Nitrogen Delivery Method and Monensin Effects on Productivity, Nutritive Value, and Botanical Composition of Grazed Annual Ryegrass Pasture

Nitrogen fertilization is a major input cost of forage production, and alternatives that maintain yield and nutritive value would be advantageous. A 3‐yr study was conducted to evaluate forage nutritive value and clover proportion when N fertilizer was replaced partially with interseeded clovers ( Trifolium spp.) or protein supplements for stocker cattle grazing annual ryegrass ( Lolium multiflorum Lam.). Nitrogen delivery methods with or without monensin included annual ryegrass fertilized with 112 kg N ha −1 in split application (NFERT), and other methods that received 56 kg N ha −1 , including annual ryegrass interseeded with crimson clover (CC, Trifolium incarnatum L.) or arrowleaf clover (AC, Trifolium vesiculosum Savi), or grazing cattle supplemented with distillers dried grains plus solubles at a rate of 0.65% body weight daily (DDGS) or whole cottonseed ( Gossypium hirsutum L.) at the rate of 0.65% body weight daily (WCS). Clover proportion was greater ( P = 0.003) for CC than AC across all 3 yr of the study, and CC was more ( P = 0.003) abundant when monensin was fed. Year affected forage in vitro true digestibility (IVTD, P < 0.001) and crude protein (CP, P < 0.001) concentration such that IVTD and CP were greatest in Year 3, intermediate in Year 2, and least in Year 1. Forage degradable intake protein (DIP) concentration was affected by N delivery method ( P < 0.001) and year ( P < 0.001) such that CC was less than NFERT, DDGS, WCS, and AC, and Year 1 was greatest, Year 2 was intermediate, and Year 3 was the least. Results are interpreted to mean that year affected forage nutritive value more than did N delivery method.