Journal of Environmental Quality 31:954-961 (2002)
© 2002 American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America
TECHNICAL REPORTS
Surface Water Quality
Poultry Litter Ash as a Potential Phosphorus Source for Agricultural Crops
Eton E. Codling*,
Rufus L. Chaney and
John Sherwell
Maryland Dep. of Natural Resources, Tawes State Office Building, B-3, Annapolis, MD 21401
* Corresponding author (codlinge{at}ba.ars.usda.gov)
Received for publication June 25, 2001.
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ABSTRACT
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Maryland will impose restrictions on poultry litter application to soils with excessive P by the year 2005. Alternative uses for poultry litter are being considered, including burning as a fuel to generate electricity. The resulting ash contains high levels of total P, but the availability for crop uptake has not been reported. Our objective was to compare the effectiveness of poultry litter ash (PLA) and potassium phosphate (KP) as a P source for wheat (Triticum aestivum L.) in acidic soils, without and with limestone application. Two acidic soils (pH 4.25 and 4.48) were studied, unlimed or limed to pH 6.5 before cropping. The PLA and KP were applied at 0, 39, and 78 kg P ha-1, after which wheat was grown. Limestone significantly increased wheat yield, but the P sources without limestone did not. The two P sources were not significantly different as P fertilizer. At the 78 kg P ha-1 rate, wheat shoot–P concentrations were 1.10 and 1.12 g kg-1 for the PLA treatment compared with 0.90 and 0.89 g kg-1 for KP in the nonlimed and limed soils, respectively. Trace element concentrations in wheat shoots from the PLA treatment were less than or equal to KP and the control. The low levels of water-soluble P and metals in the soils and the low metal concentrations in wheat suggest that PLA is an effective P fertilizer. Further studies are needed to determine the optimum application rate of PLA as a P fertilizer.
Abbreviations: EC, electrical conductivity • KP, potassium phosphate • M3P, Mehlich 3–extractable phosphorus • PLA, poultry litter ash • WSP, water-soluble phosphorus
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INTRODUCTION
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THE RAPID GROWTH of the poultry industry in recent years and the application of poultry waste to agricultural lands has resulted in excessive soil P in many locations. Many fields on the eastern shore of Maryland have accumulated soil P levels in excess of 800 mg kg-1 Mehlich 3–extractable P and 50 mg kg-1 WSP (Codling et al., 2000). Such high levels of soluble P endanger the environment in the Chesapeake Bay region. Addressing this concern, the Maryland State Legislature passed the Water Quality Act of 1998, which prohibits the use of poultry litter on fields with elevated phosphorus levels after 2005 (Simpson, 1998). Efforts are being made to reduce P input into the poultry diet and to find alternative uses for poultry litter. These include crop breeding for low phytate grain, using phytase enzymes in poultry diets to reduce the amount of P in the litter (Abelson, 1999), on-farm composting (DeLuca and DeLuca, 1997), transporting the litter to agricultural lands with low levels of P, gasification, and burning litter as a fuel to generate electricity (Power Plant Research Program, 1998).
Feasibility studies on the burning of poultry litter to generate electricity on Maryland's eastern shore and a test burn have been conducted (Power Plant Research Program, 1998, 2000a,b). One of the major concerns raised by the burning of poultry litter to generate electricity, however, is the disposal of the ash. Most coal ash produced by coal-burning electrical power plants in the USA is disposed of by landfilling at great expense to the producers (USDA Agricultural Research Service, 1997). Unlike coal ash, however, poultry litter ash (PLA) is high in phosphorus and potassium. Akpe et al. (1984) found that PLA had potential as a phosphorus supplement in poultry nutrition. Total P concentration in PLA is higher than the P concentration of the litter itself due to the high carbon content of the litter. For example, total phosphate concentration (as P2O5) in PLA at 0% carbon was 244 g kg-1 compared with 207 g kg-1 in poultry combusted PLA with 15% carbon (Bock, 1999). In addition, the concentrations of trace elements (e.g., Cu, Zn, and Mn) ranged from 1 to 3 g kg-1. With such high nutrient levels, poultry litter ash has a potential as a viable P fertilizer for agricultural crops. Poultry litter ash is also alkaline, with pH above 12 (Power Plant Research Program, 1998), and could also be a potential liming material for acidic soils. Plant nutrients are more available when acidic soils are limed compared with nonlimed acidic soils (Saha et al., 1999).
Use of PLA as a source of P fertilizer would help mitigate the present concerns of poultry litter disposal on Maryland's eastern shore, while reaping economic and environmental benefits. For example, presently it is costing some poultry farmers about $8.80 Mg-1 to remove litter from their chicken houses; however, it is estimated that farmers would be paid about $22.00 Mg-1 for the poultry litter by the power plant. The ash would then be sold by the power plant for a price equivalent to $5.60 Mg-1 of the poultry litter (Power Plant Research Program, 1998).
Wheat is one of three crops, along with corn (Zea mays L.) and soybean [Sorghum bicolor (L.) Moench], grown in rotation in areas where PLA could potentially be used as P fertilizer in Maryland. Several studies have been conducted on wheat tolerance to acidic soils (Bona et al., 1994; Carver and Ownby, 1995; Foy, 1996; Foy and Peterson, 1994; Mesdag and Slootmaker, 1969). Some cultivars of wheat are extremely sensitive to acidic soil condition and require liming. For these reasons, wheat was used as the test crop in this study. The objectives of this study were to (i) compare the effectiveness of PLA with that of KP as a P source for wheat and (ii) investigate the effect of lime application on P availability to wheat from PLA and KP.
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MATERIALS AND METHODS
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Poultry Litter Ash Collection and Characterization
The PLA used in this study was the bottom ash from the burning of poultry litter as fuel to generate electricity, and was obtained from a pilot study conducted by the Maryland Department of Natural Resources, Annapolis. The material was crushed and sieved to <250 microns to insure homogeneity. The pH was determined in a 1:2 (PLA to deionized water, by weight) mixture using a glass electrode. Electrical conductivity (EC) was determined using an Orion Model 160 conductivity meter (ThermoOrion, Beverly, MA) with a 1:2 (PLA to deionized water by weight) mixture. Total metal concentrations were determined by digesting PLA samples using an aqua regia method (McGrath and Cunliffe, 1985), followed by analysis using flame atomic absorption spectrometry with deuterium background correction as appropriate.
Soil Characterization
Two soils, a Galestown sandy loam (siliceous, mesic Psammentic Hapludult) and a Gilpin silt loam (fine-loamy, mixed, semiactive, mesic Typic Hapludult), were collected from wooded areas in Maryland and West Virginia, respectively. These soils were chosen because they are from areas where PLA would probably be used for crop production and low in available P. Bulk soils were collected from the surface (0–15 cm), air-dried, sieved to less than 2 mm, and stored in plastic containers until use. Soil texture was determined using the hydrometer method (Gee and Bauder, 1986). Soil pH was measured in a 1:1 (soil to deionized water, by weight) solution after 1 h of equilibration. The WSP was extracted by shaking 5 g air dry soil and 25 mL deionized water for 1 h and then filtering through Whatman (Maidstone, UK) #42 filter paper. The M3P was determined as reported in Sparks (1996). The DTPA-extractable Cu, Zn, Mn, Fe, Ni, Cd, and Pb were determined using the method of Lindsay and Norvell (1978). Calcium, Mg, and K were determined following Mehlich I extraction (Sparks, 1996) using a flame atomic absorption spectrophotometer.
Pot Culture Experiments with Wheat
One portion of each soil was mixed with amorphous reagent-grade calcium carbonate in 3-kg batches. The soils were brought to 20% (w/w) moisture content (approximately 33 kPa soil moisture tension) with deionized water and incubated for two weeks to obtain a stable pH of 6.5. The pH of each treatment was determined from a 1:1 (soil and water mixture) during incubation, and adjustments were made with additional lime if necessary. The soils were limed because farmers generally maintain their soils at a pH of 6.5 for wheat production. The second portion remained strongly acidic and was also incubated moist for two weeks. The nonlimed soils were used to determine the effect of the acidic soils on the availability of P from PLA for uptake by wheat in comparison with limed soils. Poultry litter ash P rates used in the study were based on Mehlich 3–extractable P (Table 1). The PLA and KP were added at rates of 0, 39, and 78 kg P ha-1 to kilogram quantities of limed and nonlimed soil, mixed, and placed in plastic pots (15 cm in diameter x 15 cm high) with three replications. The holes in each pot were sealed to prevent leaching. The amended soils were adjusted to 20% (w/w) moisture content weekly by weighing each pot and adding distilled water as needed. Twelve seeds of ‘Renville’ wheat were planted in each pot. The pots were placed in a growth room and arranged as a randomized block design, and environmental conditions were set as follows: day length of 16 h; day and night temperatures of 23°C and 20°C, respectively; relative humidity of 70%; and a photosynthetically active photon flux density (PAP) of 200 µE m2 s-1. Three days after germination, plants were thinned to eight per pot and 100 mg kg-1 each of N, Mg, and K (as NH4NO3, MgSO4, and KNO3) were applied in solution to each pot. Magnesium and K fertilizer applications were adjusted for the PLA treatments based on their concentrations in the ash. Wheat plants were harvested at the boot stage by cutting at the soil surface. Dry matter yields were determined after oven-drying the tissue at 65°C for two days. Plant tissue samples were ashed at 480°C for 16 h, then 3 mL concentrated HNO3 was added to each sample and brought to dryness on a hot plate. After drying, 10 mL of 3 M HCl was added and the mixture was allowed to reflux for 2 h. The digest was filtered through Whatman #40 filter paper. The filtrate volume was brought to 25 mL with 0.1 M HCl and 40 mg Co L-1 added as an internal standard. The filtrate was then analyzed for nutrients using inductively coupled plasma atomic emission spectroscopy (ICP–AES; PerkinElmer [Wellesley, MA] Plasma 40).
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Table 1. pH, electrical conductivity (EC), water-soluble phosphorus (WSP), Mehlich 3–extractable phosphorus (M3P), and total elemental composition of the poultry litter ash.
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After harvest, soil from each pot was placed in plastic bags, roots were removed, and the soil was mixed before soil samples were collected and analyzed for pH, EC, WSP, M3P, and DTPA-extractable Cu, Zn, Mn, Fe, Ni, Cd, and Pb. Calcium, Mg, and K were determined on Mehlich 1 extractions (Sparks, 1996). Both macro- and micronutrients were determined using an atomic absorption spectrophotometer (Varian [Sugar Land, TX] 5000). Statistical analysis of the data was performed using a 2 x 2 x 2 x 3 factorial (SAS Institute, 1988), with the main effects being soil, lime, P source, and P rate. Means were separated using Duncan's multiple range test (Steel and Torrie, 1980).
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RESULTS AND DISCUSSION
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Characteristics of Poultry Litter Ash and Soils
Results of the PLA characterization of selected chemical properties are presented in Table 1. The pH of PLA was alkaline (12.2), with electrical conductivity of 27.5 mS cm-1. With this EC value, PLA could pose salinity problems if applied in large quantities. The WSP concentration in the PLA was low (<0.1 mg P kg-1) due to the high pH (Lindsay, 1979). Total and Mehlich 3–extractable P concentrations were 53 and 43 g kg-1, respectively, which was more than three times higher than the concentration observed by Codling et al. (2000) in poultry litter. The higher P concentration in the ash resulted from elimination of the carbon during burning of the litter. With exception of iron, manganese, and zinc (with concentrations of 4.3, 1.6, and 0.6 g kg-1, respectively), metal concentrations (including arsenic) were within the normal range for soils in the USA (Shacklette and Boerngen, 1984). Gilpin silt loam soil had higher levels of measured elements than the Galestown sandy loam soil, with the exception of WSP and Cu (Table 2).
Plant Dry Matter Yield
Wheat dry matter yields were significantly affected by soil, lime, P source (p < 0001), and P rate (p < 0.05), but not by their interactions (Table 3). Lime application significantly increased wheat dry matter yields when averaged over the soils (Fig. 1)
. In the nonlimed treatments, yields did not change significantly with the addition of either KP or PLA. The lower yields observed with the nonlimed treatment may have been due to reduction in soluble nutrients such as P, resulting from their adsorption by Al and Fe oxides in the soils at the low pH (Table 1). Foy and Murray (1998) reported that P applied in acid soils becomes unavailable for crop uptake because of the reaction of P with metals such as Al, Fe, and Mn. Van der Watt et al. (1994) reported similar findings with sudax [Sorghum bicolor (L.) Moench.] on acid soils. Salt toxicity resulting from the high EC of PLA does not appear to be a factor in the lower yields observed in the nonlimed treatments, since yields were not significantly different between the PLA and KP treatments. Further, the EC values at the highest (78 kg ha-1) PLA application rate at the end of the study were less than the 4 mS cm-1 value at which the growth of most agronomic crop species is inhibited (Bernstein, 1964; Townsend and Gillham, 1975). The marginal yield increase observed with the 78 kg ha-1 PLA treatment may be the result of a slight liming effect of the PLA on the acidic soils (Table 1). The delay in seed germination in the nonlimed treatments may also have influenced yield. Seeds in the limed treatment germinated three days after planting, whereas those in the nonlimed soils germinated in five days. Phosphorus deficiency symptoms (leaf purpling) were observed in the wheat plants on both the KP and the PLA treatments on the nonlimed soils. However, the symptoms disappeared in the PLA treatments over time. It has been shown that applying insoluble P such as phosphate rock to acid soils provided sufficient P for crop production (Baligar et al., 1997; Chien et al., 1980; Kanabo and Gilkes, 1987). The lime plus P treatments significantly increased dry matter yield compared with the limed control (Fig. 1). Shoot yield at the 78 kg ha-1 KP rate was the greatest, but was not significantly different from that of the 39 and 78 kg ha-1 PLA rates. Dry matter yields on the Gilpin silt loam were slighty higher than those of the Galestown sandy loam soil when averaged over lime and P sources: average yields were 4.5 ± 0.5 and 3.1 ± 0.5 grams per pot for the Gilpin and Galestown soils, respectively. This difference in crop yields between the two soils may have resulted from the higher initial nutrient content of the Gilpin soil (Table 2). During the early stage of growth, plants growing on the Galestown soil amended with lime and 78 kg ha-1 PLA developed leaves that were light green with white spots; however, after 15 d the symptoms disappeared. These symptoms were not observed on the Gilpin soil (Table 2).
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Fig. 1. Wheat yield as affected by lime, poultry litter ash (PLA) and potassium phosphate (KP), averaged over soils.
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Tissue Nutrient Concentrations
Wheat tissue P concentrations were significantly affected by soil, lime, and P source (Table 3). Tissue phosphorus concentration was higher for the plants grown on the PLA-amended soils compared with those grown on the KP and control treatments when averaged over soil and lime (Table 4). However, only at the 78 kg ha-1 rate was the foliar concentration significantly different from the KP and the control. In all cases, tissue P concentrations were equal to or less than 1.5 g kg-1, values considered deficient for wheat (Ward et al., 1973). Tissue P concentration did not change significantly with P rate without lime (Table 5). Tissue P concentrations were highest at the 78 kg ha-1 PLA rate for both the limed and the nonlimed treatments.
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Table 4. Effect of poultry litter ash (PLA) and potassium phosphate (KP) on phosphorus, calcium, magnesium, and potassium concentration in wheat (averaged over soils and lime application).
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Table 5. Lime, poultry litter ash (PLA), and potassium phosphate (KP) effect on nutrient concentration of wheat (averaged over soils).
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Tissue Mg and K concentrations were significantly affected by soil, lime, P source, and soil x P source (Table 3). Tissue Ca concentration did not change significantly by P source and rates when averaged over lime (Table 4). However, Mg and K concentrations were lower with the application of both phosphorus sources with the exception of the 39 kg ha-1 KP rate in which the Mg concentration was slightly higher than the control. The highest Mg concentrations were observed in the limed and KP treatments, which were significantly higher than the limed and PLA treatments (Table 5). Tissue K concentrations were lowest in the plants grown on the soils that received PLA treatment with and without lime. The lower tissue Mg and K concentrations observed with the PLA treatment may have resulted from the fact that Mg and K in the PLA were less available for plant uptake, and only a small amount of additional Mg and K was added to the soil amended with PLA, compared with the KP and control treatments.
An ANOVA table showing significant treatment effect on tissue trace element concentrations is presented in Table 3. With the exception of Mn at the 39 and 78 kg ha-1 KP rates, tissue trace element concentrations for both P treatments were less than the control values (Table 6). There was little variation in trace element concentrations in wheat tissue between the two P sources (Table 6). However, tissue Mn concentrations were significantly higher for the plants grown on the KP treatment compared with the PLA treatment. For example, Mn concentrations when averaged over P rates on the nonlimed soils were 620 mg kg-1 for the KP treatments compared with 444 mg kg-1 for the PLA treatments. The lower Mn concentrations in the PLA treatments may have been due to the higher pH of the PLA (Table 1). These tissue Mn levels are near or exceed the phytotoxic threshold levels of 475 mg Mn kg-1 reported by Fales and Ohki (1982). Copper and Mn concentrations increased with lime treatment while Fe, Ni, and Cd concentrations were reduced (Table 7).
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Table 6. Trace element concentration in wheat grown in soils amended with potassium phosphate (KP) or poultry litter ash (PLA) (averaged over soils and lime application).
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Table 7. Trace element concentration in wheat grown in poultry litter ash (PLA)- and potassium phosphate (KP)-amended soils (averaged over soils).
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Tissue P, Ca, Mg, Zn, and Fe were higher for the plants grown on the Galestown soil, while K, Cu, and Mn were highest in the plants grown on the Gilpin soil when averaged over P source and lime application (Table 8). The lower plant P concentration in the Gilpin soil may have been due to less available P as a result of fixation of soluble P by the silt and clay in the Gilpin soil. Tissue P, Ca, K, and Fe concentrations were reduced with lime application, while Mg, Cu, and Mn concentrations increased (Table 8). The increase in tissue Cu and Mn concentrations with lime are not the typical response expected. However, Kukier and Chaney (2001) observed similar results with wheat when limestone was applied to muck soils. Van der Watt et al. (1994) found reduction in sudax tissue Cu and Mn concentrations when acid soil was limed. Similar reduction in tissue Cu and Mn upon liming was also observed by Saha et al. (1999).
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Table 8. Soil and lime effects on nutrients levels in wheat shoots when treated with poultry litter ash or potassium phosphate (averaged over P rates).
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Soils
An ANOVA table showing significance of treatment effects on soil properties at the end of the experiment is presented in Table 9. Soil pH was significantly affected (p < 0.05) by lime, P source, P rate, and the interactions of soil x P source, soil x lime, and soil x lime x P source (Table 9). When averaged over soil and lime, soil pH at the end of the study was significantly higher for the PLA treatments compared with the control and the KP treatments (Table 10). This may have been due to the higher pH of the PLA. Soil EC was significantly affected (p < 0. 0001) by soil, lime, P source, and the soil x lime and soil x lime x P source interactions (Table 9). The EC values were significantly lower with the application of PLA compared with the KP and control treatments (Table 10), even though the EC value of the PLA was 27.5 mS cm-1 before the experiment (Table 1). Soil-extractable P concentrations were significantly affected (p < 0.05) by soil, lime, P source, and their interactions (except for the soil x lime x P source interaction for M3P) (Table 9). In most cases, both WSP and M3P concentrations from the PLA treatments were significantly higher than in the KP and control treatments (Table 10). The higher concentrations of WSP and M3P in the PLA treatments may have been due to the slow release of P from initially insoluble phosphate compound in PLA. The differences in Ca concentrations were not significant among the treatments (Table 10); however, Mg and K concentrations were significantly lower for PLA treatments. As mentioned above, those low levels of Mg and K may have resulted from the smaller amount of additional Mg and K that was added to the soil with the PLA treatments. The DTPA-extractable soil Cu, Zn, Mn, Cd, Ni, Fe, and Pb concentrations were significantly affected (p < 0.05) by soil, lime, and P source. The soil x lime interaction was also significant for the above elements with the exception of Fe. Both Cu and Zn concentrations from the PLA treatments were equal to or greater than those from the control and the KP treatments (Table 10). Manganese concentrations, however, were significantly lower for the PLA treatments compared with the control and the KP treatments (Table 10). The WSP and M3P levels were highest in the nonlimed soil amended with PLA (Table 11). For example, at the 78 kg ha-1 rate, the WSP and M3P values were 1.47 and 28.6 compared with 0.62 and 22.8 mg kg-1 for the PLA and KP treatments, respectively. The Ca concentrations in limed soil, with either P source, were twice as high as in nonlimed soil (Table 11). Magnesium and K values were much higher in KP amended soil compared with the PLA treatment for both the limed and nonlimed treatments (Table 11). In most cases, DTPA-extractable Cu, Zn, Mn, Fe, Ni, Cd, and Pb concentrations in soil amended with PLA were equal to or less than the values for the KP and control treatments, with the exception of Cu in the nonlimed treatment (Table 12). When averaged over lime and P source, elemental composition of the soils after the study varied with soil texture (Table 13). For example, WSP and M3P were lower on the Gilpin soil compared with the Galestown. The higher WSP and M3P concentrations observed in the Galestown soil may have resulted from its higher percentage of sand, which has less P fixing capacity, compared with Gilpin soil, which has higher silt and clay (Lindsay, 1979). The DTPA-extractable Cu concentrations were six times higher in the Galestown soil compared with the Gilpin soil, while DTPA-extractable Fe and Mn concentrations were higher in the Gilpin soil. In all cases DTPA-extractable Cu, Zn, Fe, and Mn concentrations were higher in the nonlimed treatments (Table 13). However, the concentrations of Cu and Zn were much less than the 20 mg kg-1 Cu and the 230 mg kg-1 Zn that is considered to be toxic for corn and peanut (Arachis hypogaea L.), respectively (Borkert et al., 1998).
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Table 10. Soil pH, electrical conductivity (EC), and concentrations of water-soluble phosphorus (WSP), Mehlich 3–extractable phosphorus (M3P), calcium, magnesium, potassium, and DTPA-extractable Cu, Fe, Zn, and Mn after cropping with wheat (averaged over soil and lime).
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Table 11. Soil pH and concentrations of water-soluble (WSP), Mehlich 3–extractable phosphorus (M3P), and Mehlich 1–extractable Ca, Mg, and K in poultry litter ash (PLA)-amended soils after one cropping of wheat (averaged over soils).
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Table 12. Concentrations of DTPA-extractable trace elements in soils amended with lime, poultry litter ash (PLA), and potassium phosphate (KP) after wheat (averaged over soils).
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Table 13. Effect of soils and lime on pH, electrical conductivity (EC), and concentrations of water-soluble phosphorus (WSP), Mehlich 3–extractable phosphorus (M3P), Mg, K, Ca, Cu, Zn, Fe, and Mn when treated with poultry litter ash (PLA) after one crop of wheat.
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CONCLUSIONS
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Experiments conducted to evaluate the effectiveness of PLA to KP as potential phosphorus sources for wheat indicated that PLA is an inexpensive P source for agricultural crops. The results of the studies indicated that wheat dry matter yield with the PLA treatments were equal to that of KP when the soils were limed, while nonlimed treatments did not significantly increase wheatdry matter yield. Tissue P concentrations were higher with PLA application compared with the control and KP treatments, but all P levels were in a range considered to be deficient for wheat. Copper, Zn, and Mn concentrations in wheat tissue were lower in plants grown in the soils amended with PLA compared with the control and KP treatments. Soil pH, WSP, and M3P concentrations in the soil after the wheat was harvested were higher in the PLA treatments. The higher soil P from the PLA treatment could be a potential environmental risk if similar rates were used without additional crops to utilize the applied P. The DTPA-extractable Cu and Zn concentrations in the soil after the wheat harvest were not significantly different among the treatments. However, DTPA-extractable Mn concentrations in the PLA treatment were significantly lower than in the control and KP treatments.
The results of this research indicated that PLA is a potential P source for crop plants. However, further research is needed to determine the optimum rates of PLA application if PLA is to be used as a P fertilizer for wheat or other agricultural crops.
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ABSTRACT
INTRODUCTION
