Submitted to: Nutrient Cycling in Agroecosystems
Publication Type: Peer reviewed journal
Publication Acceptance Date: 11/13/2008
Publication Date: 3/1/2009
Citation: Read, J.J., Sistani, K.R., Oldham, J.L., Oldham, J.L. 2009. Double-cropping annual ryegrass and bermudagrass to reduce phosphorus levels in soil with history of poultry litter application. Nutrient Cycling in Agroecosystems. 84:93-104. Interpretive Summary: Double-cropping forages may help to ameliorate excess soil phosphorus (P) at manure-impacted sites and minimize potential risks to the environment. Agronomists and soil scientists determined the amount of P removed by two common forages, bermudagrass and annual ryegrass, following the cessation of broiler litter applications (0, 2, 4, 8, and 16 tons/acre) on a site with 30-year of litter. Due to the nutrients provided in litter, forage biomass yield and P uptake increased as antecedent litter rate increased. Averaged across litter rates, the additional harvest of annual ryegrass removed significantly more P than the bermudagrass winter fallow. Double-cropping appeared to influence soil P cycling, as soil P at 0 and 4 tons/acre litter was about 23 parts per million greater in ryegrass-bermudagrass than bermudagrass winter fallow. For the same soil and climate, the potential for increased biomass production and P removal demonstrated an advantage of the ryegrass-bermudagrass forage system for the purposes of removing more P and having a year-round green pasture for haying or grazing. Results impact the forage and broiler industries in the Midsouth USA by providing information on the long-term economic value and sustainability of fertilizing bermudagrass hay fields with broiler litter.
Technical Abstract: Double-cropping forages may help to ameliorate excess soil nutrients in manure-impacted fields. Studies were conducted on Savannah soil with a 30+ yr history of broiler litter to determine the yield of biomass and P in bermudagrass (summer) and ryegrass-bermudagrass (year-round) forage systems. During a 3-yr ‘build up’ phase, bermudagrass was fertilized with 0, 4.5, 9, 18, and 36 Mg/ha litter. During the ‘drawdown’ phase, half the plot area was overseeded with annual ryegrass in 2001, 2002, and 2003. All plots were fertilized in summer with ammonium nitrate to provide 268 kg N/ha/yr. Soils analysis (0-15 cm depth) in April 2004 found Mehlich-3 extractable P (M3-P), Cu and Zn were elevated when 9 Mg/ha litter was used. Total P uptake by forages was greatest at 18 and 36 Mg/ha litter, and the additional harvest of ryegrass removed significantly more P, Cu, and Zn than bermudagrass in 2002 and 2004, but not 2003. Analysis of M3P within four sampling dates found no significant effect of forage system or its interaction with litter rate. Across sampling dates, M3-P decreased by 52, 61, 58, 87, and 131 mg/kg at 0, 4.5, 9, 18, and 36 Mg/ha litter, respectively. When 0 and 9 Mg/ha litter was used, M3-P averaged 23 mg/kg greater in ryegrass-bermudagrass than bermudagrass winter fallow, suggesting increased P cycling in soil by the double-cropping system. Results demonstrate an advantage of ryegrass-bermudagrass for enhanced nutrient removal, particularly when rainfall was less than adequate for optimum bermudagrass yield.