RESPONSE OF MAIZE HYBRIDS TO IRRIGATION TREATMENTS AT SEMI-ARID ENVIRONMENT

This experiment was carried out during season of 2020 and 2021 at Erbil governorate to study the forage and grain yield performance of three maize hybrids Zea mays L . as influenced by irrigation skipping at different times. The experiment was laid out in split-plot design with three replications. The irrigation treatments were located at the main plots


INTRODUCTION
Crop production in arid and semi-arid regions faces the challenge of ensuring high yields with a limited supply of water.This raises the question to which extent irrigation supply can be reduced without detriment to yield (32). Maize (Zea mays L.) is a multipurposes crop with wide adaptability to different agroclimatic conditions.The grown in most parts of the world, up to 3000m above mean sea level (11,39).This crop is preferred by farmers due to its grain production potential being the highest among cereals (7,18), its dual-purpose use (grain and fodder) (19,42); used as a cash crop (specialty corn: green ear, baby corn, sweet corn, and popcorn) (18), and raw materials for industry.Maize are not a food crop but an industrial crop, as only 12-13% of its production was used for human consumption globally (6).It was cultivated at area of nearly 150 Mha in approximately 160 countries, which constitutes 36% (782 Mt) of the global grain production (5).The total maize grain produced in the world, approximately 70-80% is used as feed (40).Global climate change was predicted to increase ambient temperatures and also the frequency and severity of drought in various growing regions that are highly dependent on maize (16,43).Drought stress is a major constraint in modern agriculture (38) and especially for C4 plants such as maize (Zea maize L.) with high water demand and short growing season.With ongoing climate change, models predict increasing frequencies and severity of drought spells; therefore, a better understanding of the role of the recovery process in overall drought resistance is important (8,9,10,32).With the warming of the climate in recent years, drought has become more and more critical to maize production, and has become the most important abiotic factor threatening maize production (4,16,36).Breeding droughtresistant varieties is an essential means to cope with climate change.Drought adversely affects cereal yields worldwide, with maize (Zea mays L.) having greater sensitivity to drought stress than wheat (Triticum aestivum L.) (21) and (22).Breeders have explored the genetic variability associated with tolerance against drought and heat stresses, which are among the most limiting factors for crop production (30).

MATERIALS AND METHODS
The response of maize hybrids (Zea mays L.) to soil moisture stress in the semi-arid environment of the Erbil region for the growth period and growth stages were conducted in two field experiments during the summer season of 2020 and 2021.

Location of the experiment
The governorate of Erbil is located at the north of Iraq.A Field Experiment of Gerda-Rasha, College of Agriculture Engineering Sciences/ University of Salaheddin (Lat 36 o 11' 356''; N, Long 44 o 01' 987''; E, 418 masl.), 5km south of Erbil city.The present study was designed to compare three skipping irrigation treatments on different dates with wellwatered conditions, and evaluate the influence of drought conditions in three maize hybrids DKC6664 (H 1 ), DKC5401 (H 2 ) and DKC6589 (H 3 ) with respect to growth, forage and, kernel yield and its related characters at two successive seasons.At the location, a composite soil sample of about 5 kg was obtained by mixing subsamples from 6 sites using a shovel.Each the soil sample was freed from plant roots and other debris.All the samples were dried at room temperature for seven days.Each sample was cleaned using a 2 mm stainless-steel sieve.Factorial experiment within split plot was used Full and deficit irrigation as the main plot was replicated three times.The water deficit of various degrees was imposed at different growth stages with the irrigation treatments.There were three maize growth stages which are vegetative (S1), tasseling (S2), and milking (S3) stages.The four levels of irrigation treatments were: full irrigation (I1), add half of irrigation at emergency until tassling stage (17), add half of irrigation at tassling until milk stage (18), add half of irrigation at milk until physiological stage (19).Table 1 exhibits the details of the irrigation treatments.Table 2 shows the sum of water applied at different treatments for both seasons.The sub-plot factors encompassed the genotypes which, were hybrids DKC 5401, DKC6589 and, DKC 6664.The size of each sub-plot was 3m by 3m and consisted of four rows, 0.75 m apart.The spaces between plants within the row 0.25 m.Cultural practices before planting and delineating the plots, an area with a gentle slope was selected and irrigated.The field was then plowed with a moldboard plow at the optimum water content for tillage.In both seasons, three maize seeds at a depth of 2-5 cm were placed in each hole on July 1 st , 2020, and 2021.After two weeks, the seedling was thin out to one per hole.Nitrogen fertilizer in the form of Urea (21%N) applied one before the second irrigation and the other before flowering at a rate of 40 kg ha - 1 as recommended.Hand weeding practiced as needed.There was not treated with any pesticide.

Erbil governorate climate
The climate of Erbil governorate is considered a semi-arid environment: cold and wet in winter, hot and dry in summer.The average temperature from July to August is between 42-39°C and42-41 1n 2020 and 2021, respectively, and often reaching nearly 50 °C.In October means high temperatures are 32 and 30°C in 2020 and 2021, respectively, and slightly cooling down in November.The rainfall is limited to the winter and spring months (Kurdistan Regional Government, 2020 and 2021; Table 3).

Analytical methods and laboratory
The results of the studied soil parameters are show in Table 3. Particle size fractionation and distribution were conducted by the international pipette method as recommended by Black et al (14).EC and acidity (pH) of soil sample were measured in 1:10, soil to H2O ratio suspension according to (43) by using these models of instruments; pH-meter (model WTW 330i/ Germany); EC-meter (model WTW 330i/Germany).The percent of organic carbon (o.m%) in soil samples was determined by the Walkley-Black method (wet oxidation by potassium dichromate K2Cr2O7 and concentrated H2SO4) as described by (14).The content of organic matter (O.M.) was calculated as follows: % Organic matter = % organic carbon × 1.724 (factor).The percent of the total (CaCO3%) was determined by the acid-neutralization method according to the method 23c of U.S. Salinity Laboratory Staff, 1954.A small auger 5 cm in diameter (30) was used to observe soil water content.The average water requirement (consumptive crop use) was calculated from soil moisture.The soil moisture was brought to field capacity when the available soil moisture was depleted by 55%.The net depth of applied water was calculated from ( 35

Statistical analysis
Statistical analysis for all measured variables was performed using the XLSTAT software (XLSTAT, 2017) (44).For; direct comparison of treatments, the least significant difference tests (LSD) at levels of 0.05 and 0.01 were used.For; testing the main effects of deficit irrigation on maize genotypes in a semi-arid region, the data were subjected to analysis of variance (ANOVA).

RESULTS AND DISCUSSION
Data in Table (5) illustrates the mean squares of studies characters at both seasons and their average.The analysis of variance (ANOVA) severally displays great significant change within the irrigation treatments and hybrids acts for most investigated characters.The effect of irrigation treatments was highly significant for the characters fresh forage yield, dry forage yield, ear weight, ear diameter, number of kernels/row, kernel yield, while it was significant for plant height, number of leaves/plant, ear height, ear length, number of rows/ear, but it was not significant for the other studied trails, during the first season.In the second season, the effect of irrigation treatments was highly significant for fresh forage yield, dry forage yield, number of kernels/row, and kernel yield, at the same time, it was significant for plant height, number of leaves/plant, leaf area, ear height, ear length, ear weight, ear diameter and number of rows/ear.As the average of both seasons, all studied characters responded high significantly to the irrigation effect except for 1000 kernels weight which responded significantly.Regarding the effect of hybrids, it was found that this effect was highly significant for plant height, number of leaves/plant, leaf area, still, it was significant for stem diameter, ear height, and 1000 kernels weight, and did not significant for others at the first season.In the second season, the differences among hybrids were highly significant for plant height, number of leaves/plant, leaf area, ear weight, ear diameter, and number of rows/ear, but it was significant for stem diameter, ear height, number of kernels/row and 1000 kernels weight, but did not significant for the others.On the average of both seasons, the differences among hybrids were highly significant for all characters except for fresh and dry forage yield, and ear length, which did not significant.The effect of the interaction between irrigation treatments and hybrids was highly significant for ear diameter and a number of rows/ear, at the same time it was significant for dry forage yield, ear weight, 1000 kernels weight, and kernel yield, and it was not significant for the others at the first season.In the second season, the interaction effect was highly significant for the number of rows/ears, the number of kernels/row, and kernel yield, at the same time it was significant for the characters plant height, fresh forage yield, ear weight, and ear diameter, but did not significant for the others.In the average of both seasons, the interaction effect was highly significant for all characters, exception forage dry yield which was significant, and not for leaf area and ear length.Significant effect of interaction between soil moisture content (irrigation levels) and maize varieties was obtained for growth, yield, and yield components except number of ears/ plant, ear length, no. of rows/ear, ear grains weight, grain yield /plant and shelling% in the combined analysis (33).Data results in Table 6 show the effect of irrigation treatments at both seasons and their average on studied characters.A treatment of full irrigation I1 produced the highest value for all characters compared to the skipping treatment at different dates during both seasons and their average.A minimum value changes according to characters and skipping treatment.The lowest values of most growth characters occurred at skipping treatments of I2 and I3 as the average of both seasons, in contrast, for fresh and dry forage yield and kernel yield with most of its related components, the lowest values exhibited at the last skipping treatment I4.At both seasons and their average, under drought condition, the significant differences among skipping treatments were found to be low in reduction of biomass compared to the treatment of control I1.A water requirement of maize is most significant during the late vegetative to early reproductive stage, with drought stress during these stages causing severe yield loss (15,28).(46) reported that under drought stress, plant height, ear length, rows ear -1 , row grains, 1000 kernel weight could be used as identification index of drought resistance of maize in different periods.Results in Table 7 show the mean of studied characters in both seasons and their combined.Significant differences represent among hybrids for all trails except fresh and dry forage yield; and ear length in both seasons and they're combined, while there were no significant differences among hybrids due to a number of kernels/row in the first season, and for kernel yield in both seasons.Hybrid DKC6664 produced the highest value for plant height at both seasons and they're combined, ear height at the second season, and the average of both seasons.Hybrid DKC 5401 exhibited the maximum significant value for the traits number of leaves/plant; leaf area; stem diameter; ear weight and 1000 kernels weight at both seasons and their combined, and number of kernels/row in the second season and the average of both seasons and kernel yield as the average of both seasons only and ear height during the first season.Hybrid DKC 6589 produced the maximum significant value for the ear diameter and the number of rows/ear in both seasons and their average.Mehasen and El-Gizawy (33) indicated that maize varieties exhibited significant differences for kernel yield and all studied yield attributes in both seasons and they're combined.Significant differences in yield and yield attribute were also reported by others (13,22,23,24,25,26,35,36); they, also confirmed that the differences among varieties in their performance might be due to the genetic differences among them.Significant phenotypes differences were seen between maize lines under stress for a maximum number of traits, and This variation was because of differences in the genetic constitution of the lines, which depends on the variability in the source populations from which the lines were obtained and developed (3,42).

Table 7. Effect of hybrids for some growth characters and yield components at both seasons and they're average
Data present in Table 8 illustrate the impact of the interaction between irrigation treatments and hybrids for the studied characters at both seasons and their combination.In the first season, was highly significant for ear diameter and number of rows/ear, but it was significant for dry forage yield, ear weight, and number of rows/ear, while did not significant for the others.A maximum dry forage yield was produced for hybrid 1 under the first irrigation treatment (full irrigation) reached 11.970 t/h, but the lowest dry yield exhibited by hybrid 3 coupled with the third irrigation treatment 7.233 t/h.maximum ear weight was 45.893gr produced by the interaction between the hybrid 2 and the full irrigation treatment, at the same time the minimum value was 14.927gr produced by the hybrid 2 coupled with the last irrigation treatment.Highest value for ear diameter and number of rows/ear was 2.786cm and 17.697 rows respectively, exhibited by the interaction between the hybrid 3 under the full irrigation treatment for both.Lowest value for ear diameter was 2.200 cm produced by the interaction between the hybrid 2 under the second irrigation treatment, still for a number of rows/ear, the lowest value was 12.433 rows shown by the hybrid 2 under the last irrigation treatment.The minimum value for 1000 kernels weight was 335.800gr recorded by the hybrid 2 under the last irrigation treatment, while the lowest value was 236.600gr for the interaction hybrid 1 with the same irrigation treatment.Maximum kernel yield reached 11.126t/h for hybrid 2 under the full irrigation treatment.Still, the lowest yield was 3.166t/h obtained by the interaction of hybrid 1 with the last irrigation treatment.In the second season, this effect was highly significant for the number of rows/ear, number of kernels/row, and kernel yield, but it was significant for plant height and ear diameter, while it does not significant for the others.The maximum value for the traits plant height, fresh forage yield, ear diameter, and a number of rows/ear produced by the interaction of hybrid 3 under the full irrigation, recording 196.433cm, 45.246t/h, 2.963cm, and 13.130t/h, respectively.Lowest value for plant height was recorded by hybrid 3 under the third irrigation treatment with 127.333, but the lowest value for forage yield, ear weight, and kernel yield was 28.783t/h, 25.927gr, and 5.200t/h, respectively recorded by the interaction of hybrid 1 under the last irrigation treatment.Highest value for ear weight, number of kernel/row, and kernel yield reached 56.893gr, 35.900 kernels, and 13.130t/h respectively, recorded by the hybrid 2 under full irrigation.The lowest value for a number of rows/ear and number of kernels/row was 13.933 row and 20.933 kernels respectively, by the hybrid 2 under the last irrigation treatment.Regarding the average of both seasons, the interaction effect was highly significant for all traits except dry forage yield it was significant, and leaf area, and ear length were not significant.The hybrid 3 (29) reported that under drought, did not significant differences in biomass were observed between all hybrids.Growth parameters such as plant height, fresh and dry weight of shoot was baldly desolated by the water stress levels (5).The plant biomass is minimized by the water deficit condition, but it produces strafe shoots more than roots (47).Drought affects the seedling of maize root and shoot growth, creates different environmental disorders (1).The grain weight was important and highly correlated with grain yield in corn (13).The number of kernels/ear is agronomic trait one of the important traits correlated to grain yield, directly and indirectly (12,13).

Table 8. Effect of interaction between irrigation treatment and hybrids at both seasons and their average
depth of applied water (mm) FC = Soil water retention at -33 kPa PW = Soil water retention at -1500 kPa b = Average soil bulk density of root zone (gcm -3 ) w = Water density (gcm -3 ) P = Depletion fraction = 0.55 D = Root zone depth (mm)

Table 9 . Effect of seasons of growth characters and yield component
15)a results in Table(9)indicate the effect of seasons in studied characters; this, effect was highly significant for a number of leaves/plant; the number of rows/ear; the number of kernels/row; 1000 kernels weight, and kernel yield, while it was significant for leaf area, stem diameter, ear length, ear weight, and ear diameter, but did not significant for the others.It was observed that the second season predominated the first season by15.72;8.54; 15.34; 11.82; 22.65; 40.30; 6.99; 9.64; 33.80 and 32.24% for the trails number of leaves/plant; leaf area; stem diameter; ear height; ear length; ear weight; ear diameter; the number of rows/ear; the number of kernels/row and kernel yield respectively.Vice versa, the first season exceeded the second season in only 1000 kernel weight by 16.41%.