Make sure the emitters are set in the appropriate spacing, to allow uniform irrigation depending on your soil type. Irrigation water amounts must coincide the growing stage of your crop. Apply the minimum needed to flush salts from soil. This means that you always have to give a little more water than the crop consumption, to allow leaching of salts below the root zone.
Heavier soils require larger water applications than lighter soils, in order to avoid salinity buildup. Where AW is the amount of water to be applied and ET is the water consumption based on evapotranspiration. Irrigation regimen and intervals must be appropriate to the soil conditions and to growth stage of the crop. Frequent and shallow superficial applications result in salt accumulation in the root zone, while larger applications, in longer intervals, will flush the salts below the root zone.
The fertilizers type and their quantities should coincide with to the requirements of the crop and with nutrients which are already in the soil. There are fertilizers which contain salts which are not taken up by plants in large amounts, such as chlorides.
A practical approach in order to prevent salinity buildup early enough is sampling the soil 5 times over a growing period of 8 months a test every 6 weeks or so.
It is recommended to do at least one water analysis as well. The tests will indicate any change in soil content, allowing you to adjust the fertilization and irrigation regimen as needed.
This is the cheapest, most practical way to follow up on salinity status, keeping your crop quality and yield at optimal level. When you identify a salinity problem during the growing season, it is recommended to flush the field, even if it means risking some crop damage, rather than allowing further deterioration of the crop due to salinity.
Flushing applications should be carefully planned according to the crop conditions and growth stage. In heavy soils, water infiltration and drainage problems may be encountered, resulting in excess of water and lack of air to the roots. Flushing heavy soils is a prolonged process and its final result is difficult to anticipate in advance. Therefore, extra care should be taken when growing on heavy soils, as to not reach salinity buildup at all, or at least identify the problem early enough, when salts levels are still relatively easy to flush.
If all else fails and flushing is the chosen course of action, in heavier soils, not more than the maximal water amount that can be absorbed by the soil should be applied, and the longest intervals possible should be maintained.
In the meantime, fertilization should be based only on Nitrogen and only the minimum amount should be applied. The best indicator of the extent of a salt problem is a detailed salinity analysis, in which water is extracted from a paste. This test measures the pH, electrical conductivity EC and water-soluble levels of the soil. EC is a measure of the amount of dissolved salts in the paste of soil and water. The Texas Agricultural Extension Service conducts several types of soil tests, including detailed salinity analyses.
Salt buildup can result in three types of soils: saline, saline-sodic and sodic. Saline soils are the easiest to correct; sodic soils are more difficult. Each type of soil has unique properties that require special management. Saline soils contain enough soluble salts to injure plants. They are characterized by white or light brown crusts on the surface. Saline soils usually have an EC of more than 4 mmho cm Salts generally found in saline soils include NaCl table salt , CaCl2, gypsum CaSO4 , magnesium sulfate, potassium chloride and sodium sulfate.
The calcium and magnesium salts are at a high enough concentration to offset the negative soil effects of the sodium salts. The pH of saline soils is generally below 8. The normal desired range is 6. Leaching the salts from these soils does not increase the pH of saline soils. Saline-sodic soils are like saline soils, except that they have significantly higher concentrations of sodium salts relative to calcium and magnesium salts.
Saline-sodic soils typically have an EC of less than 4 mmho cm-1, and the pH is generally below 8. The exchangeable sodium percentage is more than 15 percent of the cation exchange capacity CEC. The higher the CEC, the more problematic the removal and remediation of the salt problem. Water moves through these soils much as it does in saline soils, although the steps for correcting saline sodic soil are different.
Simply leaching the salts from this soil will convert it from saline-sodic to sodic soils. Sodic soils are low in soluble salts but relatively high in exchangeable sodium. Sodic soils are unsuitable for many plants because of their high sodium concentration, which may cause plant rooting problems, and because of their high pH, which generally ranges from 8. These high sodium levels disrupt both the chemical and physical composition of soil clays.
As a result, the soil surface has low permeability to air, rain and irrigation water. The soil is sticky when wet but forms hard clods and crusts upon drying. When salts accumulate in soils, problems arise for two main reasons: the soil becomes less permeable, and the salt damages or kills the plants.
The first problem is associated with the soil structure. In sodic soils, high levels of exchangeable sodium cause the individual sand, silt and clay particles to be separated and not clumped together into larger particles.
This dispersion makes the soil tight and impervious, so that it allows little air, rain or irrigation water to permeate into the soil. Therefore, the plants may not receive enough moisture and oxygen to grow. Salts may accumulate on the soil surface because they cannot leach out of the root zone.
Plants can also be damaged by salt effects or toxicity. In saline and saline-sodic soils, high concentrations of soluble salts reduce the amount of available water for plants to use.
High levels of sodium can be toxic to certain plants. Also, the very high soil pH in high-salt soils greatly changes the nutrients available to the plants. These high pH levels change the ionic form of many plant nutrients to forms that make them unavailable to plants. Improving drainage: In soils with poor drainage, deep tillage can be used to break up the soil surface as well as claypans and hardpans, which are layers of clay or other hard soils that restrict the downward flow of water.
Tilling helps the water move downward through the soil. While deep tillage will help temporarily, the parts of the soil not permanently broken up may reseal.
Leaching: Leaching can be used to reduce the salts in soils. You must add enough low-salt water to the soil surface to dissolve the salts and move them below the root zone. The water must be relatively free of salts 1, — 2, ppm total salts , particularly sodium salts. A water test can determine the level of salts in your water. The result is likely to be higher food prices and food shortages, he says. Many coastal regions in Bangladesh, the Philippines, Egypt, Australia, Iraq and Turkey are becoming more prone to salt intrusion as sea levels rise.
He points out that it was responsible for the decline of ancient Mesopotamian civilization 4, years ago. Salt problems exacerbated by human activity are altering habitat and farmland in the Colorado River basin. The river and its tributaries supply water to more than 38 million people and irrigate more than 7, square miles 18, square kilometers of farmland.
The salinity of the river has doubled in 60 years , mostly due to the building of dams, irrigation and evaporation in reservoirs, says researcher Gabriel LaHue, a graduate student in the Soils and Biochemistry Graduate Group at the University of California, Davis. Salinity costs farmers and states dearly. Chen says salinity caused by rising sea levels is likely to force about , farmers a year to migrate from Bangladeshi coasts.
Sign up now to receive our newsletter. In the coastal region of the U. Soil salinity can be reversed, but it takes time and is expensive. Solutions include improving the efficiency of irrigation channels, capturing and treating salty drainage water, setting up desalting plants, and increasing the amount of water that gets into aquifers. Mulches to save water can also be applied to crops. The more high-tech solution is to develop genetically engineered and other salt-tolerant crops.
But the science is not straightforward and is controversial, and the result is that not many varieties are available in large quantities. In coastal areas of many developing countries, like Bangladesh, Vietnam and Thailand, where brackish or salty water is most common, many thousands of small farmers have switched from rice to shrimp farming.
This is lucrative, but can be financially and ecologically risky, leading to more salinization and deforestation. The rush to shrimp farming has also led to conflict, with rice paddy fields being deliberately flooded in order to force farmers off their lands.
In the brackish waters of the Mekong Delta, some rice farmers have taken up raising shrimp instead of, or in addition to, rice. Photo courtesy of Vietnam News Agency. Irrigating crops has been important for agriculture for thousands of years, but the lesson is that unless societies learn to avoid the waterlogging and salinization that so often comes with it, disaster will follow.
But the heavy demand it makes on freshwater supplies is now straining food supplies and harming biodiversity.
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