Agriculture Reference
In-Depth Information
and to citrus blight. In the Mediterranean area, increasing interest is being shown in
Citrumelo CPB4475 selection.
Citrus macrophylla
Wester, also named 'Alemow', produces vigorous and pro-
ductive trees, but has some serious limitations, such as sensitivity to nematodes,
and CTV and other virus diseases, and to blight. With the exception of lemons, the
internal quality of most varieties is poor on macrophylla. Since lemon/macrophylla
trees do not developed CTV disease, 'Alemow' is recommended for lemons in some
citrus producing areas.
Edaphoclimatic Requirements for Production
and Improved Fruit Quality
Environmental factors include climate (temperature, wind, rainfall, hail), gas ex-
changes, soil quality, orchard location (altitude and latitude) and pollution. Others,
such as drought, salinity, brightness of light, are consequences of the former factors.
Some of these factors are necessary for production and quality, but sometimes be-
come damaging and reduce yield and fruit quality. Climate is the major factor deter-
mining crop load and internal and external fruit quality. For further information see
reviews by Agustí (
1999
;
2003
), Davies and Albrigo (
1994
), Jones and Embleton
(
1973
), and Reuther (
1973
).
Soil Requirements
Citrus trees can be grown satisfactorily on a wide range of soils. They only need
soil as physical support and as source of essential elements, oxygen and water. Both
physical and chemical soil characteristics determine the ability of the soil to supply
these materials.
Clay soils reduce root development. Roots are shorter and less developed than
those developed in sandy soils. Comparing clay and sandy soils, the former develop
smaller sized fruits of thicker and rougher peel, lesser juicy, but of higher TSS and
vitamin C content.
Citrus trees need soils of good drainage. Accumulation of free water in the root
zone results in poor aeration and root injury. Soil permeability between 10-30 cm h
−1
is considered optimum for citrus growth; values higher than 40 cm h
−1
and lower
than 5 cm h
−1
make the soil unprofitable.
Satisfactory soil depth for the growth of citrus roots may be limited by the pres-
ence of parent rock in residual soils, or the cemented stratum or a tight clay layer
in old alluvial ones. Because the physical and chemical make-up of the soil varies
markedly with depth, one portion of the root system may be in well-aerated topsoil
and another in poorly aerated subsoil. Thus roots are under decreasing oxygen sup-
ply and both direct and inverse mineral-nutrient gradients with increasing depth.
