Irrigation Organic Fruits

Many growers are able to produce commercial crops of apples and pears on semi-vigorous and vigorous rootstocks without irrigation. However, trees on dwarfing rootstocks (particularly pears), are very sensitive to drought and will perform poorly in years of insufficient soil moisture and excessive competition from a grass sward. In dry years, or where there is competition from the sward, irrigation from mid-May to mid-June may be necessary to achieve good tree growth and again from mid-July to mid- August to improve fruit size in established trees. Irrigation may also be of benefit during dry autumns, to help the trees build reserves for cropping I e following year. Light or shallow soils will benefit from a 'little and often' approach to irrigation. Calculating water requirements of crops is beyond the scope of this book, but there are many companies offering professional advice on the deployment and use of irrigation to meet individual grower requirements.

Should be remedied accordingly. An application of nitrogen will usually be required early in the season before flowering, as soil microbial activity is low at this time due to low soil temperatures. Care should be taken not to over-apply nitrogen during mid-summer or late in the season, as this can lead to fruit let abscission and excessive vegetative growth, which will be disease-prone, together with soft sappy wood that does not lignify properly before winter, thus reducing winter-hardiness. An over-application of nitrogen, whilst often resulting in increased yield, can also lead to deterioration in fruit eating quality and storage potential in apples, although pears are less affected.

Additional nitrogen and potash are often required during the growing season, especially where mulches are not used. However, applying additional fertilizers to trees growing directly in a grass sward may do nothing more than feed the grass, therefore foliar feeds, applied shortly after petal fall while leaves are still young but well developed, are often of benefit. Where trees are growing in a pure grass stand (or where the sward is predominantly grass), the sward should be kept short in order to minimize competition for water and nutrients during critical periods of fruit swelling and ripening. Otherwise, swards containing mixed species such as clovers may be allowed to flower, which will encourage beneficial insects. Keeping the sward under control before harvest will aid picking, although it is often difficult to mow around trees that have heavily laden and drooping branches.

Soil fertility and crop nutrition (together with symptoms of nutrient deficiency) are discussed further in Chapter 2. Full guidance on the satisfactory nutrient ranges for plant nutrients can be obtained from Defra: Fertiliser Recommendations for Agricultural and Horticultural Crops (RB209), Seventh Edition (2000), 'Section 6: Fruit, Vines and Hops'. Although based on conventional production, the figures give a good indication of the optimum levels of nutrients required.