VARIATION OF SOME BIOMETRIC PARAMETERS IN CORN EARS IN RELATION TO PLANT STATUS

. The study evaluated the variability of some plants and ears parameters in maize, and the possibility of estimating the productivity elements at the ear level depending on the plants status parameters. The study was done in the area of Sanmihaiu Roman, Timis County, Romania. The maize hybrid DKC 5075 was cultivated in a non-irrigated system, with an appropriate culture technology. The number of leaves during the vegetation period (Ln-v), the number of leaves at harvest (Ln-h) was evaluated


INTRODUCTION
Maize is an important crop, for human food, for industrialization, as fodder for animals, but also as a plant in the crop structure (Shiferaw et al., 2011;Shah et al., 2016).The importance of maize crop, and the high ecological plasticity, made corn to be cultivated in various areas and on large surfaces (Wang and Hu, 2021;Erenstein et al., 2022).
Agronomic traits of corn plants were analyzed and evaluated in relation to climatic factors (Ren et al. 2022), and parameters of corn plants were evaluated in relation to elements of cultivation technology (Djaman et al., 2022).The response of corn plants to water stress was quantified based on some physiological parameters, or at the biochemical and molecular level (Devi et al., 2022).
Production variation and yield losses in relation to the height variability of corn plants were studied under the conditions of a notill system (Boomsma et al., 2010).The authors used different types of regression analysis and clarified the variation of corn yield in relation to different factors and parameters considered in the study.
Within some corn culture systems, Yin et al. (2011) evaluated corn production in relation to plant height, in different stages of vegetation, and through regression analysis it was possible to accurately estimate yields, useful information for technological and commercial aspects.
Estimation of corn production (biomass production, grain production) has been the subject of several studies, as a result of the importance of this aspect in relation to crop management, or of some harvesting and production valorization works (Herbei and Sala, 2016;Leroux et al., 2019).Also, different methods of estimating corn production were analyzed, in relation to their accessibility, or to the level and degree of certainty of the prediction (Herbei and Sala, 2016;Chivasa et al., 2017;Tandzi and Mutengwa, 2019).

MATERIAL AND METHODS
The study took place in the area of Sanmihaiu Roman, Timis County, Romania, figure 1 (ESRI, 2014).The maize hybrid DKC 5075 was cultivated, with a density of 70,000 plants per hectare, in a non-irrigated system.Wheat was the previous crop.The land was prepared by plowing in the fall, at a depth of 25-30 cm, and the preparation for sowing was done by combination working in spring.Fertilization was done with DAP complex fertilizer (10:40:0), 250 kg ha -1 , Ferticover microgranulated fertilizer 25 kg ha -1 at sowing.400 kg ha -1 CAN were applied in the vegetation.
The maintenance works were ensured by pre-emergence herbicides (Adengo herbicide) and post-emergence herbicides (5-leaf stage; Elumis herbicide).Insecticides and fungicides were not used.
In the drought conditions that characterized the year 2022, during the vegetation of the corn crop, especially the May-August period, the production was at the level of 3000 kg ha -1 .
The climatic conditions, in the area of Sanmihaiu Roman locality, recorded for the year 2022, are presented in figure 2 (Meteoblue).In relation to the purpose of the study, observations were made during the vegetation period and samples of plants with ears were taken at the moment of physiological maturity.The number of leaves during the vegetation period (Ln-v), the number of leaves at harvest (Ln-h) was evaluated; the height of the plants (Ph) and the diameter of the plant stem (Pd) were determined.Determinations were made regarding the length of the ear (El), the diameter of the ear (Ed), the weight of the ear (Ew) and the number of grains per ear (Gn).
The recorded data were analyzed by appropriate methods (Hammer et al., 2001; Wolfram Alpha, 2020; JASP, 2022) to evaluate the variability of the studied parameters, interdependence relationships, and to estimate productivity parameters at the level of the ears, depending on plant parameters, against the background of the poor climatic conditions of the year 2022.

RESULTS AND DISCUSSIONS
In the specific climatic conditions of the agricultural year 2021-2022, and especially the climatic conditions of the year 2022, during the vegetation period of the maize crop, the plants have partially and with difficulty capitalized on the soil conditions and those ensured by the culture technology.
Thus, in the study conditions in the area of Samnihaiu Român Locality, within the maize plot, different categories of plants were recorded, in terms of growth and development, and associated with corn ears.
The values recorded for parameters determined in plants and ears are presented in table 1.For the safety of data interpretation, the values for the standard error (SE) were calculated for each parameter.It was found that the number of leaves at harvest (Ln-h) was much lower compared to those determined during the vegetation period (Ln-v), as a result of drying under the influence of heat and subsequent degradation, until the harvesting moment.
The assessment of the statistical reliability of the data series, as well as the presence of variance, was done by the ANOVA test, according to which Fcalculated > Fcrit, p <0.001 (Alpha=0.001).The variability of the studied parameters in the maize plants and ears, hybrid DKC 5075, was quantified based on the coefficient of variation (CV) and based on the diversity profile, as a complementary graphic method.
In relation to the coefficient of variation values, the highest variability was recorded for plant height (CVPh=30.4824),and the lowest value was recorded for plant stem diameter (CVPd=9.8659).High values were also recorded in the case of the number of leaves at harvest (CVLn-v=23.1179) and the weight of the ears (CVEw=23.5464).Intermediate values were recorded for the number of grains (CVGn=17.5084),for the number of leaves in vegetation (CVLn-v=13.2348), for the length of the ears (CVEl=12.3450),and for the diameter of the ears (CVEd=10.9924).The graphic method confirmed the variability of the studied parameters, the distribution of the variability of the recorded values being reproduced in the form of the diversity profile, figure 3. The correlation analysis led to the values of the correlation coefficient (r) in table 2 strong, positive correlations were recorded between the number of leaves and the height of the plants (r=0.936 for Ph and Ln-h; r= 0.917 for Ph and Ln-v), between dimensional parameters of the ears (r=0.963 for El and Ew; r=0.940 between Ew and Ed; r=0.932 between Gn and Ew).
Strong correlations were recorded between the diameter and the length of the ear (r=0.886), between the number of grains and the length of the ear (r=0.884), and between the number of grains and the diameter of the ear (r=0.886).A high number of moderate correlations were recorded between plant dimensional parameters (e.g.r=0.762 for Ln-v and Pd), as well as between ears dimensional parameters and plant parameters (e.g.r=0.750 for Ew and Pd).Correlations weaker in intensity between the other determined parameters were also recorded.Based on the recorded correlations, the interdependence relationship of some parameters, in maize plants or ears, was evaluated.Thus, equation (1) was obtained, which described the interdependence between the length and diameter of the ears, under conditions of statistical safety (R 2 =0.792, p=0.0041).The graphic representation of the El variation in relation to Ed is presented in figure 4.
(1) where: x -ear diameter (Ed) The variation of Ew in relation to Ed was described by the linear equation ( 2), R 2 =0.884, p<0.001.The variation of Ew in relation to El was described by equation (3), R 2 =0.930, p<0.001, figure 4(a), and the variation of Ew in relation to Gn was described by equation ( 4), R 2 =0.840, p =0.0016, figure 4(b  The variation of the ears weight (Ew) in relation to the diameter of the plant stem (Pd) and the number of leaves in the vegetation (Ln-v) was described by equation ( 6), according to R 2 =0.730 (Multiple R=0.854).The graphic representation of the Ew variation depending on Pd and Ln-v is presented in figure 6.The variation of the grains number on maize ear (Gn) in relation to plant vegetative parameters (plant height, Ph; number of leaves in vegetation, Ln-v) was described by equation ( 7), according to R 2 =0.856 (Multiple R=0.925).The graphic representation of the variation of Gn according to Ph and Ln-v is presented in figure 7.  deficit during the vegetation period of the maize crop, especially in the months of June -July -August (very pronounced in July), the corn plants were subjected to hydric and thermal stress, and plants growth and development were strongly affected.
Plant parameters considered in the study, namely plant height (Ph), stem diameter (Pd), number of leaves in vegetation (Ln-v) and number of leaves at harvest (Ln-h), were representative to express the level of plant growth and development at the time of determination, under the influence of vegetation and technological conditions.Although an appropriate technology was applied for the maize crop, the climatic conditions during the vegetation period had a strong restrictive effect for the utilization of the applied technology, and affected the growth and development of the plants.
A high variability of the plants was recorded, in terms of morphological parameters (plant height, CVPh=30.4824),parameters that were strongly influenced by the climatic conditions during the vegetation period.Also, the alteration of the leaves under the effect of drought was recorded, which led to the complete drying of some leaves and their loss during the vegetation period (big differences recorded between Ln-v and Ln-h).Associated with the state of vegetation of the maize plants, the formation and development of the ears was negatively influenced, and the values recorded for the parameters analyzed in the ears were below the biological potential of the cultivated hybrid.
However, a certain level of proportionality was kept between the physiological parameters of the plants and those of the productivity of the maize ears.
The recorded correlation levels show the interdependence between the level of plant development and the values of the productivity elements studied in ears, but in the specific climatic conditions of 2022, the maize plants were subjected to a high climatic stress (hydric and thermal) and for a long period, a fact that was reflected in the ears formation and development, and finally in the level of production.
From the analysis of equations ( 5) and ( 6), as well as the graphic representations (figures 5 and 6), it was found that the ears weight was closely determined by the height of the plants, by the diameter of the plant stem, and the number of leaves on the plant, but in a variable way.Analyzing figure 6, it was found that the ear weight varied more strongly depending on the number of leaves in the vegetation period (y-axis) than depending on the diameter of the plant stem (x-axis).At the same time, it was appreciated that the estimation of the productivity elements in maize ears, based on some vegetation parameters of the plants, was possible under statistical safety conditions (R 2 =0.713 for Ew in relation to Ph and Ln-v; R 2 =0.730 for Ew in relationship with Pd and Ln-v; R 2 =0.856 for Gn in relationship with Ph and Ln-v).
Various studies have confirmed the importance of estimating the production of agricultural crops, based on data and information obtained at different stages during the vegetation period, for the purpose of adequate management of crops, the establishment of intervention works, or the production valorization (Herbei and Sala, 2016;Karlson et al., 2020;Zhang et al., 2021).
Results regarding the prediction of the corn crop production were communicated both in relation to the climatic conditions, as well as to the methods and techniques used, under statistical safety conditions (Maitah et al., 2021;Li et al., 2022).
Variable levels of safety were communicated in relation to the moments of vegetation that provided the information about certain parameters and indices in the corn crop, based on which the prediction was made.Zhang et al. (2021) communicated the certainty of estimating biomass production in the corn crop at the level of R 2 =0.81 and RMSE=0.27t/ha, under the conditions of an estimate based on information from the V6 vegetation stage.In other studies, lower levels of safety were reported when the estimation was made in earlier phases of vegetation (e.g.R 2 =0.53, at flowering), and higher levels of safety in the case of estimation based on information about the culture in advanced vegetation stages (R 2 =0.98, at maturity) (Ren et al., 2023).
In the conditions of the present study, the prediction of some productivity parameters in maize ears was certified by safety parameters at variable levels depending on the vegetation parameters of the plants, but without irrigation it was not possible water deficit correction, remediation the plants vegetation status, and recover (at least partial) of the production.

CONCLUSIONS
Associated with the climatic conditions specific to the agricultural year 2021 -2022, and especially during the vegetation period of the maize crop (June -August), in the study conditions the maize plants were greatly affected by pronounced water and thermal stress.This negatively influenced the vegetation of the plants, and generated a high variability of the vegetative parameters of the plants, considered in the study.Associated with this fact, and as a direct consequence, the formation and development of the cobs was affected, with a pronounced decrease in production.
In the given conditions, a certain level of proportionality was found between the physiological parameters of the plants and those of the productivity of the maize ears.
Different levels of correlations were recorded between plant parameters and those at the ears level, which highlighted the interdependence between ears parameters and maize plants parameters.
The regression analysis facilitated the estimation of the main productivity parameters at the level of the maize ears in relation to the parameters of the plants.Based on the obtained equations and graphic models, it was found that the ear weight (Ew) was closely determined by the height of the plants (Ph), with the number of leaves on the plant in vegetation period (Ln-v), with the diameter of the plant stem (Pd), but in a variable way.
The estimation of the productivity elements in maize ears, the DKC 5075 hybrid, in the study conditions, based on some vegetation parameters of the plants, was possible with statistical safety (R 2 =0.713 for Ew in relation to Ph and Ln-v; R 2 =0.730 for Ew in relation to Pd and Ln-v; R 2 =0.856 for Gn in relation to Ph and Lnv).
From the estimation of the maize ears weight (Ew) based on the diameter of the plants (Pd) and the number of leaves in the vegetation (Ln-v), it was found that the ears weight varied much more strongly depending on the number of leaves in the vegetation period (axis y), than depending on the diameter of the plant stem (axis x).

Figure 3 .
Figure 3. Diversity profile for determined parameters in maize plants and ears, the DKC 5075 hybrid

Figure 4 .Figure 5 .
Ew variation in relation to El (a), and Ew variation in relation to Gn (b) in maize ears, the DKC 5075 hybrid The estimation of the ears weight variation (Ew) in relation to the vegetative parameters of the plants (plant height, Ph; number of leaves in vegetation, Ln-v) was described by equation (5), according to R 2 =0.713 (Multiple R=0.845).The graphic representation of the Ew variation depending on Ph and Ln-v is presented in figure 5. (5) where: Ew -ear weight (g); x -plant height (Ph,cm); y -leaf number in vegetation (Ln-v); a, b, c, d, e, f -coefficients of the equation (5); a= 238.829710; b= 13.546231; c= 1080.757910;d= -300.974307;e= -101.961215;f= 1772.434803Ew variation in relation to Ph (x -axis), and Ln-v (y -axis), the maize hybrid DKC 5075

Table 1 .
Statistical description of the parameter values determined in maize plants and ears, the DKC 5075 hybrid . A series of very