Harvest management effects on bermudagrass yield and nutrient utilization in a swine-effluent spray field

Authors: Read, John; Adeli, Ardeshir; Fairbrother, Timothy

Submitted to: Journal of the Mississippi Academy of Sciences
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/25/2020
Publication Date: 7/1/2020
Citation: Read, J.J., Adeli, A., Fairbrother, T.E. 2020. Harvest management effects on bermudagrass yield and nutrient utilization in a swine-effluent spray field. Journal of the Mississippi Academy of Sciences. 65:3.

Interpretive Summary: The manure produced on swine farms in Mississippi is washed into lagoons to facilitate anaerobic digestion. The swine-lagoon effluent is often used to irrigate bermudagrass, the predominant warm-season forage in the southeastern USA, in summer (April – October) for hay production in fields nearby the lagoons. Hay production provides both high quality forage for ruminant livestock and a means of exporting manure nutrients, particularly nitrogen and phosphorus, to reduce potential surface and ground water impairment; the nutrients taken up by the plants are removed when the hay is harvested. A team of scientists in Mississippi conducted studies in a swine-effluent spray field on a commercial farm to determine if increasing the leaf-to-stem ratio in common bermudagrass hay increases the rate of removal (kg per ha) of P and other nutrients in biomass. They harvested all plots in early May and subsequently sampled the regrowth forage at harvest intervals of 4, 6, 8, 10, and 12 weeks and cutting heights of 3 and 9 cm. The ranking of harvest intervals for annual P removal was not consistent among years, probably due to seasonal changes in plant maturity, effluent N and P concentrations, or irrigation timing. Cutting forage at 3-cm height consistently increased bermudagrass P removal by 18% in 2001, 28% in 2002, and 29% in 2003, as compared to 9-cm height. Results provide information to land managers on methods to enhance plant uptake of N and P and thereby reduce the loss of nutrients from bermudagrass hay fields irrigated with swine effluent. If the goal is to produce a high-quality forage, bermudagrass should be cut frequently (< 5-week interval) and as tall as practical in order to harvest more leaf tissue. If the goal is maximum utilization of manure nutrients in the effluent, bermudagrass should be cut at 6-10 week intervals as close to the ground as possible in order to maximize annual forage yield.

Technical Abstract: Swine waste management plans often include the use of lagoon effluent for the production of bermudagrass [Cynodon dactylon (L.) Pers.], the predominant warm-season forage in the southeastern USA. A 3-year study (2001-2003) was conducted at a commercial farm in northeast Mississippi on a Prentiss sandy loam to determine cutting height and frequency effects on yield and P removal of common bermudagrass. Small plots (2 x 4 m) were irrigated with 7.5 cm ha-1 swine effluent from April–October each year, which provided about 520 kg ha-1 N and 110 kg ha-1 P during the growing season. After an initial harvest in early May, regrowth forage was harvested at 4, 6, 8, 10, and 12 week intervals and at 3- and 9-cm cutting heights using a sickle-bar mower. A significant (P < 0.001) year x harvest interval interaction for P removal is attributed to obtaining maximum P removal with 10-week interval in 2001 and with 6-wk interval in 2002 and 2003. Bermudagrass P removal was affected by year x cutting height interaction (P < 0.05); however, cutting at 3-cm height consistently increased P removal by 18% in 2001, 28% in 2002, and 29% in 2003, as compared to 9-cm. If the goal is maximum utilization of manure nutrients in the effluent, bermudagrass should be cut at 6-10 week intervals as close to the ground as possible in order to maximize annual forage yield. Cutting more frequently (< 5-week interval) with 9-cm height reduced total yield, but can result in high-quality forage.