The quality of agricultural irrigation water, the parameters to consider, and pH all influence crop and soil quality.
Agricultural Irrigation Water
Ideally, plants would have rainwater, preferably fine water that meets their needs. This would also wash their leaves and improve their respiration.
However, this isn’t always the case, especially in the central and southern regions of the Iberian Peninsula.
Farmers are forced to compensate for the lack of rainwater with irrigation, and one of the problems they have to solve is whether the available water is suitable.
Pure water contains no salts and therefore does not conduct electricity. Its components are oxygen and hydrogen in the ratio H₂O. For this reason, to assess whether water contains salts, we examine its electrical conductivity.
Agricultural irrigation water is the main source of salts in the soil, in addition to fertilizers.
Parameters to Consider in Agricultural Irrigation Water
Let’s look at the parameters to consider in agricultural irrigation water in detail:
Salinity
This is the amount of salts in the water. The most common salt is sodium chloride (NaCl).
We say that water is fresh in rivers and lakes because the sodium chloride content is low.
Salinity varies with the rate of evaporation. The water that evaporates does not contain salts, and these accumulate in the soil.
- Salinity is measured by electrical conductivity in dS/m (deciSiemens per meter), which is the water’s ability to conduct electricity per meter.
- Comparing the conductivity results of irrigation water with rainwater, which has a conductivity of 0.15 dS/m, is a way to determine if it has a high salt content or not.
- In irrigation water, salinity typically ranges from 0.8 to 2.6 dS/m. In seawater, salinity ranges from 30 to 60 dS/m.
- Excess salts induce an ionic imbalance and stress in plants, leading to water scarcity. Salinity directly affects:
- Germination.
- Growth.
- It alters transpiration by reducing leaf growth.
- Leaf stomata are reduced.
- Flowering is delayed.
Sodicity
This is the amount of sodium concentrated relative to calcium and magnesium, which must be analyzed in the laboratory. It is measured in SAR, or the soil’s sodium absorption ratio.
Sodium tends to disperse the soil, especially clay particles. This blocks pores and increases the risk of waterlogging. The soil becomes compacted and poorly aerated, making it difficult for the plant to absorb water and nutrients.
Sodium salts increase pH.
pH or acidity/alkalinity issue
pH is a measure of acidity or alkalinity that indicates the amount of hydrogen ions present in water.
| Category | pH range |
|---|
| Low or acidic | pH ≤ 6.5 |
| Normal for irrigation | 6.5 ≤ pH ≤ 8.5 |
| High or alkaline | pH ≥ 8.5 |
Medición del pH
pH of irrigation water
pH range | Classification |
|---|---|
0 – 6 | Acidic |
7 | Neutral |
8 – 14 | Alkaline |
Color Scheme for Visualizing Water Accumulation – Acidic and Alkaline Environments in Irrigation Water pH
Importance of pH in Agricultural Irrigation Water
The pH of the water directly affects the crop.
- High pH: influences nutrient absorption because nutrients become insoluble and are not easily absorbed. The plant shows signs of nutrient deficiency, and the soil accumulates excess salts.
Accumulation will be greater as the agricultural irrigation water becomes more acidic.
- Low pH: seriously harms the roots and therefore the plant’s absorption. Soils with high acidity can make the plant toxic due to aluminum accumulation.
How to Lower pH:
We can add nitric acid, phosphoric acid, or sulfuric acid, which acts much more slowly on plant absorption. If the pH is acidic and we don’t raise it, the plants will show a potassium deficiency and later a nitrogen deficiency.
To Raise pH:
Caustic soda or caustic potash is used. We must raise the pH carefully; slightly acidic is better than more alkaline. If the pH is too alkaline, plants will experience iron and zinc deficiencies, and in the long term, phosphorus deficiencies.
We can easily measure pH with litmus paper strips. Simply compare it to the color chart to determine the acidity or alkalinity.
Problem of salt accumulation in the soil
When a plantation is irrigated, even with perfect water, salts accumulate, leading to soil salinity due to accumulation, as shown in the following diagram.
Types of water, accumulated salts, and the soil moisture bulb. Sensors/probes at two depths. 1-System. 2-Root system. 3-Soil moisture bulb. 4-Medium salinity zone. 5-High salinity zone. 6-Soil infiltration. 7-Transpiration. 8-Evaporation. 9-Drip irrigation.
We have already dedicated an article to the problem of salinity in intensive and super-intensive crops.
If we add low-quality water to the traditional problems caused by continuous irrigation, the problem worsens and crops suffer.
During hot periods, evaporation and irrigation increase, leading to greater salt accumulation.
If salinity is not controlled, the soil becomes increasingly less productive. We must maintain a balance between salt application and the salts needed by the crop to prevent soil accumulation.
Accumulated salinity is sometimes proportional to irrigation management. We must maintain rigorous control over both water quality and quantity, ensuring it meets the crop’s needs.
We can measure subsoil conductivity and moisture levels in real time using Plantae sensors and view the data on a mobile phone or tablet.
1- Sensors at two depths. 2- Drip irrigation with two pipes. 3- Flow meter. 4- Almond trees with agricultural irrigation water and salinity controlled by sensors/probes for soil moisture, temperature, and conductivity.
Plantae sensors help you control soil moisture and salt accumulation in crops.
CONTROLLING AGRICULTURAL IRRIGATION WATER.
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