Submitted to: Biosystems Engineering
Publication Type: Peer reviewed journal
Publication Acceptance Date: 7/22/2005
Publication Date: 10/11/2005
Citation: Haggard, B.E., Vadas, P.A., Smith, D.R., Delaune, P., Moore Jr., P.A. 2005. Effect of poultry litter to water ratios on extractable phosphorus content and its relation with runoff phosphorus concentrations. Biosystems Engineering. 92(3):409-417. Interpretive Summary: Various factors affect phosphorus loss from the landscape including phosphorus in the soil and that surface applied in fertilizers and animal manure. Recently, studies have shown that the amount of water soluble phosphorus applied in fertilizers and animal manure is an important factor in determining the potential for phosphorus loss from the landscape. This study evaluated the effect of different extraction ratios (poultry litter to water by weight) on water soluble phosphorus content and the relation of soluble phosphorus application rates to phosphorus concentrations in runoff water from small plots during rainfall simulations. Six different poultry litters were used in this study and applied to the small plots at equivalent total phosphorus rates (6lbs per acre); this was the first study to evaluate phosphorus loss from poultry litters which had been pelleted. We discovered that water soluble phosphorus content increased with an decrease in the amount of poultry litter used in the 200-mL water extraction. Phosphorus concentrations in runoff water were strongly related to the amount of water soluble phosphorus applied to each plot. It also appears that the pelleting process increases soluble phosphorus content in poultry litter and the potential for phosphorus loss from the landscape when surface applied - however, we need further study on the effects of poultry litter pelleting.
Technical Abstract: Source factors with regard to P loss in runoff waters are often soil test P and P content of fertilizers applied; more recently, water soluble P (SP) fractions in fertilizers and animal manure have been the focus of many field and plot-scale studies. SP content of animal manure has been shown to vary with differences in extraction methods, particularly the ratio of animal manure (dry weight equivalent) to water used in the extraction. This study evaluated changes in the SP content of six poultry litters by varying the extraction ratios from 1:10 (e.g., 20 g fresh poultry litter to 200 mL water) to 1:200 and also the relation between SP content determined at these different ratios and P concentrations in runoff water collected during rainfall simulations. The six different poultry litter treatments (pelleted compost, pelleted litter & raw litter from a nearby pelleting plant; alum litter, pelleted alum & untreated litter from a local farm) were surface-applied at equivalent total P (TP) application rates (~67 kg/TP ha) to 1.52 by 6.10 m grass plots on a 5 percent slope which received artificial rainfall at 5 cm/hr until 30 min of continuous runoff was observed; four plots were used per treatment including four control plots (no poultry litter application). SP content of the various poultry litters increased with a decrease in the amount of poultry litter used in the 200 mL water extraction, i.e. from an extraction ratio of 1:10 to 1:200. SP and TDP application rates were positively correlated to P concentrations in runoff waters from the small plots although some dichotomy existed between the two sources of poultry litter. In general, it appeared that pelleting poultry litters increases the SP content as well as the potential for P loss in runoff water during precipitation events; however, these results should be interpreted cautiously. This study reaffirmed the importance of SP content of poultry litter when determining the potential for P loss in surface runoff.