PHOSPHORUS MANAGEMENT Plant Availability of Phosphorus in Swine Slurry and Cattle Feedlot Manure

that are in excess of the crop P removal. Excess P can accumulate in the soil and can increase P in runoff. Pote To utilize manure P for crop production, P release and plant availet al. (1996, 1999) found increased P loss in runoff as ability needs to be quantified. An incubation study was conducted to determine P availability from swine (Sus scrofa) and cattle (Bos tauthe soil P test increased. Eghball et al. (2002b) showed rus) feedlot manure in three soils. Treatments for each manure inthat soil test P was not a significant factor when manure cluded temperature (11, 18, 25, and 32 C), water regime [constant was applied shortly before rainfall; however, P loss in 60% water-filled pore space (WFPS) vs. four dry-down cycles of 60 runoff was related to soil test P when manure application to 30% WFPS], time, and soils (Catlin silt loam, Sharpsburg silty clay was made a year earlier. loam, and Valentine fine sand). In another study, synthetic P fertilizer To provide P needs of a crop, the amount of P minerwas used to determine the fraction of P that becomes unavailable alized following manure application needs to be deterwith time to compare with manure P. Time, soil, and manure applicamined. Phosphorus in manure is in various forms but is tion were factors that influenced soil test P and water-soluble P during mostly inorganic (Sharpley and Moyer, 2000; Eghball, incubation. At the low synthetic P fertilizer rate of 6 g g 1, about 2003), indicating that P availability following application 12 kg P ha 1, none of the applied P remained available in the Catlin soil while about one-third remained plant available in the Sharpsburg should be high if the inorganic P converts to plant availsoil and two-thirds in the Valentine soil. At the high P rate, 68 mg able form after application. Mineralization of organic P kg 1, 38 to 83% of fertilizer P remained available in the three soils. in the soil is catalyzed by various enzymes, including phyPhosphorus availability was 60 to 100% of applied cattle manure P tase (He and Honeycutt, 2001). Water-soluble P (WSP) and 52 to 100% of swine slurry P in the three soils. Phosphorus was 19% of swine manure P (Sharpley and Moyer, 2000) availability in the Sharpsburg soil was 100% of P in both manure and 8% of beef cattle feedlot manure P (Eghball and types. Phosphorus availability from manure is high, and manure can Gilley, 1999). Kleinman et al. (2002) showed that disbe used similar to inorganic P fertilizer in soils where P-based applicasolved P in runoff was highly related with the WSP tion is made in areas susceptible to P loss in runoff. In P-deficient content of manure. Based on the soil test P changes and soils, a P availability of 70% should be used. plant P uptake 1 yr after application, P availability in the first year after application was 85% for beef cattle feedlot manure and 73% for composted feedlot manure M contains significant amounts of P that can (Eghball et al., 2002a). Slightly lower P availability from be utilized for crop production. Manure is usually composted than noncomposted manure indicated chemapplied to provide N needs of a growing crop. However, ical reaction of P during composting that involved turnbecause of concerns about surface water pollution with ing and mixing caused P to become less plant available. P and the subsequent eutrophication, P-based manure Motavalli et al. (1989) found that P availability from application is becoming more common in a number of injected dairy manure ranged from 12 to 89% based on states (Weld et al., 2002; Sharpley et al., 2003). The P uptake. The low P availability in this study was due USDA and USEPA (1999) jointly issued the Unified to a small crop P uptake response from applied manure Strategy for Animal Feeding Operations in which P-based P. In a field study, Wen et al. (1997) found that 69% management approaches were emphasized for sites vulof composted manure P was plant available. Ebeling et nerable to P loss. The final Confined Animal Feeding al. (2003) found that composition of the P source added Operation’s rule was registered on 12 Feb. 2003. Eghball influenced soil test P. and Power (1999) found that P-based manure or comSoil and environmental factors influence manure P post application resulted in soil test P levels similar to and N mineralization and availability. Soil and manure the original soil P level after 4 yr of application, but N mineralization increases with increasing temperature N-based application resulted in significant P buildup of under conditions found in agricultural soils (Cassman up to 265 mg kg 1 in the soil. This is because N/P ratios and Munns, 1980; Eghball, 2000). Mineralization is of most manure types are narrower (e.g., 3:1) than the greatest when soil moisture is near field capacity and N/P uptake ratios of most crops (e.g., 6:1 for corn). declines with soil drying (Cassman and Munns, 1980). Therefore, N-based manure application provides P rates The variables that influence P release and availability need to be evaluated so that manure P availability in B. Eghball (deceased) and B.J. Wienhold, USDA-ARS, Lincoln, NE the soil can be estimated. The objective of this study 68583; B.L. Woodbury and R. A. Eigenberg, USDA-ARS, Clay Cenwas to evaluate the effects of temperature and soil water ter, NE 68933. Joint contribution of USDA-ARS and Univ. of Nebraska Agric. Res. Div., Lincoln, NE, as Paper no. 14356. Received 4 May 2004. *Corresponding author ([email protected]). Abbreviations: BKP, Bray and Kurtz no. 1 phosphorus; T0, soil samples taken when the experiment started; T1–T4, sampling cycles when Published in Agron. J. 97:542–548 (2005). © American Society of Agronomy the soil in the varying water content treatment was reduced from 60 to 30%; WFPS, water-filled pore space; WSP, water-soluble phosphorus. 677 S. Segoe Rd., Madison, WI 53711 USA