Recent cow-calf model analysis from the Beef Cattle Institute at Kansas State University indicates that forage yield per acre is a very important driver of profitability; more so than increased reproductive efficiency, decreased maintenance energy requirements or increased forage digestibility (Figure 1). Increasing reproductive efficiency reduced replacement heifer costs. Decreasing maintenance energy requirements or increasing forage digestibility increased calf growth and calf revenue. But the reduction in replacement costs or increase in revenue was not as great as the reduction in winter feed costs from more forage yield and longer grazing season. Thus, increasing forage yield per acre is one of the most powerful management tools to increase cow-calf profitability.
Plant biodiversity is beneficial for grassland ecosystems by providing food and habitat for wildlife and improving nutrient cycling, soil organic matter, water infiltration, and total biomass production to name a few. Monocultures are easier to manage but may be hurting the productivity of the grassland and making it less resilient to drought and heavy grazing. Mixtures of forbs, legumes, and grasses can boost grassland productivity in the long-run and are more sustainable ecosystems.
When we think of cattle grazing pasture or rangeland, we picture cattle consuming grass, but cattle consume much more than grass. Many plants/forbs considered weeds such as ragweed actually have better nutritional profile than many grasses, and cattle will eat many of them at different stages of plant development. Some of these plants have large tap roots that bring water and nutrients up to the soil surface where the fibrous roots of grasses have access. Non-grass plants can grow between clumps of bunch grasses and provide increased forage through both primary production but also by improving nutrient cycling and soil function for growth of the whole plant community. Additionally, mixtures of grass species that have primary growth at different times of the year such as fescue and crabgrass also increase grassland productivity. The difference in timing of primary growth allows nutrient cycling in a grazing system as the defecated nutrients from one grass fertilize the other.
Not all forbs are consumed by cattle, but forbs that fix nitrogen can be beneficial by adding nitrogen to the soil through decomposition even when not consumed. However, some forbs such as sericea lespedeza can have negative effects on overall grassland productivity, and must be kept in check.
Herbicide sprays often kill both harmful (e.g., sericea lespedeza) and beneficial (e.g., Illinois bundleflower) forbs and legumes, which may reduce overall productivity rather than increase it. Assessing the plant species composition of harmful to beneficial forbs is critical to evaluate whether herbicide application will be cost effective. Other tools such as prescribed burning can also be used to manage the plant species composition without detrimental effects on all forbs and legumes. The take-home message is that a clean field of grass is likely not the most productive or profitable, but neither is a field of weeds: the goal should be to balance the species composition to maximize consumable biomass over the long term.