Grazing Duration Effects on Wheat Growth and Grain Yield

Winter wheat (Triticum aestivum L.) is frequently grazed from November until March in the Southern Great Plains. The effects of grazing on growth and grain yield are not clearly understood. Irrigated grazing trials were conducted on Pullman clay loam, a fine, mixed, thermic Torrertic Paleustolls soil, to determine the growth and grain yield responses of a semidwarf winter wheat cultivar (TAM 105) planted in late August using five dates of grazing termination in the spring. An ungrazed (grain-only) treatment that was planted in early October and managed for high grain yield was included for reference. Wheat forage was removed to a 50- to 70-mm stubble height (15 to 30% ground cover) by stocker cattle (Bos taurus L.). Growing conditions were good, and heading dates averaged near normal. Growth and grain yield responses to grazing duration were basically the same for all growing seasons. Three-year-average grain yields were 4.79,4.79,4.29,3.70,3.20, and 2.40 Mg ha⁻¹ dry weight for grain-only, 1 February, 6 March, 17 March, 31 March, and 13 April grazing termination dates, respectively. The wheat grazed until 1 February had reduced leaf area index (LAI), biomass, mean tiller weight, height, and single-seed weight; but grain yield, tiller density at heading, and harvest index were not reduced when compared to the grain-only wheat. Grazing until 6 March or later progressively reduced LAI, biomass, tiller weight, height, and single-seed weight. Heading was delayed by late grazing. Tiller density and harvest index were not reduced unless grazing continued past 31 March and 17 March, respectively. Grazing until 6 March or later appeared to reduce grain yield by limiting LAI and biomass in the spring. Since grain yield was reduced even by grazing until 6 March and the wheat did not reach Feeke's stage 6 until about 1 April, removal of spikes by grazing cattle can not be a primary cause of the loss in wheat grain yield. It was observed that grazing past the period of initial elongation of the first internode delayed internode elongation. This delay in reproductive development caused by continued grazing will need to be considered if grazing termination decisions are based on stage of development.