Leaching of phosphorus (P) mobilizes edaphic and applied sources of P and is a primary pathway of concern in agricultural soils of the Delmarva Peninsula, which defines the eastern boundary of the eutrophic Chesapeake Bay. We evaluated P leaching before and after poultry litter application from intact soil columns (30 cm diameter × 50 cm depth) obtained from low- and high-P members of four dominant Delmarva Peninsula soils. Surface soil textures ranged from fine sand to silt loam, and Mehlich-3 soil P ranged from 64 to 628 mg kg. Irrigation of soil columns before litter application pointed to surface soil P controls on dissolved P in leachate (with soil P sorption saturation providing a stronger relationship than Mehlich-3 P); however, strong relationships between P in the subsoil (45-50 cm) and leachate P concentrations were also observed ( = 0.61-0.73). After poultry litter application (4.5 Mg ha), leachate P concentrations and loads increased significantly for the finest-textured soils, consistent with observations that well-structured soils have the greatest propensity to transmit applied P. Phosphorus derived from poultry litter appeared to contribute 41 and 76% of total P loss in leachate from the two soils with the finest textures. Results point to soil P, including P sorption saturation, as a sound metric of P loss potential in leachate when manure is not an acute source of P but highlight the need to factor in macropore transport potential to predict leaching losses from applied P sources.

The use of enhanced efficiency N fertilizers can increase crop N utilization and lead to lower emissions of the greenhouse gas N 2 O. To determine the potential benefit of four enhanced efficiency fertilizers with rainfed corn (Zea mays L.) production in central Pennsylvania, N 2 O emissions and grain yield were monitored during a 4-yr field study and compared with untreated urea prills and urea-NH 4 NO 3 (UAN). The tested enhanced efficiency products were ESN (polymer-coated urea), SuperU (urease and nitrification inhibitor treated urea), UAN treated with AgrotainPlus (urease and nitrification inhibitors), and PiNT (cationstabilized amine-N). Additionally, 28-d laboratory incubations were conducted to verify the potential differences in N cycling rates among N sources. The laboratory incubations indicated that ESN, SuperU, and treated UAN all had the potential to delay accumulation of NO 3 relative to untreated urea and UAN, but N cycling was similar with PiNT and the untreated fertilizers. Extended dry periods limited the denitrification potential and overall N 2 O emissions in the field, but spikes of N 2 O emission were seen within 1 mo after fertilizer application in each year. However, variation in emission rates was high within treatments, and no consistent differences among N sources were seen. Cumulative growing season N 2 O emissions and grain yield were similar for all N sources in each year of the study. Enhanced efficiency fertilizers do not appear to be an effective means to reduce N 2 O emission in a rainfed system, at least when rainfall is inconsistent.

First and second harvests of lucerne (Medicago sativa L.), perennial ryegrass (Lolium perenne L.) and a lucerneperennial ryegrass mixture [80 or 144 g kg )1 dry matter (DM) of ryegrass] at the first and second harvests were cut and conditioned, wilted to 500 or 700 g DM kg )1 then baled and stretch-wrapped for silage on the same dates. Lucerne bales were denser (411 kg m )3 ) than bales of perennial ryegrass (331 kg m )3 ) (P < 0AE05). After an 8-month storage period, silage made from high DM-content forage had a higher concentration of neutral-detergent fibre (NDF) and was less digestible than that made from low DM-content forage. Daily DM intakes by beef steers, when the silages of the second harvest were fed ad libitum, were 31AE2, 31AE2 and 22AE3 g kg )1 live weight for lucerne, lucerne-perennial ryegrass mixture and perennial ryegrass silages, respectively (P < 0AE01), when the herbage had been wilted to 500 g kg )1 . In vivo digestibility of NDF in the lucerneperennial ryegrass mixture silage (0AE587) was significantly lower than that of perennial ryegrass silage (0AE763) but higher than lucerne silage (0AE518). Higher intakes of baled lucerne silage tended to offset its lower digestibility values. Lucerne-perennial ryegrass mixture silage had a higher DM and NDF digestibility than lucerne silage, indicating perhaps the presence of associative effects.

A gronomy J our n al • Volume 10 0 , I s sue 6 • 2 0 0 8 1541 (Van Horn et al., 1994;Pell, 1997). Th e benefi t of dairy compost application to agricultural soils can be attributed to the improvement of physical and chemical edaphic properties (DeLuca and DeLuca, 1997;Butler and Muir, 2006).Manure application to crop fi elds can recycle animal wastes and be a valuable soil nutrient resource. For example, Singer et al. (2007) reported soil amendment through manure compost application increased P uptake 19% and K uptake 21% in corn. However, excessive application of manure can create nutrient imbalances of surface water, groundwater, and soil. For example, elevated levels of N and P concentrations in several reservoir and stream sites in the upper north Bosque River watershed of central Texas have created eutrophic conditions (McFarland and Hauck, 1999). Sanderson and Jones (1997) suggested annual compost application rates need to be <44.8 Mg ha -1 in the southern United States to reduce the risks of soil-P accumulation and NO 3 -N leaching in coastal bermudagrass [Cynodon dactylon (L). Pers]. Muir (2001) reported P removal of Kenaf (Hibiscus cannabinus L.) was only 6.8% of the P equivalent added by the yearly application of 20 Mg dairy compost DM ha -1 and that plant P uptake was not suffi cient to prevent soil-P accumulation in fi elds receiving dairy manure compost. Recent research showed single dairy manure compost applications to tall wheatgrass [Th inopyrum ponticum (Podp.)] increased soil-P concentrations 400 to 480% through two growing seasons (Butler and Muir, 2006).Yield response of 'Coastal' bermudagrass [Cynodon dactylon (L.) Pers.] to compost application is slower than to the comparable rate of conventional inorganic fertilization (Sanderson and Jones, 1997). However, the slow release of organically bound N and P in soil may be more completely used by crops (Gershuny and Martin, 1992). In a comparison of inorganic-N and manure application in corn fi elds, Ma et al. (1999) found the synchrony of N-release from manure coincided more closely with early grain fi lling stage in corn.Generally, N-P-K concentration of compost is low when considering its volume. Another limitation to agricultural application of manure compost is the high cost of transportation and application compared to IF. Newton et al. (2003) were skeptical that manure compost at lower application rates combined with supplemental inorganic N fertilizer were a viable option for forage production. However, the eff ects of compost application and residual carryover involving supplemental-N fertilization systems are not well defi ned. Moreover, maximum compost rates that avoid excessive soil P buildup in warmer climates are not well understood. Butler and Muir (2006)

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