Submitted to: Journal of Environmental Quality
Publication Type: Peer reviewed journal
Publication Acceptance Date: 3/16/2008
Publication Date: 7/15/2008
Citation: Read, J.J., Brink, G.E., Adeli, A., McGowen, S.L. 2008. Swine effluent application timing and rate affect nitrogen use efficiency in common bermudagrass. Journal of Environmental Quality. 37:S-180-S-189. Interpretive Summary: In the southeastern USA, swine waste management plans often include the use of lagoon effluent for the production of bermudagrass hay. These plans are based on agronomic rates which guide the timing and amount of swine effluent applied and also minimize negative impacts on water quality. Frequent summer precipitation may delay the application of swine effluent to bermudagrass until late summer or early fall. Due to declining growth of this warm-season forage in fall, there is potential for excessive nitrogen (N) accumulations in soil and hence, nitrate-N leaching. To understand this potential risk, we applied swine effluent at rates of 10 and 20 cm/ha (about 260 and 480 kg N/ha, respectively) in four spray seasons: April to September (full season), April to May, June to July, and August to September. The percentage of applied N recovered in bermudagrass hay averaged about 70% in June-July spray season. This value decreased to 46% in August-September spray season at 10 cm rate and to 42% at 20 cm rate. Applying 20 cm effluent in August-September increased soil nitrate by about 208% in 2000 and 116% in 2001, as compared to unfertilized controls. Results suggest increased risk of N loss to the environment if effluent application to bermudagrass is delayed until late in the growing season, particularly at higher application rates. Additionally, N utilization by bermudagrass was reduced by dry summer conditions that further protracted the growing season and annual yield of this warm-season forage grass.
Technical Abstract: Frequent summer precipitation in southeastern USA may delay the application of swine effluent to bermudagrass [Cynodon dactylon (L.) Pers.] hay fields until late summer or early fall. Due to declining growth of this warm-season forage in fall, there is potential for excessive N accumulations in soil and hence, nitrate leaching. Field studies were conducted on a Prentiss sandy loam soil to determine if irrigation timing and rate influence N utilization and postseason soil N concentration. Effluent was applied at rates of 10 and 20 cm/ha (260 and 480 kg N/ha, respectively) in four spray seasons: April to September, April to May, June to July, and August to September. Doubling the effluent rate increased bermudagrass N uptake from about 130 to 276 kg/ha in 2000, and from about 190 to 290 kg/ha in 2001. Applying effluent in August-September led to lower N uptake, as compared to other seasons, and for 20 cm rate, to greater soil nitrate to 30-cm depth in spring 2001. Elevated levels of soil N for 20 cm rate were associated with lower forage yield in 2000 than 2001 (10.5 vs 16.4 Mg/ha). Averaged across spray seasons, postseason soil nitrate values to 5-cm depth were significantly greater for 20 cm rate than unfertilized control (39.6 vs 8.5 mg/kg). Results indicate as little as 30-38% of the effluent N applied late in the growing season was utilized by bermudagrass, which could lead to increased groundwater N under high leaching conditions.