Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/14/2012
Publication Date: 7/1/2012
Citation: Read, J.J. 2012. Spring nitrogen fertilization of ryegrass-bermudagrass for phytoremediation of phosphorus-enriched soils. Agronomy Journal. 104:908-916.
Interpretive Summary: Intensive broiler chicken production generates manure nutrients in excess of crop needs. As a result, soils that continually receive broiler litter can become overly enriched with nutrients, particularly phosphorus (P), which increases the likelihood of transport to water bodies and degradation of ecosystems and water quality. A useful strategy for ameliorating high soil P is to overseed annual ryegrass (a cool-season annual) in autumn in dormant bermudagrass (a warm-season perennial), harvest the resulting biomass, and utilize the harvested forage at a site remote from the source. A team of scientists conducted field studies in 2007-2009 following the cessation of litter application at a private farm in Noxapater, Mississippi. The work examined the effect of timing and total rate of nitrogen (N) fertilizer on productivity and nutrient uptake by ryegrass-bermudagrass, and levels of N and P in the soil. Spring N fertilization at 168 kg N/ha increased forage yield and uptake of P in ryegrass, as well as total annual uptake of P in ryegrass-bermudagrass. Results are consistent with previous studies that suggest ryegrass-bermudagrass hay production is effective in ameliorating high soil P. Although increased N fertilization was not effective in further reducing soil P levels, the amount of N remaining in the soil did not differ between the manured and unfertilized treatments, suggesting N fertilization was good agronomically and environmentally. This data supports more accurate N management in double-cropped forage systems, which provide economic and environmental advantages to forage producers who utilize broiler litter as fertilizer.
Technical Abstract: Nitrogen fertilization of forage grasses is critical for optimizing biomass and utilization of manure soil nutrients. Field studies were conducted in 2007-09 to determine the effects of spring N fertilization on amelioration of high soil P when cool-season, annual ryegrass (Lolium multiflorum L.) is overseeded in warm-season, hybrid bermudagrass [Cynodon dactylon L. (Pers.)]. Treatments comprised antecedent broiler litter rates of 8.96 and 17.92 Mg/ha applied in spring 2004-2007 and N regimes of 112 and 168 kg N/ha provided at different dates and rates in winter-spring 2008-2009. Based on two harvests of each grass and averaged across years, dry matter (DM) yield was greatest at 17.92 Mg litter/ha; across litter rates, P uptake increased by 32% in ryegrass and 24% in bermudagrass. The litter rate by N regime interaction effect was not significant for nutrient uptake. Among N regimes, ryegrass P uptake was greater at 168 than 112 kg N /ha (P < 0.01) and values ranged from approximately 26.7 to 35.8 kg P/ha. Similarly, ryegrass-bermudagrass P uptake increased 27% across litter rates, from approximately 50 to 64 kg/ha, and maximum uptake of 61 kg P/ha was obtained with N fertilization in March (112 kg/ha) and May (56 kg/ha). Harvest removal of P for two years led to reductions in soil test phosphorus (STP, 0-15 cm, Mehlich-3 extraction) of approximately 38% at 8.96 Mg litter/ha (173 – 108 mg/kg) and 44% at 17.92 Mg litter/ha (104 – 58 mg/kg). Soil residual NO3-N in May was elevated in treatments with recent N fertilizer additions; however, levels were greater than unfertilized bermudagrass in 2008 only. Applying N fertilizer in March and May increased DM yield and uptake of P, but did not consistently elevate soil N levels.