Acting on soil test results after second-cut silage
Now that a lot of second-cut silage has been cut, farmers who are not opting for another cut of silage should be looking at their soil test results and act on these results when they can.
As many may have secured their final cut of silage, now that these fields are just after being harvested, it is an ideal time to go in with a lime application.
However, you cannot lime without soil testing, as this testing is a crucial aspect of dairy farming and fundamental to nutrient management plans, effective fertiliser usage, and maximising grass growth.
Stricter regulations around fertiliser allowances is enticing many to be more efficient with their fertiliser, which will lower costs of production.
Constant regulations within the dairy sector has left many farmers with a sour taste in their mouths, but it is important to know how to navigate regulations and turn them into opportunities.
Testing your soil is the key to optimal soil fertility, as there is no point in applying fertilisers to land if you do not know what nutrients are lacking or the pH of the soil.
Over the last number of years, fertiliser costs have increased, meaning it is crucial to have accurate and precise application to cut down your spending.
You will only be able to have accurate and precise application, along with correct fertilising decisions through the data pulled from a soil fertility test.
A standard soil test will provide major nutrient analysis such as soil pH, lime requirement, phosphorus (P), and potassium (K) for a cost of €1.23/ha/year.
Considering the cost of soil testing, it can prevent purchasing excessive amount of fertiliser, as the data can be collected and put towards a nutrient management plan that allows optimal fertiliser efficiency
Getting your soil tested will not much good to you if you do not react with the appropriate treatment and application.
The table below further highlights the importance of soil testing, as it indicates that not all paddocks are going to require the same amount of fertiliser. Some will require more or less, but it is important to identify what needs what.
When you have the results, you need to first identify the paddocks that will require a lime application, followed by targeting organic manures to low fertility paddocks (soil index 1 and 2 for P and K).
The response to fertilisers and fertiliser strategy for different soil indexes is as follows:
| Soil Index | Response to fertilisers | Fertiliser strategy | P (mg/L) Grassland | P (mg/L) Tillage | K (mg/L) |
|---|---|---|---|---|---|
| 1 | Definite | Build-up + M | 0-3.0 | 0-3.0 | 0-50 |
| 2 | Likely | Build-up + M | 3.1-5.0 | 3.1-6.0 | 51-100 |
| 3 | Unlikely | Maintenance (M) | 5.1-8.0 | 6.1-10.0 | 101-150 |
| 4 | None | None | >8.0 | >10.0 | >150 |
For soils with a good fertility status at a soil index of three, the nutrient P and K offtake should be replaced in order to maintain fertility.
Any demanding crops, such as silage fields, should receive sufficient nutrient applications, as there will be major P and K offtake.
Any paddocks with a fertility status of index 4 will not require additional fertiliser.
Spreading lime has one of the quickest returns on investment across any measure taken on farms. For every €1 invested, it will return €4-€7 in the form of extra grass growth, reduced N usage, and increased soil fertility.
Liming acidic soils increases grass production by 1.0t DM/ha, which is valued at €180/t DM on dairy farms – an application 5t/ha/year costs €25/ha/year over five years.
Lime should be applied ‘little but often’ without exceeding 5t/ha in a single application. Applying a split application of 2.5t/ha over a number of years will allow you to build up soil pH in stages over time.
