AGROTECHNOLOGIES AND AGRICULTURAL INDUSTRY

. Under the conditions of irrigation in the southern zone of the Steppe of Ukraine, it is important to take a differentiated approach to the selection of the sowing period and plant density, which are one of the main factors affecting the yield of corn grain. Spatial and quantitative placement of plants are one of the most important elements of varietal agricultural technology, so they are considering in close interaction

Proceedings of the 7th International Scientific and Practical Conference «Current Issues and Prospects for The Development of Scientific Research» (April 19-20, 2023).

No 151
Sowing time is one of the main factors in obtaining high yields of corn. This issue has been studding for a long time, but every year in the State Register of plant varieties suitable for distribution in Ukraine, new hybrids of corn, different in terms of ripeness and morphological characteristics, appear, which react differently to the influence of environmental factors. Therefore, for each group of hybrids, it is necessary to determine the optimal sowing period, taking into account the culture's requirements for germination conditions and the peculiarities of spring agroecological conditions.
Dr. S.-G. of Sciences, professors of the Institute of Irrigated Agriculture of the National Academy of Sciences of Ukraine S. V. Kokovikhin and Yu. O. Lavrynenko believe that when determining the sowing date, it is worth focusing on the maturity group of the hybrid. In particular, the relatively late sowing date of the parent forms of early-ripening and mid-ripening hybrids makes it possible to carry out a set of measures to accumulate moisture and destroy weeds before sowing.
After studying the biological characteristics of corn, it became knowning that the culture uses solar energy, heat and moisture inefficiently during the first two months after sowing in the first half of the growing season, while growing slowly. However, during the second half of the growing season, when the use of these factors is more necessary for the plant -the inflow of solar radiation declines, air temperature and soil moisture reserves become lower. To improve the efficiency of the use of all agro-ecological resources, it is possible to vary the timing of sowing and, accordingly, the time of passage of all phenological phases of crop development.
According to the established multi-year terms, in the Southern Steppe of Ukraine, sowing begins in mid-April, but the temperature of the soil at the depth of seed wrapping is the main factor that determines the start of sowing because when wrapping seeds in insufficiently warmed soil, the death of part of the seeds in the soil, damage may occur seedlings by wireworms, mold diseases and, as a result, uneven growth and development of corn plants in the future.
According to the results of research conducted by domestic  No 151 scientists, it is necessary to inlay seeds to improve field germination, shorten the growing season by several days, and increase crop productivity by 0.9-1.1 t/ha. However, with the use of encrusted seeds, the corn sowing time becomes 5-10 days earlier, compared to the usual ones. Very dry weather conditions are observing in Ukraine every 2-3 years due to simultaneous atmospheric and soil droughts. In such periods, it is very important not to be late with sowing campaigns, otherwise the grain may fall into an insufficiently moist soil layer and the result will be poor field germination. In the event of a 10-day delay with relatively optimal sowing dates, the productivity of corn grain decreases by 0.6-0.8 t/ha [1].
At different times of sowing, the combination of temperature and moisture should be optimal. It should be taken into account that during the early sowing period, the depth of wrapping the corn grain should be less, and under the conditions of late sowing -greater, soil moisture is very important. The fact that soil moisture reserves in this period are greater than in the later ones speaks in favor of early sowing periods, which is important during the phase of panicle ejection and waxy seed maturity. Under such conditions, a higher yield of early-maturing and medium-early hybrids, which belong to the siliceous group and are characterizing by increased cold resistance, is obtaining due to better adaptation to growing conditions, more complete use of productive moisture of the arable soil layer. Nevertheless, plants during the early sowing period are subject to the danger of damage by spring frosts, biotechnical factors are activating -pests, diseases, weeds.
In particular, corn is more affecting by the corn moth because the plants will already be sufficiently developing by the time the butterflies fly and lay their eggs. Field germination decreases -the scientist D. P. Tomashevskyi connects this with the aggressive effect of low temperatures in combination with fungal diseases, pathogens of Pythium, Pénicillium, Alternaria, Fusarium species.
Therefore, when choosing the optimal sowing time, it is necessary to first of all take into account such criteria as heat resources, the temperature regime of the soil and air No 151 during the period of seed germination and seedling formation, phytosanitary state of crops, precociousness of hybrids and heat supply, the level of plant protection, the total length of the growing season, cultural requirements to the consumption of moisture for the formation of products. Due to the diversity of these factors, the complex and a priori unknown nature of their interaction, the solution to the issue of optimal sowing dates can only be obtaining because of longterm research, in multifactorial field experiments.
Plant density is one of the important factors in modern technologies for growing agricultural crops, which determines the effectiveness of the vital components of agrocenosisgrowth processes and their development, allows the maximum realization of plant productivity and the most efficient use of soil moisture and soil nutrient reserves. With the expansion of corn-sown areas in Ukraine, the study of the influence of plant stand density on crop yield has become particularly relevant [3].
Under the leadership of O. I. Zinchenko, research was conducting at the Uman State Agrarian University regarding the study of the influence of seeding density on the productivity of corn per grain. The results of the experiments indicate that the best corn yield can be obtaining under the conditions of compliance with the density of standing of medium-ripening hybrids and varieties: in the southern arid areas of the Steppe within 25-30 thousand plants per one ha, in the central, more humid steppe areas, 35-40 thousand. , in the north -40-45 thousand, in the forest-steppe and Polissia -55-65 thousand, on the irrigated lands of the South -70-75 thousand plants per 1 ha. According to the results of research by scientists, it was established that the density of planting hybrids in areas with insufficient moisture is 55 thousand units/ha, in areas with sufficient moisture -60-65 thousand units/ha, and in irrigated conditions -up to 80 thousand units. /Ha. The optimal stand density changes annually depending on the biotype of hybrids, weather and climate conditions, in particular arid conditions, especially in the second stage of plant development. The density of the stand depends on the moisture of the soil, as well as the supply of nutrients to the plants. Non No 151 optimal stem density threatens with significant yield loss, in particular in the drought conditions of the Southern Steppe of Ukraine [4]. The density of standing corn strongly affects moisture availability. Plants in the most densely planted crops use the moisture reserves of a meter-long soil layer for the development of vegetative organs, mainly in the first half of the growing season. The crisis period in terms of moisture supply in corn begins after the formation of 12-13 leaves in mid-early and mid-ripening hybrids and 14-15 -in mid-late and late-ripening hybrids. During the formation of cobs, the moisture supply of plants deteriorates sharply, which, when the crops are thickened, leads to inhibition of growth processes, a decrease in the intensity of photosynthesis, and, as a result, to a decrease in plant productivity. On a well-fertilized agricultural background, moisture is useding more economically. Thus, with an increase in fertilizer rates and moisture availability of plants -with a sufficient amount of precipitation, the efficiency of thickening increases with irrigation [5].
The density of plant stands has a considerable influence on the hydrothermal mode of agrophytocenosis, water and physical properties of the soil, phytoclimate of crops, which is decisive for the passage of the stages of organogenesis of corn plants. In particular, Bomba M.Ya. and Bomba M.I. expressed the opinion that the yield of agricultural crops depends on the components of varietal agricultural technology by approximately 60% and proved with their research that the rates of growth and development of corn directly depend on the density of the stand, but in different ways are found. This is primarily due to soil and climatic conditions, agrotechnical cultivation, as well as biological and morphological features of the culture [3].
Zaporozhchenko A. L. expressed the opinion that the density of corn stalks should be regulating depending on the indicators of the agrochemical composition of the soil and the moisture supply of the crop plants. According to the scientist, the formation of the optimal density of planting of plants contributes to obtaining the maximum productivity of the culture, because both thickening and thinning of the

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No 151 stand density cause a sharp decrease in yield [2].
Optimizing the density of plant stands is important for the formation of the photosynthetic apparatus, because these concepts are physiologically related. In particular, the researcher A. A. Nychiporovych noted that the optimal indicators of the leaf surface area for crops of the grain group are set at a stand density of 40-50 thousand units/ha. At the same time, due to the process of photosynthesis, 90-95% of the mass of the crop is forming. As for the further increase in the area of the leaves, it was ineffective, the mass share of cobs in the structure of the crop decreased significantly [2].
Foreign scientists conducted similar studies, during which it was found that with an increase in the density of stalked corn -more than 50-60 thousand pcs./ha, the total area of the leaf surface increased in direct proportion to the thickening, but the yield of corn grain decreased. This indicator affects the flowering time of corn hybrids (with excessively thickened sowing, the flowering process is significantly delayed), as well as the number of cobs on the plant -thickening of the crops leads to a decrease in their number on the mother plants, their grain size, weight and yield of grains from the cob.
Conducted by the scientist Kalenich V.I.studies have shown that the influence of the density of planting plants on the size of the cobs was manifesting both in favorable and unfavorable years. At a stand density of 70 and 100 thousand plants per 1 ha in medium-ripe hybrids, the cobs were significantly shorter and with fewer grains than in the case of the sowing density of the same hybrids, but already at a stand density of 60 thousand plants/ha and 40 thousand units/ha. At the same time, the length of the cobs decreased by 6-14%, and their weight by 19-21% [3].
Researches of many scientists prove that the density of crops affects the growth of corn and affects both the height of the plants and the height of the attachment of the cob. In particular, G. E. Shmaraev, based on the results of his research, concluded that the later the parental form of the crop and the higher the height of the plants, the higher the cobs are planting. An increase in the stem density of corn No 151 hybrids is accompanied by an increase in the total area of the leaf surface, which becomes an obstacle to the arrival of PHAR, as a result -poor pouring of grain, an increase in the number of small cobs and laying of plants, postponement of harvesting dates towards later ones, loss of harvest [4].
Candidates of rural and urban areas of sciences O. M. Grigorieva and T. M. Grigorieva proved in practice that an increase in stand density reduces productivity, regardless of the morphological characteristics of hybrids. Conducted experiments on the influence of plant density on the growth and development of corn of different maturity levels showed that early-ripening hybrids in the phase of panicle shedding with an increase in stand density from 60 to 100 thousand units/ha increased the height of the stem by 11-17 cm.
At the same time, the diameter of the second underground internode decreased by 0.2 cm, the area of the leaf surface also decreased. At the same time, when crops are thickened to certain limits, especially in years favorable for moisture, although the individual productivity of plants decreases, the number of productive plants per unit area increases significantly, which leads to an increase in the yield for hybrids of all maturity groups. In thinned corn crops, despite the ability to obtain high individual productivity of plants, without sufficient stem density per unit area, there is no increase in productivity [5].
According to Sytnyk K. M., primarily hereditary features, and only then determine the total number of flowers on cobs by the influence of growing conditions, because different varieties, lines, and hybrids react differently to these conditions [2].
During the study of the influence of the density of standing corn plants on productivity, researchers O. V. Tarasov, V. S. Kochetkov and V. F. Malikhina came to the conclusion that the grain yield is also affected by the width of the rows and recommended that when the width of the rows is reduced, the sowing rate should also be reduced seeds, but so that it does not differ much from the recommended one [2].
The analysis of literary sources shows that hybrids of different maturity groups have different reactions to changes in stem density. In connection with this, the performance of  hybrids of different precociousness can be determined only under conditions of differential selection of stand density, taking into account natural and climatic conditions.
With the correct spatial and quantitative distribution of corn plants on the cultivation area, which is determined by the time of sowing and the density of plant standing, the phytosanitary condition of crops, the water, air and nutrient regime of the soil is improved, favorable conditions are created for increasing the productivity of the crop. Formation of optimal standing density of corn plants at different sowing times per unit area is an important agrotechnical technique for increasing crop yield.
Thus, a review of literary sources confirms the dependence of grain productivity of corn hybrids of different maturity groups on the sowing date and stand density. Therefore, our research is aiming at establishing the optimal sowing period and stand density for corn hybrids of different maturity groups for irrigated cultivation, which is extremely relevant.
Corn is one of the main crops at the current stage of world grain production, it ranks third after wheat and rice, and in terms of biological yield, which reaches 30 t/ha, it generally ranks first among cereals. In various countries of the world, approximately 20% of corn grain is unseeing for food purposes, 15-20% in the industrial and industrial sphere for the production of oils and fuel, and the rest -for fodder needs in the livestock industry. The increase in demand for the consumption of corn and the increase in its production volumes are primarily relating to the increase in energy resources, when the crop became the main raw material for the production of bioethanol.
Conducting sustainable agriculture, against the background of the global problem of warming and lack of moisture, requires regulation of moisture conditions, which becomes possible only with the use of irrigation -a guarantee of obtaining high yields. Thanks to irrigation, the increase in the yield of corn grains in the Southern Steppe is from 3.0 to 5.0 t/ha and more.
An important role in increasing the yield and improving the quality of corn grain is playing by the correct selection  No 151 of hybrids for cultivation. New culture hybrids of Ukrainian selection have valuable biochemical indicators, and in terms of productivity, they are not inferior to the best foreign samples, while having an indisputable advantage over themthey were cratering in the Steppe zone, so they have genetically determined mechanisms of adaptability to the soil and climatic conditions of the southern region of irrigated agriculture.
From the review of literary sources, it can be concluding that the most effective influencing factors in the conditions of the Southern Steppe of Ukraine on the level of grain productivity of corn are the hybrid composition, the use of irrigation, the time of sowing and the density of plant standing.
Most of the analyzed studies using different sowing dates and stand density for growing corn hybrids were conducting in non-irrigated conditions, and therefore it is appropriate to conduct similar experiments in the irrigated conditions of the Southern Steppe of Ukraine in order to fully studying the effect of the studied factors on the formation of grain productivity of modern hybrids.
An important role in increasing the yield and improving the quality of corn grain is playing by the correct selection of hybrids for cultivation. New culture hybrids of Ukrainian selection have valuable biochemical indicators, and in terms of productivity, they are not inferior to the best foreign samples, while having an indisputable advantage over themthey were creating in the Steppe zone, so they have genetically determined mechanisms of adaptability to the soil and climatic conditions of the southern region of irrigated agriculture.
From the review of literary sources, it can be concluding that the most effective influencing factors in the conditions of the Southern Steppe of Ukraine on the level of grain productivity of corn are the hybrid composition, the use of irrigation, the time of sowing and the density of plant standing.
Most of the analyzed studies using different sowing dates and stand density for growing corn hybrids were conducting in non-irrigated conditions, and therefore it is appropriate to The maximum values of the index of accumulation of green mass reached in the phase of milky grain ripeness for all variants of sowing dates, hybrids and plant stand density. A comparison of the yield of raw mass in relation to hybrids in the phase of milk ripeness of the grain made it possible to reveal a clear trend of increasing the yield of raw mass in hybrids of later ripening groups -Skadovsky and Kakhovsky. The highest productivity of plants in terms of the formation of green mass was on the option for sowing in the third decade of April of the hybrid Kakhovsky and the density of standing 70 thousand pieces/ha -51.39 t/ha. In the phase of physiological ripeness, a decrease in the yield of green mass was recordeding in all variants of the experiment, which is explaining by the redistribution of plastic substances from vegetative organs to reproductive organs, mainly for the formation of grain. The highest value of the green mass yield indicator -45.78 t/ha was recorded for sowing in the 3rd decade of April and the stand density of 70,000 pieces/ha of the Kakhovsky hybrid.
The dispersion analysis proved that the hybrid composition had the greatest influence on the accumulation of crude mass -the share of influence is 69.5%. Sowing dates and stand density influenced this indicator much less -their share of influence was 15.2 and 3.8%. The dynamics of the processes of dry matter accumulation almost completely coincided with the trends that were revealing during the analysis of the indicators of the growth of the raw mass of corn hybrids. However, at the end of the growing season, in the interphase period from milk to physiological ripeness, an increase in the yield of dry matter per unit area was noteding. In the early stages of the growing season, the process of accumulation of dry matter by culture plants was slow. Thus, in the phase of seven leaves, on average over the years of research, this indicator was 0.78-0.94 t/ha, depending on the options of the experiment. Later, especially during the period of intensive linear growth, the increase in  No 151 dry matter increased significantly. Thus, in the flowering phase of the cobs, the mass of dry matter of the Tendra hybrid plants was 11.29-13.37 t/ha, and on the Skadovsky and Kakhovsky hybrids it increased and amounted to 11.89-14.02 and 12.75-15, respectively. 12 t/ha. The previously identified tendency to increase the yield of dry matter as the plants thickened at this stage of growth began to manifest itself more significantly.
The indicators of dry matter of corn plants were maximal in the phase of physiological maturity, thereby differing from the indicators of raw mass, the maximum values of which were observing in the phase of milky grain maturity. On average, during the period of research, in the period of physiological maturity of the grain, the maximum mass of dry matter was possessed by corn plants of the Kakhovsky hybrid, the value of this indicator, depending on the options of the experiment, varied within the range of 21.57-25.18 t/ha.
The accumulation of dry matter mass was significantly influenced by the time of sowing -the maximum values of this indicator of the culture plant were for sowing in the third decade of April -21.09-25.18 t/ha. A tendency to increase the yield of dry matter as the plants thicken was also revealing.
A dispersion analysis was carried out, the results of which established that the hybrid composition (factor B) had the maximum effect on the accumulation of dry matter by the culture plants. The share of influence of this factor is 72.3% (Fig. 3.16). To a lesser extent, this indicator depended on the timing of sowing (factor A) and density of standing (factor C) -the share of influence of which was 12.7 and 2.5%, respectively.
The interaction of AB factors was the largest and amounted to 4.9%, it was somewhat smaller for other options: ABC -3.1%, AC -0.5%, BC -1.4%. At the same time, the remaining amount was 2.6%.
Photosynthesis is the main process of creating organic products in nature by converting solar energy into the energy of chemical bonds of organic compounds. The share of organic compounds created during photosynthesis accounts for about 85% of the total biomass of a plant organism. Therefore, the

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No 151 change in dry mass can be quite objectively manifested in the assimilation activity of plants. This indicator is the basis of the method of determining "net assimilation", or the net productivity of photosynthesis [4].
Net photosynthetic productivity (NPF) reflects the efficiency of agrotechnical cultivation measures and represents the increase in dry weight of plants in grams for a certain time (day) per unit of leaf surface (m ). it is calculated by periodic selection of plant samples, in which the total mass, the mass of individual organs and the area of the leaves are determined. It is knowing that the productivity of photosynthesis significantly depends on the area of the leaf surface of plants, which is regulated by the creation of an optimal crop structure. This, in turn, determines the main task of the size of the assimilation surface -it must completely cover the soil surface during the growing season of plants.
One of the effective opportunities for more complete use of photo synthetically active radiation is to ensure the accelerated development of the leaf apparatus already at the beginning of the growing season due to the use of intensification factors, in particular, the establishment of optimal sowing dates and stand density for corn hybrids of different maturity groups [2].
The analysis of the results of our experimental studies shows that the net productivity of photosynthesis changed significantly depending on the phases of plant development and, to a lesser extent, on factors.
In the interphase period of "seedlings-7 leaves" of crop plants, the difference in the value of CPF between the parameters of the factor of sowing dates was, on average, 0.11-0.39 g/m per day. The use of corn hybrids of different maturity groups for sowing also made it possible to reveal a tendency towards an increase in the PPF index when moving from early maturity groups to medium maturity groups. Significant fluctuations of this indicator were recording already at the beginning of the growing season in the interphase period "shoots-7 leaves". It varied by hybrid composition -from 6.95-7.82 in the Tendra hybrid to 7.59-8.47 and 8.05-8.96 g/m2 per day, respectively, in the

No 151
Skadovsky and Kakhovsky hybrids. In the subsequent phases of growth, a rapid growth of PPF was establishing in the variant with the Kakhovsky hybrid. The maximum value of the net productivity of photosynthesis on this hybrid -14.18 g/m per day, on average during the period of research, was obtained in the interphase period "7 leaves-12-13 leaves" for sowing in the third decade of April and using a plant stand density of 70 thousand pcs./ha. The density of the stand also affected the process of photosynthesis. The best indicators of the net productivity of photosynthesis for all phases of growth of crop plants were established at a stand density of 70,000 plants/ha. Plant thickening contributed to a decrease in the net productivity of corn crops. In order to determine the influence of the research factors on the formation of PPF in the flowering phase of corncobs, dispersion processing of the obtained data was caring out. The dispersion analysis established that the hybrid composition (factor B) had the greatest effect on the process of photosynthesis; the share of its influence is 61.4% (Fig. 3.18). The influence of other factors was much smaller and amounted to 24.7% -for factor A (sowing period) and 3.8% -for factor C (standing density).
One of the main factors that determines the level of productivity and reflects the photosynthetic activity of corn plants, both in individual periods of growth and development, and during the entire growing season, is the photosynthetic potential. Determining the optimal type of plants capable of stably realizing their genetic potential and at the same time adequately responding to changing growing conditions constantly attracts the attention of many scientists.
Certain temperature, light and other conditions are necessary for the vital activity of a plant organism. Important manifestations of the vital activity of plants are their growth processes, which are associated with quantitative changes. When growing corn plants, it is necessary to take into account their adaptive capabilities, that is, sensitivity to growing conditions. The intensity of growth processes of corn plants, as is known, depends on the maturity group of hybrids and varieties, these processes are affecting by weather conditions during the growing season, as  It was determined that the photosynthetic potential of crops, as well as the previous indicators, especially the leaf surface area, depended on the phases of development, the use of different sowing dates, hybrid maturity groups and stand density.
From the table, we can see that sowing in the third decade of April, due to the improvement of production processes, contributed to the increase of the photosynthetic potential of crops, compared to other periods. This indicator reached its maximum value in the interphase period "12-13 leavesflowering of cobs" and, depending on the options of the experiment, varied within 1336-1686 thousand m2/ha days. The maturity group of the hybrid also had an effect on the formation of the photosynthetic potential of culture plants. This indicator was the maximum for all sowing variants of the mid-ripening Kakhovsky hybrid and varied during the period of "12-13 leaves-flowering cobs" within 1375-1686 thousand m2/ha days.
The maturity group of the hybrid has the greatest influence on the duration of individual phases of the development of corn plants, followed by the sowing time, and the density of the stand was the least influential. This indicates a clear genotypic determination of the trait, which has high environmental stability.
Research has established that the most intensive growth processes of corn plants in height occurred before the flowering phase of the cobs. In this phase, a significant increase in the height of culture plants was noted, depending on the options of the experiment. Studying the range of stand density, the following pattern was observe ding -as the density increased from 70 to 90 thousand plants per hectare, the height of the plants increased. A similar trend was observed for all phases of plant growth, i.e., with an increase in the density of their standing, the height of the plants increased and was in the phase of 12-13 leaves -137.9-161.2 cm, flowering of cobs -217.9-249.8 cm, physiological maturity -220.2-256.8 cm.
The green mass accumulation index reached its maximum values in the phase of milky grain ripeness for all options (sowing dates, hybrids and plant stand density). A comparison of the yield of raw mass in relation to hybrids in the phase of milk ripeness of the grain made it possible to reveal a clear trend of increasing the yield of raw mass in hybrids of later ripening groups -Skadovsky and Kakhovsky.
The maximum productivity of plants in terms of the formation of green mass was on the option for sowing in the third decade of April of the hybrid Kakhovsky and the density of standing 70 thousand pieces/ha -51.39 t/ha. Dry matter indicators of corn plants were maximum in the phase of physiological maturity. On average, during the period of research, in this period the maximum mass of raw matter was possessed by Kakhovsky hybrid corn plants, the value of this indicator, depending on the options of the experiment, varied within 21.57-25.18 t/ha. The accumulation of dry matter mass was significantly influenced by the time of sowing -the maximum values of the plants of which crop were sown in the 3rd decade of April.
The conducted studies established that the increase in the area of the leaf surface of corn increased with the growth and development of plants. The maximum values of the leaf surface area on all warrants of the experiment were observed in the flowering phase. This indicator was the highest for sowing in the 3rd decade of April of the mid-ripening hybrid The maximum value of the net productivity of photosynthesis, on average during the period of research, -14.18 g/m per day, was obtained in the interphase period "7 leaves-12-13 leaves" when sowing the Kakhovsky hybrid in the third decade of April and using a stand density of 70 thousand pcs./ha. Sowing in the third decade of April, due to the improvement of production processes, contributed to the increase of the photosynthetic potential of crops, compared to other periods. This indicator reached its maximum value in the period of 12-13 leaves-flowering cobs -1189-1686 thousand m /ha per day.
The maturity group of the hybrid influenced the formation of the photosynthetic potential of culture plants. This indicator was the highest among all options sowing in the medium-ripening hybrid Kakhovsky and varied in the period from 12-13 leaves to the flowering of cobs in the range of 1375-1686 thousand m / ha per day. An increase in the density of standing corn from 70 to 80 thousand units/ha, on average for 2014-2016, led to an increase in the photosynthetic potential of crop plants by 7.76%, and from 80 to 90 thousand units/ha -by 2.38%.
Summarizing the observational data, it can be concluded that the formation of the main morpho-physiological and biometric indicators of corn plants was influenced by all factors of the experiment, namely: sowing dates, hybrid maturity groups, and plant stand density.