Effective filling: what it takes to improve grain filling

During the grain filling phase, we must pay special attention and understand which factors can affect the best production result. This will help with decision-making on the farm.

All farmers want to maximize their production without the need to explore new areas and, of course, reduce costs. The fruit and grain filling phase is the moment in which the producer crowns the efforts that have been made in the field so far and contribute to the best productive and economic performance of the crop.

Fruit and grain filling

Grain filling is the phase of soybean cultivation with enormous metabolic action. The plant directs the photoassimilates accumulated during its vegetative growth and during fruiting preferentially towards the fruits.

During the filling phase, competition for nutrients and reserves naturally occurs between the vegetative and reproductive parts of the plants. Young fruits have a strong capacity to drain mineral salts, sugars and amino acids. During the accumulation of these substances in the fruits, there is a proportional decrease in the leaves.

Taking care of the factors that influence this phase when filling grains creates conditions for a better uniformity profile and a significant improvement in final weight gain.

Efficiency in filling and transporting carbohydrates

The duration and, mainly, the efficiency of capturing solar radiation, in addition to the transformation of solar energy into carbohydrates captured in the leaves and sent to the reproductive structures, constitute the main limiting points for high productivity in crops in general.

As the plant advances its phenological phases, a greater need for adequate accumulation of energy is necessary, to meet the natural demands for the formation of all its structures and sent to the fruits. As the plant has the conditions to continue with the full sending of photoassimilates to the pods, the better the uniformity and weight of grains will be at the end of the cultivar's life cycle.

To grow soybeans, it takes 2g of photoassimilates to produce 1g of grains. Therefore, the need to keep the leaf photosynthetically active, respecting its physiological maturity, guarantees better filling and excellent quality in productivity performance in the plantation.

Another relevant factor for effective filling is to provide the plant with the best condition for pods to remain during the critical phases of R2/R3, as in this phase environmental conditions can influence greater or lesser abortion of these organs.

Changes caused by environmental stresses can lead to severe losses. Water stress has emerged as one of the main problems, as its incidence causes a drastic reduction in photosynthesis and leads the plant to produce more hormones, which cause an increase in abortion, such as ethylene and abscisic acid.

Components that compromise the filling process

Understanding the metabolic process of grain filling helps to better define what actions can be taken to increase the effectiveness of this phase to improve productivity and how to mitigate the components that can most affect this stage.

1. Abiotic stresses on filling

They cause physiological changes in the plant, such as stomatal closure and leaf curling and reduce the sending of solutes to the grains. Such effects produce a series of compounds that consume the plant's energy and reduce productivity.

2. Low potassium availability

Potassium is one of the macronutrients most required by plants, acting directly in photosynthesis. It is present in numerous functions, such as:

Plant resistance to pests and diseases;

Nitrogen metabolism;

Meristematic growth;

Enzyme activation;

Osmoregulator acting on stomatal movement;

Translocation of synthesized and photosynthesis;

Fruit quality.

3. Nitrogen supply by N-fixing microorganisms

For the filling phase, N supply is significantly reduced due to the lower activity of N-fixing bacteria and preferential allocation of carbohydrates by the plant. As a result, a significant amount of carbohydrates may no longer be translocated to the grains, reducing the productive response. During the filling phase, the greatest demand for nitrogen remobilization for the fruits occurs.

4. Reduced photosynthetic efficiency

In the filling stage, it is essential that the photosynthetic rate is adequate and working very well, that is, leaves with full photosynthesis activity to increase the sending of photoassimilates to the fruits. Keeping the leaf green for longer guarantees better fruit filling and quality.

Grain filling rate

The grain filling rate is a major factor that must be considered at this stage for soybean cultivation. This index reaches average values ​​of 8,3 mg[grain]/day from stage R5 to R7. Therefore, it is possible to interpret the increase of one day between these stages, which could represent an increase of 2,49k/ha in a population of 300.000 plants with 1 grain per plant. In other words, prolonging the grain filling phase is essential to enable large productivity gains. 

In addition to what was presented, it is necessary to consider the variables:

• Genetics

• Availability of photoassimilates

• Drain activity

• Phenological stage 

These variables directly affect the grain filling rate, which may be further optimized or delayed depending on the management used.