STONE FRUIT
Potassium nitrate for use in stone fruit production Adequate potassium is essential for optimal photosynthesis and plant functioning, in horticultural crops.
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lthough potassium does not play a structural role in plants, it does however activate at least 60 enzymes, regulates a plants water balance and the functioning of stomata, plays a role in energy production, is involved in the transportation of sugars through the phloem, the translocation of nutrients upwards in the xylem and in many steps in protein synthesis. There can be no general fertilizer recommendations or applications for stone fruit varieties for all conditions. Published recommendation guidelines are there as a guideline only and are calculated on the plant and crop removal figures. These general guidelines are modified to on-farm specific conditions using regular leaf and soil samples. This will optimise yield, fruit quality and fruit size in a cost-effective manner. Potassium requirements for stone fruit will depend on the yield and the cation exchange capacity of the soil. Potassium requirements will vary between 0 – 140 kg K / ha at bloom and perhaps half that again post-harvest. Leaf levels (monitored annually), according to the norms for the stone fruit type, will assist in the correction of the macro-element levels. It is important to note that stone fruit are very sensitive to salt stress and high chloride conditions.
For soil applications, by supplying K as potassium nitrate, both the N and the K are utilised in full by the crop. If the K is supplied in full by potassium sulphate or potassium chloride, the excess sulphur (up to eight times the plant’s requirement) and all the chloride (except for trace amounts) respectively may create soil salinity issues. In addition, the negative nitrate counter ion of potassium nitrate facilitates the uptake of all the positively charged cations of potassium, calcium and magnesium, optimising plant dry matter production (yield and quality). Foliar potassium nitrate applications*** (two to four applications pre-harvest and one to two post-harvest) are often considered remedial and can be beneficial in stone fruit under the following conditions:
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• If physical soil conditions are unfavourable for root growth or nutrient uptake such as unfavourable structure (compaction or lack of aeration) and water stress. • Under conditions of high root disease pressure affecting nutrient uptake. • Where chemical imbalances exist (excess competing nutrients) for example high Ca and Mg levels with relatively low K levels. • In unfavourable pH conditions where element uptake is restricted. • At known phenological stages with high potassium demand. • When annual foliar analyses show low potassium levels. • When nutrient demand to developing organs (for example rapid fruit growth) is more than nutrient uptake and supply by the roots. • Factors affecting transpiration can affect potassium uptake by the roots and transportation in the xylem. • Possible inadequate soil nutrient applications and unpredictable soil nutrient deficiencies resulting in a decision to apply “insurance” foliar applications. Make the right choice to ensure optimum return on your investment by using Ultrasol K Plus*. ***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. ***Please consult your agronomist for correct foliar application rates and procedures. Disclaimer The information herein contained is given 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 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.
VEGETABLES & FRUIT | MAY • JUNE 2022
