The other day they were talking about some techniques to take advantage of the calcium and magnesium that the irrigation water carried . It seemed that we ate the world when you had water of not very good quality and we could save a lot of money. However, we must also have other anions and cations that are not so beneficial for our crops that our irrigation water can carry . 

One of the most serious problems facing agriculture could be, without any qualms, the progressive deterioration of our soils. It is the consequence of an intensive agriculture where we have done real outrages to our necessary but forgotten «creator of life».

And, of course, since we are talking about salinity , when we irrigate with saline or alkaline waters, we only make the soils worse. The direct consequence is a drop in production of everything we plant.

HOW MUCH DO WE LOWER PRODUCTION WITH SALTED WATERS?

To know this data, we have to pull the bibliography, a table that we have already put in other related articles such as electrical conductivity .

After this long table, we continue with the article.

The electrical conductivity measured basically the amount of salt with which we water, and many crops are paid based on a conductivity meter. It is something like controlling how much food is added to the soil so that the plants take advantage of it. However, it is not a standard that values ​​the quality of such food.

Based on this parameter, which we can know with conductivity meters, we can draw some conclusions, such as:

• Salt content in water (meq / L): CE (dS / m) 10
• Osmotic pressure of the final solution with which we irrigate (atm) = CE (dS / m) 0.36
• Salt content of the solution (mg / L): EC (dS / m) · 0.64 (at 25º C temperature)

The salt content of the solution is a very interesting piece of information, whether measured in meq / L or mg / L. This last value is very manageable and allows us to know, in a simple way, how many solids in salts we contribute for each liter of irrigation water.

WHAT CAN IRRIGATION WATER CONTAIN?

As we do not irrigate with distilled water, we add anions and cations to the soil . When said water has a large amount of an anion or cation, with total security we are unbalancing the soil solution, increasing the amount of elements that we will not need and that will become harmful , and reducing (by antagonism) others that we will miss. Does iron chlorosis sound familiar to you ?

CATIONS CONTRIBUTED TO THE SOIL EXTRACT FROM IRRIGATION WATER

The ones that we are going to find in greater quantity are:

• Ca2+
• Mg2+
• Na +
• K+

ANIONS CONTRIBUTED TO THE SOIL EXTRACT FROM IRRIGATION WATER

The ones that we are going to find in greater quantity are:

• Cl-
• HCO3 (2-)
• SO4(2-)
• CO3(2-)
• NO3-

Of this set of anions and cations , if any of them stands out above the rest, toxic reactions will occur for the culture or, blockages or immobilization of important elements for the development of the culture.

Of all these, the most common problems are derived from the high presence of chlorine , sodium and boron,  especially in desert regions or with little rainfall, since it is not possible to wash all these elements successfully.

WHY DO THEY ACCUMULATE IN THE SOIL AND BECOME TOXIC? 

Let’s put ourselves in a real situation that occurs daily on our soils. If we irrigate with a low amount of water (due to restrictions), there is a high evaporation rate and, on top of that, the water supplied is of poor quality and has a high content of these elements, when the heat takes effect and all the moisture accumulated in the Soil extract disappears, the salts will be concentrated in the upper layer of the soil .

If the rains are scarce or you do not have the opportunity to wash the soil (providing a large amount of water through irrigation), we will not be able to transport these salts to deep layers (where there are no roots). Therefore, the problem will still be there.

SODIUM PROBLEMS

If we pull the bibliography, we will come to the conclusion that sodium is not of much use in our plants either. Our plants, which are wise, have managed to develop a technique to prevent Na + from concentrating in the leaves and becoming toxic. However, in cases where the irrigation water is of very poor quality, we observe necrosis on leaves and necrotic spots .

Even more serious is the detrimental effect that sodium has on the soil. Apart from the toxicity generated on the plants, we seriously lose quality in the substrate. The sodium is calcium antagonist and in large quantities, find move or immobilize.

The same goes for magnesium. Therefore, the moisture retention capacity and the water-oxygen ratio of this are unbalanced.

Also remember that the more sodium is added to the soil, the more pH the extract will have and the greater the blocking of important elements for plants. See the following image:

At high pH  or alkaline soils  we will have absorption problems with nitrogen, calcium, magnesium, iron, manganese, copper, zinc, etc. It seems serious, right?

CHLORINE PROBLEMS

Irrigation water contains a lot (a lot of chlorine). Is a reality. Although it is not given importance because we always have it in abundant quantities, this element performs vital functions for the development of the crop, including photosynthesis .

However, a crop does not seem to need more than 0.5 meq / L in the saturated soil extract. However, the continuous application of poor quality water causes this value to multiply exponentially . Therefore, we have an excess of toxic chlorine for most plants. Let’s look at the problems:

• Lack of development in the plant (reduction of photosynthesis).
• Reduction of the water capacity or potential of the leaves.
• Lack of root development.
• Reduction in production due to lack of development in the fruits.
• Precipitous fall of leaves, flowers and fruits.
• Necrosis on the tips of the leaves (burns), due to excessive application of chlorides.

DIFFERENCE OF SALINE SOIL AND SODIUM SOIL

It is not the same to have a saline soil than a sodium soil . Both are equally bad, but it is not the same.

There are differences regarding the soil structure, the final pH of the extract, the permeability, etc.

Let’s see it.

CHARACTERISTICS OF A SODIUM SOIL

• Soil structure is generally bad.
• Aeration and permeability are reduced.
• A typical white crust forms.
• The pH of the soil extract is high, above 8.5.

CHARACTERISTICS OF A SALINE SOIL

• The pH is generally less than 8.5.
• The structure and permeability of the soil do not appear to be affected.
• The soluble salt content is high.

HOW TO SOLVE THESE PROBLEMS WITH IRRIGATION WATER?

Logically, the best solution is to irrigate with good quality water. However, it is clear that it is not done for pleasure and it is what it is. There are a few ways to alleviate this growing problem.

• Incorporation of organic matter in the soil to improve its structure.
• Reduce the soil pH in cases where this value is high.
• Apply plaster on soda floors.
• Plant crops tolerant to the medium conductivity of the soil.