Seed vigor level in association to fertilizer distribution

This work aimed at evaluating yielding responses of soybean seeds production fields in response to the association between seed vigor level and fertilizer distribution systems at the sowing line.Experimental design was randomized blocks design, with two growing Research, Society and Development, v. 9, n. 10, e5999108658, 2020 (CC BY 4.0) | ISSN 2525-3409 | DOI: http://dx.doi.org/10.33448/rsd-v9i10.8658 3 environments (Passo Fundo RS and Ernestina RS) x three vigor levels (high = 90%, medium = 70% and low = 60%) x three fertilizer distribution systems (absence, conventional and by transhipment), arranged in four replicates, grain yield (GY). For grain yield (GY), it was applied the method genotype main effects and genotype environment interaction (GGE). Seed vigor levels and fertilizer distribution systems influence on seed yield, first pod insertion height, plant height, number of pods in the main stem and ramifications, magnitude and length of ramifications in soybean.The high vigor level in the conventional and by transshipment fertilization systems provided an absolute increase of 10.9 and 5.6% in seed yield, respectively, in Ernestina-RS. The conventional fertilizer distribution system, in Passo FundoRS, increased seed yield in 12.5% in plants originated from low vigor seeds.


Introduction
Soybean (Glycine max (L.) Merrill), originating from China, is the Fabaceae with the greatest economic expression in the world, being Brazil the second largest producer. A survey carried out by CONAB (National Food Supply Company) shows how much soybean production in Brazil corresponds to the country´s growing area, reaching 35.2 million hectares in the 2017/18 harvest, with production of approximately 117 million tons (CONAB, 2017).
World populational growth is directly related to the demand for food, thus, improved growing techniques for productivity increase are essential. In order to set high yielding fields, plants of high performance are necessary, which come from seeds of high quality that efficiently use the available resources.
Many factors influence soybean yield, among them, the use of high physiological quality and high-vigor seeds are highlighted. These factors provide uniformity in germination, emergence and seedling growth at field conditions, improving grain yield (Marcos Filho et al., 2009;Szareski et al., 2018a;Troyjack et al., 2018;Szareski et al., 2018b;Meneguzzo et al., 2020).
The seek for uniform fields and superior performance of the plants is closely related to seeds of high physiological potential and the uniform amount of fertilizer in the sowing line.
These effects may be hampered by peculiarities expressed in some growing environments, such as sharp slopes that may impair the proper functioning of the tractor-sowing set, Development, v. 9, n. 10, e5999108658, 2020 (CC BY 4.0) | ISSN 2525-3409 | DOI: http://dx.doi.org/10.33448/rsd-v9i10.8658 5 especially regarding the correct fertilizer distribution (Pelegrin et al., 2016;Ferrari et al., 2016;Rosa et al., 2019) The use of high quality seeds is fundamental for the maximum expression of the productive potential of species and variety being cultivated. It occurs because the seed is the vehicle of advances achieved by plant breeding, and its performance is influenced by physical, sanitary and physiological attributes. Among physiological quality attributes of the seeds, vigor stands out for being related to germination, emergence, seedling growth, uniformity rates and uniformities at field, influencing grain yield strongly.
Due to the lack of researches combining seed vigor and the efficient fertilizer distribution, as well as its effects on the main components of soybean yield, this work aimed at evaluating yielding responses of soybean seeds production fields in response to the association between seed vigor level and fertilizer distribution systems at the sowing line.

Methodology
The experiment was stablished in two growing fields (environments) in the agricultural year of 2016/2017, being, Ernestina-RS, located at latitude 28º29'56 "S and longitude 52º34'24" W with altitude of 493 meters, and Passo Fundo-RS, with latitude 28º15'46 ''S and longitude 52º24'24''W, and altitude of 687 meters. The soils were classified as typical dystrophic red latosol (Streck et al., 2008), and the climate for both environments was characterized by Köppen as subtropical humid Cfa type.
Experimental design was randomized blocks design, with two growing environments (Passo Fundo -RS and Ernestina -RS) x three vigor levels (high = 90%, medium = 70% and low = 60%) x three fertilizer distribution systems (absence, conventional and by transhipment), arranged in four replicates.
Before sowing, the seeds were stratified in lots of different vigor levels through the accelerated aging method (AOSA, 1983). For this, seeds were distributed in single layers of approximately 250 grams and arranged on an aluminum screen fixed inside a plastic container. 240 mL of water was added to each vessel, which were placed at the aging chamber set at 41 °C. After 48; 84 and 96 hours of exposure, the seeds were submitted to germination test (BRASIL, 2009). This criterion was established to define vigor levels at 90% (high); 70% (medium) and 60% (low).
Three fertilizer distribution systems were used in the sowing machine. The conventional one, which is composed by an endless screw and gravity system; by Development, v. 9, n. 10, e5999108658, 2020 (CC BY 4.0) | ISSN 2525-3409 | DOI: http://dx.doi.org/10.33448/rsd-v9i10.8658 6 transhipment, which is composed by endless screw and transshipment system, where the fertilizer is driven by the impeller (endless) and taken to a damming chamber, occurring the transshipment in uniform and homogeneous volumetric quantities through the level regulator into the nozzle discharge to the soil. There was also a treatment level representing the absence of fertilizer distribution.
Seeding was carried out in the first half of November 2016, using as biologic model the cultivarDM5958RSFIPRO®, with indeterminate growth habit. The sowing density corresponded to 30 seeds m -2 , and the experimental unit was composed by five lines with five meters length, spaced by 0.45.m, totaling 11.25 m 2 . For the evaluations of traits of interest, 3,96m² was collected, which corresponds to the useful area of the experimental unit.
Soil fertility and acidity correction was performed based on the previous soil analysis, following the instructions from the manual of fertilization and liming (CQFS, 2004). It was used 300kgha -1 of NPK fertilizer in formulation 02-20-20, and control of weeds, pest insects and diseases were performed preventively to minimize biotic effects in the experiment´s results. The evaluated traits were measured through the random selection of ten plants from the useful area of each experimental unit, being: Contribution of the number of seeds in the pods: Pods containing one (N1); two (N2); three (N3) and four (N4) seeds were evaluated, counting the number of pods with viable seeds. The results were expressed as percentage (%). Development, v. 9, n. 10, e5999108658, 2020 (CC BY 4.0) | ISSN 2525-3409 | DOI: http://dx.doi.org/10.33448/rsd-v9i10.8658 Seed yield (RS): obtained by the ratio of seed mass in the useful area of each experimental unit, which was weighted by the number of plants contained in the experimental unit area, after weighting to 12% of humidity and population density adjusted for hectare. The results were expressed in bags per hectare (bgha -1 ).
The data were submitted to diagnosis of normality and homogeneity of variances.
Then, variance analysis was performed at 5% of probability in order to verify the presence of interaction among growing environments x vigor levels x fertilizer distribution systems. When significant, the factors were sliced into simple effects. In contrast, in the absence of interaction, the variation factors were sliced into principal effects.
For seed yield (SY), it was applied the method genotype main effects and genotype environment interaction (GGE). It allowed to gather the effects attributed to growing environments, tested vigor levels and fertilizer distribution systems. Through this test, it was possible to identify which treatment levels presented higher performance (Yan, 2001;Woyann et al., 2017).

Results and Discussion
The analysis of variance revealed significant effect at 5% of probability for interaction among growing environments x vigor levels x fertilizer distribution systems (Table 1)   Significant interaction was evidenced between levels of vigor x fertilizer distribution systems for the contribution to seed yield through pods with one seed (N1). Significant interaction between growing environment x fertilizer distribution system was verified for the contribution to seed yield through pods with four seeds (N4). Significant interaction was also expressed between growing environment x levels of vigor for the contribution to seed yield through pods with one (N1) and two seeds (N2).
First pod insertion height (FP) revealed ( Table 2) that in the absence of fertilization, and through conventional fertilizer distribution system, the Ernestina -RS environment increased this trait´s magnitudes when plants originated from high and medium vigor levels. For management with by transhipment fertilizer distribution, there was higher first pod insertion height for plants from low vigor seeds. For Passo Fundo-RS, the absence of fertilizer Development, v. 9, n. 10, e5999108658, 2020 (CC BY 4.0) | ISSN 2525-3409 | DOI: http://dx.doi.org/10.33448/rsd-v9i10.8658 increased this trait in plants from low vigor seeds.The high level of vigor, for Ernestina -RS, resulted in increased first pod insertion height for all fertilizer distribution systems, while the low vigor level increased this trait in the by transshipment distribution system (Table 2).In Passo Fundo -RS, the high level of vigor increased first pod insertion height in the management compound by absence and conventional fertilizer distribution. For Ernestina -RS, the high and medium vigor levels increased first pod insertion height regardless the fertilizer distribution systems. The low vigor level potentiated this trait in Ernestina -RS when plants were grown in the by transshipment distribution system (Table 2). These results corroborate with Carvalho et al. (2010), which determined that the first pod insertion height does not result in soybean yield loss, as long as its magnitude is close to 10 cm, indicating that soybean plants were ideal for mechanized harvesting, and losses were minimal.
The lowest plant height was obtained through the by transshipment fertilizer distribution system for high and medium vigor levels, and the low vigor did not differ for any of the fertilizer distribution systems for both growing environments (Table 2). Sediyama et al. (1999) reported that taller plants, or whit thinner stem, tend to lodging, which is positively associated with plant height and causes serious damage to soybean seed productivity (Sherrie et al., 2011). Regarding vigor levels, superiority is verified for the high vigor level in the three fertilizer distribution systems for Ernestina-RS. Similar results were expressed for Passo Fundo -RS when the soybean was submitted to absence and conventional fertilizer distribution system. The height of soybean plants should be between 60 and 90 cm in order to potentiate seed production and minimize losses with mechanized harvesting (Garcia et al., 2007). In Ernestina-RS, the highest plant height was verified for medium and low vigor levels, regardless the fertilizer distribution system. According to Rossi et al. (2018), quality and especially the vigor of seeds used may determine the growth of soybean, as well as the insertion of the first pod. Schuch et al. (2009) define that soybean from seeds of high physiological quality present increased stem height, stem diameter and grain yield by 25% when compared to plants from low quality seeds.
For the three fertilizer distribution systems, seeds with high vigor increased the number of pods in the main stem (NM) in Ernestina -RS (Table 3). For Passo Fundo -RS, it was evidenced that high vigor seeds increased the number of pods in the main stem at absence and conventional fertilizer management. Between growing environments, vigor levels do not differ in function of fertilizer distribution systems for number of pods in the main stem. The number of pods from ramifications (NR) was increased with medium seed vigor level in the conventional fertilizer distribution system. For Passo Fundo -RS, it was observed that seeds Research, Society and Development, v. 9, n. 10, e5999108658, 2020 (CC BY 4.0) | ISSN 2525-3409 | DOI: http://dx.doi.org/10.33448/rsd-v9i10.8658 11 of high vigor increased NR. When using low vigor level seeds, better responses were expressed for the by transshipment system (Table 3). Passo Fundo -RS was superior for this trait through the conventional distribution system and by transhipment.  (Table 3). Regarding seeds of medium vigor, the environment Passo Fundo -RS showed similarity for this trait in function of fertilizer distribution systems. According to Peixoto et al. (2008), soybean may express from one to ten ramifications per plant, because this magnitude is due to the spatial arrangement of plants in the canopy, plant population, intraspecific competition and genotype characteristics, as well as edaphoclimatic factors. Regarding the number of ramifications in the main stem (NRM) in the growing environment of Passo Fundo -RS, the conventional fertilizer distribution system resulted in superiority for plants from medium and low vigor level seeds. Otherwise, for by transhipment fertilization system, satisfactory responses were obtained for low vigor seeds.

Seeds of all vigor levels, in Ernestina
Furthermore, the magnitude of soybean ramifications is determined by intraspecific competition, edaphoclimatic factors, quantity and quality of solar radiation, plant arrangement, sowing time, and genotype characteristics (Martins et al., 1999).

Ramification length (RL) was potentiated in Ernestina -RS when plants were
submitted to conventional fertilizer distribution systems and high vigor seeds (Table 3). In Passo Fundo-RS, this trait did not differ in function of fertilizer distribution systems and vigor levels. Regarding growing environments, Passo Fundo -RS was superior when plants came from low vigor seeds, under the by transshipment fertilization system.  (Table 4). In Ernestina-RS, high vigor seeds increased this trait´s magnitude even in the absence of fertilizer. Seed yield (SY) showed similar tendencies between high and medium vigor level of the seeds, independently of the fertilizer distribution system used in Ernestina -RS (Table 4). For Passo Fundo -RS, vigor levels expressed tendency to increase SY, similar for all fertilizer distribution systems.
However, it can be observed that the high vigor level, in association to conventional and by transshipment fertilization system, provided an absolute increase of 10.9 and 5.6% in the yield of seeds, respectively, for Ernestina-RS. The conventional fertilizer distribution system, in Passo Fundo -RS, increased seed yield in 12.5%, when plants originate from low vigor seeds. CV-Coefficient of variation. 1 means followed by the same lowercase letter in the column, for fertilizer distribution systems within growing environments and each vigor level, uppercase letter in the line for vigor levels within fertilizer distribution systems in each environment, and Greek letter in the line for growing environments within fertilizer distribution systems at each vigor level, did not differ among themselves by Tukey test (p <0.05). Source: Authors.
The employment of high quality seeds is fundamental for expressing the maximum productive potential of the species and variety being growth. Seeds are the carriers of Development, v. 9, n. 10, e5999108658, 2020 (CC BY 4.0) | ISSN 2525-3409 | DOI: http://dx.doi.org/10.33448/rsd-v9i10.8658 14 advances brought by plant breeding, expressed by genetic attributes, and has its performance influenced by physical, sanitary and physiological features. Among the attributes of seed physiological quality, vigor is highlighted as relevant because it relates to germination, emergence, seedling growth, uniformity rates at field with the possibility of influencing grain yield in different crops (RossI et al., 2018). Research from França Neto (1984) revealed increases of 20-35% in grain yield when using high-vigor seeds. Kolchinski et al. (2005) determined that the use of high vigor seeds increased soybean yield by 35%, while Rossi et al. (2018) evidenced that lots of high vigor seeds are closely related to high yields in this crop.
Therefore, the importance of seed vigor level and its effects on soybean growth and development is confirmed, being essential to yield components and seed productivity (Table   5).     (Table 7). Regardless of seed vigor level and fertilizer distribution system, the highest contributions to soybean yield in both environments were achieved through pods with two and three seeds ( Table 8).
The contribution of pods containing four seeds (N4) was higher in Passo Fundo -RS for plants originated from low vigor seeds. It may be related to problems in the initial establishment of soybean, resulting in a smaller population per unit area, smaller intraspecific competition and consequently greater possibilities of directing assimilates for filling more seeds per legume.
The detailed visualization of the multivariate trend of seed yield and the effects of vigor levels, growing environments and fertilizer distribution system (Figure 1) was possible through the method of genotype main effects and genotype environment interaction (GGE).
Under these conditions, the biplot graph shows the average trend and represents 90.94% of the total variation involved in soybean seed yield. The effects attributed to seed vigor levels ( Figure 1) show that high (HV) and medium vigor (MV) provide high performance for grain yield, because they are distant from the origin axis. Close relationship was verified between conventional distribution systems (EC) and by transshipment (EC), attributing similar trends to plants produced from low vigor seeds.
In view of the scenarios expressed in this study, it was verified that high vigor seeds, in association to conventional distribution system, potentiated grain yield, number of pods in the main stem, plant height and first pod insertion height. When medium vigor seeds are used in association to conventional fertilization system, the benefited traits are length and magnitude of ramifications, as well as the contribution of pods with one seed for grain yield.
In general, low vigor seeds reduced the phenotypic expression of most measured traits, mainly in the absence of fertilizer. As reported in this study, high vigor seeds are fundamental for achieving high-performance plants, which have the ability to better use the available environment's resources, and consequently increase yields.

Final Considerations
Seed vigor levels and fertilizer distribution systems influence on seed yield, first pod insertion height, plant height, number of pods in the main stem and ramifications, magnitude and length of ramifications in soybean.
The high vigor level in the conventional and by transshipment fertilization systems provided an absolute increase of 10.9 and 5.6% in seed yield, respectively, in Ernestina-RS.
The conventional fertilizer distribution system, in Passo Fundo-RS, increased seed yield in 12.5% in plants originated from low vigor seeds.
In view of the results of this work, it is necessary to carry out further studies in order to verify the real influence of biotic and abiotic factors on seed vigor.