GrowSmart Hub

Why soil test?

Knowing whether your soil fertility is low, medium or high is a great grass and crop management tool plus it can save you money in terms of fertilizer purchases. The quantities of individual nutrients applied each year should at least replace those removed by the crop. The levels of nutrients removed depend on the crop type and yield so sometimes a special fertilizer blend may be required to meet your specific requirements.

Start with soil pH

According to Teagasc, optimizing the pH of grassland soils can increase the annual output of grass by at least 1ton DM/Ha.

The plant will never get the benefit of any fertilizer applied if the pH is incorrect as nutrients will remain locked in the soil. The ideal pH for grass is 6.3 and for cereals is 6.5.

Lime (calcium) is a very cost effective input that removes acidity and can help unlock major nutrients in the soil. It also improves plant response to chemical fertilisers and some soils drain better and till easier after liming. It is best applied in the autumn as it avoids any interaction with urea and slurry.

Then address P & K

Going from Index 1 to Index 3 in P & K will grow an extra 3 ton of grass per hectare.

Once the pH issue has been addressed it is time to focus on fields low in P and K. For optimum yields aim to have soils at Index 3 so target the lowest fertility soils first (ie Index 1 & 2) as these will have the greatest response to P and K applications.

Phosphorus (P) is essential for root development and plant growth and must be in abundance in the soil for adequate nutrition. Low levels of P in grassland will reduce growth by 15-30% with those losses greatest in spring and autumn when grass is needed most.

Potassium (K) is necessary for plant strength and provides resistance to stress and disease. Deficiency of K reduces yield of grass by at least 10%.

When is ideal time to soil test:

• Before autumn fertiliser application as soil is hungry nutrient wise
• Sample every 3 years