Due to the growing need to increase food production worldwide, carrying out two harvests per agricultural year has occurred more frequently in recent years, aiming at relevant productivity and greater financial return on the property.
For this dynamic to occur, enabling the sowing of cultures in the appropriate window of time, and with the best conditions of solar radiation and temperature, pre-harvest desiccation of soybeans is necessary due to its benefits.
Benefits:
• Anticipation of the soybean harvest, contributing to the sowing window of the subsequent crop (“safrinha”);
• Uniformization of the crop, reducing variability in maturation between grains;
• Control of weeds in the desiccated area.
In order for this practice to be effective, it is necessary to pay attention to some details related to the application, as we will list below.
When to desiccate?
The main point to be observed in carrying out pre-harvest desiccation is the appropriate time for application. This is because early applications can cause losses in productivity and reduced seed vigor, while late application does not meet the desiccation objective, presenting a result that is not as significant as expected.
The beginning of the plant's physiological maturation process occurs at the R7 phenological stage of development, when the grain is still physiologically dependent on the plant. Seed maturation begins at the time of fertilization of the ovule and ends with the maximum accumulation of dry matter, with physiological maturity being the stage that shows increased germination, vigor and dry matter.
Therefore, desiccation must be carried out from the moment the seed reaches its maximum point of physiological maturity. Thus, an ideal time to carry out desiccation is considered when the soybean crop has 76% of the leaves and pods yellow and the grains are between 50% and 54% moisture content, more specifically, at the R7.3 stage (Maturity physiological: above 75% of the leaves and pods yellow), this is the moment when the greatest accumulation of dry matter occurs and more than 98% of the beans are detached from the pod.
In addition to the stage recommended for desiccation, there are precautions to be observed regarding time. Excessive rain and delay in harvesting can harm the stage and cause grain losses, making it susceptible to the occurrence of pod opening and even soybean germination inside the pods, especially in cases with significant humidity in the crop.
Which products to use in desiccating soybeans?
The desiccation of the soybean crop consists of the application of herbicides, predominantly from the class of non-selective herbicides that have a broad spectrum of action. Although there are several herbicides on the market, it is always recommended to use registered products.
A herbicide widely used for this management practice was Paraquat (photosystem I inhibitor), however, its use was prohibited from 2020 onwards due to potential health risks arising from its use and handling. Currently, the main products recommended for this purpose include Diquat, whose mechanism of action is the inhibition of photosynthesis in photosystem I, as it competes with NADP+ as an electron acceptor; Ammonium glufosinate (except for tolerant technologies, such as Liberty Link, Enlist and Conkesta) which is a contact herbicide, that is, it is not translocated inside the plant and acts by inhibiting the glutamine synthetase enzyme that results in the accumulation of ammonium inside of the plant, generating toxicity. There is also the use of Saflufenacil, which is a contact herbicide that inhibits the Protox enzyme, affecting the route of chlorophyll synthesis in plants.
It is worth mentioning the importance of consulting an Agricultural Engineer for the most appropriate recommendation of the product, the correct dose and the best management to be used for desiccating the crop, since this practice also aims to control weeds present in the area.
The use of mineral or vegetable oil-based adjuvant can be an alternative to break down the lipids that make up the cuticle and cell membrane, facilitating the absorption of the product and increasing its fixation on the leaf, reducing losses due to evaporation or washing by rain. . Therefore, the use of adjuvants can increase the efficiency of the herbicide used for desiccation.
We should also pay attention to the grace period, which varies according to each commercial product. As a rule, you should respect around 10 days after application before carrying out the harvest. When dealing with fields for the production of soybean seeds, all care must be redoubled so that they do not affect the desirable physiological attributes of the seeds, such as vigor and germination.
