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.
(Source – Agriland – Breifne O Brien – 12/06/2022)
The inter-Relationship Between Sulphur And Nitrogen
Due to the key role of both sulphur and nitrogen in the synthesis of proteins, the supply of these plant nutrients is highly inter-related.
Studies have shown that one nutrient will accumulate in plants when the other is deficient.
But when this deficiency is corrected, the accumulated nutrient is then used in protein synthesis.
In reality, a shortage in the availability of sulphur will reduce the efficiency of nitrogen use.
With the availability of nitrogen sulphur grades is likely to be limited for the 2022/23 growing season, this brings into focus the strategy for ensuring tillage and grass crops receive enough sulphur.
Sulphur and Nitrogen
Where ammonium sulphate-based products have been used previously, but are not available or limited, alternative sulphur options will need to be considered.
The options for this include solid organic materials, such as farmyard manure and bio-solids.
They contain significant amounts of sulphur. But they are slow release sources of crop nutrition. This is because the organic sulphur must be mineralised to sulphate so the plant can take it up.
This takes several months and warmth, so the likes of farmyard manure needs to be applied in the autumn, despite a small amount potentially being lost through leaching of the sulphate over the winter.
Liquid organic materials, such as slurries and poultry manure, are also valuable sources of sulphur. These materials supply available sulphur much more quickly and should be applied early in the year.
This is because autumn applications are very susceptible to leaching of the sulphate over the winter.
Trials have confirmed that between 5% and 10% of the sulphur contained in autumn applied farmyard manure is crop-available the next spring. This figure rises to 20%, where bio-solids are concerned.
Up to 60% of the sulphur contained in poultry manures is available to crops, if applied in the spring.
Elemental sulphur fertilisers are also available. However these need to convert to the sulphate form to become crop available.
Again, they need more time to be effective and must be applied well in advance, such as the previous autumn.
There is an inevitable risk that a significant amount of the sulphur is mineralised to sulphate in the autumn, and this may be lost by leaching, over the winter.
Included in this category are potash/sulphur/magnesium fertilisers, such as Polysulphate and PotashpluS.
Polyhalite is a complex sulphate molecule, with progressive release characteristics that can be applied straight or incorporated in compound fertilisers.
(Source – Agriland – Richard Halleron – 10/06/2022)