Advances in seeders boost corn cultivation
By Luan Solér Francischinelli and Paulo Roberto Arbex Silva, from Unesp
The profitability of a farm depends on a number of factors: market, input prices, productivity, climate, among others. Higher productivity indicates more efficient use of soil and resources, and most often results in a greater economic return for the producer.
It depends on several variables, whether those that are not controllable, such as climate and solar radiation, or those that are controllable, such as seed quality and genetic resources of the seeds. Because it depends on several variables, it is normal for the productivity of a crop in the same area to vary from cycle to cycle. However, if there is efficient control of those controllable variables, the production per area does not undergo major changes.
Sowing quality is essential to ensure the ideal stand of a crop for a given region. Once the appropriate stand has been defined for the area and region explored, the seeder is adjusted to distribute the quantity of seed necessary to achieve the ideal stand. If the sowing is inadequate, it will contribute to one of two opposite situations: either it will promote a stand below the ideal, which will reduce the productive potential of the crop due to a lack of plants, or it will provide a stand above the ideal, which reduces the productive potential of the crop due to excessive competition between plants.
Defects in the functioning mechanisms of seeders cause poor sowing, whether due to seed deposition at inadequate depths, failure to distribute, double or triple seeds or high soil compaction. All of these failures result in unsuitable stands for the crop, which leads to low efficiency in agricultural exploration and reduced economic returns for rural landowners.
Several factors interfere with the operation of a seeder and the main problems found in seeders that cause deficiencies in sowing, therefore reducing the productive potential and profitability of the cultivar, will be addressed below.
The function of a seed drill is to dose and distribute seeds in the soil according to previously established rates. The main functional processes in a seed drill are: furrow opening, seed dosage, distribution, furrow closing and compaction. Any impairment of these processes leads to deficiencies in seeding and line failures, implying a reduction in the productive potential of the cultivar and losses for the producer.
In most seeding machines, furrow opening is done by means of furrowing rods, double discs or furrowers. Both the furrowing rod and the furrower require looser soil, which is often used in conventional soil cultivation. The double disc is used for both loose soils and more compacted soils, such as those found in minimum and conservationist cultivation.
The furrow opening system is equipped with a depth-controlling spring. This spring, if properly adjusted to the tension, ensures the same seeding depth, even on slightly undulating terrain. For terrain with greater undulations, the pantographic mechanism is what maintains the furrow opening depth, which is also equipped with a depth-regulating spring.
Machines that are not adjusted or that have broken adjusting screws or springs produce variations in seeding depth along the planting line. This variation in depth can make it difficult for seedlings to emerge, favoring attacks by pests and diseases, or exposing the seed to birds. Both problems lead to a reduction in plant stand and, therefore, reduced productivity.
Reports of published studies address the effect of seed depth on seedling emergence and its development as a plant. All studies obtained similar results in the aspect that each type of crop has a seed deposition depth suitable for achieving better plant vigor. Any variation above or below the ideal depth range generates difficulties in germination or seedling emergence, which reduces the productive potential of the crop. It can be concluded that the best depth is the one recommended by the seed lot.
Each seed metering system has a characteristic efficiency. There are different types of seed metering systems on the market: gravitational, fluted cylinder, vertical rotor, perforated horizontal disc, pneumatic system, perforated belt, gripper fingers, perforated vertical cylinder and inclined disc. Each system is suitable for certain crops and types of sowing, so before buying a seeder check which is the best metering system for the crop to be cultivated. In this article we discuss the most widely used system on the market for grains, which is the perforated horizontal disc system or pneumatic system.
The error associated with the metering system is related to the deviation of the distance between seeds in the row compared to the ideal distance for a given plant stand. In addition, the metering error can cause damage to the seed, preventing germination and causing failures in the planting row.
Scientific studies on the factors that affect the performance of metering devices have concluded that the main causes are: seed characteristics (shape, size, roughness); size and shape of the cells and those of the seeds; disk rotation; wear of mechanical components; adjustments; ease of flow (the addition of graphite powder increases the precision in finger-grip, pneumatic and horizontal disk metering devices); geometry of the seed reservoir (the shape of the reservoir must allow continuous flow into the metering device); quality of the disk, ring and base, and sliding between them; performance of auxiliary mechanisms (malfunctioning of seed ejectors and expellers can cause damage to the seeds and generate failures or multiple doses).
Recent research carried out by renowned institutions has shown that in a regulated metering system with adequate maintenance of the seeder, the main factor affecting the metering system performance is the increase in the machine's movement speed. Therefore, the adjustment of the seeder's movement speed by the operator is essential to avoid errors in the metering system.
There are basically three types of seed distribution systems on the seeding machine market: gravitational, pneumatic and centrifugal. Gravitational and pneumatic seed distribution systems are present in precision seeders, while centrifugal seed distribution systems are present in seeders for broadcast distribution. Centrifugal distribution is random, so the distribution error is due to the rotation of the centrifugal mechanism. In pneumatic and gravitational systems, the distribution error is associated with the time taken for the seed to reach the bottom of the furrow, which implies spacing between seeds in the planting line.
The main factors that cause seed distribution errors to the soil are: the vertical distance between the metering outlet and the bottom of the furrow (it should be as small as possible), the deposition method (by gravity or air flow), the speed of the seed leaving the metering outlet (the higher the speed, the lower the precision) and the characteristics of the conductive tube (diameter, internal roughness and inclination).
The amount of soil covering the seed, as well as the degree of compaction produced in the soil, influences the amount of water and air available to the seed, and the resistance of the soil imposed on the seedling during emergence. Therefore, any failure in the seed covering, as well as the presence of compacted soils, is a factor that hinders seedling emergence and reduces the vigor of plant development.
Seeders have different furrow closing mechanisms, such as hoe mechanisms, discs, chains, plates and wheels. Each mechanism is suitable for a certain type of seed. In modern seeders, furrow closing and soil compaction around the seed are performed by a single wheel, called a “V” compacting wheel. After the compacting wheel, an additional compacting wheel, known as a floating compactor, can be attached.
Factors that cause closing and compaction errors are mainly in the choice of the covering and compactor mechanism and their adjustments. Each type of covering and compactor mechanism is suitable for each type of seed, whether small or large.
Studies show that regulating the vertical load of the covering and compacting mechanism at 20,3 kgf reduces the speed and emergence percentage of the cotton crop. Loads between 10,2 kgf and 15,3 kgf were beneficial for development. For the bean crop, vertical loads of 30,6 kgf or above negatively affected bean emergence and the best would be between 15,3 kgf and 20,4 kgf. Each cultivar has an ideal load and this information is obtained from the seed manufacturer.
Correct sowing with quality seeds is essential to maximize the crop's productive potential. A lack of maintenance and/or adjustments to the seeder's operating mechanisms leads to failures in the crop stand, difficulty in seed germination and seedling emergence. This reduces productivity and, as a consequence, reduces crop profits.
The seeder is a machine with complex and interconnected functional mechanisms. Therefore, an error in one mechanism should not be treated in isolation; maintenance must be periodic and preventive, and carried out in conjunction with all the mechanisms of the functional processes.
Every seed drill manufacturer provides manuals with information on the necessary adjustments and periodic maintenance of the machine, therefore it is the utmost responsibility of the operator and property manager to be attentive, since a well-adjusted machine is “synonymous” with greater productivity.
*Per Roberto Alves, ... e Laercio Zambolim, from UFV
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