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 air temperature on any spring day differs from year to year, so the amount of heat energy available for plant development for any calen-dar date, hence development stage, will also vary from year to year. It is important to understand the difference between plant development and plant growth 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.
For determining grazing readiness we are most interested in the number of leaves formed on the plant. It is obvious that there is a correlation between development and growth. However, from a management viewpoint, initiating grazing at a specific development stage can be repeated each year, whereas initiating grazing at a specific dry matter yield would be difficult. The Haun plant development stage scale is routinely being used in North Dakota to determine plant devel-opment stage of cereal crops from emergence to grain harvest for proper timing of herbicide and fertilizer applications. For determining grazing readiness of grasses, we are only interested in plant vegetative development that occurs prior to head formation.