Kiwifruit Nutrition diagnosis of nutritional disorders
Phosphorus deficiency can reduce the growth of kiwifruit without the development of obvious visible symptoms (Photo 5a). the stems of affected plants tend to be much thinner and the size of the leaves considerably reduced.
Clearly recognisable symptoms only appear on deficient plants when growth is severely restricted. Symptoms include a pale green interveinal chlorosis of the older leaves which spreads from the leaf tip back towards the point of attachment of the petiole (Photo 5b). Reddening of the midrib and major veins on the underside of the older leaves may also occur, the colour being more intense towards the base of the leaf blade (Photos 5c and 5d).
On healthy plants the midrib and major veins on the underside of the leaf usually remain light green (Photo 5c).
The petioles of deficient plants can also be more pigmented than usual. However, this symptom is not particularly useful for diagnosing phosphorus deficiency in kiwifruit as there is considerable variation in the degree of pigmentation of the petioles, even amongst healthy vines. In the field, the upper side of affected leaves may develop a burgundy tinge, particularly at the margins of the leaf (Photos 5e and 5f).
Phosphorus concentrations in fully expanded leaves of healthy plants sampled in the field at mid season usually range from 0.18 to 0.22 per cent of the dry matter. Results from the solution culture studies and analysis of leaf samples taken from the field indicate that symptoms of phosphorus deficiency do not usually appear until the concentration of phosphorus in youngest fully expanded leaves falls below 0.12 per cent dry matter.
Despite most New Zealand soils being naturally low in phosphorus, phosphorus deficiency of kiwifruit is not common. The relatively high rates of phosphorous fertiliser (56 kg/ha/yr of phosphorus) generally recommended for kiwifruit36, and the development of orchards on ex-dairy pastures (usually areas of high soil fertility) probably account for the low incidence of this disorder in the field. In addition, only small quantities of phosphorus are removed in fruit (Table 2).
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| 5a | 5b | 5c |
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| 5d | 5e | 5f |
