Do You Have Alkali Soils?
Updated: Aug 30
Salt is a hot topic amongst Wyoming gardeners - and for good reason. And like so many other "sciency" things in the garden, it can be confusing.
Most of Wyoming is a desert. This means we lose more water through evaporation than we gain through precipitation. The high mountain regions that feed our rivers (and fill our reservoirs) are an exception.
Learn more about evaporation and precipitation in Wyoming from the Wyoming State Climate Office.
As water evaporates from the surface of the soil it leaves behind water-soluble salts, just like a pot of water on the stove. Water-soluble salts are positive and negative ions that dissociate in water. For example:
NaCl - table salt
MgSO4 - epsom salt
CaSO4 - gypsum
NH4NO3 - ammonium nitrate fertilizer
Most of these ions are also plant nutrients, and sometimes we just have too many!
Excess salts can severely limit plant growth and cause soil compaction. Salt in the soil can come from irrigation water, ground water, fertilizers, manure or compost, and soil minerals.
The term Alkali is a confusing one, and does not have a clear definition.
It likely comes from a combination of "alkaline" and "saline".
Saline Soil
Soil very high in salts. Measured by electrical conductivity (EC), which indicates the total water-soluble salts but does not measure specific salts. A tell-tale sign of saline soils are the white crystals that form on the surface of the soil, especially in low-lying areas. A lab analysis can help identify which salts are present. Clean water can be used to leach salts below the rooting zone.
Sodic Soil
Soil very high in sodium, specifically. These soils are very challenging to manage and sometimes called “black alkali.” Typically have very high pH very poor drainage caused by a loss of soil structure.
A soil test is the only way to diagnose sodic soils. Leaching salts without the addition of calcium (usually from gypsum) can make sodic soil conditions even worse.
Alkaline Soil
Soil with a very high pH (>7). Most soils in Wyoming are are alkaline due to the high levels of calcium carbonate (lime).
Calcareous soils occur in regions with less than 20 inches of precipitation - most of Wyoming!
Several essential plant nutrients are limited in alkaline soils and it is common to see plant deficiencies (iron, zinc, phosphorus, copper, boron).
Did Manure Burn Your Plants?
Plants absorb water and dissolved nutrients (ions) through their roots. When the soil water that contains these dissolved nutrients becomes saline (too many dissolved ions), the plant has to use more energy to get the water it needs.
This condition is known as “physiological drought”, and the symptoms include stunted growth, wilting, yellowing in older leaves, and crispy leaf margins that make the plant look like it got burned. This is why people will say their plants were “burned” by “hot” manure.
This "burn" is not a result of temperature, but of too many ions in the soil solution. This is more common in poorly drained clay soils because the excess salts do not as easily leach out of the root zone with irrigation. It is this very same water and nutrient and holding capacity of clay soils is what makes them so productive with the right management.
Some plant species are more tolerant to saline conditions than others. For example, beets, corn, and squash are among the most salt-tolerant vegetables.
Beans, peas, carrots, and onions are very sensitive.
Seedlings are more sensitive than mature plants. Russian olives and junipers are more tolerant of saline conditions than fruit trees and aspens.
Learn more about salinity tolerance of various landscape and garden plants here.
The nutrients in mineral (synthetic) fertilizers like MiracleGro are typically in the salt form. Nutrients in organic fertilizers are primarily in the organic form (proteins, lipids, carbohydrates, etc). The nutrients in compost and manure are in both the organic and salt form. Unlike synthetic fertilizers, organic fertilizers and compost are also a source of active soil carbon. Active carbon provides energy for the soil microbes and helps build healthy soil.
Plants want most of their nutrients from the soil in the ionic or salt form. This causes an interesting challenge for the gardener. We need to give our plants some salts but not too many.
Feeding plants with synthetic fertilizers (salts) means the nutrients will be readily available to plants and we will likely see rapid results. However, it is easy to over-do it, especially if we also have salts in our irrigation water. We will also be feeding only mineral nutrients and not the soil. Soil needs to be fed carbon-based energy sources for long-term health.
The nutrient and salt content of compost and manure will vary depending on what it is made of. Manure-based compost will typically be higher in nutrients (and salts) than a plant based compost. Chicken manure or manure from cattle in feedlots is much higher in nutrients than manure from rabbits, alpacas, or horses. This is why many people say these manures are safe and “will not burn plants”. More of the minerals are in an organic form instead of a salt form and will take longer to become plant available.
So What Can You Do About It?
Without any help from us, salts accumulate in the soil from weathering rocks in areas with very low precipitation or poor drainage. However, many of our farming or gardening practices can make things worse.
A basic soil test can help you determine if salinity is causing problems in your garden.
As bare soil warms, water evaporates from the surface, pulling more water from deeper in the soil profile. As water moves toward the surface, it brings more salts, which are left behind on the surface as the water evaporates.
Keep the soil covered! Grass clippings work well for this, as do wood chips, straw, hay, and leaves. Mulch will also reduce weeds in your garden, add nutrients to the soil, and keep your plants happier.
If you are trying to grow more food in an area with saline soils and water, try these tactics:
Build raised beds and fill with compost and soil that is low in salts.
Choose vegetables that are more tolerant to saline conditions and use transplants when possible.
Keep the garden well-watered to make up for the fact plants are working a lot harder to get the water they do need.
Mulch heavily with high-carbon materials like woodchips, leaves, and wool.
Add biochar to your soil to help adsorb some of the excess salts and pull them out of the soil solution, and improve soil drainage.
If you have access to water that is low in salts and the soil is well drained, you can leach excess salts deeper into the soil and below the plant rooting zone. Six inches of clean water will leach away about half of the soluble salts as long as the water can move down through the soil and carry the salts below the rooting zone of the plants.
Learn More
Saline and Sodic Soils and Water:
Alkaline Soils:
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