Water Quality. Release of Nitrogen and Phosphorus from Poultry Litter. J. S.Robinson* and A. N.(arp1ey ABSTRACT

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1 / Water Quality Release of Nitrogen and Phosphorus from Poultry Litter J. S.Robinson* and A. N.(arp1ey ABSTRACT Although it is well established that poultry litter is a valuable N-P-K fertilizer, it is often applied at rates considerably higher than necessary for supplying crop N or P requirements (Edwards and Daniel, 199; Wood, 199). The build up of N and P at the soil surface, resulting from continual poultry litter applications, increases the potential for the degradation of surface and groundwater resources (Edwards and Daniel, 199; Sharpley et al., 199; Sims and Wolf, 199). It has been shown that the application of poultry litter can increase the edge-of-field losses of N and P in surface and subsurface runoff. Nitrate-N losses can accumulate to levels in groundwater that exceed acceptable limits for human consumption (1 mg L', USEPA, 1976). Liebhardt et al. (1979) applied poultry litter at rates of to 179 Mg ha (wet weight basis) to sandy soils in Delaware and found a direct relationship between application rate and NO -N in groundwater. Application rates of 1, 7,, and 179 Mg ha' resulted in -yr mean NO -N concentrations of 1, 1,, and 19 mg L', respectively, in a water table m below the surface (Liebhardt et al., 1979). In a survey of long-term littered tall fescue pastures in the Sand Mountain region of Alabama, Kingery et al. (199) detected concentrations of soil NO -N > mg kg - ' at or near the underlying bedrock. These conditions also create the potential for transport of NO -N released from litter to groundwater in concentrations exceeding 1 mg L'. Although both N and P stimulate eutrophication, P is often the nutrient limiting algal growth (Schindler, 1977; Sharpley et al., 199). Therefore, much attention is focused on levels of P in surface runoff. It has been suggested that the loss of P from fields receiving surface applications of poultry litter is one of the primary factors influencing surface water quality in northwest Arkansas (Edwards and Daniel, 199). Even so, little direct information is available on the effect of management of land-applied poultry litter on P loss in runoff. The dissolved P fraction in runoff consists of varying amounts of organic P as well as inorganic P. Dissolved organic P is not generally used by algae, however, unless it is hydrolyzed to inorganic P (Sonzogni et al., 198). As dissolved inorganic P concentrations from nonfertiized and fertilized watersheds are often greater than the critical level associated with accelerated eutrophication (.1 mg L) (Vollenweider and Kerekes, 198), it is assumed that in most aquatic environments, inorganic P is the main P form utilized by algae. Many factors influence the form, concentration, and loss of N and P transported from fields receiving surface applications of poultry litter. These factors largely depend on the properties and management of the soil and In areas of intensive poultry production, large amounts of litter produced are often applied as fertilizer to local agricultural land. To assess the agronomic and water quality implications of poultry litter applications, we quantified the effects of recurring, simulated rainfall ( x -min rainfalls of. cm h -') alternated with different drying temperatures (,,, and C for 1 h) on the release of dissolved N and dissolved P from two types of poultry litter (pine bark shavingsand wheat straw-based). Amounts of litter leached were equivalent to a 1 Mg ha -' application, containing an average of 6 kg N ha -' and 18 kg P ha. A total of 7 kg ha N11 -N, which accounted for >9% of the dissolved N, and 1 kg ha 'inorganic P were released by the end of five rainfalls (averaged for the two types of poultry litter, and for all drying temperatures). Although the pattern of N and P release from litter was similar for all drying periods, the magnitude of losses was a function of drying temperature. The average portion of total N present in the litters released as NIL-N during five rainfalls decreased from % for titter dried at C to 18% for litter dried at C. This decrease was attributed to an increase in N volatilization at the higher temperature. Conversely, the portion of litter P released as dissolved inorganic P, increased from 8% at C to 1% at C. Thus, the influence of drying temperature on the release of N and P should be considered when determining the optimum timing of poultry litter application. It is suggested that the timing of poultry litter application should coincide with active periods of crop growth to combine maximum agronomic productivity with minimum edge-of-field losses of N and P to surface and groundwaters. As much as 6% of the N and % of the P released during the five rainfalls was lost during the first rainfall. This initial rapid N and P release stresses the importance of avoiding litter applications during periods of heavy rainfall. OULTRY PRODUCTION in the USA is becoming inp creasingly concentrated, both at the farm and regional level. The states of Alabama, Arkansas, Delaware, Georgia, North Carolina, and Oklahoma generate more than one-half of the country's poultry products. A growing number of farmers in these states are economically attracted towards broiler chicken production, due to decreasing returns from crop production and cattlerearing. These farmers may stock two or more houses with as many as broilers in each. A growing problem associated with intensive poultry production is the utilization of the large amounts of poultry litter produced. Poultry litter is a mixture of manure and wheat straw, pine bark shavings, peanut hulls, or other bedding material. Often, local agricultural land becomes a disposal site for large quantities of litter. J.S. Robinson, Soil Science Dep., 16 Newell HaIl,iiv. of Florida, Gainesville, FI\61 I; and A.N. Sharpley, USDA-ARS, NatI. Agric. Water Quality Lb., P.O. Box 1, Durant, OK Received 18 Jan *Corresponding author. Published in J. Environ. Qual. :6-67 (199). 6

2 ROBINSON & SHARPLEY: RELEASE OF NITROGEN AND PHOSPHORUS FROM POULTRY LITTER land surface; the method, rate, and timing of litter application; and rainfall intensity and duration (McLeod and Hegg, 198; Westerman et al., 198; Edwards and Daniel, 199). The prerequisite for the transport of N and P from any litter-treated land is rainfall. Irrespective of land management, information on the release characteristics of N and P from poultry litter is essential to assess the water quality impacts of land applications of poultry litter. Further, no data is available on the kinetics of N and P release from poultry litter during repeated rainfalls. The objective of the present study is to quantify the effects of recurring, simulated rainfall and intermittent drying temperatures on the release of N and P from poultry litter. MATERIALS AND METHODS Poultry Litter Two samples of poultry litter, containing different bedding materials (pine bark shavings or wheat straw), were collected from broiler houses in southeast Oklahoma. After thoroughly mixing each sample, subsamples were ground to pass through a -mm sieve, and stored in polythene bags at C. Poultry litter was ground to increase uniformity of subsampling and of water movement through the material. Preliminary leaching studies showed that amounts and rates of dissolved N and P release were not affected by grinding of litter. These subsamples were used for determination of total N, total P, mineralizable N and P contents, and for all rainfall trials. Litter was stored as collected at house moisture. Moisture contents ( C basis) of the pine bark shavings- and wheat straw-based poultry litters determined by gravimetric analysis for correction of N and P contents, were 9.8 and 8.%, respectively. Leaching Columns and Rainfall Simulation A circle of filter paper (Whatman ), mounted on a perforated disk of the same diameter (1 cm), was fitted 1 cm above the base of a Plexiglass leaching column (1 cm, i.d., height 1 cm) (Fig. 1). Twenty grams of thoroughly mixed, lightly ground poultry litter was spread uniformly over the paper. This amount of litter corresponds to an application rate of 1 Mg ha', commonly used by poultry producers in southeast Oklahoma (Sharpley et al., 199). The column base drained the leachate through an outlet for collection. Simulated rainfall was applied to the column by a capillary tube-type rain simulator, which generated drops. mm in diam. (Munns and Huntington, 1976). Rain fell onto the litter from a height of. m (to achieve terminal velocity), at an average rainfall intensity of. cm h' (1 ml min'). This rainfall intensity has a -yr return frequency in southeast 1cm [////Poultry litter 1 cm fifter paper perforated disc -column outflow Fig. 1. Schematic diagram of the column used to leach poultry litter. 6 Oklahoma. Splash losses of water or litter were prevented during the simulated rainfall by the 1-cm high column wall. Leaching Trials Eight leaching trials were conducted in triplicate, to evaluate the effect of four different drying temperatures (,,, or C) on dissolved N and dissolved P release from the two types of poultry litter. During each trial, a fresh sample of litter was subjected to five rainfalls. Each rainfall alternated with a 1-h drying period in a forced air oven, at one of the four temperatures. Individual drying periods lasted 1 h so that a full leaching trial could be completed in the same day. Each rainfall was applied until ml of leachate was collected. Thus, each rainfall lasted mm. The -ml fractions, all of which contained negligible visible particulate matter, were filtered (. gm) and analyzed for dissolved N (NO -NandIL),theiorgancd fmsoisolved P (inorganic P and organic P). Losses of N and P per leaching trial were calculated by summing the amounts released in the five successive -ml, volumes. Each of the eight leaching trials were conducted in triplicate and the mean of NH-N, NO -N, inorganic P, and organic P concentrations of the three replicates of all leaches are presented. In a separate experiment, total N and total P contents of all samples of litter after the first rainfall were measured before and after incubation at,,, and C, to determine the effect of temperature on N volatilization and P loss from poultry litter during drying. Chemical Analyses Total N and P content of the litter were determined by a semi-micro-kjeldahl procedure (Bremner and Mulvaney, 198). Potentially mineralizable N and P was extracted from litter by autoclaving in.1 M CaC1 (Smith and Stanford, 1971). Nitrate-N and NIL-N extracts, and NO -N and NIL-N in filtered litter leachate were measured colorimetrically, following reduction to NO -N by Cd (Greiss-Ilosvay method), and indophenol blue procedures, respectively (Keeney and Nelson, 198). All P extracts were measured by the colorimetric molybdenum-blue method of Murphy and Riley (196), as was the inorganic P content of filtered litter leachate. Total dissolved P in leachate was measured following acid persulfate digestion (Bowman, 1989). Organic P in leachate was calculated as the difference between total DP and IP. All chemical extractions and N and P measurements were conducted in duplicate. RESULTS AND DISCUSSION The total N and total P contents of pine bark shavingsbased poultry litter were slightly greater than those of wheat straw-based litter (Table 1). These values are similar to mean total N (1 g kg - ') and total P (1 g kg-') Table 1. Nitrogen and P content of the pine bark shavings-based and wheat straw-based poultry litters. Mineralizable Bedding P N Total N Total P material gkg %of total N %of total P

3 6 J. ENVIRON. QUAL., VOL., JANUARY-FEBRUARY 199 contents of poultry litter reported by Edwards and Daniel (199) from a review of published data. The mineralizable N and P contents of the pine bark shavings-based litter were -9 and %, respectively, compared with 8 and % in the wheat straw-based litter (Table 1). Effect of Consecutive Rainfall-Drying Cycles Ammonium-N, NO -N, inorganic P, and organic P concentrations in leachate from the fresh, pine bark shavings-based litter averaged 17,.,, and 1 mg L', respectively, during the first rainfall (Table ). Corresponding concentrations for the wheat straw-based litter averaged 18,.,, and 9 mg L', respectively (Table ). These high values demonstrate the rapid release of N and P from poultry litter during initial rainfalls following application. Analysis of variance showed that mean NH -N, inorganic P, and organic P concentrations of leachate from both types of litter with C intermittent drying periods, significantly (P < 1 %) decreased with consecutive rainfalls (Fig. ). During the fifth rainfall, average NH -N, inorganic P, and organic P concentrations in leachate from the pine bark shavings-based litter had decreased to 7., 1., and mg L', respectively (Fig. ). Corresponding concentrations from the wheat straw-based litter were 7.,., and. mg L, respectively (Fig. ). Similar, statistically significant (P < 1 %) release trends were observed at the other drying temperatures (Table ). For the two types of litter, the average NH -N, inorganic P, and organic P concentrations of leachate from the fifth 1 1 I E Ca C C) C 1 C.) 1 1 Rainfall Event Fig.. Relationship between ammonium-n, dissolved inorganic P, and dissolved organic P leached from poultry litter during five consecutive rainfalls. rainfall were only, 1, and 1% of those during the first event. Nitrate-N concentrations varied from. to.7 mg L between the first and fifth rainfall, however, indicating no consistent effect of consecutive rainfalls on NO -N release (Table ). Consistently low NO-N concentrations lost to rainfall following drying periods Table. Effect of consecutive rainfall events and drying temperature on leachate concentrations of dissolved NH -N, NO-N, inorganic P, and organic P from pine bark shavings- and wheat straw-based poultry litters. Rainfall eventt Ammonium-N Nitrate-N W heat straw Drying temperature ( C) Drying temperature ( C) Organic P mg L' a.16b.1c.d.d a.a.1b.1b.9c a.6b.a.c.c a.b.1c.18a.1a Inorganic P.18a.1a.1b.9c.d.19a.1b.1lb.1b.7c.9a.7a.b.1c.d.1d.8b. 16c.1d. 1d teach rainfall was for mm, at an intensity of. cm h - '. Mean NI -N, inorganic P, and organic P concentrations for each drying temperature were significantly different (P <.1) between rainfalls, and NO-N values followed by the same letter were not significantly different (P <.) as determined by analysis of variance.

4 6 ROBINSON & SI-IARPLEY: RELEASE OF NITROGEN AND PHOSPHORUS FROM POULTRY LITTER 7 Table. Portion of dissolved P as organic P released from poultry litter as a function of intermittent drying temperature. Litter type Drying temperature Organic P/Dissolved Pt % oc 8a 8a 1a 1a b b b 7b The proportion of dissolved P released as organic P during the different rainfall trials was almost constant at all drying temperatures (Table ). This suggests that there was negligible conversion of organic P to inorganic P in the poultry litter as a result of different drying temperatures. Thus, the effects of drying temperature on the release of P are discussed in terms of inorganic P only. The pattern of NH -N and inorganic P release from pine bark shavings- and wheat straw-based litter was similar for all drying temperatures between rainfalls (Table ). The sum of the mean losses of NIL-N and inorganic P after five rainfalls, however, was affected by drying temperature (Table ). Values are expressed on a land area basis (kg ha 1), and represent losses after h of rainfall (. cm h 1 ) and h of drying (Table ). For both types of litter, the lower drying temperatures of and C had a statistically negligible (P < 1%) effect on the sum of mean losses of NIL-N or inorganic P (Table ). Sum of mean losses NIL-N decreased significantly (P < 1 %) with increasing drying temperature from to C (Table ). For pine bark shavingsbased litter, NH -N release decreased from 87 to 68 kg ha', while that from wheat straw-based litter decreased from 7 to 9 kg ha (Table ). Nitrate-N release did not exceed. kg ha'. Increasing drying temperature from to C, however, significantly Table. Effect of drying temperature on dissolved NIL-N and inorganic P leaching losses from poultry litter during five rainfalls.t Inorganic P kg ha-1 87a 87a 78b 68c 7a 7a 68a 9b C Ca Effect of Drying Temperature Ammonium-N 6 U) Cl) -J ) are probably the result of denitrification losses during drying. Drying temperature I- type followed by the same letter are not t Proportions for each litter significantly different (P <.) as determined by analysis of variance. Litter type Ca 1a 1a 17b 18b ha ha 1b 1b t For each litter type, NH. -N and inorganic P values followed by the same letter were not significantly different (P <.) as determined by analysis of variance. - z - Pine shavings r = A- r =.99 1 Drying Temperature ( C) Fig.. Relationship between gaseous N loss from poultry litter and intermittent drying temperature between rainfalls. (P < 1 %) increased the release of inorganic P from 1 to 18 kg ha for pine bark shavings and from 11 to 1 kg ha' for wheat straw-based litter (Table ). The decrease in NH -N release with increasing drying temperature > C, may be due to an increase in gaseous N loss during the drying period. These gaseous N losses offset any increase in release of NIL-N due to rainfall. Factors that favor N volatilization include: high temperature, high rate of air movement across the litter surface, and a NH gradient between the litter and the surrounding air (Reddy et al., 1979). All these conditions were met in the forced air oven used to dry the litter. Effects of drying temperature on gaseous loss N from litter were investigated. Total N was determined in samples of leached litter, before and after drying at either,,, or C, for 1 h. Loss of N (expressed as a percentage of the total N content of litter) from pine bark shavings-based litter increased linearly (r =.98) from 9% during the C drying period, to 6% during the C drying period. Similarly, gaseous N losses from the wheat straw-based litter increased from 8 to 6% of total N in litter with increasing drying temperature (Fig. ). Loss of P from the two types of litters was <% of total P in all cases. Field data on gaseous N losses from poultry litter are sparse. Gaseous N losses from surface applied poultry manure, however, have been shown to significantly reduce the amount of N available for plant uptake or leaching through the soil profile (Crane et al., 1981; Giddens and Rao, 197; Wolf et al., 1988). Nitrogen volatilization data obtained in the present study indicate increased drying time and temperature would increase the volatilization losses of N from surface-applied poultry litter. A decrease in the N content and thus, N/P ratio of poultry litter, may result in higher application rates if recommendations are based on crop N requirements and account for gaseous N loss. This would exacerbate the rapid build-up of soil P in excess of crop requirements, thereby increasing the potential for P movement in runoff and subsequent downstream eutrophication. The concentration of N11 -N and inorganic P released by the end of the different rainfall trials are expressed

5 66 J. ENVIRON. QUAL., VOL., JANUARY-FEBRUARY 199 Table. Effect of drying temperature on the portion of total N and Padded in litter that was released as dissolved NIL-N and inorganic P during five rainfalls. Litter type Portion leached Drying temperature N1-1 -N/total N Inorganic P/total P as percentages of litter total N and total P content (Table ). Averaged for all drying temperatures, 1 to % of total N was released as NH -N, and 9 to 1% of total P was released as inorganic P from the pine bark shavings-based litter. These values were consistently greater (P < 1 %) than those from the wheat straw-based litter (16 to 1%, and 7 to 9% for NH -N and inorganic P, respectively). IMPLICATIONS TO POULTRY LITTER MANAGEMENT The solubility of N and P in poultry litter has implications regarding the material's agronomic effectiveness and water quality impacts. Some of the NH -N released from the litter will be derived from the NH -N in the litter, as well as from relatively easily mineralizable N (8-9% of total N). Easily mineralizable N in litter is usually in the form of uric acid (Edwards and Daniel, 199). Forms and solubilities of P in poultry litter are poorly documented. The low content of mineralizable P in the litters (-% of total P; Table 1), however, and the negligible conversion of organic P to inorganic P during the different rainfall trials (Table ), indicates that organic P is very stable, and that released inorganic P is derived almost solely from inorganic sources. Poultry diets contain at least 1 % dicalcium phosphate for bone development (National Research Council, 198). More than 8% of the dicalcium phosphate can pass through the birds undissolved, constituting a large portion of the inorganic P in poultry litter (Isermann, 199). When poultry litter is applied on the basis of crop P requirement, the stability of the organic P should assist more accurate application rates, thereby optimizing agronomic effectiveness while minimizing environmental impact. Release of NH -N in the first five rainfalls from pine bark shavings- and wheat straw-based litters, averaged for all drying temperatures, were 8 and 69 kg N ha', respectively. Corresponding release of inorganic P was 1 and 1 kg P ha'. In comparison, the N requirements for yields of 11 Mg ha' bermudagrass (Cynodon dactylon L.), Mg ha wheat (Triticum aestivum L.), and Mg fescue (Festuca arundinacea Schreb.) are, 6, and 8 kg N ha', respectively (Johnson et al., 199). Phosphorus requirements for these crops are, 11, and 1 kg P ha', respectively. Therefore, amounts of N and P released are sufficient to supply the N and P needs of wheat and fescue and a portion for bermudagrass. Land application of poultry litter can impact edge-offield losses of N and P in runoff. Because NO -N release from litter was well below 1 mg L' (range from. to.7 mg L'), and NIL-N consistently accounted for >9% of the total N released from both litters and all treatments, the environmental impact of dissolved N release are discussed in terms of NIL-N only. The NH form of N is fairly immobile in soil; however, NH -N is usually converted to NO -N, which can readily move with soil water. Depending on the amount and rate of infiltration, NO -N may be washed from the soil profile and into groundwater. Thus, litter N not taken up by the plant has the potential to be leached from the soil profile. In the case of P, Edwards and Daniel (199) found that most (8-9%) of the P in runoff from pastures receiving poultry litter is dissolved inorganic P, which will be immediately available for biological uptake (Sonzogni et al., 198). The concentration of dissolved inorganic P released from the fresh litters was times higher than the critical concentration associated with accelerated eutrophication (.1 mg L'; Edwards and Daniel, 199). Therefore, in spite of further modifications during downstream flow, these high concentrations of dissolved inorganic P have the potential to accelerate the eutrophication of receiving lakes or impoundments. The rapid initial release of N and P from poultry litter has also been demonstrated by Westerman and Overcash (198) and Westerman et al. (198). These workers investigated the effects of drying time (1 and d) on the concentration of N and P forms in runoff from bare soil. They showed that concentrations of total N and NH -N decreased with increasing drying time between application of poultry litter or manure (containing no bedding material) and simulated rainfall. These observations are consistent with those of McLeod and Hegg (198), who applied poultry manure to fescue grass plots. One day after application and at weekly intervals thereafter, the plots were exposed to simulated rainfall (intensity of.6 cm h'). Runoff concentrations of NIL-N and dissolved P decreased by 8 and % after two runoff events. Thus, downstream impacts of poultry litter applications could be reduced by avoiding applications shortly before a runoff producing rainfall. Edwards and Daniel (199) stress the importance of using weather forecasts to avoid application before severe storms. The decrease in N and P release with consecutive rainfall is rapid (Fig. ). Also, plant N and P requirements and uptake vary during the growing season. Therefore, the timing of litter application, in respect to crop uptake and rainfall-runoff susceptibility, is important from agronomic and environmental standpoints, respectively. If N and P release was constant with the number of rainfall events, then the timing of litter application would be less critical. For example, N and P released from litter in excess of plant needs would have the potential to be transported from the site of application in runoff or leachate during subsequent rainfalls.

6 ROBINSON & SHARPLEY: RELEASE OF NITROGEN AND PHOSPHORUS FROM POULTRY LITTER CONCLUSIONS The release of dissolved NH -N and inorganic P from poultry litter was rapid, with 8 kg N11-N ha and 6 inorganic P ha' released from pine bark shavings-based litter in the first rainfall. -based litter lost 9 kg NH -N ha and 6 kg inorganic P ha in the first rainfall. Dissolved losses decreased rapidly with subsequent rainfalls. Type of bedding material had no effect on the pattern of N or P release from litter at several drying temperatures. As drying temperature increased, N volatilization reduced the amounts of dissolved N11-N released, but amounts of released dissolved inorganic P and organic P increased. During five rainfalls, 8 kg NH -N ha and 1 kg inorganic P ha were released from pine bark shavingsbased litter, and 69 kg N11 -N ha and 1 kg inorganic P ha from wheat straw-based litter (averaged for all drying temperatures). These losses represented % of the total N and 9% of the total P in pine bark shaving sbased, and a respective 19 and 8% for wheat straw-based litter. These losses are comparable to annual N and P requirements of wheat (6 and 11 kg ha -1, respectively) and fescue (8 and 1 kg ha', respectively) in the Southern Plains, but insufficient for Bermudagrass requirements ( and kg ha, respectively). Consequently, timing of poultry litter application will be important in supplying annual crop N and P requirements during periods of active nutrient uptake. Due to the rapid release from litter, N and P not taken up by plants will be potentially available for transport in infiltrating or surface runoff water during rainfall. Thus, where practical to landowners, timing of land applications of poultry litter should be considered when aiming to develop reliable best management practices. Careful timing of litter applications can maximize agronomic benefit via crop N and P uptake, while minimizing environmental impacts via transport of released N and P during infiltration and runoff. k REFERENCES Bowman, R.A A sequential extraction procedure with concentrated sulfuric acid and dilute base for soil organic phosphorus. Soil Sci. Soc. Am. J. :6-66. Bremner, J.M., and C.S. Mulvaney Nitrogen-total. p. 96. In A.L. Page et al. (ed.) Methods of soil analysis. Part. nd ed. Agron. Monogr. 9. ASA and SSSA, Madison, WI. Crane, S.R., P.W. Westerman, and M.R. Overcash Short-term transformations following land application of poultry manure. Trans. ASAE :8-9. Edwards, D.R., and T.C. Daniel Environmental impacts of on-farm poultry waste disposal-a review. Bioresour. Technol. 1: 9-. Edwards, D.R., and T.C. Daniel Effects of poultry litter application rate and rainfall intensity on quality of runoff from fescuegrass plots. J. Environ. Qual. :61-6. 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