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volume. The effect of a correct irrigation schedule is measured by tree growth and yield, since incorrect watering affects the tree water status and its physiology.

Flood or furrow irrigation (surface irrigation) has historically been used in many citrus-growing regions. The water loss in such systems is high and its efficiency poor (about 30-35 per cent). The labour needed is also expensive. The pipe line system has improved water efficiency (more than 70 per cent) by reducing losses. Reduction of labour is consequent. Under soil and over soil pipes are now used in many citrus-growing areas.

The sprinkler system is popular in many countries where water is sufficient and its cost low. Microirrigation systems have been developed for zones where watering is problematic for some reason (shortening, cost, etc.). Microirrigation is based on the concept of wetting limited surfaces and soil depths where roots are obliged to grow. Water efficiency is high. Low pressure emitters (1.5—1.6atm) deliver low water volumes at frequent intervals. Microsprinkler emitters release 40—801/h, a drip emitter only 4-81/h. Low-pressure lines allow the use of fertirrigation (see fertilization chapter). They need an efficient water filtration system.

Water quality must be checked before planting and samples taken in the critical period (second part of the dry season), when dissolved salts are more concentrated. The choice of rootstock depends on water quality, since, as we know, there are rootstocks which are more or less tolerant to salinity. Chloride, sodium and boron are the most frequent elements found in irrigation water. They are a limiting factor to the growth of citrus trees and their effects can be detected on leaves. The negative effects of salinity are reduced in porous soils and by delivering abundant amounts of water from time to time to leach salts in depth. Water quality can be measured by various methods: total salinity, chloride percentage, electric conducibility. FAO suggestions are reported in Table 3.3.

Table 3-3 Soil and water irrigation salinity (mmhos/cm) related to decrease in yield (%)

ECe

ECw

Decrease

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Aromatherapy Ambiance

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