Wednesday, November 7, 2007
327-6
Effect of Swine Effluent Rate and Timing on Nitrogen Utilization and Residual Soil Nitrogen in Common Bermudagrass.
John Read1, Geoffrey Brink1, Steven Mcgowen2, and James G. Thomas3. (1) P.O. Box 5367, USDA-ARS, Crop Science Research Lab, 810 Hwy 12 E, Mississippi State, MS 39762-5367, (2) USDA-NRCS, USDA-NRCS, 4900 Oklahoma Avenue Suite 300, Woodward, OK 73801, (3) Agricultural and Biological Engineering, Mississippi State University, Box 9632, Mississippi State, MS 39762-9632
Frequent summer precipitation in southeastern USA may delay applications 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 soil N and nitrate (NO3) leaching. Studies were conducted on a Prentiss sandy loam to determine the effects of application rate and timing on forage dry matter (DM) yield, N uptake and postseason soil N concentrations in common bermudagrass. Effluent was applied at 10 and 20 cm ha-1 (about 260 and 480 kg ha-1 N, respectively) during four spray seasons: April to September (full season), April to May, June to July, and August to September. Plots were harvested every 7-9 wk beginning in mid-June, and soil sampled after a killing frost and the following spring. Doubling the effluent rate increased annual N uptake by forage from about 130 to 276 kg N ha-1 in 2000, and from 190 to 290 kg N ha-1 in 2001. Applying effluent in August-September led to lower DM yield and N uptake, as compared to other seasons, and for 20 cm ha-1 rate, to elevated levels of residual soil NO3 in fall 2000 and spring 2001. Increased soil N at 20 cm ha-1 rate was associated with lower DM yield in 2000 than 2001 (10.5 vs 16.4 Mg ha-1). Averaged across spray seasons, postseason soil NO3 at 5-cm depth was significantly (P<0.05) greater in 20 cm ha-1 treatment than unfertilized controls (means of 39.6 vs 8.5 mg kg-1). Results indicate effluent N applied late in the growing season, particularly at high rates, is less likely to be utilized by bermudagrass due to dry summer conditions or declining growth during the fall.