Effect of chemical and microbial amendment on phosphorus runoff from composted poultry litter

Environmental impacts of composting poultry litter with chemical amendments at the field scale have not been well quantified. The objectives of this study were to measure (i) P runoff and (ii) forage yield and N uptake from small plots fertilized with composted and fresh poultry litter. Two composting studies, aerated using mechanical turning, were conducted in consecutive years. Composted litter was collected at the completion of each study for use in runoff studies. Treatments in runoff studies included an unfertilized control, fresh (uncomposted) poultry litter, and litter composted with no amendment, H3PO4, alum, or a microbial mixture. An additional treatment, litter composted with alum plus the microbial mixture, was evaluated during the first year. Fertilizer treatments were applied at rates equivalent to 8.96 Mg ha(-1) and rainfall simulators were used to produce a 5 cm h(-1) storm event. Composted poultry litter, regardless of treatment, had higher total P concentrations than fresh poultry litter. Composting poultry litter resulted in reductions of N/P ratios by as much as 51%. Soluble reactive P concentrations were lowest in alum-treated compost, which reduced soluble P concentrations in runoff water by as much as 84%. Forage yields and N uptake were greatest from plots fertilized with fresh poultry litter. Composting poultry litter without the addition of C sources can increase P concentrations in the end product and surface runoff. This study also indicated that increased rates of composted poultry litter would be required to meet equivalent N rates supplied by fresh poultry litter.     

Effect of chemical and microbial amendments on ammonia volatilization from composting poultry litter

Research has shown that aluminum sulfate (alum) and phosphoric acid greatly reduce ammonia (NH3) volatilization from poultry litter; however, no studies have yet reported the effects of these amendments on field-scale composting of poultry litter. The objectives of this study were to (i) evaluate NH3 volatilization from composting litter by measuring both NH3 volatilization and changes in total nitrogen (N) in the litter and (ii) evaluate potential methods of reducing NH3 losses from composting poultry litter. Poultry litter was composted for 68 d the first year and 92 d the second year. Eleven treatments were screened in Year 1, which included an unamended control, a microbial mixture, a microbial mixture with 5% alum incorporated into the litter, 5 and 10% alum rates either surface-applied or incorporated, and 1 and 2% phosphoric acid rates either surface-applied or incorporated. Treatments in Year 2 included an unamended control, a microbial mixture, alum (7% by fresh wt.), and phosphoric acid (1.5% by fresh wt.). Alum and phosphoric acid reduced NH3 volatilization from composting poultry litter by as much as 76 and 54%, respectively. The highest NH3 emission rates were from microbial treatments each year. Compost treated with chemical amendments retained more initial N than all other treatments. Due to the cost and N loss associated with composting poultry litter, composting is not economical from an agronomic perspective compared with the use of fresh poultry litter.     

Relationships between biosolids treatment process and soil phosphorus availability

Laws mandating phosphorus (P)-based nutrient management plans have been passed in several U.S. Mid-Atlantic states. Biosolids (sewage sludge) are frequently applied to agricultural land and in this study we evaluated how biosolids treatment processes and biosolids P tests were related to P behavior in biosolids-amended soils. Eight biosolids generated by different treatment processes, with respect to digestion and iron (Fe), aluminum (Al), and lime addition, and a poultry litter (PL), were incubated with an Elkton silt loam (fine-silty, mixed, active, mesic Typic Endoaquult) and a Suffolk sandy loam (fine-loamy, siliceous, semiactive, thermic Typic Hapludult) for 51 d. The amended soils were analyzed at 1 and 51 d for water-soluble phosphorus (WSP), iron-oxide strip--extractable phosphorus (FeO-P), Mehlich-1 P and pH. The biosolids and PL were analyzed for P, Fe, and Al by USEPA 3050 acid-peroxide digestion and acid ammonium oxalate, Mehlich-1, and Mehlich-3 extractions. Biosolids and PL amendments increased extractable P in the Suffolk sandy loam to a greater extent than in the Elkton silt loam throughout the 51 d of the incubation. The trend of extractable WSP, FeO-P, and Mehlich-1 P generally followed the pattern: [soils amended with biosolids produced without the use of Fe or Al] > [PL and biosolids produced using Fe or Al and lime] > [biosolids produced using only Fe and Al salts]. Mehlich-3 P and the molar ratio of P to [Al + Fe] by either the USEPA 3050 digestion or oxalate extraction of the biosolids were good predictors of changes in soil-extractable P following biosolids but not PL amendment. Therefore, the testing of biosolids for P availability, rather than total P, is a more appropriate tool for predicting extractable P from the biosolids-amended soils used in this study.     

Alum treatment of poultry litter: decomposition and nitrogen dynamics

While the poultry industry is a major economic benefit to several areas in the USA, land application of poultry litter to recycle nutrients can lead to impaired surface and ground water quality. Amending poultry litter with alum [Al3(SO4)2 x 14H2O] has received considerable attention as a method of economically reducing ammonia volatilization in the poultry house and soluble phosphorus in runoff waters. The objective of this study was to characterize the effect of alum on broiler litter decomposition and N dynamics under laboratory conditions. Litter that had been amended with alum in the poultry house after each of the first four of five flock cycles (Experiment I) and litter that had been amended with alum after removal from a poultry house after the third flock cycle (Experiment II) were compared with unamended litter in separate studies. The litters in Experiment I were surface-applied to simulate application to grasslands, while the litters in Experiment II were incorporated to simulate application to conventionally tilled crops. The only statistically significant differences in decomposition due to alum occurred early in Experiment II and the differences were small. The only statistically significant differences in net N mineralization, soil inorganic N, and soil NH4+-N in either experiment was found in Experiment I after 70 d of incubation where soil inorganic N was significantly greater for the alum treatment. Thus, alum had little effect on decomposition or N dynamics. Results of many of the studies on litter not amended with alum should be applicable to litters amended with alum to reduce P availability.     

On-farm evaluation of aluminum sulfate (alum) as a poultry litter amendment: effects on litter properties

Aluminum sulfate [alum; Al2(SO4)3] amendment of poultry litters has been suggested as a best management practice to help reduce the potential environmental effects of poultry production. Past research has shown that alum treatment reduced NH3 emissions from litters, decreased the loss in runoff of P and trace metals from litter-amended soils, improved poultry health, and reduced the costs of poultry production. We conducted a large scale, "on-farm" evaluation of alum as a poultry (broiler) litter amendment on the Delmarva peninsula to determine the effect of alum on (i) litter properties and elemental composition and (ii) the solubility of several elements in litter that are of particular concern for water quality (Al, As, Cu, P, and Zn). Alum was applied over a 16-mo period to 97 poultry houses on working poultry farms; 97 houses on other farms served as controls (no alum). Litter samples were analyzed initially and after approximately seven alum applications. We found that alum decreased litter pH and the water solubility of P, As, Cu, and Zn. Alum-treated houses also had higher litter total N, NH4-N, and total S concentrations and thus a greater overall fertilizer value than litters from the control houses. Higher litter NH4-N values also suggest that alum reduced NH3 losses from litters. Thus, alum appears to have promise as a best management practice (BMP) for poultry production. Future research should focus on the long-term transformations of P, Al, As, Cu, and Zn in soils amended with alum-treated litters.     

Tillage, cropping systems, and nitrogen fertilizer source effects on soil carbon sequestration and fractions

Quantification of soil carbon (C) cycling as influenced by management practices is needed for C sequestration and soil quality improvement. We evaluated the 10-yr effects of tillage, cropping system, and N source on crop residue and soil C fractions at 0- to 20-cm depth in Decatur silt loam (clayey, kaolinitic, thermic, Typic Paleudults) in northern Alabama, USA. Treatments were incomplete factorial combinations of three tillage practices (no-till [NT], mulch till [MT], and conventional till [CT]), two cropping systems (cotton [Gossypium hirsutum L.]-cotton-corn [Zea mays L.] and rye [Secale cereale L.]/cotton-rye/cotton-corn), and two N fertilization sources and rates (0 and 100 kg N ha(-1) from NH(4)NO(3) and 100 and 200 kg N ha(-1) from poultry litter). Carbon fractions were soil organic C (SOC), particulate organic C (POC), microbial biomass C (MBC), and potential C mineralization (PCM). Crop residue varied among treatments and years and total residue from 1997 to 2005 was greater in rye/cotton-rye/cotton-corn than in cotton-cotton-corn and greater with NH(4)NO(3) than with poultry litter at 100 kg N ha(-1). The SOC content at 0 to 20 cm after 10 yr was greater with poultry litter than with NH(4)NO(3) in NT and CT, resulting in a C sequestration rate of 510 kg C ha(-1) yr(-1) with poultry litter compared with -120 to 147 kg C ha(-1) yr(-1) with NH(4)NO(3). Poultry litter also increased PCM and MBC compared with NH(4)NO(3). Cropping increased SOC, POC, and PCM compared with fallow in NT. Long-term poultry litter application or continuous cropping increased soil C storage and microbial biomass and activity compared with inorganic N fertilization or fallow, indicating that these management practices can sequester C, offset atmospheric CO(2) levels, and improve soil and environmental quality.     

Nitrous oxide emissions respond differently to mineral and organic nitrogen sources in contrasting soil types

The use of various animal manures for nitrogen (N) fertilization is often viewed as a viable replacement for mineral N fertilizers. However, the impacts of amendment type on NO production may vary. In this study, NO emissions were measured for 2 yr on two soil types with contrasting texture and carbon (C) content under a cool, humid climate. Treatments consisted of a no-N control, calcium ammonium nitrate, poultry manure, liquid cattle manure, or liquid swine manure. The N sources were surface applied and immediately incorporated at 90 kg N ha before seeding of spring wheat ( L.). Cumulative NO-N emissions from the silty clay ranged from 2.2 to 8.3 kg ha yr and were slightly lower in the control than in the fertilized plots ( = 0.067). The 2-yr mean NO emission factors ranged from 2.0 to 4.4% of added N, with no difference among N sources. Emissions of NO from the sandy loam soil ranged from 0.3 to 2.2 kg NO-N ha yr, with higher emissions with organic than mineral N sources ( = 0.015) and the greatest emissions with poultry manure ( < 0.001). The NO emission factor from plots amended with poultry manure was 1.8%, more than double that of the other treatments (0.3-0.9%), likely because of its high C content. On the silty clay, the yield-based NO emissions (g NO-N kg grain yield N) were similar between treatments, whereas on the sandy loam, they were greatest when amended with poultry manure. Our findings suggest that, compared with mineral N sources, manure application only increases soil NO flux in soils with low C content.     

Phosphorus runoff losses from subsurface-applied poultry litter on coastal plain soils

The application of poultry litter to soils is a water quality concern on the Delmarva Peninsula, as runoff contributes P to the eutrophic Chesapeake Bay. This study compared a new subsurface applicator for poultry litter with conventional surface application and tillage incorporation of litter on a Coastal Plain soil under no-till management. Monolith lysimeters (61 cm by 61 cm by 61 cm) were collected immediately after litter application and subjected to rainfall simulation (61 mm h(-1) 1 h) 15 and 42 d later. In the first rainfall event, subsurface application of litter significantly lowered total P losses in runoff (1.90 kg ha(-1)) compared with surface application (4.78 kg ha(-1)). Losses of P with subsurface application were not significantly different from disked litter or an unamended control. By the second event, total P losses did not differ significantly between surface and subsurface litter treatments but were at least twofold greater than losses from the disked and control treatments. A rising water table in the second event likely mobilized dissolved forms of P in subsurface-applied litter to the soil surface, enriching runoff water with P. Across both events, subsurface application of litter did not significantly decrease cumulative losses of P relative to surface-applied litter, whereas disking the litter into the soil did. Results confirm the short-term reduction of runoff P losses with subsurface litter application observed elsewhere but highlight the modifying effect of soil hydrology on this technology's ability to minimize P loss in runoff.     

Leachability and phytoavailability of nitrogen, phosphorus, and potassium from different bio-composts under chloride- and sulfate-dominated irrigation water

Concerns over increased phosphorus (P) application with nitrogen (N)-based compost application have shifted the trend to P-based composed application, but focusing on one or two nutritional elements does not serve the goals of sustainable agriculture. The need to understand the nutrient release and uptake from different composts has been further aggravated by the use of saline irrigation water in the recent scenario of fresh water shortage. Therefore, we evaluated the leachability and phytoavailability of P, N, and K from a sandy loam soil amended with animal, poultry, and sludge composts when applied on a total P-equivalent basis (200 kg ha(-1)) under Cl(-) (NaCl)- and SO4(2-) (Na2SO4)-dominated irrigation water. Our results showed that the concentration of dissolved reactive P (DRP) was higher in leachates under SO(4)(2-) than Cl(-) treatments. Compost amendments differed for DRP leaching in the following pattern: sludge > animal > poultry > control. Maize (Zea mays L.) growth and P uptake were severely suppressed under Cl(-) irrigation compared with SO4(2-) and non-saline treatments. All composts were applied on a total P-equivalent basis, but maximum plant (shoot + root) P uptake was observed under sludge compost amendment (73.4 mg DW(-1)), followed by poultry (39.3 mg DW(-1)), animal (15.0 mg DW(-1)), and control (1.2 mg DW(-1)) treatment. Results of this study reveal that irrigation water dominated by SO4(2-) has greater ability to replace/leach P, other anions (NO3(-)), and cations (K+). Variability in P release from different bio-composts applied on a total P-equivalent basis suggested that P availability is highly dependent on compost source.     

Liming poultry manures to decrease soluble phosphorus and suppress the bacteria population

Stabilizing phosphorus (P) in poultry waste to reduce P losses from manured soils is important to protect surface waters, while pathogens in manures are an emerging issue. This study was conducted to evaluate CaO and Ca(OH)2 for killing manure bacterial populations (pathogens) and stabilizing P in poultry wastes and to investigate the influence on soils following amendment with the treated wastes. Layer manure and broiler litter varying in moisture content were treated with CaO and Ca(OH)2 at rates of 2.5, 5, 10, and 15% by weight. All treated wastes were analyzed for microbial plate counts, pH, and water-soluble phosphorus (WSP), while a few selected layer manures were analyzed by phosphorus X-ray absorption near edge structure (XANES). A loamy sand and a silt loam were amended with broiler litter and layer manure treated with CaO at rates of 0, 2.5, 5, 10, and 15% and soil WSP and pH were measured at times 1, 8, and 29 d. Liming reduced bacterial populations, with greater rates of lime leading to greater reductions; for example 10% CaO applied to 20% solids broiler litter reduced the plate counts from 793,000 to 6500 mL-1. Liming also reduced the WSP in the manures by over 90% in all cases where at least 10% CaO was added. Liming the manures also reduced WSP in soils immediately following application and raised soil pH. The liming process used successfully reduced plate counts and concerns about P losses in runoff following land application of these limed products due to decreased WSP.     

Repeated compost application effects on phosphorus runoff in the Virginia Piedmont

Increasing amounts of animal and municipal wastes are being composted before land application to improve handling and spreading characteristics, and to reduce odor and disease incidence. Repeated applications of composted biosolids and manure to cropland may increase the risk for P enrichment of agricultural runoff. We conducted field research in 2003 and 2004 on a Fauquier silty clay loam (Ultic Hapludalfs) to compare the effects of annual (since 1999) applications of composted and uncomposted organic residuals on P runoff characteristics. Biosolids compost (BSC), poultry litter-yard waste compost (PLC), and uncomposted poultry litter (PL) were applied based on estimated plant-available N. A commercial fertilizer treatment (CF) and an unamended control treatment (CTL) were also included. Corn (Zea mays L.) and a cereal rye (Secale cereal L.) cover crop were planted each year. We applied simulated rainfall in fall 2004 and analyzed runoff for dissolved reactive P (DRP), total dissolved P (TDP), total P (TP), total organic C (TOC), and total suspended solids (TSS). End of season soil samples were analyzed for Mehlich-3 P (M3P), EPA 3050 P (3050P), water soluble P (WSP), degree of P saturation (DPS), soil C, and bulk density. Compost treatments significantly increased soil C, decreased bulk density, and increased M3P, 3050P, WSP, and DPS. The concentration of DRP, TDP, and TP in runoff was highest in compost treatments, but the mass of DRP and TDP was not different among treatments because infiltration was higher and runoff lower in compost-amended soil. Improved soil physical properties associated with poultry litter-yard waste compost application decreased loss of TP and TSS.     

Long-term effects of poultry litter, alum-treated litter, and ammonium nitrate on phosphorus availability in soils

Alum (Al2(SO4)(3).14H2O) additions to poultry litter result in lower ammonia (NH3) volatilization and phosphorus (P) runoff; however, the long-term effects of alum on soil P behavior have been unknown. The objectives of this study were to evaluate the long-term effects of poultry litter, alum-treated litter, and ammonium nitrate (NH4NO3) on P availability in soils and P runoff. Two studies were initiated in 1995: a small plot (1.5x3.0 m) study and a paired watershed (0.405 ha) study. In the small plot study 13 treatments (control, four rates of normal litter, four rates of alum-treated litter, and four rates of NH4NO3) were applied to tall fescue (Festuca arundinacea Schreb.) plots. Results show that after 7 yr water-extractable P (WEP) in surface soil samples was greater with normal litter, but Mehlich III P was greater in surface soils fertilized with alum-treated litter. When soil samples were taken at depth intervals to 50 cm in Year 7, Mehlich III P was only greater in the surface 5 cm for soils fertilized with alum-treated litter. At lower depths Mehlich III P was greater with normal litter, and WEP was up to 288% greater when normal litter was used, indicating that alum significantly reduced P leaching. Uptake of P by fescue was not affected by alum. Results from the paired watershed study showed P loss in runoff was 340% greater for normal litter than for alum-treated litter. This research, combined with earlier work that shows alum use improves air and soil quality, supports the use of alum as a long-term solution to reducing P runoff and leaching.     

Occurrence of arsenic and phosphorus in ditch flow from litter-amended soils and barn areas

Little is known about the fate of arsenic (As) in land-applied litter from chickens that have been fed roxarsone, an organic feed additive containing As. This study seeks to elucidate the transfer of As in runoff from ditch-drained soils of the poultry-producing region of the Delmarva Peninsula by tracking As and phosphorus (P) export from seven drainage ditches over two water-years (1 July 2005 to 30 June 2007). Annual losses of As from ditches ranged from 0.004 to 0.071 kg ha(-1) while P losses ranged from 0.33 to 18.56 kg ha(-1), with the largest loads associated with a litter storage shed that served as a point source. Event-based As and P losses in ditch flow fluctuated by a factor of 162 and 1882, respectively. The two elements were correlated in flow from the ditch draining a litter storage shed (r = 0.99), and in sediment extracts in soils near the litter shed (r = 0.73), pointing to similar behavior under point source conditions. Indeed, As and P exhibited similar behavior within storms for all ditches, characterized by relatively high initial concentrations subject to rapid concentration declines before peak flow, consistent with dilution of a finite source. However, As and P concentrations varied significantly between ditches and showed considerable temporal variability within ditches, with no clear seasonal trends or associations with current management strategies. The results suggest that similar management strategies might be effective for As and P point sources, but that field management practices geared toward controlling nonpoint source P losses may not readily transfer to the control of As losses.     

Dietary crude protein and tannin impact dairy manure chemistry and ammonia emissions from incubated soils

Excess crude protein (CP) in dairy cow diets is excreted mostly as urea nitrogen (N), which increases ammonia (NH) emissions from dairy farms and heightens human health and environmental concerns. Feeding less CP and more tannin to dairy cows may enhance feed N use and milk production, abate NH emissions, and conserve the fertilizer N value of manure. Lab-scale ventilated chambers were used to evaluate the impacts of CP and tannin feeding on slurry chemistry, NH emissions, and soil inorganic N levels after slurry application to a sandy loam soil and a silt loam soil. Slurry from lactating Holstein dairy cows (Bos taurus) fed two levels of dietary CP (low CP [LCP], 155 g kg; high CP [HCP], 168 g kg) each fed at four levels of dietary tannin extract, a mixture from red quebracho (Schinopsis lorentzii) and chestnut (Castanea sativa) trees (0 tannin [0T]; low tannin [LT], 4.5 g kg; medium tannin [MT], 9.0 g kg; and high tannin [HT], 18.0 g kg) were applied to soil-containing lab-scale chambers, and NH emissions were measured 1, 3, 6, 12, 24, 36, and 48 h after slurry application. Emissions from the HCP slurry were 1.53 to 2.57 times greater ( < 0.05) than from the LCP slurry. At trial's end (48 h), concentrations of inorganic N in soils were greater ( < 0.05) in HCP slurry-amended soils than in LCP slurry-amended soils. Emissions from HT slurry were 28 to 49% lower ( < 0.05) than emissions from 0T slurry, yet these differences did not affect soil inorganic N levels. Emissions from the sandy loam soil were 1.07 to 1.15 times greater ( < 0.05) than from silt loam soil, a result that decreased soil inorganic N in the sandy loam compared with the silt loam soil. Larger-scale and longer-term field trails are needed to ascertain the effectiveness of feeding tannin extracts to dairy cows in abating NH loss from land-applied slurry and the impact of tannin-containing slurry on soil N cycles.     

Alum amendment effects on phosphorus release and distribution in poultry litter-amended sandy soils

Increased poultry production has contributed to excess nutrient problems in Atlantic Coastal Plain soils due to land application of poultry litter (PL). Aluminum sulfate [alum, Al(2)(SO(4))(3).14H(2)O] amendment of PL effectively reduces soluble phosphorus (P) in the PL; however, the effects of these litters when added to acidic, sandy soils are not well understood. The objective of this study was to investigate the efficacy of alum-amended poultry litter in reducing P release from three Delaware Coastal Plain soils: Evesboro loamy sand (Ev; excessively drained, mesic, coated Typic Quartzipsamments), Rumford loamy sand (Ru; well drained, coarse-loamy, siliceous, subactive, thermic Typic Hapludults), and Pocomoke sandy loam (Pm; very poorly drained, coarse-loamy, siliceous, active, thermic Typic Umbraquults). Long-term (25 d) and short-term (24 h) desorption studies were conducted, in addition to chemical extractions and kinetic modeling, to observe the changes that alum-amended versus unamended PL caused in the soils. The Ev, Ru, and Pm soils were incubated with 9 Mg ha(-1) of alum-amended or unamended PL. Long-term desorption (25 d) of the incubated material resulted in approximately 13.5% (Ev), 12.7% (Ru), and 13.3% (Pm) reductions in cumulative P desorbed when comparing soil treated with unamended and alum-amended PL. In addition, the P release from the soil treated with alum-amended litter was not significantly different from the control (soil alone). Short-term desorption (24 h) showed 7.3% (Ev), 15.4% (Ru), and 20% (Pm) reductions. The overall implication from this study is that the use of alum as a PL amendment is useful in coarse-textured soils of the Coastal Plain. With increased application of alum-amended PL, more significant decreases may be possible with little or no effect on soil quality.     

Fate of phosphorus in dairy wastewater and poultry litter applied on grassland

Large and repeated manure applications can exceed the P sorption capacity of soil and increase P leaching and losses through subsurface drainage. The objective of this study was to evaluate the fate of P applied with increasing N rates in dairy wastewater or poultry litter on grassland during a 4-yr period. In addition to P recovery in forage, soil-test phosphorus (STP) was monitored at depths to 180 cm in a Darco loamy sand (loamy, siliceous, semiactive, thermic Grossarenic Paleudults) twice annually. A split-plot arrangement of a randomized complete block design comprised four annual N rates (0, 250, 500, and 1000 kg ha(-1)) for each nutrient source on coastal bermudagrass [Cynodon dactylon (L.) Pers.] over-seeded with ryegrass (Lolium multiflorum L. cv. TAM90). Increasing annual rates of N and P in wastewater and poultry litter increased P removal in forage (P = 0.001). At the highest N rate of each nutrient source, less than 13% of applied P was recovered in forage. The highest N rates delivered 8 times more P in wastewater or 15 times more P in poultry litter than was removed in forage harvests during an average year. Compared with controls, annual P rates up to 188 kg ha(-1) in dairy wastewater did not increase STP concentrations at depths below 30 cm. In contrast, the highest annual P rate (590 kg ha(-1)) in poultry litter increased STP above that of controls at depth intervals to 120 cm during the first year of sampling. Increases in STP at depths below 30 cm in the Darco soil were indicative of excessive P rates that could contribute to nonpoint-source pollution in outflows from subsoil through subsurface drainage.     

Managing broiler litter application rate and grazing to decrease watershed runoff losses

Pasture management and broiler litter application rate are critical factors influencing the magnitude of nutrients being transported by runoff from fields. We investigated the impact of pasture management and broiler litter application rate on nutrient runoff from bermudagrass (Cynodon dactylon) pastures. The experiment was conducted on a Ruston fine sandy loam with a factorial arrangement on 21 large paddocks. Runoff water was collected from natural rainfall events from 2001 to 2003. Runoff water and soil samples were analyzed for nutrients and sediments. Runoff was generally greater (29%) from grazed than hayed pastures regardless of the litter application rate. There was greater inorganic N in the runoff from grazed paddocks when litter rate was based on N rather than P. The mean total P loss per runoff event for all treatments ranged from 7 to 45 g ha(-1) and the grazed treatment with litter applied on N basis had the greatest total P loss. Total dissolved P was the dominant P fraction in the runoff, ranging from 85% to 93% of the total P. The soluble reactive P was greater for treatments with litter applied on N basis regardless of pasture management. Runoff total sediments were greater for N-based litter application compared to those which received litter on P basis. Our results indicate that litter may be applied on N basis if the pasture is hayed and the soil P is low. In contrast, litter rates should be based on a P-basis if pasture is grazed.     

Rapid methods to determine potentially mineralizable nitrogen in broiler litter

Although broiler (chicken, Gallus gallus domesticus) litter has long been used as a fertilizer, estimating the rate required to supply a desired amount of plant-available N is still hampered by the lack of rapid methods to estimate potentially mineralizable nitrogen (PMN). Previous research has suggested that near infrared reflectance spectroscopy (NIRS) and certain poultry litter characteristics, such as water-soluble organic nitrogen (WSON), may be useful for estimating PMN. The objectives of this study were to evaluate NIRS and WSON as tools to estimate PMN in broiler litter. Sixty sieved (2 mm) and freeze-dried broiler litter samples were mixed with Cowarts sandy loam soil (fine-loamy, kaolinitic, thermic Typic Kanhapludult) and incubated at 25 degrees C for 112 d. Cumulative net N mineralized with time was fitted to a single-pool exponential model to determine PMN for each broiler litter sample. The PMN values obtained were regressed against NIRS (780 to 2500 nm) and WSON measurements. We found strong relationships between measured- and NIRS-predicted PMN (R2 = 0.82), and between measured PMN and WSON (R2 = 0.87). These results demonstrate the feasibility of using either of these two methods to estimate PMN in broiler litter. Future work should further test both methods for their ability to estimate mineralizable N in whole, moist broiler litter under field conditions.     

The economics of land application of fresh and composted broiler litter with an environmental constraint

Land application of broiler litter is a common disposal method due to its value as a fertiliser substitute, but presents potential environmental problems because of nutrient runoff. Composting has been suggested as an alternative due to the formation of more stable organic components. The land application of fresh and composted broiler litter are compared as alternative disposal methods. The costs of land application of broiler litter are dominated by spreading because of low nutrient densities relative to commercial fertilisers. Composting broiler litter before land application appears to be substantially less economically attractive than land application of fresh broiler litter because of high costs of production and higher spreading costs due to even lower nutrient density. However, when environmental constraints are placed on the phosphorus concentration from hayfield runoff, composting becomes a more attractive alternative. Composting becomes more viable as the land base for application becomes smaller relative to broiler production; as alternative disposal costs for litter become higher; and as environmental constraints become stricter.     

Microbial mineralization of organic nitrogen forms in poultry litters

Ammonia volatilization from the mineralization of uric acid and urea has a major impact on the poultry industry and the environment. Dry acids are commonly used to reduce ammonia emissions from poultry houses; however, little is known about how acidification affects the litter biologically. The goal of this laboratory incubation was to compare the microbiological and physiochemical effects of dry acid amendments (Al+Clear, Poultry Litter Treatment, Poultry Guard) on poultry litter to an untreated control litter and to specifically correlate uric acid and urea contents of these litters to the microbes responsible for their mineralization. Although all three acidifiers eventually produced similar effects within the litter, there was at least a 2-wk delay in the microbiological responses using Poultry Litter Treatment. Acidification of the poultry litter resulted in >3 log increases in total fungal concentrations, with both uricolytic (uric acid degrading) and ureolytic (urea degrading) fungi increasing by >2 logs within the first 2 to 4 wk of the incubation. Conversely, total, uricolytic, and ureolytic bacterial populations all significantly declined during this same time period. While uric acid and urea mineralization occurred within the first 2 wk in the untreated control litter, acidification resulted in delayed mineralization events for both uric acid and urea (2 and 4 wk delay, respectively) once fungal cell concentrations exceeded a threshold level. Therefore, fungi, and especially uricolytic fungi, appear to have a vital role in the mineralization of organic N in low-pH, high-N environments, and the activity of these fungi should be considered in best management practices to reduce ammonia volatilization from acidified poultry litter.