Soil cation ratios for pip fruit, or other crops, have not been calibrated against growth or yield for any soil/crop system in New Zealand. It is clear that many crops tolerate quite wide variations in these ratios hence an alternative approach is to apply the fertiliser required for adequate growth and crop removal and monitor the nutritional status with leaf analysis.

Soil sampling is best carried out in autumn or early winter. In orchards where fertiliser is broadcast, samples (0-20 cm) should be taken at random under the drip zone. In cases where fertiliser has been banded, the samples should only be taken in areas under the drip zone which have previously received fertiliser. Occasional samples at depths of 20-40 and 40-60 cm are useful to check pH.

FERTILISER REQUIREMENTS
Nitrogen use in pip fruit orchards should be based on the inherent fertility status of the soil. On deep fertile alluvial soils N need not be applied unless low foliar N concentrations, poor fruit set-biennial bearing problems or pale fruit problems in green varieties occur. On soils of average fertility annual rates as high as 300 kg N/ha have been advocated although 80-120 kg N/ha should have been sufficient in most circumstances. On soils of low fertility application rates should be based on 25 kg N/ha/10 tonne of crop once plateau yields have been reached.

Rates for P and K, (Table 2) are based on the soil fertility status. Use of potash needs to be approached with caution. Excessive applications of K tend to depress Ca and Mg uptake and increase the incidence of Ca related disorders in fruit and Mg deficiency.

NUTRIENT DISORDERS
There are no peculiarities that set the visual symptoms of nutrient disorders in pip fruit apart from those of other crops (see Introductory Section for symptoms of nutrient deficiencies). The most common disorders affecting pip fruit production in New Zealand are the deficiencies of N, Mg, Ca, Mn, Zn and B.

Good N status over the blossom/fruit set period is essential and shortages at this stage of development can lead to poor fruit set and accentuate biennial bearing. With some varieties, the threshold for fruit set may be higher than that required for vegetative growth. Pears and certain green apple varieties such as Granny Smith appear to have higher N requirements than red or quarterly colored varieties. With these latter varieties, high N levels tend to reduce fruit colour so N fertiliser needs to be used with caution and only sufficient applied to maintain regular fruit set.

Magnesium deficiency (Mg<0.12%) has been particularly prominent in young nashi orchards outside of the Hawkes Bay-Poverty Bay region. With this disorder patches of necrotic tissue gradually develop in the interveinal tissue of older leaves from mid summer onwards. Soil applications of Kieserite at 500 kg/ha, or Epsom salts (MgSO₄) or Causmag at rates of 200 kg Mg/ha are suitable long term corrective measures. Successive foliar applications of 1-2 kg MgSO₄/100l) are beneficial for alleviation of deficiency symptoms on a season by season basis.

Zinc deficiency (Zn<10 ppm) is occasionally seen in parts of Central Otago and Canterbury and may be corrected with sprays of zinc sulphate (1-2 kg/100l) during dormancy or regular sprays of Zinc in the fungicide programme. Zinc chelates are also suitable for foliar application.

Manganese deficiency is occasionally seen, but in pip fruit Mn toxicity symptoms are more common. These occur on very acid soils, or heavy clay soils with poor drainage and may be overcome by correction of drainage and pH problems. Where deficiency occurs it can be overcome by lowering the soil pH through use of acidifying fertilisers, or with early season sprays of manganese sulphate plus lime at concentration of 600 g MnSO₄ plus 800 g hydrated lime/100l).

Boron is the only common trace element deficiency occruing in pip fruit orchards in New Zealand. Boron deficiency is usually associated with the development of internal cork tissue similar to bitter pit. It can be distinguished from the latter disorder (which results from the presence of inadequate Ca in the fruit) in that the cork tissue tends to extend right into the core zone. Sometimes external fruit distortion is present and this may be associated with fruit russet or cracking. Symptoms of deficiency while evident in the fruit, may be absent on the foliage. Twig dieback symptoms and visual symptoms on the foliage may be observed where new pip fruit orchards have been established on soils containing very low levels of B. Nashi cultivars such as Nijisseiki and Shinseiki are susceptible to B deficiency, corky spots developing in the flesh at the calyx end of the fruit. These taste bitter and are undetectable from the exterior of the fruit. With pears the predominant symptom is blossom blast in which the blossoms may wilt, die, or fail to burst. the symptoms accur randomly, rarely affecting more than 10-20% of the trees in an orchard and are usually confined to 1-2 leaders per tree.

On soils with an established history of B deficiency (eg, in the Nelson region ) annual dressing of borax (10 kg/ha) are necessary. Early season sprays of boric acid (100 g/100 l) or borax (200 g/100 l) are alternatives to soil application.

Attempts to increase B levels in nashi fruit by foliar applications of borated compounds have proved unsuccessful in Japan although it is not known if early season sprays were tried. Japanese recommendations for correction of B deficiency in nashi orchards (B<13-18 ppm in mature leaves) determined by hot water extraction, should be above 0.3 ppm B. Deficiency symptoms are associated with soluble B levels of less than 0.2 ppm B.

Like B, deficiencies involving Ca are manifest in fruit without the appearance of visual symptoms on foliage. Good subsoil Ca levels are thought to reduce the incidence of bitter pit. Hence on acid, low Ca soils, deep incorporation of lime pre-planting followed by regular lime applications of at least 2.5 tonne/ha every 2-3 years are suggested. Potash imputs should also be reduced if bitter pot occurs through over fertilization with K.

With most apple varieties, foliar sprays of calcium nitrate (600 g/100l) or calcium chloride (400 g/100l) can be used as an aditional means of elevating fruit Ca levels. A minimum of six sprays should be applied at regular intervals during the period from early December through to harvest to be effective. Chemical analysis of fruit can be used to predict the likelihood of bitter pit occurring. Standards for optimum Ca concentrations in particular cultivars are not widely available however, and it is not usual for growers to request this type of analysis.

Similar strategies need to be adopted to control 'hard flesh' Ca disorders in nashi, Ussurian pea pear rootstock (P. betulaefolia) is recommended where Ca deficiency is likely to occur in poorly drained orchards. Removal of young extension shoots in November-December, and thinning of flowers and immature fruit are also practices advocated by the Japanese to control Ca deficiency in fruit. There have been indications from New Zealand work that where Ca sprays at concentrations suitable for bitter pit control have been applied to Hosui and Kosui, significant foliar damage has resulted. The Japanese recommend that foliar application to Asian pears. At the present time however the timing and concentration of these sprays is not known.

FURTHER READING
Boynton, D. and Oberly, G.H. (1966). Apple nutrition. In: Temperate to Tropical Fruit Nutrition. (Childers, N.F.,Ed), Horticultural Publications, Rutgers - The state university, USA, pp. 1-50

Clark, C.J. and Kajiura, I. (1986). Nutritional disorders in nashi. Growing Today, February: 11-13

Edmeades, D.C. (1984). The use of the base cation saturation ratio concept for making fertiliser recommendations on soils in New Zealand. New Zealand Soil News, 34: 147-151