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Obtaining Better Fruit Quality – Potassium

Potassium is particularly important in terms of berry quality providing a high sugar and acid content, and a good taste to the fruit. It is important for transpiration and regulates stomatal opening and closing, helping improve water use efficiency particularly in periods of moisture stress. Potassium is involved in a range of transport and accumulation processes within the plant, including the translocation of nitrates and activation of some enzymes. It can also help minimize the effects of stresses such as frost by increasing the osmotic potential and therefore lowering the freezing point of the cell solution.

Graph 47 - Potassium – Fruit Quality
Graph 48 - Potassium – Quality

Key quality characteristics such as fruit acidity and TSS continue to rise with levels of potassium up to 600kg K2O/ha and beyond (Figure 47). Potassium also influences the levels of vitamin C within the fruit and has a direct effect on anthocyanin levels, improving berry color (Figure 48). Rate of K use needs to be balanced by that of nitrogen and adjusted according to growth stage of the crop.

Graph 49 - N-K Ratio – Yield and Fruit Quality

During vegetative growth around 2.5 times more nitrogen is required than potassium, but during production a molar N:K ratio of 2:1 or 1:1 is more appropriate and will help improve fruit quality (Figure 49).

Similarly, the ratio between potassium and calcium also needs to be in balance to ensure a mix of good fruit taste, fruit strength for a better shelf life and optimum yield. (See section on cationic balance on page 38). It is also important to recognize that high levels of potassium will not necessarily increase fruit firmness if it restricts calcium uptake (see calcium section on page 41).

Graph 50 - K Form – Yield and Salinity
Graph 52 - Potassium – Amelioration of Salinity

Strawberries are sensitive to salinity and this makes the use of potassium chloride, with its high salt index, unsuitable for this crop. Yield improves when other potassium forms such as potassium sulphate or potassium nitrate are used (Figure 50). Potassium can help to reduce the effects of salinity, reducing membrane leakage and helping to maintain fruit quality and reducing yield loss (Figure 52).

Recommended Yara Fertilizers for Soft Fruit

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YaraLiva CALCINIT

15.5% N + 18.8% Ca - Fully water soluble nitrogen and calcium fertilizer which is a free flowing and dissolves quickly in water without any residues so is suitable for application through all fertigation systems.

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YaraTera KRISTALON SCARLET

7.5-12-36 + 4.5% MgO 10% SO3 - A water soluble NPK fertilizer for liquid feeding and contains a full range of chelated micronutrients ideal for all fertigation systems.

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YaraTera KRISTALON RED

12-12-36 + 1% MgO 2.5% SO3 - A water soluble NPK fertilizer for liquid feeding and contains a full range of chelated micronutrients ideal for all fertigation systems.

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YaraTera KRISTALON LILAC LB

20-8-8 + 2% MgO 25% SO3 - A water soluble NPK fertilizer for liquid feeding and contains a full range of chelated micronutrients ideal for all fertigation systems.

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YaraTera KRISTA K PLUS

YaraTera KRISTA K PLUS 13.7% N 46.3% P2O5 - A fully water soluble nitrogen and magnesium fertilizer. It is a free flowing fine crystalline powder which dissolves quickly in water without any residues.

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YaraTera KRISTA MAG

YaraTera KRISTA MAG - 11% N 15% MgO - A fully water soluble nitrogen and magnesium fertilizer. It is a free flowing fine crystalline powder which dissolves quickly in water without any residues.

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YaraTera REXOLIN Q15

YaraTera Rexolin Q15 is a high performance microgranular EDDHA iron chelate containing 7% iron with 1.5% of the iron as the ortho-ortho isomer. The micro granular formulation is stable, fully water-soluble and non-dusting. Ideal for use in agriculture and horticulture in soil applications. The product is specifically formulated to provide maximum crop safety. This helps to ensure that application will not cause damage to the crop which can reduce it's market value. Analysis 7% w/w = 70 g/kg Fe (chelated by EDDHA) Pack Size 25kg Available in England and Wales, Scotland and Northern Ireland..

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YaraMila GROWER

15-3.9-16.6 + 3.8% S + 1.1% Mg - Compound field grade NPK fertilizer based on 35% SOP and 65% MOP for use on a wide range of horticultural crops.

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YaraVita BORTRAC 150

A liquid micronutrient fertilizer containing 150 g/l boron for foliar application to provide additional boron or to treat boron deficiencies in a wide range of crops.

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YaraVita SENIPHOS

A liquid micronutrient fertilizer containing high concentrations of phosphate and calcium for foliar application to improve yield and quality in fruit and potatoes.

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YaraVita MAGFLO 300

A flowable liquid fertilizer containing 300 g/l magnesium for foliar application to cereals and potatoes or treat magnesium deficiency in a wide range of crops.

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YaraVita STOPIT

A liquid micronutrient fertilizer containing 160 g/l calcium for foliar application to control and reduce calcium related disorders in top fruit and other crops.