Persimmon (Diospyros kaki) is an emerging commercial fruit crop in New Zealand. Orchards predominantly consist of non-astringent cultivars, such as Fuyu and Matsumoto Wase Fuyu. Current nutritional recommendations are based on Japanese and New Zealand studies.

PLANT ANALYSIS
Leaf samples for chemical analysis are normally collected approximately two months prior to harvest (i.e. February-March). Samples can also be collected earlier in the season and results are related to seasonal changes in nutrients. For a standard orchard, between 25-50 youngest mature leaves should be obtained from non-fruiting extension shoots on trees selected at random (omitting pollinisers) throughout the orchard. In young blocks prior to fruit production, youngest mature leaves should be selected from the most recent vegetative growth. This is generally growth which has occurred during summer flush and has a lighter green colouration than the older leaf material produced in spring.

The nutrient concentrations listed as 'optimum' (Table 1) are based on surveys of Fuyu blocks in New Zealand orchards. Those defining deficiency arise from orchard surveys and sand culture studies done in Japan.

SOIL TESTING
Persimmons grow on a wide range of soil types, but prefer deep, fertile, well drained soils. They can grow on clay soils if well drained, or on lighter sandy soils if well irrigated.

The general fertility levels of soil should be adjusted before planting. Adjustment of pH is particularly important in this regard. Persimmons require a pH between 6-6.5; preferably closer to 6.5. As this plant develops a large tap root (development of an extensive network of lateral roots does not seem to occur in some of our soils), it is important to influence the pH at depth. This is most easily done prior to planting.

Soil testing should be done annually at the same time of year. Samples should be taken about 1.5 m out from the trunk in the herbicide strip. It is suggested that samples be taken at two depths, 0-20 and 20-40 cm; the latter sample to check soil pH in this zone.

Optimum soil test levels (Table 2) are based on samples taken in June from Fuyu blocks in New Zealand.

FERTILISER REQUIREMENTS
Persimmons take about 10 years to reach full cropping and the fertiliser programmes should be increased accordingly.

Young Trees

• Year 1: A balanced NPK fertiliser should be spread around each plant providing it with 50 g N, 50 g P, 50 g K/tree in three applications: half in late dormancy (end of August), a quarter in mid October, and the remaining quarter at the end of December. Most formulations will supply sufficient Mg (25 g Mgt/tree).

• Years 2-5: Each year the application should be increased so that by year five each tree is being supplied 200 g N, 150 g P, 200 g K and 100 g Mg. Applications can then be reduced to two a year. As the trees start cropping the relative supplies of potassium are increased.

NUTRIENT DISORDERS
To date, nutrient disorders observed in New Zealand grown persimmons are restricted to deficiencies of Mg, Mn, Ca and Fe; the former two in orchards, the latter common in seedlings grown in planter bags.

The leaf symptoms for Mg deficiency (Mg < 0.13%) are similar to those for other crops. At this stage it seems that Fuyu may be more susceptible to this deficiency; necrotic tissue appearing in the interveinal regions of the young summer growth about March. Soil applications of soluble Mg sources at a rate of 200 kg Mg/ha or several foliar sprays containing 1-2 kg MgSO₄/100 l are effective.

Manganese deficiency (Mn < 27 ppm) has been observed on calcareous alluvial soils in Poverty Bay when the pH exceeds 7.0. Correction by application of acidifying compounds to lower the soil pH is preferably; however, foliar applications of MnSO₄ in spring (300 g MnSO₄ plus 400 g hydrated lime/100 l - repeated at 10 day intervals if necessary) will control the deficiency on a seasonal basis.

Leaves with Ca deficiency (Ca < 0.26%) are excessively puckered and crinkled, particularly near to the leaf apex. Soil applications of soluble forms of Ca such as calcium nitrate should alleviate this deficiency.

The most severe and widespread disorder however is "Green Blotch", a problem brought about by excess manganese (or inadequate Ca) which creates a Ca/Mn imbalance within the fruit. Although the concentration of Mn in leaves may be elevated (Mn > 1000 ppm) symptoms of the disorder are confined to the fruit only. Indeed, concentrations of Mn as high as 6800 ppm have been observed without symptoms of Mn toxicity being present in leaf tissue. Prominent green blotches appear at the distal end of affected fruit in mid March. If the blotches have not disappeared by harvest, as can occur, the appearance of the fruit makes it unsuitable for export even though the interior flesh remains unaffected.

Corrective measures, while simple in theory, have not proved to be entirely satisfactory. Increasing the pH to 6.5, particularly at depth, is necessary to both increase Ca, and to decrease the availability of Mn. Alternatively, if the pH is already adequate addition of gypsum (CaSO₄) is advocated. Foliar sprays of calcium nitrate applied around fruitset may assist in correcting Green Blotch. At present however the concentration, number of sprays, and their timing is still experimental.

FURTHER READING

Clark, C.J. and Barrett, L.J. 1985. Leaf analysis of persimmons: A guide to sampling and interpretation of results. Growing Today, August: 30-31.

Clark, C.J. and Kajiura, I. 1986. Nutritional disorders in persimmons. Growing Today, April issue.

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

Clark, C.J. and Smith, G.S. 1986. Leaf analysis of persimmons. Growing Today, February: 15-17.

Kitagawa, H. and Glucina P.G. 1984. Persimmon Culture in New Zealand. New Zealand DSIR Information Series No. 159, Science Information Publishing Centre, Wellington. pp. 74.