Guideline Index

Chapter 2: Limits to Plant Growth

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Pasture and crop performance is only as strong as the weakest link. Before applying fertiliser, find out which factors can limit production so that these factors can be managed.

2.1 Introduction

For optimum pasture performance it is important to have an understanding of how the plant functions and responds to the various growth limiting factors. Each factor, whether acting as an individual or interacting with another, can become the limiting factor to pasture or crop production.

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2.2 Water

The availability of soil moisture is a basic requirement for all plant functions. Soils hold and provide varying amounts of water to plants depending on factors such as texture and structure. The amount of water held in a soil is called the soil moisture content, and the optimal level for plant growth is referred to as “field capacity”. Crops or pastures that are irrigated can achieve more consistent growth and production, as long as the extra nutrient demands for the increased dry matter production are met.

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2.3 Nutrients

There are optimum levels of nutrient availability that should be met in the soil and plant for maximum pasture production. Understanding and managing plant nutrients for dairy production is the key focus of this manual.

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2.4 Light

Adequate sunlight is important for plant or pasture growth. 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.

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2.5 Temperature

Plants require a certain amount of accumulated heat from the sun in order to photosynthesis and produce carbohydrates for growth. Each stage of a plants growth requires a certain accumulated amount of heat units per day to complete that part of its growth. Generally, how plants respond to temperature relates to the part of the world in which they evolved.

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2.6 [no explanation]Soil constraints[/no explanation]

Soil constraints can be any physical or chemical restriction to the normal root proliferation into the subsoil. Constraints can be naturally occuring, or as a result of management. Some soil constraints can be identified by soil testing, or a physical or visual examination. Soil constraints can often be minimised with the use of correct nutrition or the addition of soil ameliorants.

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2.7 Plant disease and insects

Pests and diseases can severely impact pastures and contribute to pasture rundown. Crops and pastures should be inspected regularly for pests as well as disease and deficiencies. A combination of biological, chemical and cultural control measures to control pests is considered the most effective and sustainable approach to addressing pest problems.

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2.8 Weeds

Weeds can result in competition with pasture or cropping species for nutrients and soil moisture; the tainting of milk; stock poisoning, reduction of dry matter yields from lucerne paddocks; as well as reduced quality of the hay due to weed presence. One of the best ways of reducing weed infestation in pastures is by maintaining a dense, healthy sward of desirable pasture species. Management strategies to favour desirable pasture species integrated with the use of herbicides, offers the best approach to reduce the impact of weeds.

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2.9 Management strategies to reduce limitations to plant growth

It is important to remember that while there are a many factors that can be managed and manipulated, the key is to identify the most limiting factors and target these with cost-effective strategies to optimise production.

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2.10 References

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