Foliar fertilization of soybeans is a critical step in achieving greater yields. In recent years, we have burnt the proverbial candle at both ends when it comes to crop micronutrients. On one end, yields have increased and with each additional kernel or bean removed from the field, we have taken away more nutrients.
On the other end of the candle, we have not returned micronutrients to the soil as quickly as in past years. That’s right, we applied micronutrients for decades, long before they became a hot issue. The micronutrients were in the manure we spread, in the rain that fell downwind from factories and even in the N-P-K fertilizer that we used to apply.
Manure is now applied to fewer acres, and the Clean Air Act has resulted in cleaner air technology that has also removed trace elements like zinc, a critical micronutrient for root development and stalk extension. And finally, in formulating more concentrated N-P-K fertilizers, we have removed the micronutrient by-products in those fertilizers.
Another concern in recent years has been that glyphosate may alter the chemistry of micronutrients inside plants and the availability of micronutrients in the soil. However, this is not true as empirical research has shown no significant differences in manganese uptake in soybeans that are glyphosate tolerant. Rather, the specific variety of beans will show different manganese uptake from soil.
Therefore, we need to add micronutrients to our soybean program – especially manganese and boron. Broadcasting these nutrients in dry form, however, makes them more difficult for plants to intercept. Banding these nutrients in the root zone improves their availability, however, in-row starters are less common in soybean production.
The most efficient and common way to feed micronutrients to plants is through the leaves. Foliar application of micronutrients to soybeans allows us to bypass chemical reactions in the soil that may reduce micronutrient availability. It also allows nutrients to enter the plant during dry conditions, when soil moisture may be too low to move micronutrients toward plants.
Dry soil conditions not only threaten micronutrient availability to plants, but nitrogen, potassium and phosphorus availability as well. Potassium deficiencies are exacerbated by low soil moisture. Add to this a general reduction of K soil test levels across the region and we now have need for supplemental K along with critical applications of Mn and Boron.
Balanced nutrition is also important in a foliar program. Single-nutrient approaches can be dangerous. Too much of a single nutrient may block the availability of other nutrients to plant cells. In addition, supplying only one nutrient will provide a short-term solution until the next most-limited nutrient slows plant growth. Remember, micronutrients are required in very small amounts, so highly-concentrated single nutrient products that look like a bargain may supply that nutrient far in excess of what the plant requires.
Among the micronutrients recommended for soybeans are manganese, which is important in chlorophyll development and enzyme activation, and boron, which promotes reproductive growth and stem branching in soybeans. Plant growth regulators can also be added to the foliar mixture to more precisely shape soybean development.
Some foliar ingredients may trigger the plant’s immune system. This trigger gives the plant the advantage of manufacturing defense proteins before the attack of fungi and bacteria, thereby reducing the time required to contain an infection.
Finally, soybean foliar products should include a basic sugar such as sucrose, which has been shown to reduce leaf burn in soybeans. It is also thought to act as a humectant, raising moisture levels at the leaf surface so nutrients stay dissolved for uptake.
Foliar nutrition is an important step in taking good soybean management programs to a higher level.
PCT | Sunrise offers three foliars developed in-house: Soy Foliar BAM, Soybean Foliar LITE and Soybean Foliar EXTRA, along with a late-season foliar, PCT Soy Finisher.