Management Effects on Forage Productivity, Nutritive Value, and Legume Persistence in Rotationally Grazed Pastures

Abstract

The ability of legumes to fix N and improve forage productivity and nutritive value makes them a vital component of temperate pastures, but reduced productivity and persistence can occur under grazing compared with mechanical harvest. Our objective was to determine plant maturity and stocking density effects on productivity, nutritive value, and legume persistence of legume–grass mixtures. Temperate grass paddocks were overseeded with alfalfa (Medicago sativa L.), red clover (Trifolium pratense L.), white clover (Trifolium repens L.), birdsfoot trefoil (Lotus corniculatus L.), or nothing in 2013 and rotationally grazed with Holstein (Bos taurus) heifers (450 kg mean body weight [BW]) in 2014 and 2015 at a low (78,400 kg BW ha−1) or high (336,000 kg BW ha−1) stocking density, or mechanically harvested, when red clover was at a mature or vegetative stage of development. Forage yield and nutritive value were measured at each defoliation event. Legume persistence was measured each spring. Grass monoculture and overseeded canopies generally had greater productivity when grazed at vegetative stage compared with mechanical harvest or grazing at mature stage. Alfalfa was the only legume to consistently respond to stage of development, having 14% greater cover when defoliated at mature stage. Legumes generally had the lowest cover when grazed at high stocking density; white clover was persistent under all defoliation regimes. Although grazing at a high stocking density and mature developmental stage may provide soil benefits, our results suggest that grazing at vegetative stage and a low stocking density optimizes productivity, nutritive value, and persistence of legume–grass mixtures.