Four macronutrients — nitrogen (N), phosphorus(P), potassium (K) and sulphur (S) — usually get most of the attention in fertility plans. But while needed in smaller amounts, 13 other micronutrients are just as essential for crop health.
It might be hard to imagine that as little as one pound of copper (actual) per acre would be as important as 100 pounds of nitrogen (actual) for that same acre. However, Mother Nature throws a curveball to crop roots trying to utilize it. Producers can help them hit that curveball by understanding the science of how plants absorb nutrition.
Three methods of uptake
All plants take up nutrients in three ways:
1. Massflow. More than 95 per cent of nutrients taken up by the crop move to the roots in this way. The flow of water into the plant carries the dissolved nutrients needed for growth. Water is used to move the dissolved nutrients from the soil and through the roots to the leaves, where both the water and the nutrients are needed most. The key is that the nutrient must be soluble in water so that the plant can absorb and then translocate it.
2. Root interception. Roots and root hairs can intercept and absorb some nutrients by chance. Applying a micronutrient coating on granular fertilizer granules (urea) might aid in distribution, but science tells us that the amount of absorption through root inception is only approximately one per cent.
3. Diffusion. This type of nutrient movement is from an area of higher to lower concentration and can happen very slowly. Phosphorus, potassium and zinc are mostly moved by diffusion in the soil.
Mass flow is the primary method (about 95 percent) of moving nutrition to the crop root zone and in the resulting absorption of nutrients into roots. If a nutrient like copper is not water soluble, the plant cannot absorb its nutritional requirement. This is Mother Nature’s Curveball.
Once we understand how solubility affects nutrient uptake into plants ,we can look at the chemical forms of micronutrients available to feed the crop. The three most common are:
- Sulphates: They meet the need to feed the plant immediately (highly water soluble), but this form is not always compatible with typical macronutrient blends.
- Oxysulphates: A combination of sulphate and oxide to provide the need to feed immediately and build soil levels for following years. Water solubility is 30 to 50 per cent.
- Oxides: (very low water solubility).
What is the right source?
How does a producer or agronomist know if a micronutrient can be absorbed by the crop? By asking “What micronutrient form is the right source for the crop to use?” This question relates to the 4 Rs of Nutrient Stewardship: Right rate, Right time, Right place and Right source. The goal of this framework of best management practices is to match nutrient supply with crop requirements and to minimize nutrient losses from fields.
Understanding the source of the micronutrient addresses the time in which it’s available to the plant. Sulphates will be available for your crop immediately and will address deficiency rapidly within days. An oxide tends to be the least costly form but will not provide nutrition until converted into a soluble form. Predicting the date of actual availability to the plant is very difficult.
Producers can hit Mother Nature’s plant nutrition curveball out of the park by using micronutrients in the form of oxysulphates. This source of crop nutrition will feed the crop’s present nutritional needs and build the soil for future needs.
Let’s look at the secret to hitting Mother Nature’s Curveball which is simply using the right source of crop nutrition. Compared to other crops, wheat is a high user of copper. Applying a granular form as an oxysulphate will feed this year’s wheat crop because some of the product is very soluble. With an investment in granular micronutrient as an oxysulphate, you can feed and build the soil to ensure sufficient copper for both the current and future crops. Accomplishing this in one pass in the current year is a smart use of time and a grand slam on Mother Nature’s Curveball.
To ensure the best bang for your micronutrient dollar, consider the solubility of the different fertilizer formulations:
- An oxide (low solubility)
- Sulphate (high solubility)
- Oxysulphate (high solubility and soil-building capacity)
Remember: If it’s not soluble in water, your crops cannot readily access the nutrient, no matter how well it’s distributed in the soil.
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