Agr50178 946..950

Effluent from a swine (Sus scrofa domesticus) lagoon is often applied repeatedly to nearby fields because of logistical constraints and costs of transportation. To minimize accumulation of soil nutrients and sustain use of spray field, best management practices must maximize the rates of removal of manure nutrients. Research determined summer hay and nutrient yields of bermudagrass [Cynodon dactylon (L.) Pers.] following winter cover crops ‘Kenland’ red clover (Trifolium pratense L.), ‘Bigbee’ berseem clover (T. alexandrinum L.), or ‘Marshall’ annual ryegrass (Lolium multiflorum Lam.) subjected to five harvesting systems. Also, summer and winter forage yields were combined and analyzed to find best annual performance. Nutrient yields of bermudagrass were statistically affected by winter cover crop species and harvest date. Summer production was maximized following berseem clover harvested on a two-harvest-day system of 15 May and 1 June. Harvesting the winter cover crop in addition to the bermudagrass increased extraction of N (82%), P (76%), K (90%), Mg (95%), Mn (67%), Ca (158%), Fe (80%), Zn (83%), and Cu (97%). For environmentally sensitive nutrients N, P, Cu, and Zn, annual yields were maximized with a two-harvest-day system of 15 April and 1 June of a cover crop, which was not the best harvest system for either the winter or the summer trials in isolation. Tests on summer performance and winter performance in isolation were informative and did indicate the best winter cover crop species, berseem clover, but did not indicate the best management system for annual production. FERTILIZATION of a forage crop with animal manure at rates to meet the N requirements of the crop results in an over application of P. This is the result of animal manure having an N/P ratio in the range of 1:1 to 4:1 whereas ratio for nutrients extracted in the harvested forage varies from 5:1 to 12:1. With repeated applications of this relatively high P fertilizer, the soil P levels attain the critical level or change point and the result is excessive P leaching with any substantial rain (Hesketh and Brookes, 2000). Even when the change point is not attained, P may leach into shallow ground water via preferential flow (van Es et al., 2004). As soil concentrations of manure P increase, the probability of nutrient pollution of surface water and eutrophication of ponds or lake is increased. To manage this hazard in the MidSouth, where severe rain events are frequent in the winter, a winter cover crop is recommended to protect soil surface from erosion and to capture available nutrients. In swine production, the waste in the swine lagoon is commonly land applied via summer irrigation to nearby forages, which are harvested for hay. Transporting this liquid waste to more distant fields is logistically difficult and prohibitively expensive. It is critical that best management practices be developed for removal of maximum amounts of manure nutrients in harvested forage from fields to which swine manure effluent is applied. Surveys indicate the inequality between rate of nutrient removal and manure nutrient application is leading to accumulation of manure nutrients in the soil. In the South, Ribaudo et al. (2003) estimated the percentage of swine farms with less than 300 animal units that meet the N-based standard for land application is 32% and the farms meeting P-based standard for land application is 12%. For larger farms the percentage of farms meeting the N-based or P-based application rate is lower. A common, summer perennial forage of the MidSouth, which is fertilized with swine effluent is bermudagrass (Brink et al., 2001). This is the species of choice for many southern farmers because this grass is aggressive, responds rapidly to fertilization, has good feed value, and tolerates drought. Common bermudagrass fertilized with swine effluent has been shown to perform very well in comparisons with ‘Costal’ hybrid bermudagrass, Eastern gammagrass (Tripsacum dactyloides L.), indiangrass [Sorghastrum nutains (L.) Nash], johnsongrass [Sorghum halepense (L.) Pers.], and switchgrass (Panicum virgatum L.) for quantity of nutrients extracted from the soil (McLaughlin et al., 2004). None of the other perennial, summer grasses exceeded the common bermudagrass yield of nutrients or hay and most were significantly less productive. The harvesting of a winter cover crop of annual ryegrass has been proposed for remediation or control of soil nutrient concentrations (Brink and Rowe, 1999). Alternative winter cover crops have been evaluated and with a single spring harvest, annual ryegrass removed as much or more P than three grains and 12 legumes in fields fertilized for many years with poultry litter (Brink et al., 2001). Brink et al. (2001) estimated harvesting the winter cover crop increases the total P removal by 10 to 25% over that removed with harvesting only the summer forage. Since harvesting date does affect feed value and hence the nutrient concentration of the forage, a test was conducted using two harvest dates in the spring and comparing that response to the single harvest. A twoharvest-day of 1 April and 1 June for the winter cover crop ‘Bigbee’ berseem clover, the P, Cu, and Zn removal rates were increased by 24, 40, and 72%, respectively, over the single harvest of annual ryegrass (Rowe and Fairbrother, 2003). A 12-mo agronomic management system for the swine effluent spray field requires double cropping of summer and winter forages. Choice of summer and winter species is difficult because compatibility of the crops planted in tandem is greatly affected by the manageD.E. Rowe and T.E. Fairbrother, USDA-ARS, Waste Management and Forage Research Unit, 810 Highway 12 East, Mississippi State, MS 39762-5367; K.A. Sistani, USDA-ARS, Animal Waste Management, Bowling Green, KY. Received 15 June 2005. *Corresponding author ([email protected]). Published in Agron. J. 98:946–950 (2006).