THE BEHAVIOR OF SOYBEAN VARIETIES AT DIFFERENT SOWING SEASON

. Soybean (Glycine max (L.) Merrill) it is one of the most important cultivated plants, and due to the beneficial properties it represents, it can bring considerable benefits to farm management. Thus, the growth and development of the soybean crop depends a lot on biotic and abiotic factors. In the present study, 5 soybean varieties created at SCDA Turda were analyzed during two experimental years 2021 and 2022 sown when in the soil are recorded for three consecutive days 5ºC and sowing season II - when the temperature of 7ºC is reached in the soil. Of the two experimental years, the year 2022 was less favorable for soybean cultivation compared to 2021. The obtained results were interpreted according to known statistical mathematical methods


INTRODUCTION
During the growing season of a crop, biotic and abiotic factors can affect growth and development, potentially compromising crop yield (Szareski et al., 2016).Drought and high air temperatures, increasingly frequent phenomena due to climate change, are important constraints for the yield of agricultural crops.
The challenge of increasing crop production to meet future demands can be met by increasing the rate at which climate change adaptation practices are identified and adopted (Mourtzinis et al., 2019).
In Romania, most of the areas cultivated with soybeans are in areas where there is no possibility of using an irrigation system and therefore the culture is totally dependent on the climatic conditions of the area.
Because lately climate changes are becoming more and more evident, and the Intergovernmental Group on Climate Change estimates (IPCC, 2007) that by 2050 global temperatures will rise by 2°C more and more emphasis is placed on the management of natural resources in the most efficient way, so that the modification of some technological stages becomes for our area and not only a starting point in order to adapt to these changes.
Changing the sowing period implies early sowing to avoid heat stress and drought that occurs during the growing season, being probably the least expensive management of increasing production (Popp et al, 2002).
Adverse climatic conditions during the reproductive phase of soybeans can reduce seed yield by as much as 74% compared to normal conditions (Jumrani et Bhatia, 2018).Therefore, the adoption of sowing season that ensure climatic conditions close to those required by plants is extremely important for a good productive performance of crops (Peixoto et al., 2000).

MATERIAL AND METHOD
The research has been developed during 2021-2022, at the Agricultural Research and Development Station Turda, on a type soil chernozem, characteristic of the Transylvanian Plateau.As a chemical description, the soil has a weakly alkaline neutral pH, neutral to high humus content, well supplied in nitrogen and potassium, medium supplied in phosphorus.
In order to achieve the proposed objectives, a bifactorial experience was organized, with the following factors: factor A -sowing season with two graduations: sowing season I -when in the soil are recorded for three consecutive days 5ºC and sowing season II -when the temperature of 7ºC is reached in the soil; factor Bfive varieties of soybeans: Felix (00), Iris TD (00), Ziana TD (00), Raluca TD (0), Isa TD (000).
Soy was sown at a density of 55 germinative grains/m 2 , with a row spacing of 50 cm, without being fertilized.The seed was not treated before sowing, nor was it sterilized.
The climatic data presented in this paper were recorded from the Turda Meteorological Station, located on longitude coordinates: 23º47'; latitude 46º35'; altitude 427 m.
Analyzing the climate data from the two years, it is noted that the average monthly temperatures are higher than the multiannual, except for April and May in both experimental years, in 2021, where the average temperature is lower than normal.
In the spring of 2022, although the average temperature had higher values than the multi-year average, the fact that temperatures during the night were lower, with important differences between day and night, resulted in a longer period between the two-sowing season in terms of sowing compared to 2021, where there were no significant differences between day and night temperatures.
During the research period, the highest temperatures were recorded in July, with deviations of up to 3.0ºC in 2021 and 3.3ºC in 2022.

Figure 1. Average temperatures recorded in Turda during 2021-2022
The rainfall regime was different for the two years, in 2021, the recorded precipitation was within normal limits, except for June when there was a deficit of -39.8 mm, however, in 2022, the lack of precipitation in the months of June (-42.8mm) and July (-52.8mm) led to an important drought that left its mark on the development of the vegetative processes of plants.
Drought correlated with high temperatures played an important role in the soybean crop, outlook climatic both experimental years can be considered less favorable for soybeans.

RESULTS AND DISCUSSION
For the germination emergence process to develop in optimal conditions, soybeans need the temperature in the soil to exceed 7ºC (Dencescu et al., 1982), therefore, the temperature considered as control is 7ºC and 5ºC is considered an early sowing season.Laboratory research by Inouye (1983) has shown that soybean germinates slowly as low as 3ºC, although there is a possibility that soybean seedlings may not survive under field conditions.
Calendar-wise, for the study area, in the two experimental years, the sowing dates were different for the two-sowing season.In 2021, the difference between the two sowing seasons was 13 days.Because the temperatures during the night were lower, in 2022 it led to a greater difference in the period between the two sowing seasons, of up to one month.
Although soybeans were sown more than 10 days apart in 2021, the difference in days from sunrise is about 3-7 days, in the year 2022 the difference in days from sunrise is more than 20 days between sowing seasons (Table 1).According to the data presented in table 2, the number of days between the two sowing season in 2021 is quite small, of only 3-4 days, similar results being obtained by O'dell (2000), who stated that there are no differences in the flowering date between the first sowing seasons.A difference between the two sowing season was observed in 2022, of about 14-16 days for the moment of flowering, a difference that reduces with each stage of development compared to the moment of sowing, when more than 20 days were achieved between the two of sowing season.Climatic conditions during the growing season are the most important factor in an agricultural culture totally dependent on the abiotic factors involved in the production, as stated by Nico et al., (2015) the most important time for determining soybean yield is the period from flowering to seed filling.
As Stepanova (1985) claims, essential for productivity is the availability of moisture during the period from flowering to pod formation, the longer the period and the greater the amount of precipitation, the greater is the productivity of the crop.
The determinations made at the beginning of the formation of the pods show us that in the year 2021 there is no longer any difference between the two sowing seasons, the only difference between the sowing seasons being visible only in the year 2022, but this is also decreasing.If at the time of sowing there were more than 20 days between the two sowing seasons sown in 2022, in the phase of pod formation this difference was reduced by half (Table 3).From the research executed in the period 2021-2022 it follows that soybean reacts very well when it is sown at 5ºC in the soil, recording an increase of 109 kg/ha compared to the season sown at 7ºC in the soil (1967 kg/ha), difference statistically assured as distinctly significantly positive (Table 4).
The development of soybean plants during the vegetation cycle is influenced by the time of sowing (Albrecht et al, 2008), in our study sowing soybean earlier led to a 6% increase in yield compared to sowing at the optimal time, by extending the period of plant development under favorable environmental conditions.As stated by Knott et al. (2019), early planting can lead to increased yields, because early planting allows for longer vegetative and reproductive periods.
Heatherly (1999) concluded that farmers who had already adopted an early sowing strategy of 5 and 30 days, respectively, compared to what is currently used, experienced increases in yield.The results obtained by Mourtzinis et al (2017) show that the interaction between early sowing (end of April -beginning of May) and using the longest maturity group (MG 2) had the greatest production potential, according to the data obtained for the five varieties used in the experiment, the Raluca variety, a variety from maturity group 0, recorded the highest production (2334 kg/ha), with a very significantly positive difference of 433 kg/ha compared to the control variety (Table 5).Temperature, precipitation, humidity, and solar radiation are important climatic elements that affect the production of a crop (Sowunmi et Akintola, 2021) and that is why it is very important to monitor them.The irregular distribution of rainfall during the soybean growing season is a limiting factor in production potential (Zanon et al., 2016), a fact also observed by us following the executed analysis on the production recorded in the two experimental years and the climatic conditions during the vegetation period.The high temperatures during the summer, in parallel with the deficient rainfall regime during the flowering phase, led to an average production of 2497 kg/ha in 2021.The highest production losses were recorded in 2022 (1546 kg/ha), the year in which the environmental conditions during the flowering-grain filling period were unfavorable for the development of soybean culture (Table 6).
The drought stress during the summer months led to significant production losses caused by the decreases in the values of production elements, these results being similar to those obtained by Mandić et al (2020), unfavorable climatic conditions during plant growth and development being one of the main causes of soybean yield loss (Mandić et al, 2017).The yields results obtained during the research period highlight the importance of choosing the biological material and the optimal time for sowing, with the aim of obtaining satisfactory yield results at the lowest possible production cost.By sowing soybean varieties earlier than the optimal period for the study area, are recorded yield increases of up to 371 kg/ha (Table 7).These results are similar to those of Pederson et Lauer ( 2004) who found in their study that the average yield achieved in early sowing was higher than that in late sowing.Avilla et al (2003) hypothesized that by growing drought-resistant soybean varieties in combination with the no-input agrotechnical factor (sowing datethe negative impact of weather on production would be reduced, sowing soybeans at the optimal date being one of the most important and least expensive agronomic practices that can influence production (Kumagahi et Takahasi, 2020; El-Harty et al, 2010).

CONCLUSIONS
From the results obtained in the two years of study, it emerges that under certain climatic conditions the sowing season can be an alternative for the considerable increase in soybean production in the Transylvanian Plateau.
By changing the time of sowing, varieties with a longer vegetation period can be introduced into the culture, which are generally more productive.

Figure 2 .
Figure 2. The amount of precipitation recorded in Turda in the period 2021-2022

Table 2 .
The beginning of flowering

Table 3 .
The beginning of pod formation

Table 4 .
Influence of sowing season on average soybean yield

Table 5 .
Influence of variety on average soybean yield

Table 6 .
The influence of climatic conditions on the average yield of soybeans

Table 7 .
Yields results obtained in the soybean crop