Evaluation of Soybean Cultivars of Contrasting Cycles according to the Level of Investment in Fertilization

The objective of the present study was to characterize the duration of the phenological stages, the agronomic characteristics and grain yield in soybean cultivars with contrasting cycles and indeterminate growth type, submitted to different fertilization investment environments under no-tillage system in the central region of Minas Gerais. The work was conducted under field conditions, in an experimental area of Embrapa Maize and Sorghum, in Sete Lagoas, MG, in the harvest of 2015/2016. Ten soybean cultivars with different relative maturity groups (RMG) were studied, representing almost all RMG materials currently sown in Minas Gerais, in two environments with different levels of fertilizer investment. The variables were submitted to analysis of joint variance, in order to verify the existence of interaction between cultivars and investment in fertilization environments. Fertilizer investment levels influence grain yield of soybean cultivars of contrasting cycles. The higher height of the soybean plants implies higher lodging and lower grain yield. This situation is aggravated by the greater investment in fertilization. The difference between the cycles of the cultivars is in the duration of the vegetative stages, being greater in the later cultivars.


Material and Methods
The experiment was conducted during the 2015/2016 harvest, under field conditions, at Embrapa Maize and Sorghum, in SeteLagoas-MG, with coordinates of 19˚28'30''S, 44˚15'08''W and 732 m of altitude. The soil was characterized as a very clayey dystroferric Red Latosol [10]. The climatic classification of the region according to Köppen is type Aw, typical of savannah, with dry winter and average temperature of the air of the coldest month superior to 18˚C.
The experimental area has been established in a no-tillage system for eight years, with crops mainly soybean and corn. In 2012, the area was divided into two conditioned environments under medium or high technological investment in fertilization [11] and since then it has been maintained with different fertilization in each environment. In the off-season of 2013, millet + crotalaria were planted as cover plants in both environments, followed by maize cultivation in the summer (average grain yield of 8780 kg·ha −1 for the medium-investment environment and 9945 kg·ha −1 for the high-investment environment), and beans (average grain yield of 1464 kg·ha −1 for the medium-investment environment and 1747 kg·ha −1 for the high-investment environment) were grown in the 2014 off-season. In the 2014/2015 crop, summer maize (mean grain yield of 10744 kg·ha −1 for the medium-investment environment and 11,304 kg·ha −1 for the high-investment environment) was cultivated and, after grain harvest, the seeding of forage turnip in total area. Table 1 shows the maximum, minimum and rainfall data collected in the climatological station located at Embrapa Maize and Sorghum during the period of conduction of the experiment, as well as the average of the last 50 years. Before the sowing of the experiment, in November of 2015, soil sampling was performed at depths of 0 to 20 cm depth in both environments, whose chemical attributes are: in the environment of medium investment were: pH in water 6.1; organic matter 3.8 dag·kg −1 ; P and K (Mehlich 1) contents of 11.5 and 13.5 The experiment consisted of the cultivation of ten soybean cultivars in medium and high fertilization environments, whose transgenic technologies and agronomic characteristics informed by the companies that own the seeds are presented in Table 2. The cultivars used in the experiment were selected by different groups of relative maturity (RMG), which represent almost all the material with RMG currently sown in Minas Gerais.
For each environment, the experimental design was in randomized blocks with four replicates, each experimental unit consisting of eight lines of 7 m in length, spaced 0.5 m apart. As a useful area for the evaluations the four central lines were considered, discarding a meter at the edges as border.
In November of 2015, the vegetation cover of the area was desiccated by ap-  The phenological stage evaluations were performed weekly by means of the visual evaluation of the experimental units and adopting the phenological scale of [12]. The date of the emergency was considered when 50% of the plants were with the cotyledons above the ground and the durations, in days, of the emergency to the V4 stage were determined; the last vegetative stage; the period of overlap (period of transition between the vegetative and reproductive stages) according to Zanon et al. [5], start from R1 to R5. The variables were submitted to analysis of joint variance, in order to verify the existence of interaction between cultivars and investment in fertilization environments. The Scott-Knott averages test (p > 0.05) was used for the comparison of treatments, using the SISVAR statistical program [13].

Results and Discussion
In Table 3 are the results of the interval in days of the four phenological stages of soybean evaluation, in addition to the maximum and minimum average temperatures and rainfall for each evaluation period. It was found that the maximum temperature was higher than the average of the last 10 years. This variation did not occur for the minimum temperature. In addition, accumulated rainfall E. Borghi et al. Temperature averages (˚C) during the development period was 33% lower than the average of the last decade, indicating that during the growing season there were high temperatures, especially in the reproductive phase. About 67% of all accumulated precipitation was concentrated in the vegetative phase. Moreover, the cumulative precipitation during the soybean driving period is in the interval considered ideal for the crop that, according to Farias et al. [14], can range from 450 to 800 mm per cycle. According to the authors, the need for water increases with the development of the plant, reaching the maximum during the flowering phases until the filling of grains, reaching 7 -8 mm per day.
When analyzing the number of days elapsed between phases R1 to R5 (Table   4) and multiplying by water demand at this stage, it was observed that the ideal water requirement for soybean would be 252 mm, however, the amount of accumulated precipitation was of 42.9 mm, much less than the required quantity.
From this information, it was found that during the conduction of the experiment the water demand for the soybean was sufficient during the vegetative phase, but inferior in the reproductive phase, indicating a water restriction in the stage of grain filling. The highest concentration of water in the vegetative phase influenced the agronomic characteristics, especially plant height and lodging ( Table 6). The lower precipitation allied to high temperature in the reproductive phase also contributed to the productivity and mass differences of 300 grains among the cultivars (Table 9), mainly in cultivars with a 101 day cycle.    environment, the variations between the cultivars were larger compared to the high investment environment. In two cultivars there were inverse variations in the overlapping period, due to the investment environment. In the cultivar BRS 8180, the highest investment in fertilization provided a shorter overlap period, being the inverse for cultivar ST 797. According to Heatherly et al. [15] and Zanon et al. [5] in late or late sowing, the duration of the vegetative and reproductive phase overlapping period may change according to the meteorological con-  (Table 4).
Thus, discounting the number of days to complete the cycle and the vegetative period, the period of the reproductive phase was 61 days. Performing the same calculation for cultivars with a cycle of 94 days, the reproductive period was 60 days, on average. Thus, it is possible to infer that the earliest materials have the shortest vegetative cycle and, even with overlapping and reproductive periods similar to the later cultivars, the sowing period is decisive so that these materials can express the maximum productive potential. In later sowing, especially in regions with water restrictions or with irregular rainfall distributions in the summer, cultivars with a later cycle may present better adaptability due to the longer vegetative period. This feature may be interesting because, if water restrictions occur in flowering, the influence on productivity will be greater.
The final plant stand was significantly influenced by the cultivars ( Table 6).  phenomenon. In addition, when analyzing plant height data (Table 6) with the number of days between emergence and the last vegetative stage (Table 4), it was found that the cultivars that presented the highest heights were statically superior also in the duration of the vegetative stage. The same analogy can also be made for the cultivars that obtained the lowest heights. Thus, in addition to genetic expression and investment in fertilization, the duration of the vegetative stage determines the agronomic characteristics, such as number of nodes, inflorescence, number of branches and pods per plant [5].
The lodging also presented a direct relation with the height of plants and, consequently, with the duration of the vegetative stage. The highest plant heights identified in medium and high investment environments also provided the highest lodging rates (Table 6) (Table 7). In addition, with the exception of the cultivar Flecha, the cultivars that presented the lowest numbers of grains per plant also presented statistically lower values for the number of grains per pod in the same investment environment. Table 8 shows the values referring to the mass of 300 grains and grain yield of the soybean cultivars as a function of the investment in fertilization environments. In both variables, the greater investment gave a greater mass of 300    As in the SPAD values, the mean investment in fertilization did not provide a significant difference between cultivars for NDVI (   The correlation analysis presented in Table 10 showed that, among the eva- because the readings were taken at the stage R3, characterized in [12] as the maximum accumulation of biomass of aerial part of the plant and, therefore, the chlorophyll content and also at the beginning of the formation of green beans.
The productivity showed a negative correlation with the height of plants, indicating that the higher height influenced negatively the productivity. This statement corroborates the lodging values shown in Table 6.
E. Borghi et al.

Conclusions
The difference in cycle of soybean cultivars occurs in the reproductive period.
Early-cycle cultivars tend to use precipitation more efficiently if the rain occurs between the end of the vegetative stage and the beginning of the reproductive stage.
Soybeans cultivars with longer cycle are greater number of pods per plant.
This effect doesn't have relation to grain yield, regardless of the level of investment in fertilization.
In cultivars with relative maturity groups (RMG) above 7.7, investment in fertilization leads to higher lodging of plants.
Medium investment in fertilization implies less lodging of plants soybeans. In this mode of cultivation, the chlorophyll content is higher due to the smaller size of the plants, however, there is a reduction of the productivity components, compromising the production of soybean grains.
Fertilizer investment increased significantly influences grain yield in contrasting cycles soybean cultivars.