Winter Cover Crop Responses to Nitrogen Fertilization in a Swine Effluent Spray Field.

For the sustained, safe use of swine lagoon effluent spray fields, the annual management of nutrients is critical, not just the summer yields. This 2-yr study was conducted at a commercial swine to determine the effects of spring N fertilization (0, 50, 100, 150 kg N ha^-1) on forage dry matter (DM) yield and nutrient uptake by fall-overseeded annuals, annual ryegrass, cereal rye, and berseem clover, as compared to bermudagrass-winter fallow. Our hypothesis was that even with repeated manure applications in summer (April–Oct.), N availability limits growth and uptake of other nutrients by winter forages. Nutrient uptake was analyzed based on a single spring harvest and on two summer harvests of bermudagrass. The relative yield in spring, defined as DM yield at a given N rate divided by the maximum observed DM yield, varied from 77 to 98%, suggesting N nutrition was not strongly limiting, even at the lowest N rate. Cover crop N concentration increased as N rate increased (P < 0.05), and averaged approximately 15.2, 17.2, 18.4, and 20.8 g kg^-1 across N rates in 2000 (5% LSD = 7), and 21.6, 22.1, 25.4, and 27.1 g kg^-1 in 2001 (5% LSD = 2.4), respectively. The N rate by crop interaction was significant for herbage N in 2000, as values increased linearly in ryegrass from approximately 10 to 20 g N kg^-1 as N rate increased, and did not vary significantly in cereal rye and berseem clover.  Averaged across 2000 and 2001, P uptake in spring was greater in annual ryegrass than the other species (23.2 vs. ~17.7 kg ha^-1) and was associated with 27% greater DM yield. This data supports more accurate N management in double-cropping forage systems, which provide environmental and economic advantages to producers who regularly utilize manure as fertilizer.