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Influencing Almond Weight
Optimum tree nutrition is essential for achieving top nut yields. Potassium is particularly important and needed in large quantities for nut-fill and highest yields.
Potassium
Potassium (K) is needed for the transport of sugars and starch formation, increasing kernel and nut size. Potassium aids photosynthesis and so is important to productive growth, enabling the plant to use light more effectively.
Within the tree it is essential for maintaining the turgor of the cells and involved in stomatal regulation, improving water use efficiency. A substantial amount of potassium is removed from the soil in the hulls of the nut, but also in the shell and kernels.
In almonds, average removal is about 40 kg K/t of kernels and more than two-thirds of this is found in the hull. Other nut crops remove less potassium and the figures vary depending on whether the hull is also removed with the nut.
Potassium will help to build early tree growth, but the key period of uptake in the mature grove is during fruit formation, and applications need to ensure that K supplies don’t limit yields and almond quality at this time.
It takes time to build K reserves and the effects of fertilizer applications do not usually result in significant differences within the first few years that they are made.
Responses vary in trials, but annual application rates of 130-260 kg K/ha have been shown to produce positive yield responses, with correspondingly higher K-offtakes. Higher application rates, may give no advantage.
The build-up of reserves in the tree over the season and throughout the life of the grove is also critical for spur survival, fruit set and production in subsequent seasons.
In the trial shown in the graphs below, spurs from almond trees with or without K supply were tagged in 1999 and classified as vegetative or fruiting spurs. In the following year, the development of these spurs was monitored and spurs were classified as vegetative, fruiting or dead.
In the trial shown above, spurs from almond trees with or without K supply were tagged in 1999 and classified as vegetative or fruiting spurs. In the following year, the development of these spurs was monitored and spurs were classified as vegetative, fruiting or dead.
While there was little difference in vegetative spur production, the fruiting spurs were clearly affected by K application, which lead to a higher percentage of vegetative and fruiting spurs.
The critical value for potassium varies between 1.0 and 1.8%DM in leaves, dependent on nut type.
