FORAGE AND ARABLE
Lots to gain in keeping potassium replenished Potassium (K) is critical for pasture quality and productivity but large amounts of it are removed when hay or silage is harvested.
What about K in the soil?
existing reserves of K will help to refine
“Most K in the soil isn’t plant available so the soil can’t provide new pasture with the K it needs,” Ian says.
the rate. Use either a Quick Test to
“Repeatedly cropping a paddock
Unlike other nutrients, K is not stored in soil organic matter and 90 to 98 percent of K in the soil is in mineral form. This slowly becomes available to plants as soil minerals weather and break down.
readily and slowly available K.
“Potassium leaching is also an issue in some soils. Pumice soils and sands, for example, have a low cation exchange capacity so can’t hold onto mineral K and if high rainfall occurs, K can easily be lost via leaching.”
virtually all other fertiliser products. It
without replacing K and other nutrients removed at harvest can lead to declining pasture quality and productivity and leave pasture increasingly vulnerable to undesirable species,” Ballance Science Extension Manager Ian Tarbotton says. “Herbage contains a lot of K as plants take up more than they need, which is known as ‘luxury uptake’. Potassium is
measure K readily available for plant uptake or the TBK test to measure both On soils prone to K leaching, frequent applications will minimise losses and maximise plant use. MOP is inert and may be blended with is contained in the Superten range (5K, 7K, 10K, 15K and 25K options), which replenish the phosphorus, sulphur and K removed by pastures and crops during their growth cycle. To boost growth with nitrogen and replenish K
the second most concentrated nutrient
Replacing K
in herbage, after nitrogen, so large
Muriate of potash (MOP), a concentrated source of K that dissolves readily when applied, is the most widely used, affordable K fertiliser on pastoral farms.
comes in 15K, 20K and 25K options.
“Applying K at the right rate and time can minimise luxury uptake of K, as well as leaching losses,” Ian says.
fertiliser is still needed.
amounts are removed at harvesting.” Potassium is especially important for clovers, which are poorer foragers of the nutrient than grasses so are more prone to K deficiency. Lack of K can limit clover growth, affecting longerterm nitrogen fixation and pasture production and quality. Post-grazing or silage-making clovers in particular need potassium as they recover from being shaded out by grasses.
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Potassium requirements are largely driven by the amount removed in product, so more intensive farming activities will require more K to be applied. Soil testing to determine
levels at the same time, SustaiN also Post-harvest fertiliser takes care of the nutrients removed by the harvest but regular maintenance
For more information, contact your Ballance Nutrient Specialist, your Farmlands Technical Field Officer or the friendly team at your local Farmlands store. Article supplied by Ballance Agri-Nutrients
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