Kiwifruit Nutrition diagnosis of nutritional disorders
Nitrogen deficiency severely reduces the growth of kiwifruit (Photo 3a). Deficiency symptoms develop first on the older leaves and spread progressively to young leaves until the whole plant is affected (Photo 3b).
Initially, there is a gradual change in the colour of the leaf from the usual dark-green to light-green (Photos 3b and 3c). As the deficiency becomes more pronounced the affected leaves may become uniformly yellow (Photos 3d and 3e). However, even on severely deficient plants the veins remain conspicuously green, particularly on the older leaves (Photos 3b, 3c, 3d and 3e).
Solution culture studies indicate that a marginal scorch may also develop on the older leaves. The orange-tan scorch develops first at the tip of the leaves and then spreads along the margins towards the point of attachment of the petiole. There may be a slight upward rolling of the necrotic tissue (Photo 3b). Observations of nitrogen deficient vines in the field mid season suggest that fruit size may be reduced (Photo 3f).
Nitrogen concentrations in fully expanded leaves of healthy plants sampled at mid season in the field usually range from 2.2 to 2.8 per cent of the dry matter. Results from solution culture taken in the field indicate that symptoms of nitrogen deficiency do not appear until the concentration of nitrogen in youngest fully expanded leaves falls below 1.5 per cent dry matter.
Without regular annual applications of nitrogen fertilisers, most horticultural soils in New Zealand which are cropping regularly will sooner or later become deficient in nitrogen. To maintain vigorous healthy growth of mature kiwifruit vines, broadcasting moderate amounts of nitrogen fertiliser (170 kg/ha of nitrogen) over the entire orchard, is recommended36.
Maintenance of a clover sward in the orchard, particularly under T-bar structures which allow sufficient light to fall on the sward for growth, can make a sizeable contribution to the over-all nitrogen fixed by the clovers (up to 50 kg/ha/yr).
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| 3a | 3b | 3c |
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| 3d | 3e | 3f |
