Don’t let your soybean field retreat too easily

The death of a soybean plant follows a pre-determined path. You first notice a few yellow leaves on plants. Then several more yellow leaves follow with the leaves rapidly falling off the plant. At this time if you walk through a soybean field if you touch the petiole still attached to the stem it will break off the plant with just a light touch. Stems go next.

The plant is simply digesting all available starch and minerals remaining in tissue in order to maximize grain fill. When we hear complaints of green stem in beans at harvest this typically is associated with higher grain yield as the soil was able to mineralize more nutrition late season and provide beans a more peaceful end.

Later this summer, soybeans in their early reproductive stages will similarly march toward
self-destruction, believing the short-term goal of filling seeds is aligned with your broader production targets. Soybeans will sacrifice roots and abandon nodules at late V5 and V6, cutting off nitrogen supply. Leaves, unable to maintain protein, will lose photosynthetic capabilities and, in turn, be cannibalized to fill beans. Yields will retreat from what they could have been if they had better command of the plant’s resources.

Plant development must include a balance of resource allocations. Some resources should be used for immediate needs, while others maintained for future plant needs.

In the soybean plant at R3, a balancing act should occur with sugar. The plant has an immediate need to develop pods and nourish developing seeds. At the same time, the plant must invest in roots and nodules for nutrient uptake and nitrogen fixation to produce new leaves that make sugar to fill future pods and seeds.

However, too often at R3, a soybean plant fills the first seeds and invests in the future. It doesn’t maintain roots. It doesn’t make new leaves. It raids nutrients from existing leaves to move them to seeds. Early-setting seeds, seize all the sugar they can get, then release a barrage of hormones that force pods to abort.

A soybean plant exemplifies this poor strategy for two reasons. As a legume that requires far more nitrogen than corn for grain fill, it’s decision to prematurely stop support for the roots and nodules that supply this nitrogen has a dramatic effect on crop yield and quality. Secondly, soybean yield is not determined early, like corn. Late-season behavior continues to affect seed number and yield.

What can be done about it? As growers we may better command these processes with soybean finisher products that improve crop growth and seed production. Unlike many other yield-improving practices, these new technologies are deployed later in the season, instead of being crammed in with other early-season applications.

Our most fundamental tactic is to ensure soybeans have adequate nutrition. Potassium, manganese and boron are critical in maintaining leaf tissue and the adequate movement of sugars throughout the plants. Micronutrients are best fed through the leaf; in dry soils, foliar potassium is important.

Supplemental nitrogen can be used and may increase the amount of nitrogen as protein harvested with the crop. Beans use about 6# of N for each bushel produced.  However, mid to late season N applications have been highly inconsistent providing return on investment.

Plant growth regulator gibberellin will help facilitate sugar movement to roots, while auxin and salicylic acid (aspirin) will suppress production of ethylene – a gas that triggers plant stress responses, including leaf senescence (death). Properly timed foliar fungicides have also demonstrated ability to reduce ethylene senescence as well.

In the future, the solution to soybeans that mature too soon may be to “apply two aspirins and call me when your bin is full.”

Progressive Crop Technology offers a late-season nutrient product, PCT Soybean Finisher to consider.

The importance of foliar nutrition in soybeans

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.