Kiwifruit
Potassium deficiency can cause significant yield losses in kiwifruit, associated mainly with a reduction in fruit number rather than the size of individual fruits.
Fertiliser potassium requirement is affected by soil supply, and crop demand. Varieties with varying yield potentials will require different application rates. For example, Hayward kiwifruit yield between 25 to 30 t/ha and applications of 250-300 kg potassium/ha are common. The newer variety Zespri Gold can yield up to 60 t/ha and is likely to require much larger applications of potassium fertiliser.
Both MOP and SOP are suitable potassium sources to use with kiwifruit. It has been suggested that the chloride content of MOP can contribute to problems of leaf necrosis in kiwifruit vines. However, research in New Zealand has indicated that leaf necrosis is linked to nitrogen deficiency, and can be overcome by adequate nitrogen application regardless of the form of potassium fertiliser. Poor root growth in summer and autumn may also contribute to necrosis in following years and can be related to soil moisture, pruning or crop load.