The electrical conductivity of irrigation water

One of the most important things that condition any crop is the soil. However, the quality of said soil can be improved or worsened depending on the water that is supplied. Bad soil will improve if good quality water is continuously supplied. On the contrary, a good soil is easy to make worse if we always irrigate with saline and low-quality water. We are going to know these parameters with electrical conductivity .

This article is closely related to the one on << how to irrigate with saline water >>. An excess of salts in the water is not good in most cases. And as you can see, we say the majority because there are some cases where the salt content and electrical conductivity are played with to “improve” the flavor of the fruits. This is done a lot in grapes and in the RAF pata negra tomato grown in Almería, where they reach levels of  3 dS / m.

On the other hand, let’s try to get off to a good start by answering this question:

WHAT IS ELECTRICAL CONDUCTIVITY?

This term, which may sound quite complicated for the user who has a small garden, shows us the ability of water, in this case, to make electric current circulate freely .

As far as agriculture is concerned,  electrical conductivity is used to determine salinity levels. It can be measured from both water (liquid) and soil (solid). A saline soil makes us predict that, surely, the water is saline and the problem will get worse.

UNITS OF MEASURE

If we look at a water analysis we can see this measurement in different units, depending on the laboratory:

  • dS / m (deciSiemens per meter)
  • mmhos / cm (millimeters per centimeter)
  • mS / m (milliSiemens per meter)

ELECTRICAL CONDUCTIVITY, SALTS VS PLANT

What happens inside a plant when salinity increases? For this you have to touch some things about chemistry and plant biology. Let us begin.

A plant cell has water inside it. Said water is regulated by a semipermeable cell membrane .

It lets in and out of water according to its discretion depending on the saline concentration inside and outside the cell. This is determined by the osmotic pressure  , which, as you know, tends to equilibrium.

If there is water with a higher saline concentration outside the cell than inside the cell, an attempt is made to balance this difference by passing water from a lower concentration to a higher concentration.

Now, in the soil, the water around the roots has a higher electrical conductivity than inside the plant (as a general rule), if the crop wants to absorb water it needs to overcome the osmotic pressure.

That is why it is said that a crop is more or less resistant to salinity , which is nothing other than its ability to “suck” water. That is, the ability to overcome osmotic pressure.

In short, the more saline the water is (higher electrical conductivity), the greater effort the plant has to make to absorb said liquid). As a reminder we put this table to see the loss of the yield of each crop.

 

Yields100%90%75%50%0%
EXTENSIVEECeECwECeECwECeECwECeECwECeECw
Cebada (Triticum aestivum)85,3106,7138,718122819
Algodón (Gossypium hirsutum)7,75,19,66,4138,417122718
Sugar beet (Beta vulgaris)74,78,75,8117,515102416
Sorghum (Sorghum bicolor)6,84,57,458,45,69,96,7138,7
Wheat (Triticum aestivum) 4.6647,44,99,56,3138,72013
Trigo (Triticum turgidum)5,73,87,65106,915102416
Soybean (Glycine max)53,35,53,76,34,27,55106,7
Cacahuete(Arachis hypogaea)3,22,13,52,44,12,74,93,36,64,4
Rice (Oriza sativa)323,82,65,13,47,24,8117,6
Sugar cane (Saccharum officinarum)1,71,13,42,35,94106,81912
Corn (Zea mays)1,71,12,51,73,82,55,93,9106,7
Flax (Linum usitatissimum)1,71,12,51,73,82,55,93,9106,7
Broad bean (Vicia faba)1,51,12,61,84,226,84,5128
Alubia (Phaseolus vulgaris)10,71,512,31,53,62,46,34,2
VEGETABLES
Zucchini (Cucurbita pepo melopepo)4,73,15,83,87,44,9106,71510
Red beet (Beta vulgaris)42,75,13,46,84,59,66,41510
Brócoli, Brécol (Brassica oleracea botrytis)2,81,93,92,65,53,78,25,5149,1
Tomate (Lycopersicon esculentum)2,51,73,52,353,47,65138,4
Pepino (Cucumis sativus)2,51,73,32,24,42,96,34,2106,8
Espinaca (Spinacia oleracea)21,33,32,25,33,58,65,71510
Apio (Apium graveolens)1,81,23,42,35,83,99,96,61812
Col (Brassica oleracea capitata)1,81,22,81,94,42,974,6128,1
Patata (Solanum tuberosum)1,71,12,51,73,82,55,93,9106,7
Sweet corn (Zea mays)1,71,12,51,73,82,55,93,9106,7
Boniato (Ipomoea potatoes)1,512,41,63,82,564117,1
Pimiento (potato)1,512,21,53,32,25,13,48,65,8
Lettuce (Lactuca sativa)1,30,92,11,43,22,15,13,496
Rábano (Raphanus sativus)1,20,821,33,12,153,48,95,9
Onion (Allium cepa)1,20,81,81,22,81,84,32,97,45
Carrot (Daucus carota)10,71,71,12,81,94,638,15,4
Bean (Phaseolus vulgaris)10,71,512,31,53,62,46,34,2
Nabo (Brassica rapa)0,90,621,33,72,56,54,3128
FRUIT
Palmera datilera (phoenix dactylifera)42,76,84,5117,318123221
Pomelo (Citrus paradisi)1,81,22,41,63,42,24,93,385,4
Naranja (Citrus sinensis)1,71,12,31,63,32,24,83,285,3
Peach (Prunus persica)1,71,12,21,52,91,94,12,76,54,3
Apricot (Prunus armeniaca)1,61,121,32,61,83,72,55,83,8
Grape (Vitus sp.)1,512,51,74,12,76,74,5127,9
Almendra (Prunus persica)1,5121,42,81,94,12,86,84,5
Plum (Prunus domestica)1,512,11,42,91,94,32,97,14,7
Delay (Rubus sp.)1,5121,32,61,83,82,564
Fresa (Fragaria sp.)10,71,30,91,81,22,51,742,7

NOTE:

  • ECe  (Soil electrical conductivity) expressed in deciSiemens per meter (dS / m) of the soil saturation extract at 25ºC.
  • ECw  (Electrical conductivity of irrigation water) expressed in dS / m.

WHEN IS WATER SALINE AND WHEN IS IT NOT?

To know the growing problems of a saline soil and how it is going to affect the plants, we have to resort to this Urbano Lump classification:

  • EC <  0.7: no problem. [(millimhos per centimeter)]
  • 0.7 <EC <3: growing problem [ (millimhos per centimeter)]
  • CE> 3: serious problem. [ (millimeters per centimeter)]

However, it is necessary to clarify, since I have seen irrigated crops with electrical conductivity greater than 2.5 and 3  millimhos per centimeter and they do not have any problem of yield or loss of production.

This denotes that cultivation tasks are as important as the choice of fertilizers low in chlorine and sodium, washing, the contribution of organic matter, etc.

The continuous control of the irrigation water or of our pond is essential to know if we have to reduce the load of fertilizers so as not to stress our plant too much.

Although the pH of the water does not usually undergo variations, the conductivity (mS / cm) does, since it is a factor that depends on the wells where water is extracted, the rain (which reduces this value), etc.

Attentive to this parameter with any conductivity meter , an indispensable tool if a minimum of professionalism is required.

PS: as a curious example, I put an article where we put an irrigation system with … sea water!

Welcome to The GardenPure! My name is Ryan Heagle, and I’m the founder of The GardenPure, I spent the first part of my adult life teaching and then living in Australia in various business ventures, the first of which was a business devoted to the sale of house plants.  I am now a full time blogger. I am a self taught gardener.

Ryan Heagle

Welcome to The GardenPure! My name is Ryan Heagle, and I’m the founder of The GardenPure, I spent the first part of my adult life teaching and then living in Australia in various business ventures, the first of which was a business devoted to the sale of house plants.  I am now a full time blogger. I am a self taught gardener.

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