Seeder maintenance

Each culture has a need for space and light to grow and develop. Therefore, seed density is an item that must be carefully observed at the time of planting, when the seeders must be maintained and well adjusted.

The optimal plant density is determined by the requirements of each species and by environmental factors that directly influence the development of the plants and, consequently, the final productivity of the crop. It is known that crops present different responses to variation in the plant population. Some authors claim that soybean cultivation, for example, supports variations of up to 15% in sowing density, without affecting yield. On the other hand, studies show that non-uniformity in the spatial distribution of plants can result in losses of up to 15% or more in corn crops; 35% or more in sunflower crops and 10% or more in soybean crops.

In this way, it can be stated that the sowing operation is considered the main operation of any agricultural cultivation. Crop productivity is directly dependent on the quality of sowing. It is during planting that the level of productivity that can be expected for the crop that is being implemented is defined.

In this context, seeders play an important role within the production process, as the productivity of a crop is significantly affected by the plant stand, mainly due to the variation in the uniformity of seed distribution in the sowing line.

THE IMPORTANCE OF PLANTING

One of the fundamental aspects for maximizing productivity concerns the number of plants to be used and their distribution in the area. This definition of plant population has been studied by research and is dependent on the interaction between the cultivar used and the growing conditions. Currently, specific recommendations from companies that own the cultivars already indicate the number of plants to be used per area for each of their cultivars and for the different regions where they are indicated.

In highly productive crops, plants are subjected to a high degree of competition for growth resources, which are normally available in limited quantities, and are therefore insufficient to meet the combined demand of all plants in the crop. . The factors that plants can compete for are: water, light, nutrients, oxygen and carbon dioxide. In this way, the position that the plant is in relation to the others within the crop affects the degree of competition to which it will be subjected and, therefore, the capacity to supply that limiting resource. Therefore, plants that are closer to each other will be subject to a greater degree of competition for growth resources. The greater the degree of competition that a plant is subject to, the lower the grain yield of that plant will be.

Crops have a certain degree of plasticity or tolerance for variation in the plant population. This plasticity is variable between species. Soybeans, in general, support considerable variations in the number of plants per area. Modern corn hybrids, on the other hand, tolerate little variation in the population, thus presenting low plasticity, due to the low tillering and production capacity, normally of a single ear per plant.

It is known that, in the case of corn, crop yield increases with increasing planting density, until reaching an optimal density, which is determined by the cultivar and external conditions resulting from the local soil and climate conditions and crop management. From the optimum density, when yield is maximum, increasing density will result in a progressive decrease in crop productivity. The optimal density is, therefore, variable for each situation, being basically dependent on three factors: cultivar, water and nutrient availability.

By measuring the distance between the seeds, the percentage of failures and the percentage of doubles are obtained. However, it is not possible to measure seeds that were simply displaced during the planting process. For this reason, there is a more appropriate way to determine uniformity, which is through the use of the coefficient of variation (CV). The higher this coefficient, the greater the variation in distance between plants.

Practice has demonstrated that the acceptable % CV is up to 25% and that, for every 10% CV, even obtaining the desired plant population, there is a reduction in yield of approximately 128kg/ha (Pioneer, 2010). Field surveys carried out by some teaching and research institutions show that, on average, the CV% of crops is above 30% and can, in some cases, be greater than 60%.

SEED DISTRIBUTION SYSTEMS

The seed distributors of precision seeders have the function of individualizing the seeds to distribute them one by one. The most frequently used mechanisms are honeycombed discs. The use of pneumatic systems for the distribution of large grains has increased considerably in all productive regions of the country. This fact can be credited to the advantages that the system offers, which, even though it presents a higher cost when purchasing the machine, the cost/benefit ratio is favorable to the producer considering the gains obtained. Among the main advantages of this system, the following can be highlighted:

- great ability to individualize seeds;

- ability to distribute irregularly shaped seeds with greater precision;

- better adaptation to the most varied types and formats of seeds;

- reduction in the occurrence of failures and double errors;

- better homogeneity in seed spacing;

- reduction of mechanical damage to seeds.

It is known that seeding quality decreases when work speed increases. Regardless of whether the machine is equipped with a honeycomb or pneumatic disc type doser, both systems are sensitive to increased work speed, to the point of considerably affecting not only the final population of plants, as well as the spacing between seeds, increasing your CV considerably.

It can be seen in Graph 1 that, regardless of the type of doser, the planting speed directly influences the uniformity of seed distribution, with a greater effect in the honeycombed disc system, starting at a speed of 6km/h.

This negative effect of increasing speed can be better understood following the following reasoning: in a corn planting with 5 seeds/meter, at a speed of 6km/h, the machine has to distribute 8,3 seeds/second. If the speed increases to 10km/h, the machine will have to distribute twice as many seeds, that is, 16,6 seeds/meter. In a soybean plantation with 15 seeds/meter, at a speed of 6km/h, the machine has to distribute 25 seeds/second. Some producers, depending on particular criteria, carry out planting at speeds of up to 12km/h. In this case, the machine will have to distribute 50 soybean seeds/second, so it is practically inconceivable to “require” that the machine distribute all the seeds evenly.

In addition to reducing the individualization capacity of the seeds, when they are released from the dosing mechanism, they suffer an increase in falling speed due to the acceleration of gravity and are also subject to the action of a horizontal force resulting from the displacement of the seeder. This horizontal force causes the seeds to undergo vibrations – ringing – within the conductive tube, changing the time it takes for the seeds to fall to the ground and, as a consequence, changing the spacing between them. Furthermore, high speed of work causes the seeds to roll and/or jump out of the furrow upon impact with the soil, causing them to be out of their correct place, which is easily and routinely confused with a “double grain”.

The use of agricultural machinery and equipment, when done correctly, improves operational efficiency and increases effective work capacity, thus facilitating farmers' tasks. It is good to remember that the success of a crop is the result of the sum of several factors, which, together, will determine the profit or loss, some under human control, others not. Therefore, for those that can be controlled, it is recommended to use every effort to adopt or minimize them.

Quality in seed distribution

The quality of seed distribution in the soil must also be analyzed in detail, since the uniformity of spacing between plants has a significant influence on crop productivity. The position of seeds in the soil can be measured through the spacing between seeds. The percentages of acceptable spacings, double spacings and failures determine the plantability index of the seed being used; therefore, the rules in the table must be followed.

PROBLEMS CAUSED BY POOR SEED DISTRIBUTION

Unevenly distributed plants imply inefficient use of available resources, such as light, water and nutrients. In this situation, two plants try to occupy the same space, and what is observed is a high degree of competition between them, with a reduction in the grain yield of both, as well as plants with thinner stems and less leaf area production.

Eduardo Copetti, Semeato SA

Article published in issue 154 of Cultivar Máquinas.