Soil Salinity
Soil Salinity and Salt-Affected Soils
Soil salinization is the process in which water-soluble salts accumulate in the seedbed and root zone in high enough amounts to become harmful to crops. The main environmental conditions and factors that result in high salinity soils are low rainfall, high evapotranspiration rates, and salt sources that transport salts to the root zone such as water sources or the soil itself. Surface, ground, and irrigation waters can also be a significant source of soil salts.
Click through the MORE sections on the infographic below to learn more about salt-affected soils, the factors that affect soil salinity, and important considerations to make under these conditions including fertilizer management and crop choice.
The Impacts of Soil Salinity & Common Ways to Manage Salt-Affected Soils
Salt-affected soils can be categorized into three main classifications: saline soils, sodic soils, and saline-sodic soils. Soil testing is used to identify the salinity classification of soil by analyzing the following soil characteristics: soil pH, electrical conductivity (EC), and exchangeable sodium percentage (ESP) or the sodium adsorption ratio (SAR).
Soil salinity can impact crop yield, plant growth, and water and nutrient uptake. It can also cause drainage problems, short- and long-term salinity stress, ion toxicities, and soil degradation. Management of salt-affected soils is based on the salinity classification identified by your soil test. Some common management techniques include maintaining adequate leaching fractions, drainage management, soil amendments, variable rate fertilization, and use of salt-tolerant crops.
Click through the MORE sections in the infographic below to learn more about the short- and long-term impacts of salt-affected soils and explore how to effectively manage soil salinity.
Leaching Fractions
Under excessive rainfall or high irrigation scenarios, salts can leach through the soil and out of the rooting zone. If water is moved through the soil profile under these conditions, providing the soil has adequate drainage, soluble salts can be removed from the soil profile. Keep in mind salt leaching will also leach other nutrients such as nitrate-nitrogen. Leaching should be planned to avoid fertilizer application seasons, where possible. The following guideline can help plan for leaching (more complicated formulas can be used with your specific water quality, soil test, and crop identity as key parameters for determining the precise volume of water to apply):
- 6 extra inches of applied water will leach ~50 percent of the salts
- 12 extra inches of water will leach ~80 percent of the salts
- 24 extra inches of water will leach ~90 percent of salts
Reclamation Plans
In sodium dominated soils, calcium must be used or solubilized from the soil to displace sodium, which can then be leached from the root zone. Along with sodium, excess chloride and boron can also be flushed out of the system.
Calcium can be supplied via gypsum or other pH-neutral calcium salts. In soils containing free lime (calcium carbonate minerals), acid generating products such as elemental sulfur or sulfuric acid may be applied to dissolve calcium minerals, which in turn displace exchangeable sodium, flocculate clays, and allow for leaching.
Specialized Products
Products such as soil conditioners and soil surfactants can be used to manage salinity under irrigated conditions where water can serve as an active ingredient carrier. These products help water to penetrate crusted soil surfaces and help water infiltrate down through the root zone to help leach salts from the soil. Building soil organic matter is also very beneficial.
Tiling
Drain tiles are often needed to permanently remove salt from the field. However, soils with excess sodium salts can cause a collapse in soil structure and prevent water from flowing deep enough to reach the tile lines. A sound reclamation plan is needed to understand the costs of restoring the hydraulic connection between the soil surface and the tile line, which requires careful planning. Additionally, tiles require a place for water to travel to that is acceptable to downstream users and regulators.
Compost, Manure, and Fertilizer Management
There are three important considerations to make when fertilizing saline soils:
- Consider whether salts in your saline soil directly impact the requirement of fertilizers applied. For example, if your saline soil is dominated by sulfates, you would likely not need to apply sulfur fertilizer.
- Fertilizer rates should reflect the yield potential of a saline soil. Consider the potentially lower productivity of the salt-affected areas and fertilize appropriately.
- If your crop is already impacted by saline soil conditions, avoid applying fertilizer salts near the developing root system as this may worsen conditions.
In fields with saline-prone areas, variable rate fertilizer applications are recommended to avoid excessive application, maximize ROI, and decrease the chance of aggravating salinity issues.
Variable-rate seed application can help to avoid growing crops in salt-affected areas and instead allows for dollars to be put into profitable parts of your operation.
