CASE STUDY: Effects of interseeding date of cool-season annual grasses and preplant glyphosate application onto a warm-season grass sod on forage production, forage nutritive value, performance of stocker cattle, and net return1

This research was conducted to determine the effect of a preplant application of glyphosate [N-(phosphonomethyl) glycine] and planting date on the performance of growing beef calves grazing interseeded cool-season annual pastures. Twenty, 0.81-ha bermudagrass [Cynodon dactylon (L.) Pers.]/crabgrass [Digitaria ciliaris (Retz.) Koeler] pastures were planted with soft red winter wheat (Triticum aestivum L. 'Roane,' 134 kg/ ha) and annual ryegrass (Lolium multiflorum Lam. 'Marshall,' 22 kg/ha) in mid-September or mid-October of 2005 using a no-till drill, with or without an application of glyphosate at 0.77 kg/ha (1.77 L/ha) at planting in a 2 × 2 factorial arrangement of treatments. A variable stocking rate was managed using the put-and-take method. Tester calves (2 heifers and 1 steer; BW = 273 ± 5.4 kg) were used to measure performance, and additional calves were added as necessary to equalize forage allowance among pastures. Daily gains of calves grazing pastures planted in September were 0.28 kg greater (P = 0.03) from April to May than the ADG of calves grazing pastures planted in October. Pastures receiving glyphosate application resulted in greater (P ≤ 0.05) overall ADG and ADG from mid-February to mid-March. Pastures planted in September with glyphosate application produced 109 more (P < 0.01) grazing days per hectare, 163 kg more (P < 0.01) BW gain per hectare, and $249 greater (P < 0.01) net returns per hectare compared with those planted in September without glyphosate application or those planted in October with or without glyphosate. Earlier planting along with reduced competition by spraying warm-season grasses before interseeding can increase carrying capacity, animal BW gains, and net returns of interseeded cool-season annual pastures.