Kiwifruit (Actinidia deliciosa) is a vigorous growing vine. In its natural habitat in the mountainous regions of central and southern China it is found growing in deep humus-rich soils on the sides of steep gullies. In New Zealand kiwifruit have been successfully grown on a wide range of soil types, but it yields best on well drained soils which are not prone to waterlogging or likely to dry out too quickly in the summer. Kiwifruit have an extensive root system which in mature orchards may overlap with that from vines in adjacent rows. Results also show that a large proportion of their roots are close to the surface of the soil, although some roots may penetrate the soil to considerable depths. However, in soils with unfavourable characteristics such as those with compacted iron pans or which are heavy and poorly draining, the root system may be restricted close to the surface. The distribution of the root system will dictate whether fertiliser should be spread evenly throughout the orchard or banded close to the plant. As 50% of the root system needs to be exposed to the fertiliser to be effective, broadcast methods of application should generally be used in preference to banding methods.

All of the nutrition work to date on kiwifruit has been done using 'Hayward'. Nutrition research on Actinidia chinensis is now being undertaken.

PLANT ANALYSIS
Leaf samples for monitoring the nutrient status of the vine should be taken at the same physiological stage of growth each year. That is, time of sampling should be measured in terms of weeks after budbreak rather than on a strict calendar basis. Leaves should be collected early in the season for chemical analysis. The youngest fully expanded leaves on current season's canes should be taken from at least 20 vines (two to three leaves per vine) within the area of the orchard to be monitored.

Samples taken 6-8 weeks after budburst allow time for remedial fertiliser to be applied in the current season to correct nutritional deficiencies identified by early leaf analysis (shaded area in each graph indicates the Normal Range).

Seasonal Changes in Nutrient Concentration in Kiwifruit Leaves

Because of the marked seasonal changes that occur in nutrient concentrations in leaves, optimum concentrations for assessing nutrient status early in the season (eg, 4 weeks - see Table 1) differ from those recorded during February (Table 2). Seasonal trends showing optimal leaf nutrient levels throughout the growing season are available from some laboratories.

Sampling leaves for diagnostic purposes is largely independent of the time during the growing season. Leaves (blades plus petioles) showing distinctive symptoms should be collected as soon as they appear on the affected vines. At the same time a second sample of leaves should also be collected from an identical position on healthy non-affected plants nearby. By taking an affected and an unaffected sample the results can be compared directly and possible disorders identified without having to rely upon standard values.

SOIL TESTING
There is little definitive information for kiwifruit on the optimum nutrient levels in soils. In the absence of well defined target levels for each nutrient in the wide range of soil types on which kiwifruit are grown it would seem that the presence of healthy high yielding vines should be the ultimate arbiter as to whether or not soil conditions are optimum for growth. Soil tests should be carried out before planting and each succeeding year with the aim of monitoring and correcting trends in nutrient levels in the soil rather than in the pursuit of attaining particular soil values.

Results have shown that kiwifruit tolerate a wide range of macronutrient concentrations in the soil, but inconsistencies relating to soil type do occur. For example, kiwifruit have been observed growing vigorously at pH values as low as 4.5 on peat soils and as high as 6.8 on calcareous alluvial soils at Gisborne and Hastings, yet a pH of 5.2 on Ohaupo silt loam has resulted in Mn toxicity.

Regular soil testing, in conjunction with leaf analysis will monitor fertility levels and allow early identification of any nutrient disorder.

FERTILISER REQUIREMENTS
Annual uptakes by mature kiwifruit vines are greatest for nitrogen, potassium and calcium (between 125 and 180 kg/ha), while smaller quantities of chlorine (60 kg/ha), phosphorus, magnesium and sulphur (< 25 kg/ha) are taken up. The quantity of nutrient recovered from fertiliser by mature kiwifruit vines is usually less than 50% for most elements. For some elements such as K the quantities that need to be replaced are large. The estimated annual removal of nutrients in fruit from a mature orchard producing 8,000 trays/ha is given in Table 3.

While generalised maintenance fertiliser recommendations can be based on the quantities of nutrients removed from the orchard in fruit, they may not be sufficiently accurate to prevent nutrient disorders arising in every situation. For example, additional inputs will be needed if prunings, either winter or summer, are removed from the orchard. Furthermore in young orchards, additional nutrients will be required for extension of the vine framework. Therefore, it is important to monitor closely the nutrient status of the crop with soil and plant analysis. Results from analysis of leaf samples collected from different parts of the plant every two weeks from budbreak until leaf fall show that over 65% of the annual accumulation of nutrients by the leaves occurs in the first 10 weeks of growth after budburst. Thus, it is essential that fertilisers be applied early in the season (August-September).

NUTRIENT DISORDERS
Nutrient disorders have resulted in serious reductions in fruit production primarily due to a reduction in fruit number, with little effect on fruit size.

Nutrient Deficiencies

• Potassium deficiency (K < 1.5%). In many cases the distinctive leaf symptoms associated with K deficiency have been incorrectly attributed to drought stress and wind damage. The first signs of the disorder include poor growth at budbreak. As the deficiency becomes more pronounced there is an upward rolling of the margins of the older leaves which is particularly noticeable during the warmer periods of the day. This symptom may disappear overnight only to reappear the following day. Eventually, the leaf margins remain permanently rolled. Later in the season large areas of tissue die giving the leaf a scorched appearance as the affected tissues dry out. Inadequate applications of K fertiliser to compensate for K required in new cane and leaf growth, and for the large annual removal in fruit, largely accounts for the high incidence of this disorder. Competition from grasses and clover can also enhance a deficiency of K. Potassium deficiency can be readily detected with leaf analysis and corrected with fertiliser. To correct a moderate to severe deficiency in a mature orchard expected to produce 6,000 trays/ha plus grow an extra 40 metres of cane per vine, an input of at least 250-300 kg/ha of K (500-600 kg/ha of potassium chloride) would be required. Generally, potassium chloride is recommended in preference to potassium sulphate because of the kiwifruit's unusually high chloride requirement (2-6g/kg dry weight of chlorine in the leaves to maintain healthy growth). Vines where potassium chloride is used (in comparison with potassium sulphate) show significantly higher K leaf levels for the first six weeks and have an accompanying increase in flowering and fruit yield.

• Symptoms of N deficiency (N < 1.5%) develop first on the older leaves and spread progressively to young leaves until the whole plant is affected. Initially, there is a gradual change in the colour of the leaf from the usual dark green to light green. On severely deficient plants the veins remain conspicuously green. Without regular annual applications of N fertilisers, most horticultural soils in New Zealand which are cropping regularly will sooner or later become deficient in this element. Up to a 50% reduction in photosynthetic rate has been measured in nitrogen deficient kiwifruit leaves. Minor nitrogen deficiencies are difficult to detect unless leaf analyses are taken early in the season. This enables correction of the disorder while the canopy and fruit growth can still respond.

• Magnesium deficiency (Mg < 0.15%). Symptoms include a pale yellow-green interveinal chlorosis of the older leaves. The chlorosis usually develops at the leaf margin and spreads inwards between the veins towards the midrib, often leaving a relatively wide zone of healthy tissue each side of the main veins and at the base of the leaf. Initially, there is no necrotic tissue associated with the chlorisis, but as the deficiency becomes more pronounced the chlorotic tissue turns bright yellow and a marginal or interveinal necrosis may develop. Symptoms of Mg deficiency are not usually observed until February and then only on the older leaves of the current season's extension canes. To correct a moderate to severe deficiency an input of at least 100-200 kg Mg/ha is required.

• Manganese deficiency (Mn < 30 ppm) produces a light green-yellow interveinal chlorosis which appears first on recently matured leaves but in severe cases it may affect almost all leaves on a plant. As the deficiency becomes more pronounced, the zone of healthy tissue recedes even further towards the veins so that eventually only the veins remain green. Leaf size is not noticeably reduced nor is there any necrosis of the leaf tissue. Manganese deficiency can occur in parts of Gisborne and Hawke's Bay, and is usually associated with soils where the pH exceeds 6.8. In most cases Mn deficiency can be corrected readily by applying sufficient quantities of compounds which will acidify the soil thereby releasing previously unavailable manganese to the plant. Such acidifying compounds include finely ground elemental sulphur, aluminium sulphate, or ammonium sulphate.

• Zinc deficiency (Zn < 12 ppm) of kiwifruit has been observed in orchards on the Waimea Plains near Nelson, at Motueka, Wanganui and near Hastings. Low levels of Zn also occur in soils at Kerikeri, but there is no evidence yet of a deficiency in kiwifruit grown on these soils. Symptoms of this disorder include a bright yellow interveinal chlorosis on the older leaves with the veins remaining dark green. Foliar sprays or soil applications of zinc salts must be applied prior to leaf emergence or shortly after if these methods are to be effective in correcting the deficiency.

Nutrient Toxicities

• As with other boron (B) sensitive plants the margin between B sufficiency and toxicity is very narrow for kiwifruit. Concentrations of B in the leaves only slightly above the required level can cause serious injury to the plant. Kiwifruit are especially sensitve to excess boron, and large reductions in fruit yield have been reported due to boron toxicity. Early symptoms of B toxicity (B > 100 ppm) include a yellow-green interveinal chlorosis developing first on the older leaves and spreading progressively to the younger leaves. it is also usual to find the affected leaves cupped either upwards or downwards. As the toxicity becomes more pronounced, the interveinal chlorosis quickly gives way to small patches of necrotic tissue which develop between the minor veins and extend to the midrib. Eventually, the necrotic patches link up forming a continuous zone of dead tissue between the major veins. As this necrotic tissue weathers it changes from brown to a silvery-grey colour. By this stage the necrotic tissue has become very brittle and may break away giving a ragged appearance to the leaf. In New Zealand B toxicity has been observed following heavy applications of B fertiliser to the soil (in excess of 2 kg B/ha), as a result of foliar sprays, or where bore waters naturally high in B (> 0.8 mg/i) have been used for irrigation.

• Kiwifruit vines are generally tolerant of relatively high concentrations of soluble salts in the root zone - the main exception being sodium. Excess Na in bore waters (Na > 100 mg/i) has damaged kiwifruit in the Bay of Plenty and Gisborne. In the field kiwifruit affected by excess Na are typically stunted with small, dull bluish-green leaves. Wilting symptoms are seldom observed. It appears that kiwifruit effectively exclude Na from the aerial tissues as the concentration in leaves of affected plants are always less than 0.12% DM. As with other plant species the mechanisms whereby Na interferes with the metabolism of the plant are not well understood.

• Manganese toxicity (Mn > 1500 ppm) can be distinguished from other nutritional disorders by the appearance of a regular pattern of small black spots which concentrate along the main veins on the older leaves. Manganese toxicity is nearly always associated with acid soils and/or poorly drained soils. This disorder can be corrected by application of lime which increases soil pH and reduces the solubility of Mn, and by improvement of drainage in the orchard.

• Chloride toxicity is not usually observed in kiwifruit until leaf levels exceed 2.5%. There is a close association between the availability of nitrate and the absorption of chloride. High nitrate levels are associated with decreased plant chloride levels, likewise nitrogen deficiency is usually associated with high plant chloride levels. Where chloride toxicity is indicated, potassium sulphate or potassium nitrate should be used in preference to potassium chloride.

FURTHER READING
Clark, C.J. and Smith, G.S. (1985). pH-induced manganese deficiency. Possible methods of correction. Southern Horticulture; 18: 21-23.

Ferguson, A.R. (1984). Kiwifruit: A botanical review. Horticultural Reviews; 6: 1-64.

Ferguson, A.R. and Eiseman, J.A. (1983). Estimated annual removal of macronutrients in fruit and prunings from a kiwifruit orchard. New Zealand Journal of Agricultural Research; 26: 115-117.

Sale, P.R. (1985). Kiwifruit Culture, Revised Edition; (Williams, D.A., Ed), Government Printer, Wellington. pp. 96.

Smith, G.S., Asher, C.J. and Clark, C.J. (1985). Kiwifruit Nutrition. Diagnosis of Nutritional Disorders;. Agpress Communications Ltd, Wellington. pp. 56.

Smith, G.S. and Buwalda, J.B. (1994). Chapter 5 - Kiwifruit. Handbook of Environmental Physiology of Fruit Crops, Volume 1, Temperate Crops;: 135-156.

Smith, G.S., Clark, C.J. and Buwalda, J.G. (1988). Nutrient Dynamics of a Kiwifruit Ecosystem. Scientia Horticulturae; 37: 87-109.

Smith, G.S., Clark, C.J. and Buwalda, J.G. (1987). Effect of potassium deficiency on kiwifruit. Journal of Plant Nutrition; 10: 1939-1946.