Soil salinity control

Sometimes dirt gets too salty.

This salt can hurt plants. It comes from water used for farms. When that water dries up, salt stays behind.

This can make it hard for crops to grow. We can fix this by washing the dirt. We use extra water to carry the salt away. This water flows out through a drain. This helps the plants stay healthy and strong.

It is a good way to help the land.

Sometimes, soil gets too much salt. This is called soil salinity.

When this happens, plants may struggle to grow. This is a big problem for many farms. About 20% of irrigated lands are affected.

How does salt get into the soil? One main way is through irrigation. This is when farmers use river or groundwater for crops. All water has some salt in it. When the water dries up, the salt stays behind.

Another cause is waterlogging. This happens when too much water stays underground. The water table, or the level of water underground, rises too high. This can trap salt in the soil.

We can fix this with drainage. This is a way to move water away. Farmers use a leaching fraction. This means they use 10% to 20% extra water to wash the salt out. The salty water flows through pipes or drains. This carries the salt away from the plant roots.

This helps the soil stay healthy for many years.

Soil salinity is a big problem for many farms around the world. It happens when too much salt builds up in the ground.

This salt makes it very hard for plants to grow well. In some places, like the Indo-Gangetic Plain, crops suffer a lot. Wheat yields might drop by 40% because of the salt. Rice yields can fall by 45% in those same areas. Cotton is even harder hit, with losses reaching 63%.

This makes it a very serious issue for food.

How does the salt get into the soil in the first place? One main way is through irrigation, which is how farmers water their crops. Even clean river or groundwater has some salt in it. When farmers water the fields, the water eventually evaporates into the air. The water disappears, but the salt stays behind in the dirt.

This can add a lot of salt every year. Some fields might receive 10,000 kg of salt every single year!

Another way salt builds up is through a thing called waterlogging. This happens when too much water stays trapped underground. Most irrigation projects are not 100% efficient. This means about 30% to 40% of the water is not used by plants. This extra water goes underground and makes the water table rise.

A high water table can block salt from moving away. It can also push more salt up into the plant roots. This makes the soil even saltier over time.

Scientists and farmers work hard to fix these salty soils. One way to fix it is through soil reclamation. This is a way to improve the land so plants can grow again.

Farmers use a method called leaching to wash the salt out. They use about 10% to 20% extra water to flush the salt down. This salty water then flows through a drainage system. The drainage water is often 5 to 10 times saltier than the water used for irrigation. This carries the salt away from the crops.

There are different ways to move this water away from the fields. Some people use horizontal drainage systems with pipes in the ground.

Other places use vertical systems, which are like deep wells.

These systems help keep the water table at a good depth. For many crops, a depth of 0.6 to 0.8 meters is just right. By managing the water, we can help keep the earth healthy for growing food.

Soil salinity control involves managing the concentration of salts in the soil. This process is vital to prevent soil degradation caused by salination. It also includes the reclamation of already salty, or saline, soils. Soil reclamation is often called soil improvement, rehabilitation, or remediation. Without these controls, agricultural land can become unusable for farming.

Salinization often occurs through human activities like irrigation. All irrigation water, whether from rivers or groundwater, contains some amount of salt. When this water is applied to fields, it eventually evaporates. While the water turns into vapor, the salt remains behind in the soil. For example, using water with a low salt concentration of 0.3 g/L can add 3,000 kg of salt per hectare each year. Some large irrigation projects can add as much as 10,000 kg of salt per hectare annually.

A secondary cause of salinity is a process called waterlogging. Most irrigation projects have an efficiency of less than 60%. This means that 30% to 40% of the irrigation water is not consumed by plants. This excess water moves underground and can change local hydrology. If the underground aquifer cannot transport this water, the water table rises. This creates several problems for crops. A shallow water table reduces oxygen in the root zone. It also blocks the removal of salts and causes more salts to seep upward into the soil.

Scientists measure soil salinity using electric conductivity (EC). This is often written as ECe, which refers to the salt concentration in a saturated soil extract. Soils are classified based on these ECe values. If the ECe is greater than 4, the soil is considered saline. When the value is between 4 and 8, it is slightly saline. A range of 8 to 16 is called moderately saline. If the ECe is higher than 16, the soil is severely saline.

Different crops have different levels of salt tolerance. Sensitive crops lose their vigor even in slightly saline soils. Most crops are negatively affected by moderate salinity. Only highly resistant crops can thrive in severely saline environments. For instance, the maize crop in Egypt shows a salt tolerance of ECe = 5.5 dS/m. Beyond this specific level, the crop yield begins to decline.

The primary method for controlling salinity is through drainage and leaching. To reclaim soil, farmers use a leaching fraction of about 10% to 20% of the irrigation water. This extra water flushes the salts down through the soil profile. This salty water is then collected by a drainage system. In stable systems, the drainage water is 5 to 10 times saltier than the irrigation water. This ensures that salt export matches salt import. When reclaiming highly salty land, the drainage water can initially be 50 times saltier than the irrigation water.

There are two main types of drainage systems used in agriculture. Horizontal drainage systems use pipes placed within the soil to collect water.

Vertical drainage systems use wells to remove water from the ground.

These systems work together to lower the water table. For many crops, a seasonal average water table depth of 0.6 to 0.8 meters is sufficient. Managing these systems is essential for maintaining healthy agricultural land.

Salinity is a massive global issue affecting millions of hectares. About 20% of the world's irrigated lands are currently affected by salinity. This is a significant increase from the early 1990s. In the Indo-Gangetic Plain, salt-affected lands cause massive crop losses. Wheat yields can drop by 40%, while rice yields may fall by 45%. Cotton is even more vulnerable, with potential losses of 63%.

Worldwide, saline land covers approximately 3,230,000 km2. Large areas are found in Australia, Africa, and Latin America. This makes salinity control a critical part of global food security.