Variation of Seed Dosage on Corn Crop Production Components

The variation in population density in a corn crop can positively, negatively or neutrally affects plant productivity depending on the productive potential of the area. The aim of this work was to evaluate the effects of the variation in corn seed dosage on crop yield, and define from which percentage of variation the productivity of the sown line is affected negatively. The experiment was installed at FCAV-UNESP, in Jaboticabal (SP), Brazil. Twelve variations on plant population were evaluated, ranging from -27% to 27%, varying with a frequency of 4.5%. The morphological and productive characteristics of each treatment were evaluated through regression analysis. Each 1% of negative variation on seed dosage was lost 1.06% in corn yield. Positive variations, however, presented changes that were 0 to -2.59%. Negative variations on seed dosage reduced corn productivity by up to 28%. The positive variation affects the productivity of the crop in a less accentuated way, with a reduction in productivity that reaches 2.59% in the largest variations and may even cause positive productivity results depending on the maximum potential of the area.


Introduction
Plant density is a determinant factor in the productivity of several crops, especially in corn, which does not have the plasticity that other crops should compensate for the absence of plants (Silva et al., 2016).When in a population inferior to to the recommended one, corn produces less grains per area, failing to take advantage of the resources available on the soil, already in superior population to the recommended one, there is an intra-specific competition by photoassimilates, especially in the flowering stage of the crop (Calonego et al., 2011).
The variation in population density in a corn crop can positively, negatively or neutrally affects plant productivity depending on the productive potential of the area (Assefa et al., 2016).It can occur intentionally to meet technical recommendations, or in a natural way, through failures in the sowing process.According to Cortez et al. (2016) the speed of sowing affects the amount of seed distributed in the rows of the sowing machine.However, in addition to sowing speed, there are other factors that contribute to the existence of variations in seed dosage throughout the operation, but which, unlike the machine's travel speed, cannot be controlled to avoid operating failures, such as curve seeding errors.
When operating in curved trajectories there is a variability on the number of seeds distributed between the rows of the seedlings, and larger seeders combined with the closed curves generate greater variability in the seed dosage, and consequently in the plant population.Similar factor occurs in operations with sprayers.Luck et al. (2011) concluded that performing curves in the sprayer operation causes a substantial portion of the field to receive dosages that vary by more than 10% relative to the target rate depending on the radius of curvature.
However, even though it is a problem inherent to the sowing operation, little is known about the effects of the variation in the density of corn plants caused by this operation.Although it is a determining factor for crop productivity, there are no studies that show the effects of variation on seed dosage with a focus on modern hybrids, so there are no reasons that motivate producers and the agricultural machinery industry to invest in technologies to remedy this problem, affecting productivity of corn crops in national scale.This work is based on the hypothesis that variations on seed dosage have negative effects on corn crop productivity.Based on the information presented previously, the aim was to evaluate the effects of the variation on seed do which per methodolo

Method
The experi Veterinary 21º14′S an is defined The clima adapted by texture and Where, R = radius of curvature; D = Line spacing ± R; and PV = Percentage of variation in seed dosage in relation to target rate.

Informations About the Experiment
The experiment was implemented in a no-tillage system on corn straw in the 2016/2017 crop.For the control of weeds, 4 liters ha -1 of RoundUp Glyphosate and 2 liters ha -1 of Atrasine Nortox 500 SC were previously applied to the experiment.Along the field, corn was sown to be used as a border for the plots with the aid of a seeder-fertilizer.However, within the blocks the seedlings stopped distributing seeds and distributed only the fertilizer with a volume of 350 kg ha -1 of NPK (N: urea, P: triple super phosphate, and K: potassium chloride) in formulation 8-28-16.
Seeding of the plots was done manually, with glyphosate tolerant 2B710 PW corn hybrid with three insecticidal proteins and an early trait with recommended final population for the region of 60,000 plants per hectare with germination, purity and survival rates 95%, 98%, and 95% respectively.It was sought by means of the use of wooden jigs with demarcations of the positioning of the seeds, in each treatment to reach the population defined by the variations presented on Table 2.Each plot had a seeding line spaced 0.9 meters from the other and with length of seven meters.The cover fertilization occurred when the crop reached the vegetative stage V4, and 350 kg ha -1 of urea (157 kg ha -1 of nitrogen) was applied in the total area with distributor to the haul coupled to the tractor.Note.* Initial seed booth.** Final population of plants based on the germination, survival and purity indexes described in seed information of the seeded hybrid.

Sampling Procedures
On reaching the first reproductive stage, the parameters were evaluated in five plants of each plot:  Height of plants: for this evaluation was used a ruler graduated with an accuracy of one cm, positioned from the soil until the insertion of the flag leaf.

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Stem diameter: a pachymeter positioned at five centimeters from the ground was used and measured the largest axis of the stem to control the samplings.

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Ear numbers: five plants were randomly selected in each plot and the number of ears in the plant checked.

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At the end of the reproductive stage, when the grain moisture was close to 18%, the ears of the central five meters of each plot were collected and evaluated:  Length of ears: five ears were collected and measured lengthwise from one end to the other using a graduated ruler with a precision of one cm.The result significanc population of product of each 1%     with coefficien e 9% variation r of cob were i e of the produ on density.

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with R² = 0.78 can be related t er mass.In gen ss.2016) that ive and negativ in general, it ductivity when ty was 11%, p the area where etition between ects the crop m her hand, the n would be mor ividually, this s present in th 80,000 ha -1 pla 9 we verified of the variatio

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Spindle diameter: the diameter of five ears was measured with the aid of a precision caliper of one mm, positioning it in the center of the spigot.
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