Plant development vs. Plant growth

Understanding the difference between plant development and plant growth is important for determining grazing readiness. Development refers to the formation of plant structures, such as leaves, in an orderly and consistent pattern. Plant growth is the accumulation of forage dry matter or the expansion of leaves and stems.

Grass plants develop in an orderly and consistent manner. Leaves are the major plant organ of interest for grazing. A new leaf becomes visible on a plant after the one preceding it is almost fully developed. The calendar time at which the first leaf appears and the rate at which each leaf develops is determined by the amount of thermal (heat) energy available for biological activity. The air temperature on any spring day differs from year to year, so the amount of heat energy available for plant development for any calendar date, hence development stage, also will vary from year to year.

For determining grazing readiness, we are most interested in the number of leaves formed on the plant. A correlation between development and growth is obvious. Thus, from a management viewpoint, initiating grazing at a specific development stage can be repeated each year, whereas initiating grazing at a growth stage would be difficult.

the NDSU Central Grasslands Extension Center. “The general rule to consider when grazing rangelands is for every day you graze in early May, you lose three days of grazing at the end of the grazing season. For every day you graze in the middle of May, you lose two days of grazing at the end of the grazing season.”

Grazing too early will reduce plant vigor, thin existing stands, lower total forage production, and increase disease, insect and weed infestations. Pastures and range damaged by grazing too early and/or severe overgrazing may take several years of deferment or even rest before the stand regains productivity.

A loss of forage production due to grazing prior to grazing readiness will reduce the recommended stocking rate and/or animal performance.

Due to the combination of cool temperatures and drought stress, ranchers should expect delays of approximately four weeks in grazing readiness this spring and manage accordingly. This would include avoiding grazing native range until grazing readiness has been achieved.

Strategies to avoid grazing native range prior to grazing readiness include:

• Grazing domesticated grass pastures, such as crested wheatgrass and smooth brome, in May. This year, domesticated pastures may not reach grazing readiness until mid-May.

• Providing supplemental forage to livestock on domesticated pasture or hay land. However, be careful not to graze your hay lands too early, too short or if muddy, as the stand will be dramatically reduced in forage production due to reduced vigor and plant damage.

• Using winter annuals that were established last fall for early spring grazing or hay.

• Continuing dry lot feeding in May.

“While it may be tempting to start grazing early due to a lack of forage resources, it can have long-term impacts on forage production,” says Meehan. “Remember, it takes grass leaves to replenish the root food reserves needed to grow grass. Early spring grazing, especially following a drought, can be costly in terms of total forage production during the entire grazing season.”

Article courtesy NDSU

Ag Communications