- How Does Gypsum Remediate Saline And Sodic Soils?
- 7 Ways to Reduce Your Salt Intake and Lower Your Blood Pressure
- Americans Are Still Eating Too Much Sodium
- Want to Cut Sodium? Look at Food Labels
- Try These 7 Tricks to Reduce Salt Intake Every Day
- Is Salt Bad for You?
- Keep the Sodium Out (Before It Gets In)
- Flush the Sodium Out (Once It’s Already In)
- You might be getting more sodium than you need, even if you never pick up the salt shaker.
- I know that too much sodium hurts my health. What can I do to cut back?
- Is my food going to taste bland with less salt?
- What about salt substitutes?
- What is the American Heart Association doing to help us break up with excess salt?
- Where can I find more information about eating less salt?
- Harvesting Sea Salt
- Extracting Salt from Sand
- Harvesting Rock Salt
- Harvesting Salt from Brine Springs & Salt Lakes
- Salt in Animal Blood
- Extracting Salt from Plant Ashes
- Final Thoughts on Salt for Preservation
- Salinity and salt
- Effects of salts on plants
- Salt buildup
- Soil testing
- Salt-affected Soils
- Saline soils
- Saline-sodic soils
- Sodic soils
- Salt problems
- Correcting salt-affected soils
- Steps for treating sodic and saline-sodic soils
How Does Gypsum Remediate Saline And Sodic Soils?
How does gypsum help? One of the most popular and best-known uses of gypsum is in reclaiming saline and sodic soils and remediating irrigation waters high in sodium salts. In the southwestern U.S. (California and Arizona), Rio Grande valley and other parts of the world, soils and irrigation water can be high in salts and sodium and displacing and removing salt and sodium is a best-management practice. Gypsum plays an important role in improving soil structure properties and soil will benefit from gypsum.
In these areas soils can be saline or sodic. Salinity is the salt content in the soil and salts are the soluble nutrient ions in the soil solution and not on the soil’s cation exchange complex. Sodic soils are characterized by exchangeable sodium on the soil’s exchange complex and need gypsum treatment.
Clay or dirt is saline when it contains a high amount of salts suspended in the soil solution (water) that fills soil pores. These salts can originate from the natural weathering of minerals that form soil. They also accumulate in the soil in arid climates with little rainfall, from applications as irrigation water or as capillary action brings salty water to the surface, leaving minerals behind as it evaporates. Soil with electroconductivity (EC) readings less than 1 to 2 dS/m (deciSiemens per meter) is not saline so won’t impact crops or microbial processes (Note that opinions differ on what constitutes saline: 1, 2 or even 4 dS/m)
A sodic soil is one with high levels of exchangeable sodium on the cation exchange complex and low levels of soluble salts. It is in need of gypsum. It is generally associated with soil with a pH of 8 or greater. A sodic soil has an EC reading less than 1 dS/m and SAR (sodium absorption ratio) reading greater than 13 or an ESP (exchangeable sodium percentage) greater than 15. This means that sodium occupies more than 15 percent of the soil’s cation exchange capacity (CEC) which is very high. Sodic dirt has poor soil structure and develop drainage issues over time because sodium ions on clay particles cause the soil particles to deflocculate, or disperse. Sodic soil is hard and cloddy when dry and tend to crust and water intake is poor. Again, gypsum plays an important role in improving structure properties and soil always benefits from gypsum.
A saline sodic clay or dirt is one that is both saline (> 1 to 2 dS/m) and sodic (SAR > 13 and ESP > 15) and contains both high levels of soluble salts and exchangeable sodium.
Leaching reclaims saline soils. Since salinity is the amount of salts (sodium and other salts) in the soil solution, chemical amendments like calcium carbonate and calcium sulfate cannot reclaim these soils. A field can be reclaimed only be removing salts from the plant root zone by applying more water than the plant needs. However, gypsum plays an important role in improving soil structure properties so that leaching can effectively remove salts from the root zone.
Applying gypsum helps reclaim sodic soils where sodium that’s attached to the cation exchange complex becomes too high. The most economical way is to add gypsum which supplies calcium. The calcium supplied by gypsum displaces the sodium held on the clay-binding sites. The sodium on the clay binding sites can then be leached from the soil with irrigation water or rainfall.
Some irrigation waters contain virtually no salts and do not penetrate well when applied. Dissolved gypsum is a salt and will increase the water’s solute concentration. Irrigation water with low levels of leachable salts either penetrate poorly into soil or causes soil particles to degrade clogging up soil pores. The problem can be corrected with surface-applied gypsum or gypsum application to the irrigation water. Soil will benefit from gypsum application. Apply gypsum today and see the difference!
7 Ways to Reduce Your Salt Intake and Lower Your Blood Pressure
We live in a society that measures and medicates. All the tools and technology and medicines deployed to maintain heart health are a help — yet heart disease remains the No. 1 killer in America. And high blood pressure, or hypertension, is a major contributor. Even so, heart disease is largely preventable, and much of that prevention lies in small steps that can make a big difference; diet is foremost among them. To lower your blood pressure, you need to reduce salt intake.
In ancient times, salt was so valuable that people used it for currency. It was used sparingly to season and preserve food. Today, we have an embarrassment of riches, and modern humans consume more salt than is good for them. But the biggest contributor to our sodium consumption is not the salt shaker: Approximately 75 percent of the sodium we eat comes from sodium added to processed and restaurant foods.
Americans Are Still Eating Too Much Sodium
Despite public health efforts over the past several decades to encourage people in the United States to consume less sodium, adults still take in an average of 3,400 milligrams (mg) per day — well above the current federal guideline of 2,300 mg or less daily. (The American Heart Association’s recommended cap is 1,500 mg, which is much less than 1 teaspoon — or 6 g — a day.) Evidence has shown that reducing sodium intake reduces blood pressure, as well as the risk of cardiovascular disease and stroke.
Many high blood pressure medications act as diuretics, which stimulate the kidneys to remove sodium and water from the body, thereby relaxing blood vessel walls and lowering blood pressure. But before choosing to take a medicine that will get rid of the salt in your diet for you, there is another option: What about cutting down on the salt yourself? If you think about it, you can monitor your salt intake and reduce it without swallowing one pill. Medication may be necessary if you can’t control spiking and consistently high blood pressure. But if you initiate your own regimen, you may be able to lower your blood pressure on your own.
Monitoring salt intake begins with avoiding packaged and processed foods, such as smoked, salted, and canned meat, fish, and poultry; ham, bacon, hot dogs, and lunch meats; hard and processed cheeses; regular peanut butter (buy unsalted instead); canned soups and broths; crackers, chips, and pretzels; breads and rolls; pizza and mixed pasta dishes, such as lasagna; and more. You can find a complete list here.
Want to Cut Sodium? Look at Food Labels
To stay under 2,300 mg or less a day, you must read food labels regularly. Look for the “no salt added ” labels (meaning no salt is added during processing, but the product is not necessarily salt- or sodium-free). Foods labeled “sodium-free” have less than 5 mg per serving; “very low sodium” foods contain less than 35 mg per serving; “low-sodium” foods have less than 140 mg per serving. Other terms you might see include “light sodium” or “lightly salted” (meaning at least 50 percent less sodium than in the regular product), and “reduced sodium” (meaning at least 25 percent less sodium than in the regular product — but probably too much for your diet!).
Sodium, despite its hazards, is nevertheless an essential nutrient needed in fairly small amounts, unless you lose a lot through sweating. Sodium helps maintain a balance of body fluids and keeps muscles and nerves working well. A mineral, sodium is one of the chemical elements found in salt. Though used interchangeably, the words “salt” and ”sodium” have different meanings: Salt, or sodium chloride, is a crystalline compound used to flavor and preserve food.
The relationship between sodium and high blood pressure is fairly straightforward. Sodium attracts water, and the higher the sodium intake, the greater the amount of water in the bloodstream — which can increase blood volume and blood pressure. High blood pressure, or hypertension, is a condition in which blood pressure stays elevated over time. That makes the heart work harder, and the higher force of blood flow can damage arteries and other organs, including the eyes, brain, and kidneys.
Sodium and potassium also affect each other along with your blood pressure: Potassium can help lower blood pressure by acting as a counterbalance to the harmful effects of sodium in your diet. To up your intake, eat foods rich in potassium, such as bananas, juices (such as carrot, orange, pomegranate), yogurt, potatoes, sweet potatoes, spinach, tomatoes, and white beans.
Try These 7 Tricks to Reduce Salt Intake Every Day
Since blood pressure rises with age, monitoring your sodium intake increases in importance with every birthday. It’s the “ounce of prevention” that can result in the proverbial “pound of cure.” So here are some tips to help you maintain that sodium-free diet:
- Read the Nutrition Facts label.
- Prepare your own meals (and limit the salt in recipes and “instant” products).
- Buy fresh meats, fruits, and vegetables.
- Rinse canned foods containing sodium (such as beans, tuna, and vegetables).
- Add spices to your food. Instead of salt, try coriander, black pepper, nutmeg, parsley, cumin, cilantro, ginger, rosemary, marjoram, thyme, tarragon, garlic or onion powder, bay leaf, oregano, dry mustard, or dill.
- Reduce portion size; less food means less sodium.
And when you’re eating in, try this recipe for a heart-healthy meal.
VEGGIE BAKE WITH OLIVE OIL AND GARLIC
- 3 tbsp olive oil, divided
- 3 cups, chopped, of any vegetables in your fridge
- 1 tsp minced fresh garlic
- 1 can (14 ounces) low-sodium chopped tomatoes, drained
- 1 can (14 ounces) chickpeas, drained and rinsed
- Salt-free seasonings, such as coriander, cayenne, parsley, or tarragon
- 2 zucchini, sliced into thin sheets
Preheat oven to 350 degrees Fahrenheit.
Place 2 tbsp olive oil in a large skillet over medium heat, then and add the chopped veggies and garlic. Sauté for about 5 minutes. Add the tomatoes and chickpeas, stirring to combine. Add your choice of salt-free seasonings to taste. Remove from heat. Spread the remaining tbsp of olive oil on the bottom of an 8-inch square baking dish. Cover with a layer of zucchini. Spread the sautéed mixture evenly across the zucchini base. Add a layer of zucchini on top. Sprinkle with oil. Bake for 30 minutes.
Yield: 6 servings
The Remedy Chicks
If you are concerned about how much salt is in your body, then you’re probably searching for ways on how to get rid of salt. Here’s a great place to start! If you’re not concerned with your salt intake, then you should be!
Really? Regardless if you have a chronic disease like heart disease, diabetes or high blood pressure (or are a healthy person), everyone should be concerned with how much salt is in your body.
In this article, we will get to the bottom of why components of salt are both essential and harmful to your health. We’ll break down the salt molecule so that you can better understand what happens when we eat salt and if salt is the main culprit of your health problems. Finally, we will give you several tips on how to flush salt out of your body so you can start living a healthier life.
Is Salt Bad for You?
When you think of a healthy diet, you may think that salt is bad for you. As salt breaks down in your body, however, it breaks into 2 minerals called sodium and chloride. These 2 minerals are essential for maintaining normal body functions, so we do need them in our diet. However, when we have an imbalance of these minerals, especially sodium, then that is when we start seeing health issues.
Your body works hard to tightly control your blood sodium levels regardless of your sodium intake, however, there are several problems that are possible when someone’s blood sodium levels are abnormal.
|Problems Linked with Too Much Sodium in the Body||Problems Linked with Not Enough Sodium in the Body|
|Fluid retention, bloating, edema or potential weight gain||Syndrome of Inappropriate Antidiuretic Hormone Secretion (SIADH)|
|Increased risk of hypertension, heart failure and stroke||Seizures
Above all, while salt consumption needs to be controlled, nutrition professionals are most concerned with your sodium intake. So, watch your sodium intake! For most adults, sodium intake should be limited to 1500mg to 2300mg per day. If you have high blood pressure, then reduce your sodium intake to 1500mg per day (1).
Keep the Sodium Out (Before It Gets In)
One of the first steps you can take to get rid of sodium from your body is to reduce consumption of it in the first place. Here are some tips on how to do that:
1. Avoid Adding Salt to Your Foods
Perhaps one of the easiest and clear-cut ways to reduce your sodium is to get that salt shaker off the table and out of your food! Just about 1 teaspoon of salt contains all the recommended sodium you need in a day! To add flavor to your foods without sodium and salt, try the Mrs. Dash flavor packets.
2. Read the Nutrition Label for Sodium
When you are trying to reduce your sodium intake, it is essential that you read the nutrition label so that you understand how much sodium is in the food you are buying. Remember to keep it to less than 2300mg per day (and less than 1500mg if you have hypertension). For information about labeling and how to understand the food label for sodium, .
3. Recognize the Patterns of Sodium in Food
Do you think at the salt in a salt shaker is where we get most of our sodium? Think again! There are various types of foods that are typically high in sodium and types of foods that are typically low in sodium. Overall, try to decrease the amount of high sodium foods in the diet while increasing the low sodium foods.
*While these foods can be part of a healthy diet to manage hypertension, portion control should be conducted.
Fun Fact: Try rinsing your canned goods (i.e. canned green beans, beans, corn) in a colander under cool water because you can rinse a little bit of the sodium off that way!
Flush the Sodium Out (Once It’s Already In)
Monitoring your sodium intake is a lifelong process that we all must work on in order to stay healthy. However, there are some ways to help your body process and flush out sodium when it is in your body.
1. Keep Your Kidneys Healthy
Your kidneys process fluid, sodium and other substances based on what your body needs (and what it doesn’t). Make sure you visit your doctor regularly so that he or she can monitor how well your kidneys are working. Check out this article to learn more about keeping your kidneys healthy and how to detox naturally.
2. Drink Enough Water
Remember this: Where water goes, sodium will follow. Drinking water will hydrate your body and help you flush out sodium, especially if there is too much sodium circulating in the body. When we do not drink enough water, our kidneys can’t work correctly, and ultimately, can’t flush out excess sodium.
3. Get Your Sweat On
We lose some sodium via sweat when we exercise, so get your sweat on with this fun workout DVD package (2)! While this is not as effective as eliminating sodium via diet, perhaps this can be yet another reason for you to exercise. One thing to keep in mind, however, is that you should stay adequately hydrated before, during and after a sweat session. If you sweat profusely (for no apparent reason), then you may have an underlying medical condition. So, always check in with your doctor!
You might be getting more sodium than you need, even if you never pick up the salt shaker.
That’s because more than 70 percent of the sodium we eat comes from packaged and restaurant foods. That can make it hard to control how much sodium you eat, because it’s added to your food before you buy it.
I know that too much sodium hurts my health. What can I do to cut back?
At the store/while shopping for food:
- Choose packaged and prepared foods carefully. Compare labels and choose the product with the lowest amount of sodium (per serving) you can find in your store. You might be surprised that different brands of the same food can have different sodium levels.
- Pick fresh and frozen poultry that hasn’t been injected with a sodium solution. Check the fine print on the packaging for terms like “broth,” “saline” or “sodium solution.” Sodium levels in unseasoned fresh meats are around 100 milligrams (mg) or less per 4-ounce serving.
- Select condiments with care. For example, soy sauce, bottled salad dressings, dips, ketchup, jarred salsas, capers, mustard, pickles, olives and relish can be sky-high in sodium. Look for a reduced- or lower-sodium version.
- Opt for canned vegetables labeled “no salt added” and frozen vegetables without salty sauces. When they’re added to a casserole, soup or other mixed dish, there are so many other ingredients involved that you won’t miss the salt.
- Look for products with the American Heart Association’s Heart-Check mark to find foods that can be part of an overall healthy dietary pattern.
While the Heart-Check mark doesn’t necessarily mean that a product is “low-sodium,” it does mean that the food meets AHA’s sodium criteria to earn the Heart-Check mark.
You can eat foods with varying amounts of sodium and still achieve a balanced and heart-healthy diet. To learn more about the Heart-Check Food Certification Program, visit www.heartcheck.org.
When preparing food:
- Use onions, garlic, herbs, spices, citrus juices and vinegars in place of some or all of the salt to add flavor. Our recipes and tips can help!
- Drain and rinse canned beans (like chickpeas, kidney beans, etc.) and vegetables. You’ll cut the sodium by up to 40 percent.
- Combine lower-sodium versions of food with regular versions. If you don’t like the taste of lower-sodium foods right now, try combining them in equal parts with a regular version of the same food. You’ll get less salt and probably won’t notice much difference in taste. This works especially well for broths, soups and tomato-based pasta sauces.
- Cook pasta, rice and hot cereal without salt. You’re likely going to add other flavorful ingredients, so you won’t miss the salt.
- Cook by grilling, braising, roasting, searing and sautéing to bring out natural flavors. This will reduce the need to add salt.
- Incorporate foods with potassium like sweet potatoes, potatoes, greens, tomatoes and lower-sodium tomato sauce, white beans, kidney beans, nonfat yogurt, oranges, bananas and cantaloupe. Potassium helps counter the effects of sodium and may help lower your blood pressure.
- Tell them how you like it. Ask for your dish to be made without extra salt.
- Taste your food before adding salt. If you think it needs a boost of flavor, add freshly ground black pepper or a squeeze of fresh lemon or lime and test it again before adding salt. Lemon and pepper are especially good on fish, chicken and vegetables.
- Watch out for these food words: pickled, brined, barbecued, cured, smoked, broth, au jus, soy sauce, miso or teriyaki sauce. These tend to be high in sodium. Foods that are steamed, baked, grilled, poached or roasted may have less sodium.
- Control portion sizes. When you cut calories, you usually cut the sodium too. Ask if smaller portions are available, share the meal with a friend or ask for a to-go box when you order and place half the meal in the box to eat later.
Ask about the sodium content of the menu items. Chain restaurants with 20 or more locations must provide nutrition information, including sodium content, to customers upon request.
Is my food going to taste bland with less salt?
With less salt, you can taste your food’s natural flavor, especially when you use cooking techniques and flavorful ingredients (see tips above) to enhance it.
Over time, your taste buds can adjust to liking less salt. Studies show that when people follow a lower-sodium diet, they start to prefer it, and that the foods they used to enjoy taste too salty. Try it and see for yourself!
What about salt substitutes?
There are many salt substitutes, and a few of them replace some or all of the sodium with potassium. Most people can use them, but certain medical conditions (like kidney disease) and medications have implications on your potassium intake. Talk with your healthcare professional about whether a salt substitute is right for you.
What is the American Heart Association doing to help us break up with excess salt?
We commend manufacturers and restaurants that have already taken steps to reduce sodium in their foods.
Successful sodium reduction requires action and partnership at all levels — individuals, healthcare providers, professional organizations, public health agencies, governments and industry. Here are a few things that the American Heart Association is doing to help:
- Encouraging manufacturers to reduce the amount of sodium in the food supply
- Advocating for more healthy foods, like fruits and vegetables, to be available and accessible
- Providing consumers with education and decision-making tools to make better food choices
Where can I find more information about eating less salt?
If you’re hungry for more, check out cookbooks from the American Heart Association. You’ll learn how to monitor the sodium you eat, reduce the high-sodium products in your kitchen, read and understand food labels, know which popular foods are salt traps, keep sodium in check while eating out and plan lower-sodium weekly menus without sacrificing taste.
Harvesting Sea Salt
I found myself wondering, how did our ancestors in landlocked regions find salt? I know. The weird things I wonder about…
It’s easy enough to harvest sea salt from the ocean, but what if you’re settled a thousand miles from the ocean?
I’ve heard explanations that even ancient peoples relied on trade, but I can’t imagine they would have relied exclusively on trade for such a vital resource.
I just cant believe it. You’re going to settle 1,500 miles from the coast. Literally months of walking, and assume that someone’s going to want what you have bad enough to bring you salt along a trade route.
Maybe. But Perhaps that’s why I’m not a pioneer. I’d need to know where to find it inland before I’d venture inland.
Salt is essential for human survival, down to basic cellular functions. It’s also required for many different preservation techniques, especially those that preserve meat without refrigeration. Beyond basic survival, salt is also one of the basic human flavors that we can taste, and it goes a long way to making food not only palatable but pleasurable.
I’m not the only one who’s wondered, and it turns out researchers pieced together 6 different ways native Americans gathered salt.
Extracting salt from seawater is by far the easiest method, but it obviously only works near the sea.
There’s a surprising amount of harvestable salt in seawater, and a single gallon contains just over 1/4 pound of sea salt. It can be extracted by boiling away the water, or by placing it in shallow trays exposed to the sun and allowing the water to evaporate.
In some areas with rocky beaches and shallow tide pools, large salt crystals can be collected daily toward the end of low tide just before the water comes back in, no boiling required.
Traditional sea salt harvesting in Vietnam.
Extracting Salt from Sand
Sandy inland soils can contain salt deposits, and local tribes would be well aware of prime sources near their homeland. Sand was placed in a basket with very small holes at the bottom and water washed through it. The water was then boiled down like seawater, resulting in salt extracted from deposits inland. Here’s a description of the process from a first-hand account:
“The salt is made along by a river, which, when the water goes down, leaves it upon the sand. As they cannot gather the salt without a large mixture of sand, it is thrown together into certain baskets they have for the purpose, made large at the mouth and small at the bottom. These are set in the air on a ridge-pole; and water being thrown on, vessels are placed under them wherein it may fall; then, being strained and placed on the fire, it is boiled away, leaving salt at the bottom.” (Source)
Harvesting Rock Salt
Those that lived near a rock salt source could travel every year to actually mine out their salt with hand tools. There are many such deposits up and down the east coast, many of which are underground and are not accessible directly. Instead, they feed brine springs where native Americans would travel to gather salt.
Harvesting Salt from Brine Springs & Salt Lakes
Brine springs are by far the most common documented source of salt for native peoples. Salt boiling pots are found in archeological records from tribes throughout the United States. Oral histories tell stories of families continuing this tradition even today.
Every year the family or settler group travels to a salt spring to collect the nearby salt, taking turns tending fires to heat stones that are then placed into clay pots to boil water. Eventually, the salt is scraped from the insides of these pots and stored for a years supply. In more modern times, metal pots are used directly over the fire, but the concept is the same.
Salt in Animal Blood
Since many plants contain salts in low concentration, you’d either need to burn a lot of them or eat a lot of them to get enough salt to survive. Herbivores, such as deer, browse the forest and actively seek out salt-rich plants and mineral salt deposits to lick. That salt accumulates in their tissues and is present in their blood. While there’s not a particularly good way to extract salt from animal blood, consuming it regularly will supply enough salt to keep you healthy in the absence of other sources.
Far from the ocean, animal and plant salt sources tend to be low in iodine, which is one reason commercially made salt is supplemented with iodine. Soils vary in iodine content, and mountainous soils tend to be especially deficient. In those areas, a salt spring or rock salt source is the most reliable for maintaining good health in the absence of commercial salt.
Extracting Salt from Plant Ashes
Explorers also recorded native Americans burning the leaves and roots of certain plants to extract their salts. Very little has been documented about which plants these may have been. Survivalists today know that boiling hickory roots will result in a black tar-like substance that is full of edible salts. Likewise, wild carrot and parsnip are good boiled salt sources.
Coltsfoot, a common weed, can be burned for salt. The leaves are first dried, and then tightly rolled. They’re lit at one end and slowly burned over a container that catches the ash. Once the plant matter has burned away, you’re left with the mineral salts accumulated by the plant. Though it takes a significant amount of plant matter to make even a small amount of salt, coltsfoot is a particularly aggressive weed, growing in even the most abused soils, especially in urban or suburban areas and along roadsides.
This method I’m particularly intrigued by. This summer I hope to gather some coltsfoot to burn for salt. It should be easy enough, it grows just about everywhere.
Final Thoughts on Salt for Preservation
In the course of writing this, I learned that using salt to preserve the meat from large animal harvests is a European practice. “The Indians of Eastern North America apparently used salt as a condiment. There is no evidence for salt ever having been used historically for preserving meat or fish, as drying game over a low fire was the standard Southeastern method of preservation.”
I assumed that salt was essential for preserving meat without refrigeration, but the practice of salt based charcuterie is a regional specialty.
None the less, salt is still tasty and living in a landlocked state, I’m excited to begin looking for our own salt springs and local sources.
Leaching of saline lands implies removal of excess salts from arable and subsurface soil horizons by flushing water; it is one of the main irrigated land salinity control methods. Before leaching, the field surface is to be leveled, deeply ploughed and dividing into check plots – parcels of 0.2-0.3 ha and more – by borders; then the check plots are flooded by water. Leaching rates (water quantity required for dissolution and displacement of salts from saline soil) are determined depending on salinization degree, composition of salts (sulphates, chlorides, and carbonates), permeability, and groundwater level. Leaching of saline lands is usually carried out in late autumn, when evaporation is minimal and groundwater level is low. Flushing water is diverted through desalting drainage.
Condition of application of soil leaching. If soil is heavily saline and contains more than 0.02…0.03% of chlorine in a one-meter-thick layer, excess of salts is to be removed by washing out, so that by beginning of sowing the quantity of chloride ion should not exceed 0.01% of its mass. To this effect, flooding irrigation is carried out with such water amount that dissolves salts and carries out their excess to lower horizons or more often to a drain.
Leaching of soil is a radical improvement of saline and alkaline soils. Effectiveness of leaching depends on the physical properties of soil and salinity degree, i.e. ratio of soluble salts of Ca and Na ions in the soil.
From alkali soils (where Ca ions prevail), salts can be easily washed out by leaching, if the soils are permeable enough. In alkaline soils (where Na ions prevail), alkalis liberate in the course of leaching, which causes physiological toxicity and deterioration of the physical properties of soil. The more Na ions, the worse soil properties. When the content of Na ions ranges from 20 to 40% of the total absorptive capacity, soil fertility disappears fully. That is why some gypsum should be introduced into alkaline soils prior to leaching; in the result of metabolic reaction, the absorbed Na is replaced by Ca ions and the generated salt is washed out by water. Leaching of alkaline soils without gypsum can be carried out if the content of Na ions does not exceed 10% of the absorptive capacity.
Leaching irrigation is the most efficient with the water application rate that comes to 30…40% of the minimum moisture capacity of the stratum being desalinated. For one-meter-thick stratum of light-textured soils, water application rate of leaching irrigation is 700…900 m3/ha; 900…1100 m3/ha on medium-textured soils; and 1100…1500 m3/ha on heavy-textured soils.
Leaching is to be done on a well-leveled, harrowed land divided into check plots 0.25 ha large at most, with compacted borders, which makes impossible water overflow or breakthrough through them. Leveling should be performed accurate to +5 cm; the height of earth addition at leveling should not exceed 20 cm. Irrigation network is to be cut in such manner that water comes to every check plot by itself.
Leaching is carried out by the blocks of land, and not here and there. When leaching is over and the soil has dried up, it is loosened to reduce evaporation and the borders are made even.
Sometimes, spots of residual salinization remain after leaching irrigation, which reduces the yield of crops. To neutralize these spots it is necessary to introduce gypsum and acid mineral fertilizers. Over the whole area of leaching, it is necessary to make soil structure by different agrotechnical methods: sowing of grass; application of manure, green manure, humus, etc.
Leaching irrigation is applicable without artificial drainage if groundwater has sufficient outflow outside a given irrigated area.
On heavily saline irrigated lands, removal of excessive salts from soil root layer can be completed by leaching irrigation. During a leaching process, water passes through soil layers, dissolves salts, and washes them out to groundwater. Contrasted with drainage, the soil leaching and desalination processes have the highest efficiency.
Leaching is carried out on the soils that contain more than 0.02-0.03% of the chloride mass in one-meter-thick layer. By the beginning of crop sowing, the content of chloride ions should not exceed 0.01%.
Soil leaching without artificial drainage is carried out when groundwater occurs deeply enough with its good natural outflow outside the irrigated area and well-permeable soils (gravel, etc.) lie at a depth of more than 1.5-2 m. If there is occurrence of mineralized groundwater with no natural outflow, artificial drainage must be provided at a depth of less than 2-3 m.
Soil leaching is performed in autumn, when groundwater lies deeply enough. Prior to leaching, the field must be leveled, ploughed up and harrowed; in this case, infiltration of irrigation water into soil will be slower and more uniform. To apply leaching, the field is to be divided into plots of land, i.e. check plots with an area 0.25 ha.
Water and salt regime of soils
Changes in the inter-irrigation, annual or many-year cycle of salt content and its qualitative composition in soil are called the salt regime of soil. It depends on groundwater table, groundwater salinity, salinity of soil solutions and irrigation water, irrigation regime, leaching regime, properties of soils, climatic conditions.
Salt regime is closely related to hydraulic regime. These processes are studied as a single set and are united by a common concept, viz. water-salt regime of soils.
Water regime of soil represents a combination of the processes of absorption, assimilation and exudation of water by soil. The water regime of soil includes such phenomena as: absorption; seepage; capillary rise; surface flow, descending and lateral; physical evaporation; desuction, freezing; defreezing; and water condensation.
Salt regime of soil represents a combination of the processes in soil related to incoming, movement, redistribution, and accumulation of salts, as well as their removal outside the soil profile.
Salt regime implies the history of salt composition and migration in value ecosystem soils. It consists in inwash of salts, particularly by impulverization, dissolving of salts that are in crystalline state, and vice versa in precipitation of salts from solutions, consumption of salts from solutions by plants and partially by soil organisms, their return with abatement, cyclic vertical migrations of salts, carry-over of salts into illuvial horizons during soil formation, carry-over of salts from the system with surface and ground waters, as well as by expulverization. Salt regime can be broken by environmental pollution.
Source: Bykov, B.A. Ecological glossary. Alma-Ata: Publishing House “Nauka”, 1983
Salt regime of soil implies change in the inter-irrigation, annual or many-year cycle of salt content and its qualitative composition in soil. Salt regime of soil is as a rule heavily dependent on irrigation and natural water regime; it (water-salt regime) is usually studied simultaneously.
Source: Soil science thesaurus. Edited by Rode, A.A. Moscow, Publishing House “Nauka”, 1975
Salt regime implies the history of salt composition and migration of salts in soils and water bodies. It is one of the most important environmental factors. It can be broken by erosion of banks, salinization and overwetting of soils, pollution of environment, etc.
Source: Dedyu, I.I. Ecological Encyclopedic Vocabulary. Kishinev: Chief Editorial Board of the Moldavian Soviet Encyclopaedia, 1989
Salt regime of soils implies recurrent movement of simple salts in the soil profile. These salts are typical for soils with non-leaching water regime the profile of which has water-soluble salts (saline soils/solonetzes, alkali soils, chernozems, chestnut soils, etc.). Salt regimes of soil differ in their intensity, i.e. in the mass of moving salts and amplitude of the movement, prevailing direction of salt movement, as well as composition of the moving salts. In alkali soils, upward flows of chlorides and sulphates prevail, which change into downward movement of these salts in wet seasons.
Forecast of the water-salt regime of irrigated lands
During operating period, prevention of repeated salinization and maintenance of optimum content of salt quantity and composition is executed by water supply for irrigation in a quantity exceeding the required by crops by 5-20%. This type of irrigation regime is called leaching regime; it intended for creation of downward movement of water and salts in aeration zone. Leaching regime is implemented by carrying out operating leaching in autumn-winter or spring periods or by raising vegetation irrigation rates.
Operating leaching and vegetation irrigation are made by furrows, border ditches or by sprinkling depending on natural and economic conditions and species of crops.
Necessity of leaching irrigation regime, its intensity and time of additional water supply is to be substantiated by drawing up and forecasting the water-salt regime of soils for a sufficiently long period. To forecast water-salt regime, they use the equation of water and salt balance of surface and subsurface waters and the equations of moisture and salt transfer in soils.
Leaching rate means the quantity of water to be supplied to the field for removal of excess water-soluble salts that are harmful for cultivated plants from soil. Leaching rate is determined experimentally or calculated by using relevant formulas.
Source: Soil science thesaurus. Edited by Rode, A.A. Moscow, Publishing House “Nauka”, 1975
To calculate the leaching rate for washing out one-meter-thick soil layer, they use the empirical formula of V.R. Volobuev:
M = 10000 * a * lg(S1 — S2)
Leaching depth in clayey soils is four times as much as it is on light-textured soils.
Leaching depth ranges from 1500 to 12500 m3/ha and more and is made up of the water volume needed for saturation of soil layer H down to minimum moisture capacity and of the water volume needed for washing out of dissolved excess salts (S1 — S2) to a drain.
Saline soils are washed out by means of consecutive water application at an interval of no more than eight days.
Net leaching depth is the water quantity needed for dissolving and carry-over of water-soluble salts from estimated soil layer’ it is measured in meters of water sheet or cubic meters per hectare (m3/ha).
Gross leaching rate is equal to the net leaching rate divided by irrigation network efficiency factor η plus the water quantity E0 evaporated from water surface during leaching period and minus atmospheric precipitation Oc for the same period.
Saline soil leaching types
Leaching of saline soils is subdivided into thorough and routine (operating) leaching. Thorough leaching is carried out at average and heavy initial salinization of soils; operating leaching is carried out at weak salinization. The rates of thorough and operating leaching irrigations depend on the composition and chemism of water-soluble salts in soil, thickness of washed out layer, hydro-physical and physical-chemical properties of soils and earth, mineralization of flushing water, and condition of diversion of flushing water.
Such leaching is called thorough (construction, reclamation) that is implemented for reclamation of highly saline soils during construction of new irrigation facilities as well as unused lands in farms with functioning irrigation systems. This leaching is carried out according to designs at year-round kind of works by applying increased leaching rates of over 10,000 m3/ha for desalination of soil root layer.
On old-irrigated soils, thorough leaching is applied in the case of introduction of highly saline lands in agriculture. Since thorough leaching requires enhanced drainage of the area, permanent drainage designed so that to meet the requirements of operating regime of crop irrigation should be strengthened by temporary drainage. At thorough leaching, the main requirements to be met are set for the depth of desalinated soil layer and subsoil, which is to be desalinated to such a degree that ensures normal development of crops.
Thorough leaching rate is determined proceeding from the condition of desalination of soil root layer and subsoil with a glance of the degree and type of salinization, hydro-physical properties of soils, as well as drainage degree of irrigated lands.
With shortage of equipment and water and unsatisfactory condition of drainage systems, such leaching irrigations are carried out more and more rarely and in many cases are not carried out at all. Under current conditions, the radical land reclamation principles should be revised, because salinization problem has become even more pressing than before, and the issues related to reconstruction, water deficit and facilities, equipment, and other resources are becoming more and more problematical.
The results of researches and field experiments proved the possibility to desalinate highly saline soils and alkali soils without thorough leaching by means of leaching irrigation regime. The Fergana Valley, Golodnaya Steppe, and lower reaches of the Amudarya river cane exemplify gradual desalination of the soils in irrigated areas with drainage and rise of crop yields on them.
Materials of numerous researches and estimates indicate that implementation of “thorough leaching”, i.e. leaching irrigation supposedly eliminating resalinization risk forever, can be carried out only with additional temporary deep drainage (the length of which is equal to or more than the length of permanent drainage required during an operating period) as well as temporary irrigation network. When developing large areas with a great part of saline lands, the cost of preparatory and liquidating abandonment works for execution of leaching will be close to the cost of construction of operational irrigation and collector & drainage networks, because on-farm network and sometimes inter-farm network too will need to be duplicated.
Thorough leaching is carried out during the growing season, when water and labour recourses become available and water losses to evaporation are lowest. To increase the effectiveness of soil desalination, leaching rate is supplied to fields by separate cycles of 2-3 ths m3/ha. The intervals between the cycles should be sufficient to ensure full absorption of the flushing water by soil.
Thorough leaching irrigations of saline soils are performed against the background of systematic horizontal or vertical drainage. With deep groundwater table (> 10 m), it is permissible to carry out thorough leaching without drainage for removal of salts from the root layer to the ground of the aeration zone.
With high rates on soils with low filterability, deep tillage of soils is accomplished to shorten leaching period and increase the effectiveness of flushing water use.
To ensure required intensity of flushing water diversion, systematic drainage is supplemented with temporary drainage, if necessary. The most reliable type of temporary drainage is shallow (0.8-1.2 m) open channel drainage.
Temporary drainage is designed taking into consideration a given leaching method. If leaching is carried out by cycles the interval between which is sufficient to ensure absorption of water supplied, then the interval between temporary drains is determined by fitting according to the formula of A.N. Kostyakov.
If leaching is carried out under permanent flooding (for rice), the interval between temporary drains is determined by the formula of V.V. Vedernikov.
Technique of thorough leaching is also very important. In an arid zone where surface irrigation method is applied, leaching irrigation is carried out: in small check plots by separate cycles without dumping of flushing water; in small check plots under permanent flooding and water bypass from one check plot to another by using partial surface method; in large check plots by separate cycles. Leaching by small check plots is one of the most widespread methods on low-permeable soils with installation of temporary drainage. In this case, the sizes of check plots are determined depending on the spaces between temporary drains and slopes of earth surface (the difference between the earth surface elevation at the extreme points of check plots should not exceed 10 cm). Check plot sizes usually range from 20 x 20 m to 50 x 50 m.
The most efficient is “border strip/check” leaching, when supply of flushing water is started from the field’s central part with gradual flooding the other parts. This leaching method is the most labour-intensive and expensive, but it provides fast and uniform desalination of soils over the field edgewise.
On well-permeable soils with slight surface gradient, where there is no need for temporary drainage, leaching is applied by large (1-3 ha) check plots. This leaching method is highly efficient and simplifies flushing water distribution over check plots. In some cases, leaching is implemented simultaneously with rice sowing. Leaching is carried out over small check plots with permanent flooding and partial dumping of flushing water. However, this method does not ensure uniform desalination over the field and, what is more, requires enormous volume of water, because a leaching rate is determined taking into account the needs for soil desalination, but according to the conditions of rice cultivation.
The highest effect of soil desalination is achieved with moisture movement under partial saturation; for this purpose, water is supplied by separate cycles or sprinkling method is applied. In this case, salts are washed out both from large and small pores of soil; with minimum influence upon the organic part of soil, uniformity of desalination over the leached area is achieved and less water is consumed for carry-over of the same quantity of salts as compared to pressure filtration under total water saturation.
The most efficient use of flushing water is ensured under the following seepage rates: in light-texture soils – 0.025-0.05 m/day; in average-texture soils – 0.01-0.03; and in heavy-texture soils – 0.01 m/day. If the seepage rate in heavy soils is less than 0.01 m/day, it is to be increased by tillage, applying manure and other amendments. Intensification of leaching process can be achieved by different agrotechnical methods (slotting, moling, deep tillage, meliorative ploughing) and chemical reclamations that allow creating a structure that will raise the filterability of soil and ground. When leaching by check plots is over, the following is to be carried out: survey of salts; leaching of unleached areas; evening up of temporary irrigation network; leveling of field surface; and deep tillage.
Routine (operational) leaching of saline soils means periodical soil desalination with the view of liquidation of seasonal salinity on poor-drained lands.
The main purpose of operating leaching is to remove salts from the root layer (0-100 cm) to optimum conditions for the rotation crops cultivated on irrigated lands without capital-intensive measures. Preventive and charge watering is a form of operating leaching for washing out of the salts accumulated in summer.
Preventive watering carried out every year or periodically (every 2-3 years) after desalination of active water and salt exchange layer ensures keeping stable salt regime of soil during the growing season.
Charge watering is an agrotechnical method which is used under certain conditions (dry spring, sandy-loam soils) for building up of required deposit of moisture in topsoil and gaining normal sprouting of crops as well as for reducing the consumption of irrigation water during the growing season when water is short. At slightly higher rates, charge watering can serve the purpose of simultaneous removal of the salts accumulated for the previous season from the root layer. In this case, it is called charge-preventive (watering).
Compulsory condition limiting the effectiveness of operating leaching is the drainage degree of irrigated lands and normal functioning of the existing collector & drainage network. Drainage (horizontal, vertical, etc.) creates conditions for descending seepage in a leached soil layer.
Operating leaching rates are fixed proceeding from the need for desalination of the root layer (0-100 cm) down to the toxicity threshold for zoning of crop varieties.
The rates of preventive charge watering are set based on the estimation of the aeration zone water balance for providing descending water flows subject to the depth of groundwater table, quantity of precipitation during autumn-winter and spring periods.
The leaching rates for every irrigated plot, crop-rotation area is fixed depending on the degree and nature of soil salinity, its water and physical properties, depth of groundwater table, technical condition and operation mode of collector & drainage network.
In the upcoming film Interstellar, Earth’s soil has become so degraded that only corn will grow, driving humans to travel through a wormhole in search of a planet with land fertile enough for other crops. In the real world things aren’t quite so dire, but degraded soil is a big problem—and one that could be getting worse. According to a new estimate, one factor, the buildup of salt in soil, causes some $27.3 billion annually in lost crop production.
“This trend is expected to continue unless concrete measures are planned and implemented to reverse such land degradation,” says lead author Manzoor Qadir, assistant director of water and human development at the United Nations University Institute for Water, Environment and Health. Qadir and his colleagues published their findings October 28 in Natural Resources Forum.
Irrigation makes it possible to grow crops in regions where there is too little rainfall to meet the plants’ water needs. But applying too much water can lead to salinization. That’s because irrigated water contains dissolved salts that are left behind when water evaporates. Over time, concentrations of those salts can reach levels that make it more difficult for plants to take up water from the soil. Higher concentrations may become toxic, killing the crops.
Qadir and his colleagues estimated the cost of crop losses from salinization by reviewing more than 20 studies from Australia, India, Pakistan, Spain, Central Asia and the United States, published over the last two decades. They found that about 7.7 square miles of land in arid and semi-arid parts of the world is lost to salinization every day. Today some 240,000 square miles—an area about the size of France—have become degraded by salt. In some areas, salinization can affect half or more of irrigated farm fields.
Crop production is hit hard on these lands. In the Indus Valley of Pakistan, for instance, salinization causes an average decline in rice production of 48 percent, compared to normal soils in the same region. For wheat, that figure is 32 percent. Salty soils also cause losses of around $750 million annually in the Colorado River basin, an arid region of the U.S. Southwest.
“In addition to economic cost from crop yield losses, there are other cost implications,” Qadir says. These include employment losses, increases in human and animal health problems and losses in property values of farms with degraded land. There could be associated environmental costs as well, because degraded soils don’t store as much atmospheric carbon dioxide, leaving more of the greenhouse gas to contribute to climate change. The total cost of salt degradation, therefore, could be quite a bit higher than the most recent estimate.
Salt damage can be reversed through measures such as tree planting, crop rotation using salt-tolerant plants and implementing drainage around fields. Such activities can be expensive and take years, but the cost of doing nothing and letting lands continue to degrade is worse, the researchers argue. “With the need to provide more food, feed, and fiber to an expanding population, and little new productive land available, there will be a need for productivity enhancement of salt-affected lands in irrigated areas,” they write.
On a cautiously hopeful note, Qadir adds that the issue is reaching the ears of policy makers: “Amid food security concerns, scarcity of new productive land close to irrigated areas and continued salt-induced land degradation have put productivity enhancement of salt-affected lands back on the political agenda,” he says. “These lands are a valuable resource that cannot be neglected.”
By: Tony Provin and J.L. Pitt
If your soil has a high salinity content, the plants growing there will not be as vigorous as they would be in normal soils. Seeds will germinate poorly, if at all, and the plants will grow slowly or become stunted. If the salinity concentration is high enough, the plants will wilt and die, no matter how much you water them.
Routine soil testing can identify your soil’s salinity levels and suggest measures you can take to correct the specific salinity problem in your soil.
Salinity and salt
The terms salt and salinity are often used interchangeably, and sometimes incorrectly. A salt is simply an inorganic mineral that can dissolve in water. Many people associate salt with sodium chloride— common table salt. In reality, the salts that affect both surface water and groundwater often are a combination of sodium, calcium, potassium, magnesium, chlorides, nitrates, sulfates, bicarbonates and carbonates (Table 1).
These salts often originate from the earth’s crust. They also can result from weathering, in which small amounts of rock and other deposits are dissolved over time and carried away by water. This slow weathering may cause salts to accumulate in both surface and underground waters. The surface runoff of these dissolved salts is what gives the salt content to our oceans and lakes. Fertilizers and organic amendments also add salts to the soil.
Effects of salts on plants
As soils become more saline, plants become unable to draw as much water from the soil. This is because the plant roots contain varying concentrations of ions (salts) that create a natural flow of water from the soil into the plant roots.
As the level of salinity in the soil nears that of the roots, however, water becomes less and less likely to enter the root. In fact, when the soil salinity levels are high enough, the water in the roots is pulled back into the soil. The plants become unable to take in enough water to grow. Each plant species naturally contains varying levels of root salts. This is why some plants can continue to thrive when others have died.
If the salinity concentration in the soil is high enough, the plant will wilt and die, regardless of the amount of water applied. Figure 1 shows how the various salt concentrations affect the movement of water from the soil to plants.
Salinity is of greatest concern in soils that are:
- Irrigated with water high in salts;
- Poorly drained, allowing for too much evaporation from the soil surface;
- Naturally high in salts because very little salt leaches out;
- In areas where the water table (the level or depth to free-flowable water in the soil) is shallow; or In seepage zones, which are areas where water from other locations (normally up slope) seep out.
The major source of salinity problems is usually irrigation water. This is a gradual process—the salts must accumulate over time before any effects are seen. Fortunately, plants take up many salts in the form of nutrients. But when more salt is added to the soil than is removed, the plants will eventually be affected.
In some soils, irrigation and rainwater move through the soil to leach out the salinity. Leaching occurs when water moves materials (such as salts or organic materials) downward through the soil. Several soil factors can inhibit leaching: a high clay content; compaction; a very high sodium content; or a high water table. Salt problems occur when water remains near the surface and evaporates, and when salts are not dissolved and carried below the root zone.
Soils naturally high in soluble salts are usually found in arid or semi-arid regions, where salts often accumulate because there is not enough rainfall to dissolve them and leach them out of the root zone. Salt spray near coastlines can also cause salts to build up in the soil.
In areas with shallow water tables, water containing dissolved salts may move upward into the rooting zone. This occurs by capillary action (similar to the way a wick works), where evaporation serves as the suction of water up through the soil (Fig. 2). Water moves the farthest through finer clay and clay loam soils; it moves less in medium-textured soils (loams); and least in coarser, sandy soils.
To determine the type of problem in your soil, collect a soil sample and have it tested. 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. For more information on soil testing, see Extension publication L-1793, “Testing Your Soil: How to Collect and Send Samples” or check the Web site of the Soil, Water, and Forage Testing Laboratory at http://soiltesting.tamu.edu. The laboratory’s phone number is (979) 845-4816.
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-1.
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 8.5. The normal desired range is 6.0 to 7.0, but many Texas soils are naturally 7.5 to 8.3. 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 8.5. The exchangeable sodium percentage is more than 15 percent of the cation exchange capacity (CEC). CEC is a measure of the soil’s capacity to hold cations, namely, calcium, magnesium, potassium, sodium, hydrogen and aluminum. 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 8.5 to 12.0.
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.
This phenomenon may not occur in very sandy soils because they lack clay content.
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.
Correcting salt-affected soils
Salt-affected soils can be corrected by:
- Improving drainage
- Reducing evaporation
- Applying chemical treatments
- A combination of these methods
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 (1,500 – 2,000 ppm total salts), particularly sodium salts. A water test can determine the level of salts in your water.
Leaching works well on saline soils that have good structure and internal drainage. To leach a highly saline soil, you may need to apply as much as 48 acre inches of water. An acre-inch is the volume of water that would cover 1 square acre to a depth of 1 inch (27,152 gallons).
Testing is often needed to determine how much water is needed to correct a particular soil. The testing laboratory can advise on how much water to add. After an application, the soil often must be retested to determine whether enough salts were leached out.
Highly saline soils should be leached using several applications, so that the water can drain well. Here again, drainage can be a problem. If the water cannot infiltrate the soil, the salts cannot be dissolved and leached out of the soil.
Reducing evaporation: Applying residue or mulch to the soil can help lower evaporation rates.
Chemical treatments: Before leaching saline-sodic and sodic soils, you must first treat them with chemicals, to reduce the exchangeable sodium content. To remove or exchange with the sodium, add calcium in a soluble form such as gypsum. Again, the laboratory analysis can determine how much calcium to add.
After the calcium treatment, the sodium can then be leached through the soil along with the other soluble salts. Gypsum is the most common amendment used to correct saline-sodic or sodic soils that have no calcium source such as gypsum or free carbonates. These are available at garden centers and agricultural supply stores. Another amendment, calcium chloride, is used in some places, but it is seldom available in most areas.
Many soils in the southern and western two-thirds parts of Texas contain significant concentrations of free limestone, which contains calcium carbonate. Unfortunately, these calcium sources do not dissolve in soils with high pH and therefore cannot help lower sodium levels.
If your soil contains free carbonates, you can add acids to it to form gypsum, which will react with the soil to remove the exchangeable sodium. Add sulfuric acid, sulfur, iron sulfates and aluminum sulfate, which will react in the soil to produce acid. The acid will then react with the calcium carbonates (limestone) to form calcium sulfate (gypsum), water and carbon dioxide. The acidity may also displace some of the sodium.
Table 2 lists typical amendments used to correct salt-affected soils. Although all of these amendments work, to use them you must know the amount of reactive limestone present. In general, gypsum is the safest and most effective material.
Steps for treating sodic and saline-sodic soils
Correcting saline-sodic and sodic soils is a slow process that must be carried out in steps:
- Treat the surface first, then continue to the lower depths.
- Apply an amendment to the soil surface and disk it in.
- Add 10 to 12 inches of water. As when correcting saline soils, you must add enough water to dissolve as well as maintain the calcium concentrations in solution and to move the salts and sodium through the soil.
However, do not add so much water that it remains ponded on the soil surface for extended periods.
Generally, this process must be repeated over time. A good goal is to remove the sodium to a minimum depth of 3 to 4 feet.
Test the soil periodically to pinpoint potential salinity problems and to measure your progress in correcting salt-affected soils.
The amount of amendment you need to correct saline-sodic and sodic soils is based on the amount of sodium in the soil. Several other factors also influence the amount applied: the leaching rate, the solubility and reaction rates of the amendments, and the conversion of free carbonates to gypsum.
If you take steps early, correcting the soil will be easier and less expensive, and it will have less negative impact on soils and plants.
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