Influence of sowing efficiency on crop quality

In any system, seeding must enable rapid and uniform establishment of the desired plant population. To achieve this, the seeder must create a sowing environment that allows the absorption of water by the seeds and the appropriate temperature and oxygen availability conditions for the germination process.

Fertilizer seeders cut the straw, open furrows in the soil, dose the seeds to be distributed, place the seeds in the furrows, cover the deposited seeds, fix the layer of soil around the seeds and apply, dose and incorporate of fertilizers. The machine must ensure uniform distribution across all rows, place the seeds at a uniform depth and cover them with a layer of earth.

The machines used for sowing winter crops or fine grain crops (wheat, oats, barley) are called continuous flow seeders, that is, they have a seed distribution system through helical channeled rotors, which distribute the seeds continuously, unlike precision seeders that distribute individual seeds. Another striking feature of small grain seeders is the spacing between rows. These machines have reduced line spacing, normally 17 cm.

Currently, for sowing fine grains, the use of multiple machines has grown year after year, from small to large producers. The use of these machines has shown excellent seeding quality with high performance, especially in areas with larger volumes of straw. The low soil disturbance and the excellent furrow finish are notable features of the use of multiple machines in sowing crops with reduced spacing.

Multiple machines are important because, in addition to providing improvements in the quality of the Direct Planting System (SPD), they enable the introduction of new species, thus enabling crop rotation, which is fundamental to the success of the system. These machines also have some particularities regarding the quality of sowing: they work with depth limiting wheels and therefore present greater uniformity in seed placement depth and less soil disturbance, which is a very favorable feature when it comes to of Direct Planting. Another important feature of multiple machines is the use of two tool holder tubes to fix the lines. This represents a greater gap between them, resulting in a greater straw flow, significantly reducing the possibility of “plugging” occurring.

In SPD, the operability of the seeders plays an important role, since several factors affect the establishment of the crop, including the speed and depth of sowing. In addition to these, the water content in the soil is also important, which in the Southern Region of Brazil tends to be excessive during the sowing season, compromising the efficiency of the seeders, which increases the importance of operational capacity in conditions of ideal sowing humidity.

BEFORE SEEDING

The management of cover crops and crop residues aims to make the land suitable for the implementation of subsequent crops. Thus, for example, if crop residues are poorly distributed and there is no management of the cover crop, bushings may occur. This indicates that the management of vegetation cover must aim to facilitate operations involved in soil conservation, with the aim of distributing them evenly on the soil surface, allowing better conditions for sowing crops or providing uniform drying of vegetation.

Thus, the correct use of the straw distributor and chopper in harvesters (deposition on the cutting width of the platform) is of great importance in direct planting, as with the use of the device, crop residues can be distributed more evenly on the soil surface.

The management of cover crops and crop residues must always consider the length of time residues remain on the soil surface, cycles and phenological stage of crops and cover crops, the need to cut straw or not, the climatic conditions of the region and release of nutrients (immobilization or mineralization), water content in the soil at the time of management, direction of movement of equipment and direction of bedding, among others (Siqueira & Casão Jr., 2004).

SEEDING DEPTH

The sowing depth must be adequate to guarantee the germination and emergence of seeds and grain yield. To achieve this, the characteristics of the seeds, the physical-chemical conditions of the soil, climate and crop management must be considered.

Greater seed placement depths can cause plant emergence difficulties due to greater energy consumption of seed reserves. Depths of less than 2,0 cm 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.

The depth of seed placement is a difficult factor to control, especially in the case of Direct Planting due to the presence of the straw layer on the soil surface. Controlling the sowing depth of winter crops is carried out using depth limiting wheels positioned slightly behind the furrowers, in the case of multiple machines. In this case, it is possible to make different adjustments for different planting situations.

SEEDING SPEED

Sowing speed has a great influence on the performance of seeders. In general, it can be stated that in the vast majority of situations and in all different seeding systems, seeding quality decreases when work speed increases. Some studies have shown that the use of higher forward speeds during sowing results in smaller plant populations, greater distances between plants and increased mechanical damage to seeds. In general, the recommended speed for sowing winter crops, according to manufacturers' recommendations, is 6,0 – 8,0 km/h.

The efficiency of seeders can be evaluated using two main parameters: the longitudinal distribution of seeds and the coefficient of variation of spacing. The uniformity of longitudinal seed distribution is a characteristic that most contributes to obtaining an adequate plant stand and, consequently, to improving crop productivity.

Percentage of Soil Coverage and Grain Yield, depending on different wheat sowing speeds.

Speed (km / h)	Soil Cover (%)	Grain Yield (kg/ha)
4,3	70,5	2.731
7,1	59,7	2.427
13,5	50,7	2.124

Speed

(km / h)

Soil Cover

(%)

Grain Yield

(kg/ha)

4,3

70,5

2.731

7,1

59,7

2.427

13,5

50,7

2.124

(Adapted from KLEIN et al, 2008)

CALIBRATION OF THE SEEDER

The machine must be calibrated according to the needs of each of the different varieties and the region in which the crop will be planted.

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 and Mato Grosso

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.

CULTURES

For triticale cultivation, the recommended sowing density is 350 to 400 viable seeds/m². For barley cultivation, 225 to 250 viable seeds/m² are recommended.

In general, density recommendations for winter crops are indicated in kg/ha, however, as the weight of a thousand seeds of these crops and different varieties can vary greatly depending on climatic conditions, nitrogen fertilization, cultivar, among others, Ideally, the adjustment should be made based on the number of seeds per linear meter.

MACHINE ADJUSTMENTS

In addition to aspects related to seed and fertilizer adjustment, some adjustments are necessary for the good performance of the seeder.

One of the precautions that must be taken into account concerns the opening of the furrow. Continuous flow seeders, whether specific to small grains or multiple ones, use a system of double discs to open the furrow, generally without the presence of cutting discs. The performance of these furrowers is directly related to the soil conditions at the time of sowing and the presence of straw on the soil surface, for this reason the different machines have adjustments for these furrowers which can be carried out through spring pressure, number of springs, adjustment of the spring stops and hydraulic cylinder travel.

The uniformity of the seed deposition depth in the soil is one of the main factors for obtaining rapid emergence and establishment of the crop. Whether through limiting rims or depth limiting wheels, depth control must be carried out carefully so that errors regarding seed germination do not occur;

During sowing, the travel speed must not exceed 8,0 km/h, as up to this speed the machines can maintain their regular performance for both seed distribution and fertilizer distribution. It is also worth mentioning that in Direct Planting, high speed is synonymous with greater soil disturbance, reduced straw cutting efficiency and lower sowing depth.

You must also observe the general condition of the seed and fertilizer dosers and check that the dosers are correctly adjusted; in addition to observing that the furrowers and conductors are not obstructed. It is still necessary to check the seeder's tire pressure, make sure that the transmission mechanisms are perfectly adjusted and always keep the seeder in perfect mechanical condition to avoid delays in sowing.

WHEN SOWING

During the sowing operation, some points must be observed to obtain a high quality operation: straw cutting efficiency, fertilizer dosage and positioning, seed dosage and positioning, furrow closure and coverage. The cutting quality of the straw is a guiding factor in the entire sowing operation process, as the functioning of the other components of the machine depends on it. Efficient straw cutting can be analyzed by the degree of straw removal caused by furrowers, as well as by the number of bushings and stops.

Regarding the quality of fertilization, the regularity of the dosage and the variation between the lines must be evaluated. The regularity of the quantity of viable seeds, their position in the soil and distribution along the planting line are the parameters that qualify the process of placing seeds in the soil carried out by the seeding unit. Finally, the performance quality of the compacting wheel can be measured by whether or not the presence of uncovered seeds or poorly closed furrows is present.

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

This article was published in issue 140 of Cultivar Máquinas magazine. Click here to read the edition.