Spring Nitrogen Fertilization of Ryegrass-Bermudagrass for Phytoremediation of Phosphorus-Enriched Soils

Because annual ryegrass (Lolium multiflorum L.) exhibits increases in herbage P with increasing soil P, biomass response to N should influence phytoremediation of P-enriched soils. Field plot (each 2 by 5 m) studies were conducted to determine the effect of six N schemes that provided 112 or 168 kg N ha(-1) on uptake of P and soil test P (STP, 0-15-cm depth) of double-cropped bermudagrass [Cynodon dactylon L. (Pers.)] and ryegrass. Bermudagrass was previously fertilized with 9 and 18 Mg broiler litter ha(-1) in 2004-2007, no litter was applied aft er 2007. At past litter rate of 9 Mg ha(-1), total uptake of P averaged 48.5 kg ha(-1) in 2008 and 51.7 kg ha(-1) in 2009. Based on initial STP levels in 2007, results in 2009 indicated STP levels decreased by approximately 50 kg ha(-1) yr(-1), with reductions of 44% at 9 Mg litter ha(-1) (104-58 mg kg(-1)) and 38% at 18 Mg litter ha(-1) (173-108 mg kg(-1)). Averaged across years and litter rates, uptake of P in ryegrass was greater at 168 than 112 kg N ha(-1) (35.4 vs. 29.4 kg ha(-1), P < 0.01) and ranged from 35.8 kg ha(-1) in scheme N5 to 26.7 kg ha(-1) in scheme N1. Schemes N5 and N6, with a total rate of 168 kg N ha(-1) in March and May, stimulated uptake of P in ryegrass and ryegrass-bermudagrass, but STP levels in 2009 were not lower than a single application of 112 kg N ha(-1) in January and March.