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Mar 19, 2009

K+S UK & Eire Ltd: Potash – your questions answered

With the recent pressures on agricultural commodities, many questions have arisen about the potential penalties from reducing or omitting crop inputs. Here are some of the questions you have been asking.


Will I see a financial return on applying Potash?

Comparing the cost of a maintenance application of K to the additional yield gained in one year is an unwise and dangerous calculation. K is applied to replace that which is removed in crops to maintain soil fertility for the long term viability of a farming system. K can be omitted often without apparent penalty in year 1, or even year 2 but the decline in soil K level eventually reaches a point where drastic yield penalties result mainly through very poor utilisation of N. In long term trials carried out by the PDA and Rothamsted, yield penalties of 2-4 t/ha were seen when soil K reached index 0. With nearly 40% of UK arable soils already fallen to K index 1, continued failure to replace K will in many soils result in similar levels where yields are drastically reduced.


Which nutrient can I omit with the least impact on yield?

When all nutrients are at their optimum levels and ratios, both soil and applied nitrogen can be utilised most efficiently. Von Liebig’s "law of limiting factors" barrel ana - logy is still valid today showing that if any one nutrient is reduced below its optimum level the yield potential is limited.

N efficiency is directly affected by potash levels as shown below. This illustration clearly highlights the potential N losses observed at a recent Rothamsted / GrowHow trial

Are there other implications from reducingfertiliser?

It has been proven that crops grown on poor fertility soils require more chemical inputs, suffer greater winter kill, are more prone to lodging and leach more N. One of the key functions of potash is transporting the products of photosynthesis from the leaves to the grains, seeds, tubers or other storage organs. If K is deficient, reduced grain weight in cereals and OSR is likely, bruising and blackening problems in potatoes can increase and peas and beans fail to set pods or produce quality proteins.


Why should I check my soil magnesium levels?

Taking a balanced approach to fertiliser is crucial. You should check the magnesium status of the soil because potash and magnesium have a very close link and an excess or deficit of one will affect the availability of the other. Products such as Korn-Kali®, deliver potash with available magnesium in the correct ratio for most arable crops with some additional sulphur.

Proven benefits of taking a balanced approach to crop nutrition

What else can I do to make savings and maximise the crop?

Precision mapping and application of fertilisers might be worth considering. There is a cost and won’t necessarily reduce the amount of fertiliser you need to buy but in most cases, by applying nutrients more accurately and where the crop needs them should mean financial savings in improved efficiencies and benefits in crop consistency throughout a field. This is likely to lead to better yields and quality across the farm with improved overall profitability.



  • Ensure base fertiliser applications at least replace what is removed with a target of 2- for potash
  • Long term yield penalties of 2-4 t/ha in cereals become a reality without applied potash
  • If all nutrients are at their optimum levels, maximum nitrogen efficiency is possible
  • A lack or inbalance of just one key nutrient can limit crop yield and quality potential
  • Poor fertility soils require more chemical inputs, suffer greater winter kill, are more prone to lodging and leach more nitrogen
  • Be conscious of magnesium and other nutrients for a balanced approach to fertiliser use
  • Consider more precise tools to optimise farm efficiencies

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