General fertiliser recommendations for strawberries (Fragaria spp.) are difficult to make because the cropping character varies markedly between regions. Past recommendations have been based on the belief that strawberries require large amounts of fertilisers. Repeated cropping on an annual replant system, which is commonly practiced in northern North Island regions, will require higher annual applications than longer plant retention systems. Fertiliser recommendations stated in this review are for production under annual replant cropping. For longer plant retention fruit nutrient removal estimations should be used to guide recommendations.

PLANT ANALYSIS
Generally, foliar nutrient analyses are better for assessing nutritional status than soil tests. Ideally, both should be used.

American nutrient monitoring has indicated that substantial nutrient accumulation occurs during fruiting. If a nutrient is limiting it is more likely to be detected during this period. Also, prior to this in a recently transplanted plant, most of the nutrients come from stored reserves within the crown and root system. Consequently, sampling should be done during fruiting, preferably at first harvest.

Approximately 50 youngest mature leaves should be selected at random throughout the area and separated from their petioles. Large plantings are best divided into halves or quarters and a sample taken from each area. Nutrient concentrations compiled from American surveys and limited local information are listed in Table 1.

SOIL TESTING
Strawberries grow well in soils with a pH range between 5.3-6.5. A pH around 6.5 is best with sandy textured soils whereas for finer textured soils a pH closer to 5.3 is preferable.

Suitable MAF soil test levels for this crop are P, 30-40; K, 15-25; Mg, 30-40; and Ca, 10-20.

FERTILISER REQUIREMENTS
Suggested maintenance fertiliser applications for annual replant strawberries are listed in Table 2. The rate for each element needs to be assessed separately depending on the previous soil use, whether or not the soil is of volcanic origin or whether nutrient disorders were evident in the previous season. Areas out of pasture, for example, may have adequate N fertility and require little or no applied N during the first season. Volcanic soils which have high allophanic clay contents (Yellow-brown loams), on the other hand, will require larger amounts of P than other mineral soils where the ability to interact chemically with added phosphate is much less.

Most fertiliser sources are suitable for application to strawberries with the exception of muriate of potash (KCl) and composite high analysis fertilisers containing chloride. Because of the sensitivity of this crop to chloride, irrigation water and fertiliser containing this element should be avoided. As a result of this, potassium should be used in the sulphate form.

FERTIGATION
With the increased use of under-mulch irrigation, the use of fertiliser application via the irrigation water (fertigation) will become more common to supplement a small basal fertiliser dressing. This is an efficient practice which can lower the fertiliser cost and improve crop performance. Fertigation enables dissolved fertiliser to be placed in the active root zone which is otherwise difficult to do because of the polythene mulch.

Generally, the fertiliser application rate can be halved if fertigation is used. However, until experience is gained, this technique should be adopted with caution and regular tissue analyses done to monitor nutrient levels. Also, soil tests before planting and after plant removal will indicate how soil nutrient levels have been influenced by fertigation.

NUTRIENT DISORDERS
The most likely disorders encountered in strawberry production are deficiencies involving K, P, Mg and N.

The first symptoms of K deficiency (K < 1.0%) appear on the upper leaf margins of the older leaves. The serration tips redden, the injury gradually progressing inwards between the veins until most of the leaf blade is affected. This is accompanied almost simultaneously by a symptom which appears to be unique to strawberries. The rachis (extension of the petiole to the central leaflet) darkens and dehydrates. The blade area either side of this tissue is similarly affected. Few runners are produced on K deficient plants. Those that are tend to be short and thin with few plants. Fruit are insipid, colourless, and pulpy.

Phosphorus deficiency (P < 0.1%) can be recognised by the dark green colour and black metallic-like sheen on the upper surface of leaves. The lower leaf surfaces may develop a reddish-purple tint which becomes evident on the upper surface of some varieties as the leaves become older.

Symptoms of Mg deficiency (Mg <0.1%) are similar to those for other crop species; tissue in the interveinal regions of older leaves which has an initial chlorosis eventually becomes necrotic as the deficiency progresses. In some instances, a marginal scorch forming a halo pattern can be observed near the base of the serrations on the older leaves.

Plants with mild N deficiency (N < 2.0%) have small chlorotic older leaves. More severe deficiencies cause shortening of the petioles which turn red and become brittle. Frequently, as the leaves and fruit calyxes age, they also become reddish, the leaves particularly so.

The symptoms of these and other nutrient disorders in strawberries are well described and illustrated in a publication by Ulrich et al. (1980). In addition, they also outline corrective measures to alleviate trace metal disorders which are less likely to arise in normal cropping situations. Fertiliser rates suitable for correcting the macronutrient disorders outlined above appear in Table 2.

FURTHER READING
Albregts, E.E. and Howard, C.M. (1980). Accumulation of nutrients by strawberry plants and fruit grown in annual hill culture. Journal of the American Society of Horticultural Science, 105: 386-388.

Boyce, B.R. and Matlock, D.L. (1966). Strawberry nutrition. In: Temperate to Tropical Fruit Nutrition (Childers, N.F., ed), Horticultural Publications, Rutgers - The State University, USA. pp518-548.

Johanson, F.D. (1981). Nutrient deficiencies in strawberries. In: The Strawberry - Cultivars to Marketing (Childers, N.F., ed), Horticultural Publications, New Jersey, USA. pp514.

Ulrich, A., Mostafa, M.A.E. and Allen, W.W. (1980). Strawberry Deficiency Symptoms: A Visual and Plant Analysis Guide to Fertilisation. University of California, USA. pp58.