A lot of people in grazing circles seem to use these terms interchangeably, but in grazing science they mean two very different things. Residual is the living plant material left behind after a grazing event. For clarity we often say ‘post-grazing residual’. Residue is dead plant material left on the soil surface. It is synonymous with litter or duff.
Post-grazing residual is what we leave standing in the pasture following a grazing event. In the growing season in a temperate environment, the residual should be green and leafy.
Leaving the appropriate residual largely determines the recovery rate of the pasture. The more green leaf residual, the faster plants regrow.
Residue is the dead or soon-to-be-dead plant material at the bottom of the canopy and in contact with the soil surface. Residue decays from the bottom up to become incorporated into the soil organic fraction. Residual provides the regrowth base for the next grazing crop.
Leaving the appropriate residue is an essential component for moderating soil temperature and building an effective water cycle. In a thinner pasture stand with low density of living plants we want to make sure the entire soil surface is covered with residue (litter). We always want to leave green leaves behind as well.
In rugged rangeland environments keeping the soil covered is critically important to developing a functioning water cycle. We can only create residue (litter) by growing plants above ground. Long recovery periods are the key to building residue in drier environments.
We are always tempted to graze more severely in the dormant season because we have the idea that grazing severely won’t hurt a dormant plant. We need to be thinking about the bigger picture of the total soil-plant-animal interface. Leaving adequate residual and residue protect the soil even in the winter and moderates soil temperature.
The greatest challenge of grazing in arid environments is growing enough above-ground plant material to still have enough residue left after grazing to create the litter layer. This pasture needs more residue left on the soil to create better water infiltration opportunity and keep the soil cooler.
Both residual and residue are important management considerations and affect almost all soil-plant-animal relationships. Let’s try to make sure we use the right terms in our conversations so we know what one another are trying to express!