Soy needs macro and micronutrients for its full development, such as nitrogen, calcium, phosphorus, magnesium, potassium, sulfur, boron, manganese, copper and zinc. Among them, we have the primary macronutrients, which are demanded in greater quantities by the crop: nitrogen, potassium and phosphorus. It is worth mentioning that these elements must be in adequate quantities and proportions so as not to harm the plant's growth.
Among the stages of the crop's reproductive phase, we have the grain filling phase (R5), subdivided into five stages (R5.1, R5.2, R5.3, R5.4, and R5.5) until complete filling of the pod. In the final phase of crop development, two main nutrients mediate full grain filling, being essential to achieve high productivity: magnesium and potassium. They will directly influence grain weight, size and protein percentage, also reflecting on seed quality.
Both at the beginning and at the end of the crop cycle, these nutrients are necessary, but it is in this final phase that they will make the most of them. Part of this nutrition necessary for grain filling comes from the translocation of other parts of the plant and part comes from the soil, from the biological fixation of nutrients and also from a possible foliar application carried out.
KEY NUTRIENTS FOR GRAIN FILLING
- Potassium
Potassium (K) has several functions in the plant, such as nitrogen metabolism, meristematic growth and enzyme activation. K also has an effect on the movement of stomata and is responsible for supplying ATP for the transport of photoassimilates. Furthermore, it has an effect on increasing the diameter of the stem, which can enable greater availability of solute from the roots to the pods in the growth stage.
Restriction of K at the R5 stage leads to the production of small, wrinkled and deformed grains and delays plant maturation, and can also cause green stem, leaf retention and flat pods (BorKert et al., 1989). A lack of potassium is also capable of causing chlorosis in the leaves, which can progress to necrosis in seriously affected areas.
Furthermore, studies carried out by the Brazilian Agricultural Research Corporation (Embrapa) in its experimental areas since the 1980s show the effects of the deficiency in the availability of this nutrient on the weight of 100 seeds (Figure 1).
