The Importance of Residual in Grazing
Late winter/early spring is the time most dairymen that graze fall planted cool season annuals in the southeastern US, start thinking about turning their cows out on to this pasture. For most, its a rewarding time of the year. The weather is still cool, there are no issues with flies and grazed dry matter intakes can be high if there is adequate forage. Managing this valuable growing resource correctly will also help producers capitalize on some of the cheapest milk they will ship all year. Adequate residual levels are most important when it comes to maintaining optimum rotation length and quality.
Grazing residual affects everything in the pasture. What is residual? Residual is the living plant material remaining after a grazing event. Residual is often confused with residue, which is the dead plant material on the soil surface. While residue is beneficial to soil health and structure, residual is everything, especially with cool season annuals.
Proper grazing residual affects pasture regrowth and plant root growth. One of the biggest factors affecting forage intake is availability. Cows grazing pastures at 2800-3000lbDM/ac are able to take in more forage with each bite, fill up faster and perform better. Cows grazing pastures at say 1800-2000lbDM/ac will have reduced intake and therefore reduced performance. Research conducted as the University of Missouri Forage Systems Research Center showed cattle will only take so many bites per day, regardless of whether they are full or not. The same can be said for dairy cows. Reduced intake is a function of reduced bite size coupled with reduced forage quality in the lower canopy as available forage decreases.
Pasture regrowth is affected by residual. Pasture plants need to photosynthesize in order to regrow efficiently. Photosynthesis takes place mainly in the leaves of the plant. It’s fair to assume then that the higher the residual left behind after grazing, the faster the regrowth response will be. Remember…..grass grows grass!
Plant root growth is also affected by residuals. Most grazers have heard the adage of ‘take half, leave half’ when managing grazing. Allowing grazing up to 50% of the total pasture available has very little effect on plant roots. Taking more than 50% however, can severely impact root growth and reduce the plant’s ability to absorb water and nutrients from the soil.
In summary, managing pastures for taller residuals can have many positive benefits. Taller residuals will encourage faster regrowth, better quality forage and produce more milk.