Soil can lose essential water-soluble nutrients needed for crop growth due to excessive rain or irrigation. This process is referred to as leaching. Depending on factors like soil structure and local climate, some soils may leach more than others. Growers around the world need to understand:
- What leaching is
- How soil leaching affects the environment and community
- Leaching’s effects on your crops
In particular, knowing how boron leaching affects your specific crops will provide a roadmap to improving yield and creating a healthier local environment.
What does leaching do to the environment?
Leaching happens when excess water, through rainfall or irrigation, takes water-soluble nutrients out of the soil. When water carries these nutrients away, they need to go somewhere.
This nutrient-rich water can flow into rivers, streams, and lakes, or be absorbed into groundwater—all of which may affect local drinking water.
When drinking water contains too many nitrates, communities are exposed to health risks. Infants and small children are most at risk because they can’t yet process the nitrates and convert them into nitrite. Without this ability, an infant’s body cannot transport oxygen via hemoglobin to all areas of the body, posing a lethal threat.
How does leaching impact my crops?
Leaching removes vital water-soluble macro- and micronutrients from the soil, causing potential deficiencies in crops. Boron is one such water-soluble micronutrient.
During periods of heavy rain, boron is flushed out of the soil quickly. If standing water is present in fields for more than 24 hours, the soil can become completely depleted of boron. Most plants also die from lack of oxygen in this same amount of time, so replanting is likely.
Additionally, as nutrients leave the soil, the soil itself becomes more toxic, causing further harm to the crop, and limiting future uses for that plot of land unless the nutrients are replaced. Toxic soil means that fewer earthworms—which are essential for maintaining healthy pH levels in soil and for composting decaying leaves and plants—can survive.
Since leaching washes away micronutrients that are required for healthy crop growth, crops aren’t able to grow strong root systems that hold the soil in place. Erosion can occur when irrigation or the next large storm happens.
How does leaching effect boron content?
Soil condition and type affects how leaching occurs and thus affects the amount of boron available for growing crops.
Sandy soils that are exposed to heavy rainfall or irrigation will leach boron more easily and readily than denser soils. As such, sandier soils are likelier to need boron supplements more frequently, especially after exposure to large amounts of water. On the other hand, denser, clay-like soils tend to retain more micronutrients than their sandy soil counterparts.
Boron deficiency in crops
When crops suffer from boron deficiency, they can exhibit symptoms including:
- Misshapen, thick, brittle, small leaves
- Short stems and a “shrunken” appearance
- Weak or dead growing points
- Necrotic and watery patches in storage tissue
- Cracks and splits in petioles, stems, and sometimes fruit
- Irregular and misshapen fruit formation
- Impaired root growth
Unfortunately, by the time your plants exhibit these visible signs, yields will already have been diminished, so the best way to determine whether you need to replenish boron is through testing. Soil testing is a good way to verify how much boron is in the soil, but it can’t tell you if the micronutrient is being absorbed. Tissue analysis, however, will indicate whether or not the plants are actually taking up adequate amounts of boron for proper development. Even if boron was applied earlier in the season, the level should be rechecked frequently to see if supplementation is needed.
Correcting boron deficiency due to soil leaching
A best practice to follow concerning tissue testing is to build data over time by testing according to planting date and heat unit accumulation. Testing every year at the same growth stage and heat unit interval will give you the best data to identify trends in boron utilization in your fields.
No matter your crop or soil type, a slow-release, water-soluble supplement will help you maintain the proper balance of micronutrients during both wet and dry weather. Controlled release boron fertilizers are widely available, but the rate at which they release can vary. The ideal release should be slow enough to protect against leaching and toxicity, but fast enough to supply essential nutrients to plants when needed.
Results from soil experiments have shown that not all boron sources provide the same amount of water-soluble boron. There is a wide disparity between refined granular sodium-only borate products such as Granubor® and granular ulexite, a sodium-calcium borate product. Ulexite minerals consist of sodium-calcium borate which is classified as only partially water soluble, while Granubor is a sodium-only borate classified as 100% water soluble, improving absorption and reducing waste.
To determine the proper level and frequency for boron application, check with your local crop consultant, or contact us to speak with a U.S. Borax agronomist.
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