Now is the time to think about soil fertility

Wednesday 27.01.2021 , events , news

Soil health drives production. Understanding the physical, biological and chemical status of your soil will support optimal grass output and help your soil reach its full potential.

Research shows a high percentage of Irish grassland soils are severely suboptimal in pH, P and K, severely limiting their production potential. Fertile soil also contains nitrogen (N), as well as other secondary nutrients in smaller quantities.

Soil testing

Soil testing gives you information about the P and K status of your ground, as well as a pH value. In order to make useful comparisons, it’s best to soil sample at the same time each year avoiding very wet and very dry conditions. The ideal time is between September and March, waiting 3-6 months after the last application of P or K before sampling. Once you have your results put together a spring fertiliser plan. With a plan based on your soil analysis, you can apply the correct levels of inputs, such as lime, P or K, boosting grass production and reducing input wastage and costs.

pH

The right pH is important; too low and nutrients remain locked-up in the soil, making them inaccessible to plants. Soil pH is also the most important deficiency to correct and the cheapest! For grassland, aim for a soil pH of 6.2 to 6.5 (pH 5.5 on peaty soils). Apply lime according to soil test recommendations but a maximum of 7.5 t/ha (3 t/acre) should be applied in any one year. For recommendations above this amount, split the application and apply the balance two years later.

Benefits of Correcting pH

  • Releases up to 80 kg nitrogen (compared to a low pH soil)
  • Makes P and K in the soil more available
  • Increases efficiency of applied N, P and K fertiliser
  • Increases grass DM yield by approx. 1.5 t DM/ha (compared to a low pH soil)

Phosphorus (P)

Phosphorus is necessary for the physiology of plants, including photosynthesis, root and tiller development. Like other nutrients, P can be locked-up in the soil if the pH is too low. Phosphorus use is restricted within the Nitrates Directive.

Potassium (K)

Potassium can be spread all year round without any restrictions on its application, although there are points to consider. In spring, a single K application should not exceed 90 kg/ha. If your requirement is above this level, it is best to apply the balance in the autumn. On rapidly growing swards, receiving high levels of K, grass tetany can occur as it prevents magnesium uptake by the grass crop.

Structure

Soil health is not just driven by its nutrient status but also its physical structure. Reducing the impact on soil, through poaching or travelling vehicles, helps improve soil health.

Take a spade and dig a hole to look at any under-performing areas. Check roots are reaching well down into the soil. Good rooting depth is important to reach those soil nutrients. Is the soil friable to the touch and does it break apart easily? What is the worm activity like? Worm activity indicates a healthy soil.

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