Kiwifruit Nutrition diagnosis of nutritional disorders
Symptoms of severe calcium deficiency develop first on recently matured leaves (Photo 13a) and spread to progressively younger leaves. Initially, the veins at the base of the leaf become necrotic and turn black (Photo 13b). As the deficiency becomes more pronounced, the necrosis spreads to the fine veins on the remainder of the leaf; these necrotic areas enlarge and coalesce to form extensive patches of necrotic tissue (Photo 13c). As the necrotic tissue dries the leaf becomes very brittle and there is a tendency for the plant to defoliate.
By this stage the growing point, which may have developed a rosette of very small leaves, will have died causing the axillary buds at the junction of the petioles and the stem to develop (Photo 13d). At the same time the oldest leaves may have developed symptoms which include an upward rolling of the leaf margin and an interveinal necrosis surrounded by a zone of chlorotic tissue(Photo 13e).
These observations suggest that calcium may be relatively mobile in the phloem of kiwifruit.
Calcium deficiency also affects the roots of kiwifruit. On severely deficient plants the root system is poorly developed, and in some cases the root apex dies (Photo 13f). Large areas of necrotic tissue may also develop some distance from the root apex and are likely sites for invasion by root pathogens.
Calcium concentrations in fully expanded leaves of plants sampled in the field at mid season usually range from 3.0 to 3.5 per cent of the dry matter. Solution culture studies at Ruakura suggest that kiwifruit are relatively tolerant of low levels of calcium, as leaf symptoms did not appear until the concentration in the youngest fully expanded leaves fell below 0.2 per cent of the dry matter.
The widespread use of lime and fertilisers which contain relatively large amounts of calcium (single superphosphate, 20 per cent w/w Ca; Calcium ammonium nitrate (CAN), 20 per cent w/w Ca), coupled with the small annual removal of calcium in fruit (Table 2) probably accounts for the low incidence of this deficiency in kiwifruit grown in New Zealand.
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| 13a | 13b | 13c |
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| 13d | 13e | 13f |
