in a particular fraction. However, between 1 and 2 yr, an appreciable increase in Al-P and organic P and a moderate increase in Fe-P were observed with a concomitant decrease in the residual fraction. Phosphorus distribution in soluble and loosely bound P and Ca-P pools did not change significantly. The average values for soluble and loosely bound P, Al-P, Fe-P, organic P, Ca-P, and residual after 2 yr of incubation for Soil III are 1.23 ± 0.11, 16.86 ± 1.62, 23.91 ± 3.6, 16.95 ± 4.22, 12.43 ± 1.64, and 28.62 ± 2.73, respectively.


   CONCLUSIONS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
REFERENCES
 
The effect of application of chemically treated manure on soil P dynamics greatly depends on the treatment type, manure (i.e., P) application rate, and the initial background P level. Application of Al- or Fe-treated dairy manure to soil decreases both soluble and plant-available P (for Bray-1 P compared with soils receiving untreated manure), especially in soils with high P background. Alum and FeCl3 treatment of liquid dairy manure and the subsequent application of treated manure can be used as a management practice to minimize the risk of off-site migration of P. On the other hand, application of lime-treated manure, which increases both the WEP and soil Bray-1 P, may be recommended on soils with low background P. More research is needed to investigate the effects on soils varying in physical and chemical characteristics. Phosphorus from several years of manure and fertilizer application appears to accumulate in soils mainly as Al-P and to a lesser degree as Fe-P, organic P, and Ca-P. Addition of treated manure had little or no effect on the distribution of P among different fractions in soils.


   ACKNOWLEDGMENTS
 
Financial support for this project provided by the Wisconsin Fertilizer Research Program and Krenz funds from the Department of Biological Systems Engineering is gratefully acknowledged.


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


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