Drip irrigation is one of the most popular forms of irrigation available today. In contrast to other popular forms of irrigation, it’s one of the most water-efficient systems available. However, many feel the benefits come with an increased risk of salinization.
Drip irrigation causes salinization. However, this feature isn’t unique to drip irrigation. Due to the natural trace amounts of salt in water, every form of irrigation will eventually raise the salt content of the soil.
The rest of this post will go into a lot more detail about salinization as it relates to irrigation and how to stay on top of both. Keep reading to learn more.
Irrigation and Salinization
Irrigation almost always leads to increased salts in the soil. As trace amounts of different salts are always present regardless of the type of irrigation you choose, salinization is essentially a necessary evil. However, not all forms of irrigation are created equal, and some do significantly more damage than others.
The best irrigation to reduce salinization is drip irrigation. Like all types of irrigation, drip irrigation also risks increased salinity. However, good drip tape management combined with reduced water use makes it easier to manage salinization.
It’s important to note that most of the time, salts present in the soil do very little damage, if any, to crops. Since salts are always present, it would be almost impossible to plant anything if they constantly interfered with plant growth.
Instead, salts accumulate over time until they reach a particular threshold. Once they’re at this threshold, they start to affect plants negatively. To effectively choose the best irrigation to combat salinization, one major thing to consider is this threshold and what form of irrigation would be best to adopt.
The Role of Drip Irrigation
Drip irrigation is a form of irrigation where water is passed to plants dropwise. This procedure is done by using pumps and pipes, similar to most other forms of irrigation. However, where drip irrigation differs is with the use of drip tapes.
Drip tapes are attachments to irrigation piping that force water to pass through them dropwise using attached emitters. The frequency and total irrigation time are dependent on a lot of factors. Still, regardless of the time involved, drip irrigation is famous for achieving similar results to other irrigation methods even though it uses far less water.
There are two significant ways that drip irrigation combats salinization:
Reduced Water Use
As previously mentioned, drip irrigation is famous for being effective on plants and extremely water efficient. Although this is good for your pocket in terms of water bills, it also positively affects salinization.
There are almost always dissolved salts in water. As a result, the more water you use, the more salt gets to your soil. On the other hand, using less water also means lower salt accumulation over time.
From this point, you can start to draw a clear parallel and see why drip irrigation is so good if salinity is a problem you’re worried about. Because it uses significantly reduced amounts of water, the reduction in salinity problems is inherent.
Localized Watering
Another benefit of drip irrigation is localized watering. Emitters release water that spreads outwards in a circle as the soil absorbs it. This outward movement of water moves a lot of the salt content away from its epicenter.
Measuring the salt content at different points shows that close to the center, the concentration is similar to the water concentration in the emitter. However, as you move towards the edges, the concentration rises significantly.
This concentration gradient, combined with the placement of multiple emitters, ensures that the highest concentration of salts is halfway between successive emitters. This feature is vital for the emitter and crop placement.
Provided you can place your crops in rows that keep them close to the center of the circle, they’ll be protected from most salinization effects. With enough time and frequent irrigation, the salts eventually get pushed deeper into the soil and away from the plants. Finally, heavy rainfall is enough to leach the rest of it out.
It’s important to understand that this feature doesn’t reduce the total amount of salts present in the soil. Instead, it works by keeping the highest salt concentration away from the plants.
Salinization Management
Salinization can be a horrible development for your soil and plants. With the ever-present introduction of salts to your soil, it might seem like there’s no way around it. Although salinization can’t be stopped entirely, it’s possible to slow it down.
Leaching is the best way to control salinization in the soil. It is the slow removal of water-soluble compounds in the soil by irrigating and allowing a particular amount of water to drain away. The water leaches the salts deeper into the soil until a drain carries the effluent.
Leaching is by far the most common and most active method to reduce salt content in the soil. To do this, farmers irrigate their land with about 10-20% more water than they need or allow the same amount of their normal irrigation water to drain. The water saturates the soil, moving downwards and taking the dissolved salts with it.
The water moves lower into the soil, dragging along previously dried salts until it empties from a drain. The drained concentration of soil is usually the inverse of the amount of water drained.
For example, 20% water would give you an effluent concentration close to five times the original concentration (20/100 = 1/5, 5/1=5).
The main downside to leaching is that water movement is indiscriminate and doesn’t choose between beneficial nutrients in the soil and salt. As a result, excessive leaching will, with time, reduce the overall nutrient density in the ground.
To counteract this problem, it’s essential to apply fertilizers to your soil periodically. Fertilizers are one of the best ways to make nutrients available for your soil.
Along with leaching, there are a few other ways to control soil salinization:
Proper Watering
There are two major benefits of watering your plants properly. First, new water introduces moisture to the soil. Moisture is critical for plant growth, but it’s also crucial because it rehydrates dried salts in the ground.
As water evaporates from the soil, it leaves behind these salts, and as plants feed, there’s a net movement of nutrients and salts towards them.
The downside of this is not that the plants absorb the salts. Rather, the accumulation of soil in the root zone can limit the amount of nutrients that plants can take in through osmosis. Water would normally move into the root hairs due to a concentration gradient, but this becomes a lot more difficult because of the increased salt presence.
Because of this, it’s important to water your plants frequently and adequately. Frequent watering rehydrates the salts and moves them away from plant roots, provided your irrigation setup is done well.
In addition, adequate watering is important. There’s not enough water to leach the salts if you underwater your plants. However, if you overwater your plants, you introduce excess salts to the soil, which will increase salinity over time.
It’s important to find a proper balance when watering, especially if the water you use is naturally high in dissolved salts. A good rule of thumb is to use enough water to feed your plants, then add about 10 – 20% extra to promote leaching.
Effective Drainage
Drainage is an essential part of leaching. It’s important to allow some of your effluent water to drain away. Since the higher salt concentration is found at the outward boundary of water absorbed into the soil, the excess water drained contains a significantly higher amount of salt.
Plant Selection
If the salt content of the soil where you’re located is particularly high, it might be best to look into some salt-tolerant crops. Not all plants are affected by salts in the same way. Although it’s bad across the board, some plants fare better in saline soils than others.
A few examples are:
- Asparagus
- Barley
- Corn
- Wheat
- Artichoke
The Detrimental Effects of Salinization
With all the talk about salinization, it’s important to know why it’s as bad as we’re treating it and its effect on plants. Increased salt content comes with various problems, but among them all, one stands out significantly.
Salinization is bad because it reduces water uptake in plants. Increased salts in the soil skew the concentration gradient in plants, reducing the osmotic potential of roots to take in water from the soil. With time, the plants will start to wither and, without intervention, die.
Salinization also causes other problems, such as:
- Ionic imbalance
- Spoilage of drinking water
- Photosynthesis inhibition due to decreased carbon dioxide content
- Stunted growth
Conclusion
All forms of irrigation will, with time, increase salinity in the soil, and drip irrigation is no different. However, drip irrigation is one of the best forms of irrigation if reducing salinity is a goal for you.
Regardless of the type of irrigation you choose, it’s always important to implement activities that make it easier to cope with salinity, like leaching and controlled watering.
