Simple Tips To Conquer Soil Sodicity
Sodicity refers specifically to the amount of sodium present in the rain or irrigation water. Excess amounts of sodium can adversely impact soil structure, making plant growth difficult. Highly saline and sodic water can cause problems for crops, depending on the soil type, crop species and growth stage. The amount of water able to seep through the root zone can also be affected.
Sodicity has serious impacts on farm production, as well as significant off-site consequences such as:
- Surface crusting
- Reduced seedling emergence
- Reduced soil aeration
- Increased run-off and erosion risk
- Less groundcover and organic matter
- Less microbial activity
The Problem With Soil Sodicity
- Reduced water infiltration and retention: Sodium ions can cause soil particles to become compacted, making it difficult for water to infiltrate and be retained in the soil. This can lead to drought stress in crops and soil crusting, which can inhibit gas exchange between the soil and atmosphere.
- Nutrient imbalances: Sodicity can cause imbalances in soil nutrients, making it difficult for plants to take up necessary nutrients and leading to reduced growth and yield. Sodium can also inhibit the uptake of potassium by plants, leading to further nutrient imbalances and reduced crop performance. In addition, the presence of high levels of sodium can disrupt the balance between potassium and sodium in the soil, leading to reduced potassium uptake and reduce plant tolerance to abiotic and biotic stress factors.
- Reduced biological activity: Sodium ions can inhibit the growth of beneficial soil microorganisms, leading to reduced biological activity in the soil.
Managing Soil Sodicity
To manage sodicity and maintain soil health: Consider leaching through irrigation, amending soils with gypsum (or in some cases lime), and building organic matter.
The intent of these management options is to improve soil structure and prevent the problems experienced on these soils. The options are:
- Destock paddocks when the soil is wet; pugging by livestock feet damages surface soil structure and increases surface sealing.
- Avoid disturbing already productive sodic soils.
- Apply agricultural lime or gypsum.
- Increase organic matter content.
- Use deep-ripping in conjunction with slotting or trenching with added gypsum.
- Use raised beds or deepened seedbeds.
- Use plants more tolerant of waterlogging and sodicity, or change land use.
Avoid disturbing already productive sodic soils
Sodic subsoils will generally maintain their structure if left undisturbed. Assess past productivity first and sodicity second. If productivity has been good, keep managing them the same way.
Apply lime or gypsum
In the right conditions, adding lime or gypsum to dispersive soils decreases the sodium exchange percentage, reduces dispersion, and increases stable soil structure. Calcium ions displace some of the sodium ions on the surface of soil particles, creating better soil structure which allows sodium ions to leach out.
Gypsum can be applied on the surface of alkaline soils. Gypsum improves the structural stability of dispersive topsoils quite quickly. The quickest and most effective way to treat sodic subsoil is to add gypsum directly to the subsoil, using deep cultivation, slotting or trenching.
Surface applications of gypsum may be less beneficial in deep sandy or loamy duplex soils where the dispersive clay subsoil is deeper than 40cm, because most crop roots are in the upper 40 cm of the soil profile.
Adding lime to Soil Sodicity
Lime should only be applied to acid soils (where pH in calcium chloride is less than 4.8) because lime will not dissolve in alkaline soils and will have no benefit. Some sodic soils in the high rainfall areas can be acid.
Increase organic matter
Organic matter binds soil aggregates together and helps resist physical breakdown of soil. This in turn makes it easier for sodium to leach out. Organic matter is best applied in conjunction with gypsum or lime.
Options to increase soil organic matter include:
- stubble retention
- green and brown manuring
- phase-cropping with a deep-rooted perennial pasture, such as lucerne.
Deep-ripping can be used to break up compacted and poorly structured soils and to help generate structure and porosity. However, the benefits can be very short-lived. Sometimes deep-ripping makes the soil worse because worked (tilled) soil disperses more readily and the area will become too boggy.
Ripping can bring up large clods of dispersive soil and bring toxic elements, such as boron and salt, to the surface. We recommend subsoil testing before ripping, or deep-ripping on a small test strip.
After ripping, apply lime (in acid soils) or gypsum, preferably with additional organic matter, to help stabilise the deep-ripped soil. A tramline (controlled traffic) farming system will help prevent re-compaction of the loosened soil.
Use raised beds or deepened seedbeds
Both of these practices involve the lifting and aeration of hardsetting topsoils or soils prone to waterlogging. This improves soil drainage and structure. Where the topsoil is structurally unstable, add gypsum and organic matter to maintain the improved structure. Raised beds rely on drainage channels.
Proper management of sodicity and salinity is crucial for maintaining soil health and productivity.
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