Strategies for good seeding density

When planting winter crops, it is necessary to prepare and adjust the seeders taking into account the importance of sowing density, which is fundamental for the good development of the plants.

A fundamental aspect for maximizing productivity concerns the number of plants to be used and their distribution in the area. This definition of the plant population has been studied by research, and is dependent on the interaction between the cultivar used and the growing conditions that are likely to occur, such as, for example, soil fertility, precipitation conditions, ambient temperature, location and season of sowing, among other factors.

In the case of fine grain crops, or the so-called winter crops in the south of the country, sowing density is also a decisive factor, as it can provide a better balance of yield components, resulting in better productivity. The sowing density of fine grains has a great influence on the tillering capacity of cultivars.

When installing a fine grain crop, the economic quantity of seed to be used must be determined in order to reduce production costs, provide better physiological development of the plant and maximize its production.

There are differences in tillering capacity between genotypes, depending on sowing density, with greater intra-plant and inter-plant competitiveness being observed when there is low and high sowing density, respectively. The effect of competition between plants is decisive in tiller production and directly affects the productivity of grains and their components. Cultivars with high tillering potential have superior capacity in maintaining high grain productivity when grown at low sowing density.

In the specific case of these crops, there is a tendency to use densities based more on empirical knowledge, established by the tradition of planting the crop, rather than on the technical rigor required by the recommendation. Therefore, to make a recommendation on the quantity of wheat seed or other small grains, one must consider intrinsic criteria to the seed, such as the weight of a thousand seeds, vigor and/or germination power, and extrinsic criteria, such as planting system, number of suitable seeds per square meter (plant stand/m²) to be achieved, spacing, soil fertility, water requirements and climatic elements prevailing in the planting location or region.

Recommendations made without technical criteria can result in poorly sized stands, with a decrease in the productive potential of the crop, waste of seeds and, as a consequence, increases in production costs with a loss in the profitability of the producer's agricultural activity.

The components of wheat crop yield: number of grains per ear, average grain mass and number of ears per unit area are highly dependent on the contribution of the number of fertile tillers per unit area, to the expression of final grain yield. . Under favorable conditions for wheat cultivation, there is uniform production in the stem population, with the emergence of regularly spaced tillers, while under stress conditions, different tillering patterns are observed, resulting in less use of nutrients, with a drop in productivity. of the crop.

The effect of competition between plants is decisive in the production of tillers, with direct implications for the yield of grains and their components. In this context, wheat genotypes with reduced tillering potential are more dependent on sowing density. In this way, identifying the ideal number of individuals per unit area, as well as which density is most stable and responsive to improving the quality of the environment, can determine the maximum grain yield, with the ideal balance of yield components, without risk of having too much or too little plants.

SEED DOSING MECHANISMS

Fluted rotor mechanisms are the most used in fine grain seeders. The main variation is in the configuration of the rotor channels, which can be straight or helical. The helical fluted rotor provides a more uniform seed flow due to the fact that the seeds are distributed gradually through the helicoid and not in handfuls, as in the case of the straight rotor.

The dosing mechanism (one for each line) is positioned at the bottom of the seed tank and is driven by one or two shafts (right and left side) that cross the entire width of the tank. The quantity of seeds to be distributed is determined by the size of the rotor section that is exposed to the mass of seeds in the reservoir and also by the rotation speed used on the rotor drive shaft.

SEEDING DEPTH

Sowing depth is one of the factors that most influence the emergence and development of crops.

When it comes to Direct Planting, controlling the uniformity of seed placement depth becomes a little more difficult, due to the presence of the straw layer on the soil surface, which results in irregularities in the microrelief. This gets worse, especially when the straw is not distributed evenly on the soil surface.

Determining the depth of seed deposition in the furrow depends on soil factors (humidity and physical and chemical characteristics), seeds, climate and cover crop management. The seed must be deposited at a depth that allows good contact with soil moisture.

The uniformity in the phenological development of plants in the field is one of the important requirements to optimize the efficiency of the plant arrangement in taking advantage of the environment's resources. Stands with uniform emergence favor the formation of homogeneous plants in terms of their architecture. Plants with late emergence have little recovery capacity, contributing little to the final productivity of the crop.

Greater seed placement depths can cause plant emergence difficulties due to greater energy consumption of seed reserves. Depths of less than 2cm can cause difficulties in germination and emergence in situations of low soil moisture content and also due to less contact between the seed and the soil. Sowing depth is one of the factors that most influence seedling emergence uniformity. Variations in sowing depth cause differences in seedling emergence time. Seeds deposited deeper generally have slower emergence than those placed closer to the surface, under favorable soil moisture conditions.

When sowing fine grains, the sowing depth should be between 2cm and 5cm.

In seeders, there are two systems to determine the seed placement depth: depth limiting wheels, used in multiple machines, and depth limiting rims, generally used in fine grain seeders.

The occurrence of dominated plants, due to the delay in seedling emergence caused by differences in seed deposition depth, is directly related to the quality of the planting operation. In this sense, all factors that influence quality planting must receive maximum attention, as it is in this operation that the number of viable plants that will be obtained at harvest is determined.

SEED ALONG WITH FERTILIZERS

The seeders used to implement fine grain crops have a single furrower for the seed and fertilizer, therefore, seed deposition occurs together with the fertilizer. In this case, the saline effect of fertilizers on the seeds is minimized, since the concentration of the product in the sowing furrows is low due to the smaller spacing between sowing lines, that is, the desired fertilizer dosage will be distributed in a number larger number of lines. Therefore, the lines distribute a small amount of fertilizer, which in most cases will not affect the seeds.

SEEDING SPEED

Seed dosages for these crops are predominantly established in kg/ha, therefore, the seeder must distribute a volume of seeds. In view of this, empirically, information has become widespread that these crops can be sown at any speed and satisfactory plant stands will still be obtained. In fact, without a careful analysis of the crop, due to the need for a high number of plants/m², it is possible that, visually, adequate stands can be obtained, however, it is known that high displacement speeds when sowing fine grains also affect seed distribution, harming crop formation and obtaining recommended populations.

In the case of fine grain crops (wheat, rice, barley, oats), recommended speeds vary between 6km/h – 8km/h. When the seeder is subjected to high travel speeds during the planting operation, there will be a significant decrease in the final population of plants. 

SPEED AND GROUND MOBILIZATION

Volume of soil mobilized represents the amount of soil that is disturbed after the passage of the seeder-fertilizer, and high values ​​can cause soil loss problems when precipitation occurs after the sowing operation, especially in sloped areas, in addition to compromising the continuity of desirable physical characteristics of agricultural soil under direct seeding. Soil moisture content is also a factor that has a significant influence on soil mobilization when sowing.

Other authors found no significant difference between treatments for wheat grain yield, as well as for its yield components, hectoliter weight, number of grains/spikelet and number of spikelets/spikelet. Some authors found that the increase in speed from 4,3km/h to 13,5km/h caused an absolute difference in productivity of 607kg/ha. The results regarding the percentage of crop residues present on the soil surface after sowing show that there was a significant reduction in the percentage of soil covered by crop residues due to the increase in sowing speed.

Sowing is a delicate operation that does not allow for errors, and attention during the operation is extremely important, as mistakes made during sowing are irreversible and could make production unfeasible. The success of a crop depends on good sowing, therefore, special attention must be given to this operation.

Sowing density in different regions

The research officially recommends the following wheat sowing densities in Brazil, depending on the producing region:

Rio Grande do Sul and Santa Catarina

The recommended sowing density is 250 viable seeds/m² for semi-late and late cultivars and 300 to 330 viable seeds/m² for medium and early cultivars. For late cultivars, when sown for dual purposes (grazing and grain harvesting or just grazing), the indicated density is 330 to 400 viable seeds/m².

Paraná, Mato Grosso do Sul and São Paulo

Densities vary from 60 to 80 seeds per meter or from 200 to 400 viable seeds/m², depending on the cycle, cultivar size and, sometimes, the types of climate and soil.

Minas Gerais, Goiás, Bahia, Mato Grosso and Federal District

The recommended density for rainfed wheat is 350 to 450 suitable seeds/m². In soils with good fertility, without exchangeable aluminum, 400 suitable seeds/m² should be used.

For irrigated wheat, the recommended density is 270 to 350 suitable seeds/m².

In the case of triticale, the recommended sowing density is 350 to 400 viable seeds/m², while for barley, 225 to 250 viable seeds/m² are recommended.

Eduardo Copetti, Semeato

Article published in issue 162 of Cultivar Máquinas.