Just the right timing needed when harvesting forage crops

By Gary Sliworsky
Ag. Rep.

Forage growth and quality goes through a transition during the growth cycle. At the beginning of the growth cycle, the forage quality is high but the yield is very low. As the plant matures there is a significant increase in the forage yield but an accompanying decline in forage quality. The pasture manager’s goal is to have livestock consume the forage at the point where there is optimum yield of quality forage to produce the best livestock performance.
Early Growth
During the early growth phase (1-2 leaves), forage quality will be over 20% protein. This is higher than livestock requirements and the extra protein will be lost in the urine. Even 16% protein levels can adequately promote optimum livestock production. In this early growth stage, the photosynthesis level is low and much of the growth is produced from root reserves.
Optimum
The ideal harvest time for pasture grasses is after the third leaf has emerged and before the seed head emerges. Pasturing at this stage will give the optimum yield of forage that is of sufficient quality to support optimum growth of the pasturing livestock. For domestic cool season grasses this will represent a forage height of 10-14 inches.
Coupled with this optimum quality and yield stage are several other factors that will contribute to optimum growth. Plant root systems tend to be a mirror image of the top growth. The more height and density to the visible forage, the greater the root mass and the deeper the roots will penetrate the soil. This larger root system will enable the plant roots to find water as dry conditions develop and continue to grow and thrive as the soil surface becomes dry. The deeper roots have the advantage of growing in cooler soil. Cool season plants will start to go dormant if soil temperatures rise too high. If the top growth is kept short, roots are shallow, and this will result in slower growth with no drought and heat tolerance. If there is no plant residue and very limited top growth there will be bare soil exposed that will be prone to over-heating and evaporation This also results in reduced plant growth and early onset of drought conditions.
High Yield & Low Quality
At the other end of the scale is the high yield and low quality scenario that happens once the seed heads emerge and mature. At maturity, the yield of dry matter is high but the feed quality has dropped significantly and will not provide the protein and energy to meet the needs of the livestock. At this stage much of the energy from photosynthesis is being directed to seed development rather than vegetative growth. Growth is slowed with very little accumulation of energy in the plant tissue.
For optimum plant growth and productivity it is important to harvest pasture forage at the 10-12 inch height and before any seed heads emerge. A forage residue of 3-4 inches should be left to support the root system and provide the photosynthesis for re-growth. If you follow these grazing guidelines you will optimize the forage quantity and quality that is produced in your pastures, as well as the livestock production.