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Potatoes (Solanum tuberosum L.) are a cultivated crop originating from the highlands of South America. The oldest centre of the potato crop was probably the highlands of Peru and western Bolivia.
Among the nutritious crops, potatoes rank fourth in terms of produced quantity. It is mainly an energy source and, in this regard, occupies the sixth place of importance in the world. Potatoes are a major role-player in food security in South Africa and a cornerstone in our daily lives. It is important to produce potatoes sustainably, which is why the correct practices must be followed.
There are many different factors that play a role in a potato yield, such as pests, diseases, sunlight, and temperature. Other factors include nutrient availability and the competition of these nutrients in the root zone. Plant nutrients are taken up as cations (+) and anions (-).
Essential cations are potassium (K+), magnesium (Mg2+) and calcium (Ca2+), whereas unwanted cations are ammonium (NH4+). Nitrate (NO3–) is an essential anion and chloride (Cl–) is an unwanted anion. Looking at the absorption of macronutrients for potatoes, the descending order is K 43%, N 27%, Mg 26%, P 3%, and Ca 1%. This highlights the importance of both K+ and nitrogen (N) in a potato fertilisation programme.
Role of nitrogen
N is important in all potato plant structures, particularly for foliage and tuber growth, since it is related to production. N is represented in the NH4+ and NO3– form in the root zone. Of the two forms, NO3- is the preferred source of N, for the following reasons:
- NO3– is taken up by the plant directly and plays a role in photosynthesis.
- NH4++ is assimilated but gets transported as amino acids, which is energy inefficient. A plant that receives NH4+ rather than NO3– will always have a lower biomass as a result.
- In addition, NH4+ (because of its charge) is in competition with essential cations such as K+, Ca2+ and Mg2+. Excess NH4+ results in the reduced uptake of essential cations.
Role of potassium
K+ plays a role in the synthesis of sugars and starch and assists in the transport of glucose to the tubers.
K+ also has a strong influence on a potato’s texture, colouring, and flavour. The role that K+ plays in shelf life and skin firmness must also not be overlooked.
K fertilisers are potassium chloride (KCl), potassium sulphate (K2SO4), and potassium nitrate (KNO3). The best source of K for potatoes is KNO3 due to the NO3– content (13%) which is combined with a high K+ content (38%). KNO3 supplies two of the macronutrients most required by potatoes in one product. In addition, with KNO3, the NO3– anion enhances the uptake of essential cations in the root zone.
Potassium nitrate forms
Ultrasol K Plus* is SQM’s water-soluble KNO3. It is a fine white crystalline product that dissolves easily, is of very high quality, and free of unwanted materials.
Qrop K** is the prill form of KNO3 and is a round white prill that is easy to work with. The uniform prill size makes for easy and even spreading in the field.
For more information, visit the SQM website at www.sqm.com or send an email to Johan Fick at Johan.Fick@sqm.co.za
Disclaimer: The information contained here is provided to the best of SQM’s knowledge and is believed to be accurate. The conditions of your use and application of the suggested recommendations are beyond our control. No warranty is given 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 this information.
All claims in this article can be substantiated with references which can be made available on request. *Reg No K5020 Act 36/1947. Registration holder Sociedad Quimica y Minera (Africa) (Pty) Ltd.
**Reg No K5021 Act 36/1947. Registration holder Sociedad Quimica y Minera (Africa) (Pty) Ltd.