Guideline Index

Chapter 2: Limits to Plant Growth

2.4 Light

Adequate light (sunlight) is important for plant or pasture growth. Light is responsible for photosynthesis in green plants, whereby the green plant pigment – chlorophyll, allows the energy from the sun to be utilised with carbon dioxide and water to create carbohydrates – See Figure 2.1 .

The photosynthesis process is a basic energy storage process that all plants and animals depend upon. Only a small proportion of the suns light energy (0.1 %) that reaches the pasture is converted into plant growth, with about half this energy being used for respiration. Ultimately the amount of growth made by a plant will be determined by the net rate of photosynthesis; which is the gross photosynthesis minus the respiration.

Management of the pastures growth is important so as to prevent rank growth and maximise the amount of light reaching fresh young leaves. Young leaves are more efficient in converting sunlight to plant growth than older leaves especially when older leaves are being shaded.

Employing good grazing management will ensure maximum light is available to the plants at all times. It will also ensure that energy, in the form of sugars and carbohydrates that are stored in the plant’s root system, are not depleted by overgrazing. Optimal stocking rates and grazing periods ensures that the plant has sufficient time to recover in between grazing cycles and prevents the depletion of reserves held in the plants roots, especially nutrients like phosphorus.


Figure 2.1  Inputs and outputs of the Photosynthesis process (Source: )
Figure 2.1 Inputs and outputs of the Photosynthesis process
(Source: )