LIKE other farming enterprises, the management of horses depends on soils to produce grass. Soil is the medium in which grass grows and soil provides a number of key functions in this role such as providing/supplying water and air to growing plants, and giving support and anchorage to plant roots. A key function of soils is to provide nutrients for grass growth. The fertility levels of a soil will determine its ability to do this.

It is important to manage soils so that the fertility levels are optimised and maintained so that nutrient supply is sufficient for grass growth requirements. With high value animals such as horses, long-term stability of grass nutrition through little and often application of fertilisers on well maintained soils is beneficial for consistency of mineral composition and nutritional quality of grass and hay/haylage. Having up to date soil analysis is critical to monitoring soil fertility and planning fertiliser applications on the farm.

Soil analysis

Soil sampling and analysis can be conducted to establish the fertility levels of your soils. Divide your farm into 2-4 ha units for sampling. It is recommended to sample soils to a depth of 10cm. Approximately 20 sub-samples should be taken randomly across the field to get a representative sample. Samples can then be sent away to a laboratory for analysis.

Standard soil analysis includes a test for the levels of the major nutrients phosphorus (P) and potassium (K), and soil pH and lime requirement. The results can be converted into a soil index level to simplify fertiliser planning. Low fertility soils are classified as Index 1 (very low) or 2 (low). The optimum Index level is Index 3 (medium), while Index 4 soils are high, and will be productive without additional P or K fertilizer. It is recommended to have soils sampled at least every five years. There is no soil test for nitrogen (N).

Soil pH and lime application

Irish soils tend to be acidic and can produce poor quality grasses as a result. Liming is the principal way of neutralising this acidity. The optimum pH for grassland soils is 6.3. Lime should be applied to manage the soil pH and the rate of lime application can be determined by soil analysis. Lime will also provide a source of calcium (Ca) for the grass.

Be careful not to overlime as it can cause trace element imbalances in the soil. Where lime requirements are greater than 7.5 t/ha (3 t/ac), apply 7.5t/ha initially, and apply the remainder after two years. Lime can be spread all year round. Apply to bare swards if possible. Application of a soil conditioner such as Physiolith is also a good way to maintain soil pH over time. By applying annually, Physiolith can give a more stable soil pH over time and avoid fluctuations in soil pH and trace element availability that can occur with irregular applications of standard lime.

Only 34% of soil samples coming through Teagasc from horse enterprises from 2007 to 2013 had a soil pH > 6.2, indicating that a substantial proportion of soils would respond to an application of lime (Figure 1). A well limed soil will have a higher grass growth potential and will give a better response to applied fertilisers.

P and K

The optimum soil Index for P and K is Index 3 (medium). Figure 1 shows that approximately half the soil samples from horse farms show soil P and K levels that are very low (Index 1) or low (Index 2). These soils would respond to fertiliser P and K applications. The fertiliser P and K advice for Index 3 soils is normally based on replacing offtakes.

However, since offtakes in horse systems are usually very low, very little P and K is required. Higher rates are advised for Index 1 and Index 2 soils as these low fertility soils would benefit from higher rates of fertilisers. Advice for hay is higher than for grazing (Table 1).

Table 1. P and K advice for

grazing and hay (kg/ha).

Grazing Hay

Soil Index P K P K

1 20 60 40 175

2 10 45 30 150

3 < 5 15 20 120

4 0 0 0 0

Farmyard manure (FYM) produced on the farm will also act as a source of N P K fertilizer. One tonne of FYM will be equal to approximately 1 kg of N, 1.2 kg of P, and 6 kg of K. It is usually better to apply FYM to hay fields, as they have the highest requirements. Always apply to a field that has a P and K requirement in order to make fertilizer costs savings.

Nitrogen

Nitrogen will be the main driver of grass production on the farm. High rates of N application used on intensive dairy and beef farms are not appropriate for horses as N-rich grass can cause digestive problems.

Using a phased released N fertiliser product such as Nutrigrass, Maxigraze, or Optigrass can reduce the risk of excessive N levels in the grass. The amount of N you apply should be based on grass requirements.

If significant amounts of grass are required in March, April and May, apply 20-30 kg/ha of N early in spring. Applying early will help in avoiding high N contents in the grass. In normal summers, when temperatures are high, there should be enough N in the soil to allow sufficient growth. If growth is poor, 20-30 kg/ha may be applied during the summer to increase grass growth.

Grass swards being conserved as hay will have higher N requirements. Apply up to 80 kg/ha of N approximately 6-8 weeks prior to expected harvest date. High rates of N will increase yield, but will make crops greener and more difficult to dry for hay. Therefore, lower N rates will make the hay crop easier to save.

More information on Physiolith or phased released N fertilisers is available from your local Grassland AGRO rep or www.grasslandagro.ie.