We are all clear that quality irrigation water is not unique. Depending on the crop, soil type, or climate, quality irrigation water considerations can vary. Even so, the excess of salts in the irrigation water is usually a problem but sometimes there is no more water than there is and it cannot be avoided. We are going to give some recommendations for irrigation with saline waters.
IRRIGATION RECOMMENDATIONS WITH SALINE WATERS
The quality of irrigation water attends to numerous factors that will influence the plant soil environment in a significant way. If we talk about small gardens the influence will go unnoticed. The matter changes when we have several hectares to irrigate. There the yields will be significantly affected according to the quality of the irrigation water. We briefly note the variables that determine the quality of irrigation water:
- Dissolved gases: The water contains in dissolution mainly the gases of the atmosphere (nitrogen, oxygen and carbon dioxide). This dissolution of gases will affect the composition of the soil system. Sprinkler irrigation and surface irrigation provide more gases than irrigation that goes through pipes or drip irrigation.
- Temperature: We have already seen the influence of irrigation in preventing frost or heat stroke depending on the season. An example: Watering with cold waters (10ºC for example) in the middle of summer at noon, in a warm climatic zone, generates a thermal shock in the root system that reduces its capacity to absorb water and nutrients.
- Suspended elements: The clearest example is the difference between surface waters of the riverbed and underground waters. The former will carry a greater amount of inorganic and especially organic suspension elements than the underground ones.
- Salinity: The most determining factor in the quality of irrigation water is undoubtedly salinity. Disorders generated in non-salinity tolerant crops are a major problem in agriculture. Yields can drop dramatically.
AMOUNT AND TYPES OF DISSOLVED SALTS
In saline waters, it is necessary to know the amount of dissolved salts as well as their composition . The types of dissolved salts can be many (sodium, magnesium, calcium among others) and it is necessary to know the concentrations of each of them. The electrical conductivity is an indicator of the amount of dissolved salts. To know the compositions a laboratory analysis is necessary .
When irrigating with saline water, it is not the water itself that can be harmful but its accumulation in the soil . The climatic zones with greater annual precipitation than evapotranspiration do not suffer from accumulation of salts as long as the drainage is adequate . These accumulations usually occur in climatic zones where evaporation and transpiration are greater than the annual rainfall, that is, in warm zones with a semi-arid or arid climate.
I DON’T HAVE MORE IRRIGATION WATER THAN I HAVE, AND IT’S SALINE. WHAT DO I DO?
This situation is more normal than it seems. If we have no choice but to irrigate with saline water, we must know which crops are the most tolerant and follow some guidelines that help alleviate the effects of salinity. We highlight:
Early stages of development: Crops in their youngest stages are generally less tolerant of salinity. A protected and controlled planting with less brackish water helps proper germination and emergence. The sowing in ridges favors the emergence and will be a way to help the plant when the water is not adequate for that crop.
Soil drainage: It is a very important aspect to irrigate with saline waters. At the entrance that we dedicated to the drainage of the soil, we saw how necessary it was to have a soil with adequate drainage. In irrigation conditions with saline waters this changes. A good drainage system is essential.
Soil humidity control: Humidity must be kept as constant as possible and close to field capacity or even somewhat higher. This means that the soil must contain as much available water as possible even reaching saturation. The problem derived from this situation is the risk of waterlogging if the soil does not drain well enough. Hence the previous point is important.
Soil leveling: This is always important and more in cases of saline waters due to their accumulation in low profiles of the terrain.
KNOW THE TOLERANCE OF A CROP TO SALINITY
Measuring a crop’s tolerance to salinity is very relative. Tolerance classifications usually attend to the yields obtained from a crop under certain salinity conditions. In other words, there is no optimal irrigation water for every crop. There are crops whose performance will be more affected than others for the same water salinity.
FAO proposes a table showing the relative tolerance of crops to salinity, expressing it in potential crop yield (100%, 90%, 75%, 50%, 0%). 0% is the maximum salinity limit that the crop supports since growth is totally inhibited.
The expression of salinity is given in:
- 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.
|Cebada (Triticum aestivum)||8||5,3||10||6,7||13||8,7||18||12||28||19|
|Algodón (Gossypium hirsutum)||7,7||5,1||9,6||6,4||13||8,4||17||12||27||18|
|Sugar beet (Beta vulgaris)||7||4,7||8,7||5,8||11||7,5||15||10||24||16|
|Sorghum (Sorghum bicolor)||6,8||4,5||7,4||5||8,4||5,6||9,9||6,7||13||8,7|
|Wheat (Triticum aestivum) 4.6||6||4||7,4||4,9||9,5||6,3||13||8,7||20||13|
|Trigo (Triticum turgidum)||5,7||3,8||7,6||5||10||6,9||15||10||24||16|
|Soybean (Glycine max)||5||3,3||5,5||3,7||6,3||4,2||7,5||5||10||6,7|
|Rice (Oriza sativa)||3||2||3,8||2,6||5,1||3,4||7,2||4,8||11||7,6|
|Sugar cane (Saccharum officinarum)||1,7||1,1||3,4||2,3||5,9||4||10||6,8||19||12|
|Corn (Zea mays)||1,7||1,1||2,5||1,7||3,8||2,5||5,9||3,9||10||6,7|
|Flax (Linum usitatissimum)||1,7||1,1||2,5||1,7||3,8||2,5||5,9||3,9||10||6,7|
|Broad bean (Vicia faba)||1,5||1,1||2,6||1,8||4,2||2||6,8||4,5||12||8|
|Alubia (Phaseolus vulgaris)||1||0,7||1,5||1||2,3||1,5||3,6||2,4||6,3||4,2|
|Zucchini (Cucurbita pepo melopepo)||4,7||3,1||5,8||3,8||7,4||4,9||10||6,7||15||10|
|Red beet (Beta vulgaris)||4||2,7||5,1||3,4||6,8||4,5||9,6||6,4||15||10|
|Brócoli, Brécol (Brassica oleracea botrytis)||2,8||1,9||3,9||2,6||5,5||3,7||8,2||5,5||14||9,1|
|Tomate (Lycopersicon esculentum)||2,5||1,7||3,5||2,3||5||3,4||7,6||5||13||8,4|
|Pepino (Cucumis sativus)||2,5||1,7||3,3||2,2||4,4||2,9||6,3||4,2||10||6,8|
|Espinaca (Spinacia oleracea)||2||1,3||3,3||2,2||5,3||3,5||8,6||5,7||15||10|
|Apio (Apium graveolens)||1,8||1,2||3,4||2,3||5,8||3,9||9,9||6,6||18||12|
|Col (Brassica oleracea capitata)||1,8||1,2||2,8||1,9||4,4||2,9||7||4,6||12||8,1|
|Patata (Solanum tuberosum)||1,7||1,1||2,5||1,7||3,8||2,5||5,9||3,9||10||6,7|
|Sweet corn (Zea mays)||1,7||1,1||2,5||1,7||3,8||2,5||5,9||3,9||10||6,7|
|Boniato (Ipomoea potatoes)||1,5||1||2,4||1,6||3,8||2,5||6||4||11||7,1|
|Lettuce (Lactuca sativa)||1,3||0,9||2,1||1,4||3,2||2,1||5,1||3,4||9||6|
|Rábano (Raphanus sativus)||1,2||0,8||2||1,3||3,1||2,1||5||3,4||8,9||5,9|
|Onion (Allium cepa)||1,2||0,8||1,8||1,2||2,8||1,8||4,3||2,9||7,4||5|
|Carrot (Daucus carota)||1||0,7||1,7||1,1||2,8||1,9||4,6||3||8,1||5,4|
|Bean (Phaseolus vulgaris)||1||0,7||1,5||1||2,3||1,5||3,6||2,4||6,3||4,2|
|Nabo (Brassica rapa)||0,9||0,6||2||1,3||3,7||2,5||6,5||4,3||12||8|
|Palmera datilera (phoenix dactylifera)||4||2,7||6,8||4,5||11||7,3||18||12||32||21|
|Pomelo (Citrus paradisi)||1,8||1,2||2,4||1,6||3,4||2,2||4,9||3,3||8||5,4|
|Naranja (Citrus sinensis)||1,7||1,1||2,3||1,6||3,3||2,2||4,8||3,2||8||5,3|
|Peach (Prunus persica)||1,7||1,1||2,2||1,5||2,9||1,9||4,1||2,7||6,5||4,3|
|Apricot (Prunus armeniaca)||1,6||1,1||2||1,3||2,6||1,8||3,7||2,5||5,8||3,8|
|Grape (Vitus sp.)||1,5||1||2,5||1,7||4,1||2,7||6,7||4,5||12||7,9|
|Almendra (Prunus persica)||1,5||1||2||1,4||2,8||1,9||4,1||2,8||6,8||4,5|
|Plum (Prunus domestica)||1,5||1||2,1||1,4||2,9||1,9||4,3||2,9||7,1||4,7|
|Delay (Rubus sp.)||1,5||1||2||1,3||2,6||1,8||3,8||2,5||6||4|
|Fresa (Fragaria sp.)||1||0,7||1,3||0,9||1,8||1,2||2,5||1,7||4||2,7|
With this we can get a rough numerical idea of the salinity tolerance of a few crops. But as we say, all this is indicative because factors such as climate, soil or agricultural practices influence tolerance. We have only extracted some of the crops. If you want to see the rest, go to table number 4 of the following FAO link .