Land application of poultry litter provides essential nutrients for hybrid bermudagrass [Cynodon dactylon (L.) Pers.] production, but ammonia (NH 3) volatilization and N mineralization influence the amount of litter N available for plant uptake. Our objective was to determine the combination of broiler litter and fertilizer N, which maximizes the yields of forage and N, P, and K by 'Coastal' bermudagrass. Studies were conducted for 3 yr (1999-2001) in pastures at Newton and Mize, MS that differed widely in soil test P (STP) due to history of litter application (0 vs. 301 yr, respectively.). Litter rates of 0, 4.5, 8.9, 13.4, and 17.9 Mg ha 21 were obtained by up to four monthly (April-July) applications of 4.5 Mg ha 21 and were supplemented with ammonium nitrate (NH 4-NO 3) to provide the same total N in each treatment. At Newton, combining litter with fertilizer N increased forage yield by 10% in 1999, 25% in 2000, and 34% in 2001, as compared to fertilizer N. At Mize, K uptake increased as litter rate increased in 2001 only. These responses to litter were related to increased soil P and K at Newton, and increased soil N, P, and Ca at Mize. Averaged across years, maximum P uptake of about 40 kg ha 21 was obtained by applying 8.9 Mg litter 1 134 kg N ha 21 at Newton and 4.5 Mg litter 1 202 kg N ha 21 at Mize. Safe and effective management of major plant nutrients in broiler litter may require the use of commercial N fertilizer.

No abstract

Forty-eight states in the United States use phosphorus (P) indices to meet the requirements of their Natural Resources Conservation Service (NRCS) Code 590 Standard, which provides national guidance for nutrient management of agricultural lands. The majority of states developed these indices without consultation or coordination with neighboring states to meet specific local conditions and policy needs. Using water quality and land treatment data from six previously published articles, we compared P loads with P-Index values and ratings using the 12 southern P indices. When total measured P loads were regressed with P-Index rating values, moderate to very strong relationships (0.50 to 0.97) existed for five indices (Arkansas, Florida, Georgia, North Carolina, and South Carolina) and all but one index was directionally correct. Regressions with dissolved P were also moderate to very strong ( of 0.55 to 0.95) for the same five state P indices (Arkansas, Florida, Georgia, North Carolina, and South Carolina); directionality of the Alabama Index was negative. When total measured P loads were transformed to current NRCS 590 Standard ratings (Low [<2.2 kg P ha], Moderate, [2.2-5.5 kg P ha], and High [>5.5 kg P ha]) and these ratings were then compared to the southern-Index ratings, many of the P indices correctly identified Low losses (77%), but most did not correctly identify Moderate or High loss situations (14 and 31%, respectively). This study demonstrates that while many of the P indices were directionally correct relative to the measured water quality data, there is a large variability among southern P indices that may result in different P management strategies being employed under similar conditions.

Factors that contribute to high soil P in bermudagrass [Cynodon dactylon L. (Pers.)] pastures include continued use of broiler litter rich in P to meet forage N requirements and removal of hay in summer only. This study determined if harvesting annual ryegrass (Lolium multiflorum Lam.) in addition to bermudagrass would reduce surplus soil P, Cu, and Zn faster than bermudagrass alone after litter application ceased on a Ruston soil (fine-loamy, siliceaous, semiactive, thermic Typic Paleudults). During a 3-yr build-up, 'Coastal' bermudagrass was fertilized with 0, 4.5, 9, 18, and 36 Mg ha 21 litter yr 21 . During the drawdown phase, plots were split and half was overseeded with ryegrass in fall 2001, 2002, and 2003. Whole plots were fertilized with NH 4 NO 3 in spring-summer to provide 268 kg ha 21 N yr 21 . Forage yield and P uptake increased as antecedent litter rate increased, and were greater in ryegrass-bermudagrass than bermudagrass in 2002, but not 2003. At 9 Mg ha 21 litter, harvesting ryegrass in addition to bermudagrass increased P uptake by 10 to 55%, depending on study year. During the drawdown phase, soil Mehlich-3 P (M3P) and water-extractable P to 15-cm depth decreased by as much as 50 and 70%, respectively. Soils analysis within each sampling date found no significant effect of forage system or its interaction with litter rate. Data for 9 Mg ha 21 litter rate indicated 2 yr of forage P removal decreased residual M3P to an acceptable agronomic level (,70 mg kg 21 ). The potential to decrease surplus soil P by ryegrass-bermudagrass hay harvests was greatest when rainfall was inadequate for optimum bermudagrass yield.

Phosphorus (P) Indices in the southern United States frequently produce different recommendations for similar conditions. We compared risk ratings from 12 southern states (Alabama, Arkansas, Florida, Georgia, Kentucky, Louisiana, Mississippi, North Carolina, Oklahoma, South Carolina, Tennessee, and Texas) using data collected from benchmark sites in the South (Arkansas, Georgia, Mississippi, North Carolina, Oklahoma, and Texas). Phosphorus Index ratings were developed using both measured erosion losses from each benchmark site and Revised Universal Soil Loss Equation 2 predictions; mostly, there was no difference in P Index outcome. The derived loss ratings were then compared with measured P loads at the benchmark sites by using equivalent USDA-NRCS P Index ratings and three water quality models (Annual P Loss Estimator [APLE], Agricultural Policy Environmental eXtender [APEX], and Texas Best Management Practice Evaluation Tool [TBET]). Phosphorus indices were finally compared against each other using USDA-NRCS loss ratings model estimate correspondence with USDA-NRCS loss ratings. Correspondence was 61% for APEX, 48% for APLE, and 52% for TBET, with overall P index correspondence at 55%. Additive P Indices (Alabama and Texas) had the lowest USDA-NRCS loss rating correspondence (31%), while the multiplicative (Arkansas, Florida, Louisiana, Mississippi, South Carolina, and Tennessee) and component (Georgia, Kentucky, and North Carolina) indices had similar USDA-NRCS loss rating correspondence-60 and 64%, respectively. Analysis using Kendall's modified Tau suggested that correlations between measured and calculated P-loss ratings were similar or better for most P Indices than the models. (Dubrovsky and Hamilton, 2010). Recent harmful algal blooms in Lake Erie caused Toledo to shut down its drinking water supply for several days, refocusing the link between nutrient enrichment (particularly phosphorus [P]) and water quality impairment (Stow et al., 2015), with many of these nutrients being agriculturally derived. To control agricultural nutrient loading to surface waters, multiple control strategies are necessary at the source and during transport into the receiving water resources. The USDA-NRCS refers to this as "avoid, control, and trap."Since the late 1990s, the USDA and USEPA jointly required all states to adopt a unified nutrient management policy through the NRCS Code 590 Standard (USDA and USEPA, 1999). States were required to establish a soil-test P threshold based on crop requirements (above which P applications were restricted), to establish an alternative soil test P threshold using water quality criteria, or to develop a P Index to identify fields at risk for P losses. Forty-eight states and some territories, including Puerto Rico, chose to use P Indices (Sharpley et al., 2003), a concept originally developed by USDA-NRCS for assigning relative risk of P loss to agricultural fields (Lemunyon and Gilbert, 1993). California and Connecticut use soil-test P crop response (Sharpley et al., 2003).To...