KEEPING YOU IN THE LOOP – PLANT GROWTH STAGES

Understanding natural elements, microorganisms and your plants’ natural growth patterns.

When the moisture returns in autumn, the plants will re-establish that healthy leaf growth until falling temperatures slow the growth back down for the winter dormancy.

Cool season grasses, such as perennial rye grass and fescues, have four unique growth stages. After the winter dormancy – or at least a period of very slow growth – vigorous leaf growth returns in spring. However, with a moisture deficit in summer, the grasses can’t support this leaf growth so growth slows right down. When the moisture returns in autumn, the plants will re-establish that healthy leaf growth until falling temperatures slow the growth back down for the winter dormancy.

Root growth follows a similar pattern. In general, a healthy, balanced plant has a well-developed root system: healthy roots will support healthy leaf growth, as the roots provide the moisture and nutrients from the soil for the leaves to grow.

The stem is the heart of the pasture plant, where energy is stored and plant growth originates.

Every stage of the plant’s growth needs particular nutrients to support the natural processes that take place, and encourage maximum output and pasture longevity.

In general, there are three main macronutrients: nitrogen (N) for leaf growth; phosphorus (P) for roots, flowers, seed and fruit development; and potassium (K) for strong stem growth, movement of water in plants, and promotion of flowering and fruiting.

Applying nutrients in support of the plant stages, rather than coercing, optimises sustainable plant growth. Applying nutrients at a different period of the growth curve might improve production in the short term, but ultimately it will wear the plant out and make it necessary to renew pastures more frequently.

The main macronutrients are supported by three secondary elements: calcium (Ca) for nutrient uptake; magnesium (Mg) for photosynthesis; and sulphur (S), a growth stimulator.

The stem is the heart of the pasture plant, where energy is stored and plant growth originates.

Micronutrients are found in the form of copper (Cu) for oxygen transport, iron (Fe) for chlorophyll production, molybdenum (Mo) and zinc (Zn) for enzyme production, and boron (B), which strengthens cell plasma. Animals also need selenium (Se) for cellular functions and cobalt (Co) for metabolism.

The stem is the heart of the pasture plant, where energy is stored and plant growth originates.

Timing of fertiliser application

To understand the best time to apply different kinds of nutrients, you need to be familiar with the pasture growth pattern in your area and take into account seasonal variations.

For example, applying nitrogen when temperatures are high and the soil is dry (high soil moisture deficit) will not increase your desired plant growth, and a large amount of the applied nitrogen will be lost back to the atmosphere as nitrogen gas. You also run the risk of stimulating summer weed-grasses like Paspalum, Poa sub-species or five-finger, which will compete with ryegrasses once autumn begins and reduce pasture quality. If nitrogen is too readily available it can change your pasture composition indefinitely, so the timing of application is important in a balanced farming system.

The diagram below (fig. 1) shows how soil moisture deficit and soil temperature relate to pasture growth rates in the Waikato, and when the different nutrients should be applied to ensure the best responses. In other areas, the timings of rapid growth and soil temperature changes will be different, so applications will need to be made at different times.

If you apply high rates of phosphate fertilisers when the soil is cold and wet, you increase the risk of losses from runoff and leaching. It’s better to wait until these risks are lower and the soils are warm enough for strong root growth – generally more than 10 degrees Celsius.
Your TerraCare consultant will be familiar with regional differences and will advise you on the best timings for your farm’s nutrient application programme.

Pasture renewal

When the pasture quality gets too low, the usual remedy is to oversow or completely renew. While the new varieties of grasses are usually higher-producing, this improvement can only be achieved when the nutrient levels are adjusted to the new plant demands. Otherwise the pasture will fall back to a state very similar to how it was before the renewal, and very little will have been gained.

Slow-release phosphates stimulate stronger root growth than faster-releasing traditional fertilisers. In a newly-sown pasture, there are fewer roots to capture the available nutrients, so when the plants begin to grow the new pasture will benefit even more from the slow-release phosphates.

The same goes for plants such as maize and grains, where slow-release phosphates have been shown to stimulate early root growth.

Annual ryegrass from recently over-sown neighbouring pastures: SSP on the left, rePlenish on the right.