Soil pH is critical for good soil health and plays an important role in maintaining grassland productivity. It’s also one of the easiest and cheapest parts of soil management to control.
The right pH supports soil structure and function, including nitrification (the conversion of ammonia to nitrates for plant use), earthworm activity and nutrient availability, reducing the need for applied fertiliser. These are all disrupted if the pH is too high or low. Nutrients can remain locked in the soil making them unavailable to growing plants, impacting grass growth and productivity.
Start with a soil test
Grassland soils in Ireland are more likely to be acidic, with a low pH, as lime is continually being lost. The amount depends on several factors, including rainfall, soil type, crops and livestock on your land. So, the first step in understanding your specific farm’s soil pH is to do a soil test. This should be carried out between September and March.
However, the results are only as good as the samples, so take note of a few important parameters. Also, avoid testing within three to six months of the last P or K application or when conditions are extremely wet or dry. These conditions can distort the results, making a subsequent fertiliser plan inaccurate and potentially costly.
Understanding the balance between all the main soil elements ensures you only apply the inputs you need. If you’re looking for a more detailed picture of your soil profile, then extensive tests measuring a wider range of micronutrients are available. At a time when fertiliser prices are high, being as efficient with applications as possible is vital.
Apply lime to correct soil pH
Correcting soil pH makes P and K already in the soil more available and improves the efficacy of any applied N, P and K fertiliser. A well-planned lime application can release up to 80kg of nitrogen and boost grass DM yield by approximately 1.5t DM/ha compared to untreated ground with a low soil pH. This makes liming a cost-effective way to improve soil fertility by reducing the level of inputs needed, as well as the environmental benefits of using less artificial nitrogen fertiliser.
For grasslands, aim for a soil pH of 6.2-6.5, or 5.5 for peaty soils. To reach these levels, apply lime according to your soil test results, remembering the annual maximum of 7.5 t/ha (3 t/acre). If more than the limit is needed, the total application should be split with the balance applied the following year.
Top tips for achieving the right soil pH
Now, here are seven tips for maintaining the best soil pH:
- Aim for a grassland soil pH of 6.2-6.5 (pH 5.5 in peaty soils).
- Always carry out a soil test before applying lime.
- Use soil test recommendations to determine your lime application rate.
- A maximum of 7.5 t/ha (3 t/acre) of lime should be applied each year.
- On silage ground, it is best to apply lime after the final silage cut is taken to avoid taking lime into the pit where it can affect silage preservation.
- Allow 10 days after a slurry application before spreading lime to reduce nitrogen losses. Alternatively, if lime has been applied, wait up to three months before applying slurry.
- No gap is needed between spreading lime and calcium ammonium nitrate (CAN) or protected urea.
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