THE RESPONSE OF SOME MAIZE HYBRIDS AT DIFFERENT SOWING SEASON IN THE CLIMATIC CONDITIONS OF THE TRANSYLVANIA PLATEAU

. In Romania, maize is one of the most important crops, it is cultivated on around 2.5 million hectares, which remained the most important crop with a share of 47.6% of the area cultivated for cereals and 30% of the overall area cultivated. Climatic conditions are the main factors that determine the production of a crop, this fact being also observed in the results obtained in the period 2021-2022, the difference between the two years of research being particularly given by the precipitation during the growing season. The maize crop was affected significantly by drought and high temperatures from a climatic perspective, both experimental years were considered less favorable for maize. Advancing the sowing date in order to avoid high temperatures as well as the water deficit during the reproduction period did not have the expected results against production obtained after sowing the crop earlier was reduced by 1648 kg/ha compared to the one obtained in the sowing season considered optimal for the Transylvanian Plateau this difference being statistically assured as very significant negative.


INTRODUCTION
Maize (Zea mays L.) is one of the most important cereal crop along with wheat and rice.It is grown extensively in temperate, tropical and sub-tropical regions of the world.Maize grain is a valuable source of protein (10.4%), fat (4.5%), starch (71.8%), vitamins and minerals like calcium, phosphorous and sulfur (Shah SR., 2007).It is second in the world, cultivating producing 206 million ha and produces about 1210 million tons of grain (www.fao.org).In Romania, maize is one of the most important crops, it is cultivated on around 2.5 million hectares, which remained the most important crop with a share of 47.6% of the area cultivated for cereals and 30% of the overall area cultivated.Between 2011 to 2021, maize yields averaged 5,802 kg/ha.(Ghiorghe and Turek-Rahoveanu, 2022).
Expanding the world's human population with greater food and energy needs has led to increased demand for greater global maize (Zea mays L.) production.Unfortunately, environmental limitations such as temperature and drought have continued to decrease maize production levels in recent decades and in many areas, and this decrease is predicted to worsen with changing climates (Meeks et al., 2013).
The effects of climate change are currently a pressing issue in the scientific community (Qadir et al., 2013) because production potential and crop quality are correlated and strongly influenced by environmental factors such as temperature, amount of precipitation and soil water reserve (Butts-Wilmsmeyer et al., 2019).
In this context, it has become a necessity to reduce undesured outcomes by means of innovative or adapted undesirable of crop cultivation.Retaining water in the soil, sowing in optimal periods so as to ensure the growth and development of plants, especially phenophases with water intake during rainy periods, as well as using hibrids with different vegetation periods, represent only a few of the possible ways of reducing the negative effects of climate change upon agricultural production (Lupu and Pîrșan, 2017).
The sowing season is a very important technological link to maximize the yield of maize (Van Roekel and Coulter, 2012) and therefore research is concentrated on the response to maize yield during sowing (Paraschivu et al., 2017).
A trend toward earlier maize planting during the past several decades has occurred and is due to improvements in technology, along with temperature and precipitation shifts from climate change (Urban et al., 2015).
Aggressive temperatures in conditions of rainfall deficits during growth phases with maximum water requirements have a significant impact on yield components, regardless of the hybrid chosen, even when using high-performance crop technologies for maize cultivation (Ion et al., 2013).
In general, early sowing is preferable, but temperatures must be high enough to ensure quick germination and emergence.Also, the sowing date must be late enough to avoid late spring frosts.As a rule, maize should not be sown until the soil temperature approaches 10 °C.Under cold soil conditions (below 10 °C), seeds will readily absorb water but will not initiate root or shoot growth, which leads to seed rot and poor emergence (Abendroth et al., 2017).

MATERIAL AND METHOD
The research was developed during 2021-2022 at the Agricultural Research and Development Station Turda (ARDS), on a type of soil characterizing the chernozem character of the Transylvanian Plateau.The soil's chemical description indicates a neutral-weak alkaline pH, a neutral to high humus content, abundant nitrogen and potassium, and a medium containing phosphorus.
To achieve the proposed objectives, a three-factor experience was organized, with the following factors: factor A, which represents the experimental years studied.a1-2021; a2-2022; factor B -sowing season with two graduations: season I -early sowing, when 6-8ºC are recorded in the soil for three consecutive days; season IIwhen 10ºC are recorded in the soil for three consecutive days (optimal season date); factor Cmaize hybrids with four grades: T 332 (FAO 380), T 380 (FAO 380), HST 148 (FAO 380), SUR 18/399 (FAO 380).
The sowing rate was 65,000 plants per ha, and the depth of seed incorporation was 5 cm.Winter wheat was the plant that preceded the maize crop.The biological material was represented by hybrids and maize lines, created at ARDS Turda.The obtained results were statistically processed by the method of variance analysis and the establishment of the smallest significant difference -DL -(5%, 1% și 0.1%) (ANOVA, 2015).
The climatic data recorded during the period under study and presented in this paper come from the Turda Meteorological Station, located at longitude coordinates: 23º47'; latitude 46º35'; altitude 427 m (Meteorological Station Turda).
According to the climatic analysis of the vegetation period of the two experimental years, the average monthly temperature increased by between 1 and 3.1ºC.The temperatures in June range between 2 and 3.3°C in July, and between 0.2 and 2.6°C in August, which plays a vital role in achieving production and quality.Spring months, particularly April, have had temperatures lower than the multi-annual average in the last two years, making them an exception to the growing season temperatures, preventing the process of sowing the crop earlier.
Precipitation has a variation between the two years, with a deficit of 42.8 mm in June and 52.8 mm in July 2022, as well as 42.8 mm in June 2021.The maize crop was negatively affected by the lack of precipitation and high temperatures, with one year being better than the other.

Figure 1. presents average temperatures recorded in Turda during 2021-2022
There was a variation in the rainfall regime between the two years.In 2021, the rainfall was within normal limits, but in June a deficit of -39.8 mm was recorded.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.
The maize crop was affected significantly by drought and high temperatures from a climatic perspective, both experimental years were considered less favorable for maize.Given that the amount of precipitation recorded in 2022, between the sowing period 14.04 and the physiological maturity 06.10, from the year 2022, the amount of precipitation was only 408.5 mm, the average production achieved was only 7028 kg/ha, with a very significant negative difference compared to the average of the 2 years and by 3958 kg compared to 2021, when the average production of hybrids was 10986 kg/ha.
The theme "climate change" is defined differently by various parties, despite the fact that the backdrop is the same.The Intergovernmental Panel on Climate Change (IPCC, 2007) defines climate change a change in the state of the climate that is identifiable by changes in the mean and/or variability of its attributes and that continues for an extended period, generally decades or longer.
The current climate changes have become a challenge for farmers all over the world, who have to adapt their cultural technology so that the production losses caused by the warming of the weather are as low as possible.
Advancing the sowing date in order to avoid high temperatures as well as the water deficit during the reproduction period did not have the expected results, on the contrary, the production obtained after sowing the crop earlier was reduced by 1648 kg/ha compared to that achieved in the sowing season considered optimal for The Transylvanian Plateau, this difference being statistically assured as very significant negative.The maize plants that emerged in the first sowing season, although they had the same conditions from a technological point of view, failed to develop in the same way as those sown on the second sowing date, especially due to the low temperatures at the beginning of the vegetation period.These low temperatures as well as the difference between the night and day temperatures led to a lower absorption of nutrients, this fact being reflected in the productions made.Key planting factors influencing maize production are sowing dates and cultivars.Different genotypes may behave differently under similar environmental conditions.Different sowing dates might create different environmental conditions from emergence to physiological maturity (Mehdi, 2012).
Each hybrid has an optimum sowing date, and the greater the deviation from this optimum (early or late sowing) increases the yield loss (Berzsenyi și Lap, 2001).
The studied biological material reacted differently to cultivation in the two sowing seasons, the best results being obtained by the hybrid T 380 (9279 kg/ha), the difference of 178 kg/ha compared to the hybrid T 332 being statistically assured as with a significant positive.
The hybrids HST 148 and SUR 18/399 obtained lower production results of 286 and 268 kg/ha compared to the control variant, the differences being statistically negatively as significant negatively.
Even if in 2022 the average production achieved was only 7028 kg/ha, this is still a satisfactory production in the climatic conditions of this year, being due in particular to the biological material created at ARDS Turda and which is adapted to the conditions in the area.
From the triple interaction, it can be observed that the year, more precisely, the climatic conditions during the vegetation period remains the most important factor in achieving production.
From the data presented in table 2, the Turda 380 hybrid and the HST 148 line can be noted, which through sowing in the second season managed to obtain production of 12424 kg/ha and 12147 kg/ha, respectively, in the climatic conditions of 2021, similar results were obtained by Lupu and Pîrșan (2017) where sowing in April on the experimental field led to an average of very significantly higher yields compared to sowing in early May.
Different results were obtained by Buriro et. al., (2015).In Pakistan's climatic conditions.It was concluded from the findings of present research work that all quantitative/qualitative traits were promising, when the sowing of a hybrid maize crop was completed up to 25th October; delay of the sowing adversely affected yield components which ultimately caused a significant decline in grain yield.
Similar research has also been carried out by Abendroth et. al., (2017), in Iowa North America, yield was lower when associated with the earliest and latest planting dates and greatest at some point in between.Research across the region has typically identified a significant yield reduction if planting is delayed beyond the optimum for that location (with "optimum" defined as late April or early May) compared with plantings in late May or early June (Van Roekel, Coulter, 2011).The yield declines as shown is most significant with delayed planting dates, such as 20 days following the optimum.
In India's climatic conditions, Sab et.al. (2020) stated that the result shows that the maize crop sown on 15th June was significantly better as compared to other sowing dates for the studied parameters of growth and yield.
The lowest yields were obtained by the T 380 hybrid (5309 kg/ha) and the HST 148 line (5557 kg/ha) under the conditions of 2022.If, in the case of the other hybrids cultivated on two sowing dates, in two years, different from the climatic point of view, the production differences are relatively small.In the case of the T 380 hybrid and the HST 148 line, things are clear, in order to obtain high yields, it is necessary to cultivate them in the second season and in favourable conditions of precipitation and temperature.
Another factor of great importance in obtaining high production is the biological material, so a variety or a hybrid adapted to the climatic conditions where it is cultivated will obtain higher production under stress conditions than a hybrid with lower tolerance.
The interaction between climatic factors and the sowing period in the production of the 4 hybrids also shows us that none of them are suitable for early sowing, the differences in production between the two periods being significantly higher.

Figure 2 .
Figure 2. presents the amount of precipitation that was recorded in Turda from 2021-2022 . MAY JUN.JUL.AUG.SEPT.OCT.