Save money through soil testing

Post decoupling, farmers are increasingly looking at controlling input costs. Fertilisers are a significant cost of grass production and should be used as efficiently as possible.

Soil analysis provides reliable information on the nutrient status of soils that can be used as a guide when selecting the type and quantity of fertiliser to apply for efficient grass production.

Soil analysis information allows the correct combination of fertilisers to be used to meet crop requirements, taking into account the level of nutrients already present in the soil. The analysis also allows farmers to make the most efficient use of slurries or manures produced on the farm. This makes good sense, both from an economic and environmental point of view.

Soil nutrient levels do not change rapidly so it is not necessary to sample soils every year. As a general recommendation soil analysis should be carried out on permanent grassland every five to six years and for cropping land every four to five years.

Three key factors are determined by soil analysis – soil pH (level of acidity) and soil phosphate and potash levels.

As well as affecting grass growth directly, an acidic soil can restrict the efficient uptake of fertiliser, especially nitrogen and phosphorous. The overall result is less grass for each bag of fertiliser. The ideal pH for grass production on most soils is within the range 6.0 to 6.5. Analysis will determine the pH of the soil and indicate how much lime is required to bring the pH back to the desired level.

With lime costing £12 per ton spread and most farmers applying over 5 tonnes per hectare (2 tonnes per acre) it makes good business sense to check the soil pH level before applying lime.

The ideal target for soil phosphate level in grassland is Index 2. Production will be reduced at Index 1 where intensive grazing or silage systems are in operation, although for extensive grazing systems, which are common on many beef and sheep farms, a phosphate Index level of 1 is quite adequate. At higher Index levels there is an increased risk of phosphate leaching from soils and in general the aim should be to have soil phosphate level at Index 2 and maintain it at that level.

Potash levels are often low on many farms, particularly on cutting areas where two cuts of silage are taken. This is because large amounts of potash are removed in the herbage at harvesting and reserves of potash must be maintained either through slurry or potash fertiliser. Low potash levels lead to thinning out of productive grasses and ultimately lower yields, especially in dry years. The ideal soil potash level is Index 2, both for grazing and silage.

Soil sampling should be carried out over the winter months and certainly before any slurry or inorganic fertilisers are applied. Provided the area being sampled is reasonably uniform one sample should cover an area of approximately 4 hectares (10 acres). Sampling equipment and guidance on the sampling procedure is available at DARD Development centres.

For information/advice on environmental issues contact Countryside Management Branch, DARD.