Crop yield response to water - Cra

Lead AuthorRaúl Ferreyraand Gabriel Selles(INIA, Santiago, Chile)Contributing AuthorElias Fereres(University of Cordoba andIAS-CSIC, Cordoba, Spain)AvocadoIntroduction and BackgroundAvocado (Persea americana Mill) is a tree that has been known forcenturies in areas of Central and South America, but only recently hasbecome a commercial crop. In 2009, there were over 430 000 ha ofcommercial plantings with a world average yield of 8.8 tonne/ha, with Mexico(100 000 ha), Chile and the United States as the main producing countries.Other countries with significant exports are South Africa, Spain, and Israel(FAO, 2011). Figure 1 presents the production trends of the main producingcountries. Avocado fruit yields are comparatively low relative to those of otherfruit trees because of the high energy requirements of producing fruit, becauseof both its large seed size and its composition, rich in oil (Wolstenholme,1986). Average yields of the variety Hass, one of the most popular commercialcultivars, are around 12 tonne/ha, but may reach 25 tonne/ha in very goodyears, with the fruit containing up to 20 percent oil. There are three avocadoraces: Mexican, Guatemalan and West Indies, with different sensitivity in theirresponses to the environment. Avocadoes have evolved in volcanic soils thathave very low bulk density, acid pH, and very high pore volume. It is thereforenot surprising that this species is extremely sensitive to waterlogging and doesnot do well in heavy soils with aeration problems. Planting on berms or ridgesis customary when feasible to improve drainage around the areas close to thetrunk base. For this reason, sandy rather than heavy soils are preferred forplanting avocados. Avocados are also very sensitive to low temperatures, andeven light frosts (temperatures below -1 to -2 ºC) may cause significant damage.Among the three races, the Mexican is most tolerant to cold temperatures, asit originated in the cool highlands of Mexico.Growth and Development in Relationto Yield Determination.Vegetative growth occurs in two flushes; a strong one in spring and aweaker one in the autumn. Flowering occurs in spring (between earlyOctober and mid-November in the Southern Hemisphere) and is followedby fruit set. Heavy fruit drop takes place during the first 3-4 weeks afterfruit set, at the end of spring, leading to a first adjustment in fruit number,which is further adjusted with an additional fruit drop period, which takesplace around the end of summer, when fruit size is between 10-40 percentof mature size. Figure 2 depicts the developmental stages of the cultivarHass in Central Chile showing also two root growth periods occurring inearly summer and at the beginning of fall.442crop yield response to water