On many beef and sheep farms, in particular where ground is rented, farmers can be reluctant to spend money on soil pH and nutrient tests and consequently fail to act accordingly with the soil-test results.
With rising input costs a hot topic currently, some farmers will try to cut corners on soil fertility to get grass growing as cheap as possible, but in many cases, this decision proves more costly in the long run.
A series of farm walks hosted by the College of Agriculture, Food and Rural Enterprise (CAFRE) in Northern Ireland last month, highlighted the impact of soil pH on nutrient utilisation.
Effect of soil pH on fertiliser utilisation:
| Soil pH | Nitrogen (N) utilisation | Phosphorus (P) utilisation | Potassium (K) utilisation | % of fertiliser wasted |
|---|---|---|---|---|
| 5.0-5.5 | 77% | 48% | 77% | 32% |
| 5.5-6.0 | 85% | 52% | 100% | 21% |
| 6.0-6.5 | 100% | 100% | 100% | 0% |
As the table above indicates, adequate soil pH is essential to ensure the full value is being obtained from fertiliser.
The optimum soil pH is between 6.3-6.5 for grassland on most soils, and slightly lower than this for peat soils.
At adequate soil pH, 100% efficiency is achieved on the fertiliser applied, but at the low pH of 5.0-5.5, up to 32% of the fertiliser applied is wasted.
This year more than ever, it is in every farmer’s interest to consult their most recent soil test results and identify the fields that need lime.
When spreading lime, the best option to correct soil pH is ground limestone or quarry lime.
Some farmers prefer to apply granulated lime through their own fertiliser spreader, however this option has little benefit over quarry lime and is significantly more expensive.
Currently, many farmers are taking out fields for bales or cutting meadows for silage. Post-cutting is a prime opportunity to get lime out on ground in need of it.
If a situation arises where land needs slurry and lime, farmers are advised to apply slurry first and give four to seven days – weather permitting – between the slurry application and lime application. This is because when slurry is spread on top of lime, a lot of the nitrogen value is lost due to volatilisation.
When spreading lime, it is recommended not to spread more than 2t/ac/year.
