POTATOES
Beneficial nutritional responses documented with potassium nitrate* Horticultural crops are high feeders of both nitrogen and potassium, with potassium being taken up in the largest quantities.
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hat growers strive to achieve are yield increases from more and larger marketable product per unit area, quality improvement – whether it be increased brix, specific gravity, total suspended solids (TSS), acidity, vitamin C, less peel defects as well as improved colour – and by reducing crop losses by increasing disease resistance. Potassium nitrate has been shown to improve all the above-mentioned parameters.
Fertigation programmes including potassium nitrate It has been well documented in many crops and many soil conditions that the combination of a positive potassium cation (K+) with the negative anion of nitrate (NO3)- act synergistically in the uptake of each other. Since both the elements of nitrogen (N) and potassium (K) are used by horticultural crops in the greatest quantities, this combination is highly beneficial in fertigation programmes. Excessive ammonium nutrition can induce calcium deficiencies in many crops, even though calcium (Ca) is supplied in adequate quantities. Examples of this are tip-burn in lettuce, blossom end-rot in tomatoes and peppers, bitter-pit in apples and internal browning in pineapples. Nitrate-N in a nutrient solution also directly proportionately limits the uptake of excess chlorides. Small amounts of chloride are essential but in many horticultural crops, excess chlorides have been shown to be detrimental to quality and yield. Chloride sensitivity is dependent on crop type. Maximising nitrate-N (NO3)- maintains an optimal pH close to the roots (rhizosphere pH). If the plant is fed ammonium (NH4)+, along with all the other cations, then there is an excess of H+ given off by the plant that causes the rhizosphere pH to drop by as much as 1,5 units (between 10 and 100 times more acidic). This acidity can be toxic to the roots per se and induce pH-dependent nutrient deficiencies. Using potassium nitrate to maximize the supply of negatively charged nitrates, is thus the ideal way of optimizing K+ uptake, N uptake and the uptake of the other cations, Ca2+ and Mg2+, into horticultural crops, while at the same time, limiting the uptake of chlorides. Greater plant dry weight, reflected in yield and quality, is always the result.
Foliar applications with potassium nitrate alone or in combination** Foliar applications are required in times of peak demand, poor rooting conditions, salinity, cold, waterlogging, drought, incorrect fertilizer applications and root diseases. Periods of rapid fruit/crop filling are periods of peak nutrient demand. Potassium nitrate foliar applications at these times can result in greater yield and quality. In deciduous trees, post-harvest foliar sprays will boost the stored N and K reserves for the following years’ budbreak and fruit set improving both fruit uniformity and yield. Potassium nitrate foliar applications have been shown to increase the resistance of plants towards diseases (systemic acquired resistance – SAR). This occurs on both the metabolic level (phenols, auxins, phytoalexins and short chain carbohydrates), as well as on a physical level (firmer cell walls and faster recovery). According to the International Potassium Institute, Perrenoud (1990) extensively reviewed the effect of potassium applications on disease severity in crops. With bacterial infections, potassium application decreased severity in 99 out of 144 cases with 14 unchanged. For fungal infections, potassium application decreased disease severity in 1 080 of 1 549 cases with 112 cases unchanged. Potassium nitrate is the preferred N and K source in horticultural crop nutrition often resulting in: • optimum K and N uptake, • stronger healthier plants, • better set and fruit yields, • increased fruit/crop size, • better colour intensity, • increased disease resistance and • enhanced stress tolerance such as drought, frost and salinity. For both fertigation and foliar applications, consult an agronomist regarding rates and timing of applications. *Reg No K5020 Act 36/1947. Registration holder Sociedad Quimica y Minera (Africa)(Pty)Ltd **All claims in this article can be substantiated with references which can be made available on request.
Disclaimer The information herein contained is given to the best of SQM’s knowledge and is believed to be accurate. The conditions of use and application of the suggested recommendations, are beyond our control. No warranty is made as to the accuracy of any data or statements contained herein. SQM specifically disclaims any responsibility or liability relating to the use of the recommendations and shall under no circumstances whatsoever, be liable for any special, incidental or consequential damages arising from such use.
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VEGETABLES & FRUIT | JANUARY • FEBRUARY 2022
