Timing of liming on a grazing platform

Liming in September is standard practice to ensure good germination of an autumn reseed. But grazing managers need to remember that calcium* is needed on the platform throughout the growing season.

This means that a traditional policy of heavy liming every five years (often a legacy from the grant-aided days) needs to be replaced with a nutrient planning budget, where timely spreading is based on paddock requirements, soil analysis, slurry tests and lime product quality, according to soil specialist Mark Tripney of isoils.

When grazing platforms are well managed, calcium’s role in growing healthy plants, transporting nutrients and creating a healthy soil structure is evident. Where there is an imbalance, it shows up as poor grass rooting or plant nutrient uptake. It also impacts turnout and extended grazing dates due to soil structural issues.

As more nitrogen is applied to the sward, there is a greater chance that calcium in the soil is utilised which not only leads to acidity but also locks up nutrients, says Mark. “For grass with high nitrogen input, soil pH is ideally 6.5. However, if it drops to 5.9, then utilisation efficiency of nitrogen drops by 11%”, he explains.

“If you apply 300 kgN/ha, you have potentially lost 33 kg N – at £1/kg this worth £33/ha over the season. This drop in pH will also lock up 40% of the phosphate. Applying 125–200 kg/ha of quality granulated lime each year to a well-managed grazing platform will maintain soil pH.”

Analysing this season’s data, together with evidence of whether cows have eaten down to a good residual or not, clearly identifies under-performing paddocks for more investigating this winter using a detailed soil analysis:  “On a high-input grassland farm, soil test at least every three years. A nutrient planning budget involves soil and slurry sampling and applying lime accordingly, then working out fertiliser requirements”, says Mark.

He points out that quality granulated lime can be applied at low rates to maintain soil pH when stock are grazing. Another practical option is to use fertilisers that contain calcium to fit in with a little-and-often spreading regime. Timing is important to avoid any leaching of nutrients over winter, which produces slight acidity in soil; hence spring applications are more effective.

Calcium is an essential nutrient:

  • It strengthens grass plant cell walls
  • Helps root development
  • Legumes use it to fix nitrogen
  • Calcium affects nutrient uptake by the grass plant
  • Aids release of soil nutrients
  • Pulls clay particles together to create an aerated soil

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