Succession

Capped Soil

A capped soil surface prevents air and water penetrating the soil profile thereby reducing the soil's ability to breathe and drain. As a result plant growth is slower, plants often need more irrigation because water holding capacity is less, and the reduced soil biology lowers nutrient cycling. Therefore, more ripping of the soil and fertiliser is needed to stimulate production and these actions increase the cost of production.

What if more pasture litter was left to cover the soil surface? By leaving a layer of pasture leaf and stalks the soil surface becomes insulated from weather, improves water retention and absorption, and lengthens growing season.

Pasture Litter

Pasture litter has an important role in soil function. Litter is found between the grazing horizon and the soil surface. It is not meant for grazing. This is the material that feeds the organisms in the soil that make humus. Humus is important for storing nutrients. Furthermore, the presence of litter reduces soil movement and weeds germinating. There needs to be an amount of dead material in the bottom of the sward for pastures to function sustainably. Litter is especially important if there are large gaps between pasture plants. It covers bare soil and stops the surface from capping or eroding.

Biological Activity

The rate at which dung and litter are decomposing provides clues to how well the soil is working. Soil biology is often invisible but its activity is essential for strong productive pastures. While soil tests are important for establishing what is in the soil, the activity of microbes and plants root systems in transferring the nutrients are the cheapest labour known. The depth of plant root systems adds another dimension to the mineral cycle by drawing up nutrients from deeper down the soil profile.

Sward Age and Diversity

There are several ways to determine diversity; annual vs perennial, monoculture vs complex, the status of the youngest plants, the presence of woody species. The more diverse a pasture, the greater its ability to perform.

An annual pasture will out produce a perennial pasture in the immediate short term, but perennials produce for longer creating a more stable environment for other species. Also the more species present, the more productive the pasture will be and the cheaper to maintain - how much is spent on keeping weeds out of a cereal crop for example?. It will also provide animals with a greater balance of nutrients. Are seedlings able to establish and compete with mature plants? If not how will the pasture renew itself? Are woody species invading? What is this telling you about grazing patterns and soil composition?

Overgrazed Plants

What do overgrazed plants look like? Why is it important to recognise overgrazed plants in the pasture?

An overgrazed plant is very flat and will have a pinwheel appearance in some cases. The density of tillers is high and the plant will have the cropped look. Sometimes the centres of these plants will be dead, especially in environments where rainfall is highly seasonal or erratic.

If you want to have a pasture like a lawn overgrazing pasture plants is fine but it will not optimise pasture production. In many cases it will lead to pasture burn out and the need to resow to invigorate the paddock. Determine how the overgrazing is occurring. Is it because the animals have been in the paddock too long and eaten the regrowth as it emerges, or have they come back to soon before the plants have recovered from previous severe grazing? Observing and understanding this feature of pasture production could save you thousands of dollars.

Drainage

The ability of soils to drain and breathe is essential for good pasture production. Aerobic (oxygen) conditions sustain a vast array of soil life to allow the retention and cycling of nutrients. A waterlogged soil will begin to putrefy as anaerobic conditions (without oxygen) suffocate plant roots and soil biology.

This pool of water is a sign of an ineffective water cycle. However, note the water is clear and there is no evidence of soil movement. The level of cover from living plants and litter is holding the topsoil in place.

This means the animals are not staying in this paddock for too long and grazing the litter. However, without quick drainage pasture production will decline and the plants will die and rot. The conditions that prevent the water draining are also limiting the growth potential of the plants shown as the clover has a small leaf and what grass species is there is narrow leaved and struggling to grow. A soil that is porous allows both air and water to encourage oxygen through the soil profile.