There is a growing interest in looking at desiccation as a tool for an earlier soybean harvest. While this practice is quite common in the southern U.S., where soybean maturation can be quite problematic, there are multiple smaller factors that have caught the attention of many MN farmers. These include: 1) earlier harvest, 2) harvest moisture management, 3) reduced harvest losses, 4) increased harvest efficiency, 5) late season weed control, and 6) reduced foreign material.
Many of these factors are interacting, and it’s important to note that stress during certain periods can lead to an increased incidence of green stem and delayed leaf senescence in some varieties. Likewise, foliar fungicides can contribute to plants retaining leaves after pods have reached maturity. Desiccation is intended to help manage these concerns. Ultimately, the primary goal of this practice is to control the harvest window, while increasing combine speed and efficiency.
Desiccant application, on the other hand, can cause significant crop damage and yield loss if not managed properly. There has been some previous research on this topic, mainly from southern states (Whigham and Stoller, 1979; Ratnayake and Shaw, 1992; Boudreaux and Griffin, 2011; Bellaloui et al., 2021); however, there is limited information on determining the optimum time for applying the desiccant in the north. Specifically, little is known regarding the earliest phenological stage at which there is no yield depression from desiccant use. Some guidelines established that desiccation by R6.5 stage does not depress yield (Monseley et al., 2021). However, crop growth studies in our lab have reported that total plant and seed biomass can continue to accrue until nearly R8. It is important to generate local information to define the effect of desiccation timing on yield. It is also important to assess the effect on grain dry down to quantify the real advantage of harvest aids. Lastly, there is also limited information about the impact of this technique on soybean grain quality.
Commonly used desiccants in soybeans are paraquat (Gramoxone®), saflufenacil (Sharpen®), and sodium chlorate (Defol 5®). Each product label specifies a pre-harvest interval, which is the minimum amount of time that must elapse from application to soybean harvest. Therefore, it seems relevant to know how the different desiccants and timing combinations affect pod shattering (and other important factors mentioned earlier) during and after this period.
Ultimately, we propose to assess the effect of desiccation timing on soybean yield and seed quality while also assessing the effect on grain dry down and shattering. The questions to address are: How early can soybean be desiccated without affecting yield? How does this practice affect harvest timing and efficiency? How is seed quality affected by desiccation?