Pasture production and profits can be increased dramatically where extra fertilizer is used to lift the productivity of run down pastures.
Pastures considered here include dry land pastures, Cereal and Pasture hay, irrigated pastures and High rainfall Dairy pastures.
Table 1: Nutrient taken up by 1.0 tonnes of clover based pasture.
Some of these nutrients are recycled through livestock and via the dry material that is left behind. Nutrients such as Nitrogen and Potassium are very mobile and available, however Phosphorus is not readily recycled once it is in the organic form. (see Nutrient Removal)
Soil pH affects the release of nutrients, the survival of fungus and bacteria (such as clover rhizobia) and the activities of soil flora and fauna such as earthworms.
An acidic soil will produce poor growth, low nodulation and hence nitrogen fixation, and will reduce the response that can be expected from applied nutrients. Good pastures will survive in a wide range of soil pH levels. Soil testing both the top soil and sub soil is essential to discovering the soil pH and predicting the response to applied lime. Some of the smaller testers are also good indicators. If the soil pH is below 4.6 in CaCl2, then apply lime, from a registered pit, at up to 2.5t/ha.
Lime is Calcium Carbonate. Heavy applications of calcium may upset the balance of with Potassium. Raising the pH too far may adversely effect the uptake of zinc, manganese or iron. If applying lime without cultivation, consider using lower rates and spreading the full application over two or three seasons.
Soil test regularly to monitor soil pH levels.
Phosphorus is a vital plant nutrient. In WA soils are very low in natural phosphorus. Legume based pastures in particular need good levels of phosphorus to be productive.
Most of our sandy soils would have less than 2ppm of Phosphorus in the native state, which would result in almost no growth if pastures were grown on them.
Phosphorus is vital in the early stages of growth, and important for root development. This can have dramatic effects during periods of stress, such as a false break to the season, dry stress, water logging, disease and insect attack. Often if the plant is low in Phosphorus early in the season, it can never recover.
( See graph below).
Plants that are low in phosphorus will have trouble synthesising other nutrients such as nitrogen and zinc. Symptoms of phosphorus deficiency: see Phosphorus