This 2021-2022 harvest, together with the scarcity of water, the quality of the resource has plummeted: salinized aquifers and surface water from rivers and canals in the central zone with electrical conductivities of irrigation water that even exceed 2.5 mS/cm.
The salinity tolerance of avocado depends a lot on the type of rootstock, but for practical purposes, the maximum limit of EC of the soil (saturated paste) for Mexican Mexícola or Zutano rootstocks is 1.5 mS/cm. If we add to that the load of fertilizers to the soil solution, we are in trouble.
In this sense, the main problem are chlorides, these are absorbed by the roots and accumulate in the leaves. A leaf with a chloride level > 500ppm is already in trouble and its contribution to the photosynthesis/production system will be low. A leaf with levels > 1000 ppm of chlorides is almost intoxicated, in the senescence phase and its contribution to producing dry matter will be null and it will be difficult for the orchard to support the ideal fruit loads. Today there is much comment and evaluation of Reverse Osmosis to totally or partially purify irrigation water for avocado trees, a very effective solution but one that implies high investment costs in Capex. An osmosis plant capable of filling a 50,000 m3 reservoir in 30 days of operation with one hundred percent osmotic water costs no less than USD 1.2 million.
The use of West Indian rootstocks has been timidly increasing in Chile. Being an aspect that determines the success/failure of an orchard, its use should not even be questioned. In Israel, almost 15 years of avocado research led by Professor Ben Ya'acov of the Volcani Institute, focused on determining among hundreds of ecotypes the best rootstocks adapted to heavy, calcareous and high EC soils, and that showed the best yields: Dgania, Ashdot, Fairchild, Tzrifin are the main West Indian rootstock varieties marketed by nurseries globally.
In these lines we analyze one by one how they behave at the field level:
Ashdot is the salinity-tolerant pattern par excellence. Its root system tolerates high EC levels without affecting Hass foliage. It has a drawback, just as it tolerates salts, its roots are affected by the accumulation of salts and are very fragile under conditions of root asphyxiation. Therefore, it is recommended in well-drained sandy soils irrigated with well water or high EC.
Dgania behaves very similar to Ashdot, but tolerates salinity a little less
Tzifrin is a pattern that performs very well in clay loam soils (medium textures) and with slightly saline water. If we bought it with Ashdot, Tzifrin in loamier soils is a larger and more productive plant as long as salinity is not a problem.
Fairchild is the rootstock selected for heavy soil conditions, it has an exploratory and very vigorous root system, which does not retain salts but rather translocates them to the foliage, visually affecting Hass. Being a very vigorous plant, it defends itself against salts with vigor and renewing foliage.
On the other hand, companies such as Westfalia and Brokaw nursery have been working for years on the development of Clonal Rootstocks, which show excellent results in the field. The main advantage over West Indians at the field level is their greater resistance to root asphyxiation and greater tolerance to Phytophthora cinnamomi. Three are the best known and most widespread: Dusa, Duke 7, Toro Canyon.
The correct rootstock selection will depend on several factors, including how much you are willing to overcharge your field planting costs.
Together with these three prevention strategies is the technical strategy that means Irrigation with Washing Fraction (a strategy that has the same number of detractors as followers), Irrigation with a high wash load and fertilizing based on Nitrate - Chloride ionic antagonisms; This last strategy works well, it is and should be complementary to the use of salt-tolerant rootstocks and be used strategically to protect the fruit, especially during physiological falls.
It should be noted that finally salt toxicity will be regulated by the capacity of the rootstock roots and their resilience to water conditions. A good rootstock tolerates salts, "poisoning" its roots with chlorides and preventing them from ascending towards the Hass productive zone. Management that favors root renewal will be essential for sustainable production
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