INTRODUCTION
Introduction
Maize (Zea mays L.) is a vital cereal crop globally, cultivated for food, feed, and industrial uses Its production has been steadily increasing across various countries, with a record output reported by the Food and Agriculture Organization (FAO) in 2014, where maize was grown on 191.27 million hectares, yielding 1052.6 million tons By 2019, the area under maize cultivation expanded to 197.2 million hectares, with an average yield of 6.41 tons per hectare, resulting in a total production of 1148.48 million tons Projections indicate that maize demand in developing countries will double from 2011 to 2050, making it the crop with the highest production demand globally by 2025.
Maize production, despite significant yield increases, faces global threats from drought, particularly during critical growth stages like flowering and grain filling (Lobell et al 2014) Droughts, as major natural disasters, can severely impact economic, agricultural, ecological, and environmental activities, making them one of the most serious environmental stresses on plant growth and crop productivity In Vietnam, the total maize area in 2019 was approximately 1.2 billion hectares, with a productivity of 4.32 tons per hectare, resulting in a total yield of 4.431.8 tons However, the domestic demand for maize exceeds 5 million tons annually for food processing and livestock, leading to a shortfall that necessitates importing over half a million tons each year This situation presents an opportunity for expanding maize production Major drought events have been recorded in recent decades and are expected to intensify across Asia and beyond, posing significant challenges for farming in various countries.
Drought stress has led to an average global decrease of about 40% in maize production, with extreme droughts causing a loss of approximately 3% of global cereal production from 2000 to 2007 This highlights the urgent need for research into drought-tolerant maize varieties tailored to specific ecological regions and countries, particularly in Southeast Asian nations As demand for maize continues to rise in Eastern and Southeast Asia, the increasing frequency of droughts due to significant weather fluctuations further exacerbates the situation.
In Vietnam, maize ranks as the second most important food crop after paddy rice, thriving across various ecological regions and seasons Known for its drought tolerance, maize plays a crucial role in agricultural production, especially under extreme climatic conditions such as drought, cold, and heat Drought significantly impacts maize yield and quality, with estimates indicating that up to 30% of maize output is affected Recently, drought-affected areas have increased dramatically, with 70-80% of regions experiencing low yields and some unable to harvest at all (Phan Xuan Hao, 2005) However, there is a lack of adequate information regarding maize's response to drought and salinity during its later vegetative and early reproductive stages.
To effectively manage drought, it is crucial to comprehend how soil water content influences the growth and physiology of maize, particularly during the critical period following the seedling stage This understanding will inform the implementation of appropriate measures to mitigate drought effects.
This study investigates the impact of water deficit conditions on the growth and yield of four maize varieties cultivated in a vinyl house By focusing on the specific needs and factual data, we aim to understand how varying water availability affects maize performance in controlled environments.
Objectives and requirements
This study was conducted to examine if the growth and development of four on the above evaluation, the maize variety adapted to drought conditions would be selected
- Evaluating effect of water deficit conditions on growth traits of four maize varieties grown in the vinyl house
- Evaluating effect of water deficit conditions on physiological traits of four maize varieties grown in the vinyl house
- Evaluating effect of water deficit conditions on yield of four maize varieties grown in the vinyl house.
LITERATURE REVIEW
Situation of maize production on the world and in Vietnam
2.1.1 Situation of maize production in the world
Global maize production has seen a continuous increase since the early twentieth century, particularly in the last decade, making it one of the fastest-growing crops in terms of yield among major food sources In 1961, maize was cultivated on 105.6 million hectares, yielding an average of 1.9 tons per hectare for a total production of 205 million tons By 2000, the area under maize cultivation had expanded by 1.3 times to 137.0 million hectares, with an average yield of 4.3 tons per hectare, resulting in a total output of 592.5 million tons The trend continued, and by 2011, the global maize area reached 172.1 million hectares, a 1.25-fold increase from 2000, with an average yield of 5.2 tons per hectare, totaling 888 million tons The peak production occurred in 2019, with over 197 million hectares harvested, achieving a yield of 6.4 tons per hectare and a remarkable total production of 1,148.5 million tons.
Table 2 1 Maize production in the world in recent years
In 2019, the United States led global maize production, with an area of 32.9 million hectares, an average yield of 11.6 tons per hectare, and a total output of 307.4 million tons (FAOSTAT, 2019) China, while ranking first in maize acreage at 41.3 million hectares, achieved a yield of 6.96 tons per hectare, resulting in a production of 260.9 million tons The US Department of Agriculture (USDA) forecasts a slight decrease in global maize harvest for 2019-2020, estimating a total of 1,108 million tons, down from 1,124 million tons in 2018-2019.
The United States and China are the leading consumers of maize, with China’s domestic consumption surpassing its national production.
The European Union plays an important role in maize consumption, followed by several major producers, including Brazil, Mexico, India and Canada
A number of the major maize importers are also among the major consumers: Egypt, Japan and Vietnam
Figure 2 1 Maize production according to countries
In Vietnam, maize ranks as the second largest annual crop by acreage, playing a crucial role in the feed industry alongside local crops like cassava and broken rice However, it is primarily cultivated in mountainous areas with poor soil fertility and limited water supply, leading to low corn yields Additionally, maize production faces challenges from pests and diseases, further impacting overall yields.
In 1961, Vietnam's maize harvested area was just 260.2 thousand hectares, yielding 292.2 thousand tons However, since 2000, maize production has experienced significant growth, with the cultivated area expanding to 730.2 thousand hectares and output reaching 2005.9 thousand tons.
Between 2005 and 2010, the maize cultivated area expanded from 1,050.6 thousand hectares to 1,126.4 thousand hectares, resulting in a production increase from 3,787.1 thousand tons to 4,606.8 thousand tons This period saw a growth of 396.2 thousand hectares in maize cultivation and an output increase of 2,600.9 thousand tons, reflecting an annual yield growth rate of 9.08% Although maize acreage slightly declined in 2018 and 2019 compared to 2010, the average yield and overall output continued to rise.
In the new stage of agricultural development, maize plays an increasingly important role, contributing to the rapid transformation of economic structure towards commodity agricultural production, safety, sustainability and diversification
Table 2 2 Maize production in Vietnam in recent years
(FAOSTAT, 2019) Argentina is the largest supplier of maize in Vietnam, accounting for nearly 71% of the country's total maize import volume and turnover
In the first eight months of 2020, Vietnam's maize imports rose by 10%, according to the General Department of Vietnam Customs Argentina emerged as the leading supplier, contributing nearly 71% of the total corn import volume, which amounted to 5.04 million tons Brazil followed as the second-largest market, supplying 1.08 million tons of maize.
Drought and the influence of drought
Drought is a pervasive natural hazard that affects nearly all regions and should not be seen solely as a physical occurrence It arises from the interaction between natural events and the demands of human water usage To understand drought, it is essential to consider it in relation to long-term averages of precipitation and evapotranspiration balance.
Drought is commonly defined as a prolonged period of below-average precipitation, lasting a season, a year, or even several years, leading to water shortages that impact various activities, groups, or environmental sectors (National Drought Mitigation Center, University of Nebraska, 2018).
Drought is considered the most destructive condition influencing the growth of crop plants consequently leading to decreased yield (Lambers et al., 2008)
Drought is a natural disaster that leads to the evaporation of moisture from leaves and soil, disrupting the water balance in plants and significantly hindering their growth and development (Nguyen Trong Hieu, 2006; Tran Duc Hanh, Doan Van Diem, 2006).
The maize plant is sensitive to drought, particularly during the critical four-week period around tassel appearance Areas receiving less than 100mm of rainfall are deemed unsuitable for maize production, while those with over 200mm are considered suitable Regions with rainfall between 100mm and 200mm fall into a water deficit category for maize cultivation (Chapman and Barreto, 1996).
In researching the causes of drought, many authors believe that the lack of regular rainwater is the main cause of drought The issue of rainy time, the rains
According to Hoang Minh Tan et al (2006) providing the concept and classification of drought as follows:
Drought occurs when there is a deficit of water in plants, leading to an imbalance that causes wilting This happens because the water absorbed by the plant cannot keep up with the evaporation from its surface There are three types of drought that affect trees.
Soil drought happens when the water available for plants in the soil is exhausted, leading to insufficient water absorption and a disruption in the plants' water balance This phenomenon is common in regions with low average rainfall, particularly in the central provinces and the Central Highlands during the dry season, where it can persist for several months each year.
Air drought arises from excessively low air humidity, which intensifies the evapotranspiration process in plants and can cause water imbalance This phenomenon typically occurs in regions experiencing dry and hot winds, such as during the southwest "Laos" wind season in central provinces, the dry season in the Central Highlands, or occasionally during the northeast monsoon when humidity levels are also low.
Physiological drought happens when a plant's physiological condition prevents it from absorbing water, despite the absence of a water shortage This occurs when roots cannot access water, leading to water loss through evaporation and an imbalance in the plant's water levels Factors contributing to physiological drought include anaerobic soil conditions that deprive roots of oxygen for respiration, high soil salinity that exceeds the concentration in root cytoplasm, and low soil temperatures that hinder water absorption.
If severe and prolonged, physiological drought is also harmful as soil and air If the drought is combined with drought, the level of damage to the tree increases much
Nearly 47% of the world's cultivated area is affected by drought (Michon Scott, 2018) A report by Guoyong Leng (2021) indicates that moderate to exceptional drought events in the US can result in yield losses of 64.3% to 78.1%, particularly in Central and Southeastern regions Additionally, data from USDA and Monsanto (2007) show significant reductions in crop yields, with the US losing 14.7 million tons, France 1.36 million tons, and Romania 1.8 million tons The FAO (2007) highlights that drought poses one of the greatest challenges for crops, especially maize.
Droughts significantly impact livestock and essential crops such as corn, soybeans, and wheat During the peak of the 2012 drought, the U.S Department of Agriculture designated over 2,245 counties, representing 71 percent of the nation, as natural disaster areas This drought also affected major agricultural regions worldwide, contributing to food price volatility In nations already grappling with food insecurity, rising costs can trigger social unrest, migration, and famine.
Drought can significantly impact crop yields, reducing them by 65-87% depending on the plant type and the severity of the drought, which is influenced by its duration and intensity (McLaughlin and Boyer, 2004) The sensitivity of plants at various developmental stages also plays a crucial role in agricultural drought effects (Le Quy Kha, 2005) Drought-tolerant maize varieties can mitigate 15-25% of yield loss compared to non-tolerant varieties, while farming techniques can account for another 15-25% However, 50-70% of yield reduction can only be addressed through irrigation (Zaidi, 2000).
Vietnam experiences varying levels of drought across different regions and times, leading to significant socio-economic losses, particularly in water resources and agricultural production As one of the five countries most impacted by climate change, Vietnam has faced 40 years of drought since 1960, with drought occurrences accounting for 75% of that time The distribution of droughts includes 15 years in the winter-spring season, 12 years in the mid-season, and 13 years in the summer-autumn season Additionally, flooding has become increasingly severe, exemplified by the significant flood in early November 2020 in the Central provinces (Ministry of Natural Resources and Environment, 2020).
Vietnam faces significant water shortages despite its abundant water resources, with 62-63% of these sources originating from outside its borders The dry season lasts 6-7 months, exacerbating the situation Research indicates that from 1960 to 2006, Vietnam experienced drought in 34 out of 46 years, a trend that has worsened in recent years The Ministry of Natural Resources and Environment projects that by 2025, the country's total surface water will decrease to approximately 96% of current levels, leading to a severe water deficit over the next 50 years.
Maize cultivation varies by region and is heavily influenced by rainfall patterns, which can be erratic and lead to frequent droughts Over the past 55 years, significant droughts during the winter-spring season have occurred 22% of the time, while the summer-autumn season has seen droughts 12% of the time Notably, more than 60% of winter-spring droughts and over 80% of summer-autumn droughts are linked to El Niño events, particularly during the critical crop years of 1962-1963, 1976-1977, 1982-1983, and 1997-1998, as well as the summer-autumn season of 1963.
1977, 1983, and 1998 were the years when El-nino caused severe droughts (Nguyen Trong Hieu and Pham Thi Thanh Huong, 2007; Tran Thuc and Le Nguyen Thuc, 2006)
In Vietnam, approximately 0.3 million hectares of maize are vulnerable to water shortages during the silk appearance stage, potentially resulting in a loss of 0.5 to 0.7 million tons of corn kernels The situation worsens when drought conditions coincide with temperatures exceeding 38 °C, leading to damage of the tassel, a phenomenon commonly observed in the region.
Effect of drought on maize
2.3.1 Effect on growth and development
Maize, a C4 plant, requires between 350 to 500 liters of water to produce 1 kg of seeds, making it highly susceptible to drought stress, which significantly impairs its growth and development Key growth parameters affected by drought include plant height, leaf area, root characteristics, plant biomass, fresh weight, dry weight, and stem diameter Research indicates that drought conditions lead to reductions in plant height, stem diameter, biomass, and leaf area.
Drought stress significantly reduces both leaf size and the number of leaves in maize Key factors influencing leaf elongation include turgor pressure, light interception, and flux assimilation (Rucker et al 1995) The presence of wedge-shaped motor cells on the upper leaf surface helps maintain leaf unfolding; however, under drought conditions, reduced turgor pressure causes leaves to curl or fold (Du Plessis 2003) This folding decreases leaf area, leading to reduced light interception and, consequently, diminished photosynthetic activity.
Drought stress leads to a decrease in cell division and elongation, resulting in a reduced leaf area in maize plants This reduction is viewed as an adaptive strategy to cope with drought conditions The leaf area index is a crucial parameter for breeding maize varieties that can withstand drought stress effectively.
Drought during the seedling stage can significantly impact plant density If a water deficit occurs initially and continues for two weeks after tasseling, it can lead to a reduction in leaf area and photosynthesis rates during the reproductive period This ultimately results in smaller ear sizes and an accelerated decline in leaf health (Banzinger et al., 2000).
Under mild drought stress, maize plant roots elongate to access deeper soil layers for increased water uptake; however, severe drought stress leads to a reduction in root length Both root density and volume, as well as the number of roots, decrease under both mild and severe drought conditions (Nejad et al 2010).
Drought significantly impacts the maize life cycle, with the reproductive growth phase being particularly vulnerable to drought stress The primary reason for this increased susceptibility is the translocation of photosynthetic assimilates to the reproductive parts instead of the roots, which are essential for their elongation.
Taiz and Zeiger 2006) Drought leads to stomata closure, reducing photosynthesis leading to undifferentiated growth top cells, or adversely affects ear and tassel differentiation that resulting to reduced yield
Drought reduces the growth of leaves the most, followed by silks, stems, and finally the seed size Drought reducing soil coverage, reducing the area of leaves that absorb sunlight
Severe drought during the reproductive stage of maize significantly hampers the transport of anabolic substances to growth organs, resulting in stunted silk growth and delayed silk emergence This leads to an extended time gap between the appearance of tassels and ears, potentially resulting in "no ear maize" or seedless plants The female flower reproductive structures are more adversely affected than the tassels Additionally, during the tassel development stage, drought conditions combined with air temperatures exceeding 35°C and humidity levels below 70% can render pollen grains nonfunctional, preventing seed formation This issue has been frequently observed in Vietnam.
Drought can affect grain yield at any stage of the maize plant
Like other cereal crops, drought is most affected during maize flowering (Heisey and Edmeades, 1999)
Denmead and Shaw (1960) demonstrated that drought conditions prior to tasseling can reduce yield by 25% During the tasseling stage, the yield decrease can reach 50%, while post-tasseling, it drops to 21% Overall, continued drought during tasseling and silking can lead to yield reductions ranging from 17% to 53% Key traits affected by drought include plant height, leaf size, and biological yield, with yield factors such as grain size, corn size, and the weight of 1000 kernels also being significantly impacted (Bolanos and Edmeades, 1996).
Maize yield declines during the critical ripening stage due to drought, which shortens seed ripening time, reduces leaf age, and accelerates leaf aging, ultimately decreasing dry matter accumulation in seeds (Banziger and Edmeades, 2000) During this period, maize faces significant stress, affecting young plants and seed quality (Le Quy Kha, 2005; Phan Thi Van, 2006).
Drought stress significantly impacts pollen, leading to increased mortality due to dehydration as moisture is lost (Aylor 2004) Key factors such as settling speed, viability, specific gravity, shape, and dispersal are adversely affected in dehydrated pollen (Aylor 2002) The primary causes of pollen sterility under drought conditions are elevated ABA accumulation and decreased invertase activity (Saini and Westgate 2000).
Recent studies and researches on drought in maize in the world and in
2.4.1 Recent studies and researches of drought in maize in the world
CIMMYT maize breeders (Edmeades, 1997; Vasal, 1999) emphasize the importance of selecting breeding materials under adverse abiotic weather conditions This approach is crucial because selecting under favorable conditions can significantly diminish genetic expression and variability in less favorable environments.
In plant physiology and genetics, researchers have determined that variations in growth and development can be harnessed By controlling experimental conditions and utilizing genetic diversity in maize breeding, it is possible to develop hybrid maize varieties that exhibit high yield and stability, particularly under water deficit conditions.
In the results of experiment using two drought levels which is medium drought and highly drought Hugh & Richard (2003), McLaughlin & Boyer (2004) concluded the loss of yield is13 – 26% and 63 – 85%, respectively
Research indicates that water stress during the vegetative and tasseling stages can lead to a reduction in plant height and a loss of 28–32% in final dry matter weight Furthermore, prolonged water stress during the tasseling and ear formation stages may result in even greater losses, ranging from 66% to 93% (Çakir, 2004).
MiaoYang (2019) conducted RNA sequencing analysis during the late stage of leaf senescence in maize to investigate metabolic regulation under post-silking drought (PD) stress The study found that PD stress significantly decreased leaf carbon and nitrogen levels.
Plants utilize various mechanisms to manage drought stress, including stomatal closure, increased production of abscisic acid (ABA), enhanced antioxidant activity, and the accumulation of metabolites such as soluble sugars, free amino acids, and polyamines.
Polyamines, such as putrescine, spermidine, and spermine, are low molecular weight aliphatic polycations present in all living organisms, including maize They play a crucial role in various physiological processes in plants, including embryogenesis, cell division, flowering, aging, and stress response The accumulation of polyamines enhances the tolerance mechanisms of plants against a range of environmental stresses.
Under water deficit conditions, plants exhibit physiological responses such as leaf drop, reduced leaf surface area, and enhanced root development Drought stress is particularly detrimental during the reproductive stage, affecting flowering and seed production as nutrients are directed to the roots The hormone abscisic acid (ABA) plays a crucial role by closing stomata on leaf surfaces, which minimizes water loss through evapotranspiration and lowers the rate of photosynthesis These adaptive mechanisms improve the efficiency of water use in plants in a short period.
Plants respond to drought conditions through specific genes that help them recognize stress and transmit stress signals A key group of these genes encodes proteins that protect cells from drought effects, regulating solute formation, water transport systems, and providing protection and stabilization These genes also play a crucial role in maintaining the structure of cell membranes against drought and reactive oxygen species (ROS).
During drought conditions, a second group of protein-coding genes is activated, which plays a crucial role in transmitting stress signals and regulating gene expression Plants utilize at least four distinct strategies to manage drought stress, governed by a complex network of various genes Among these strategies, two are dependent on the ABA hormone, while the other two operate independently of it Furthermore, these adaptive measures also enable plants to withstand other environmental stresses, including extreme temperatures and high salinity.
Under drought stress, maize exhibits an increase in the accumulation of soluble sugars in both roots and shoots, which is linked to the degradation of starch This results in a higher ratio of soluble sugars to starch, as soluble sugars accumulate while starch levels decline Soluble sugars play a crucial role in plant metabolism, serving as substrates for biosynthesis, sugar sensing, signaling pathways, metabolic regulation, and energy production They also help protect plants during drought by substituting water with hydroxyl groups to maintain hydrophilic interactions with proteins and membranes, and through vitrification, which forms biological glass in the cytoplasm to safeguard cellular organelles Research indicates that drought tolerance is positively correlated with the accumulation of soluble sugars under drought conditions (Mohammadkhani and Heidari 2008).
Anahita Ahangir et al (2020) investigated putrescine metabolism in drought-tolerant maize cultivar Karoon and susceptible cultivar 260, focusing on growth indices, H2O2 levels, and antioxidant enzyme activity Their qPCR analysis showed a significant increase in the expression of maize polyamine oxidase (ZmPAO) genes in the roots of both cultivars under drought conditions Notably, the tolerant cultivar exhibited enhanced polyamine oxidase activity, and the increase in putrescine content was more pronounced in its roots compared to the susceptible cultivar.
Drought tolerance in plants is a complex trait influenced by various interrelated reactions This characteristic enables plants to grow and thrive even in conditions of water scarcity.
Maintaining plant water relations involves key factors such as relative water content, stomatal resistance, water potential, leaf temperature, and transpiration rate An imbalance in any of these traits can disrupt these relations (Anjum et al 2011b) Relative water content is crucial for assessing the metabolic activities of plant cells or tissues, typically being higher during early leaf development and declining as the plant matures A strong correlation exists between relative water content, water uptake, and transpiration rate Under drought stress, both relative water content and water potential decrease, leading to an increase in leaf temperature due to reduced transpirational cooling (Siddique et al 2001).
Plant water requirement is reduced by reducing the leaf area and probability of plant survival is increased under limited water availability (Belaygue et al
1996) but chlorophyll contents, chloroplast contents and photo- synthetic activity are reduced which reduced the grain yield (Flagella et al 2002; Goksoy et al
Drought stress significantly affects key structural traits of plants, including root length, root volume, root density, and the number of roots, leading to disturbances in the entire aerial parts of the plant The root system of maize consists of axillary and lateral roots, with axillary roots further divided into primary, seminal, nodal, or crown roots (Cahn et al 1989) Additionally, roots exhibit functional traits such as spatial and temporal water uptake, which are crucial for their adaptation to water scarcity.
Drought conditions significantly reduce the germination index, seedling vigor index, and both fresh and dry weight of seedlings compared to favorable conditions While water scarcity negatively impacts seedling shoot length, it leads to a slight increase in root length under stress conditions (Nazima Batool, 2014).
2.4.2 Recent studies and researches of drought in maize in Vietnam
MATERIAL AND METHOD
Objects, materials of the research
In this study, the research was performed in three cultivars that are drought tolerant cultivar (CP-111, LCH-9, NK7329) and a control cultivar NK4300
Table 3 1 List of the 4 maize varieties used in the experiment
No Name Sign Collected location
1 CP-111 G1 National Maize Research Institute
2 LCH-9 G2 National Maize Research Institute
3 NK7329 G3 National Maize Research Institute
NK4300 cultivar: is the hybrid corn which has been commercialized by
Syngenta's NK4300 cultivar demonstrates impressive yields between 8 to 10 tons per hectare and has been successfully utilized in various mountainous regions of Northern Vietnam, making it an ideal choice as the control cultivar for our study.
- Potassium chloride with 60% K Plastic pots
Location and time
The experiment was conducted in green house of Cultivation science department in Faculty of Agronomy, Vietnam National University of Agriculture (latitude 21.00235170653769; longitude 105.93214475903422)
Research contents
- Studying effect of water deficit conditions on growth traits of four maize varieties grown in the vinyl house
- Studying effect of water deficit conditions on physiological traits of four maize varieties grown in the vinyl house
- Studying effect of water deficit conditions on root traits of four maize varieties grown in the vinyl house.
Methods
3.4.1 Plant materials and Growing condition
Four maize cultivars (Zea mays L.) were utilized in the experiments, with seeds incubated until root emergence A total of twelve seedlings from each cultivar were planted in 48 cylindrical plastic pots designed to withhold water, with each pot containing one seedling Each pot, measuring 35 cm in diameter and 30 cm in depth, was filled with 15 kg of fluvisols soil collected from the Faculty of Agronomy at the Vietnam National University of Agriculture.
The soil used in the experiment was ground and sieved to eliminate unwanted debris To assess the water content and weight of dry soil, five random samples of 1 kg each were oven-dried and weighed daily until their mass stabilized, indicating complete dryness (W1) This study examined soil moisture treatments under water deficit conditions of 15%, 20%, 25%, and 30%.
WD= w/w1 Where: w is the weight of water, w1 is the dry soil
Under WD conditions, each pot was weighed daily to monitor water loss, which was replenished once a day and recorded as evapotranspiration Subsequently, pots were watered multiple times to achieve a soil water content of 25%, ensuring an optimal environment for seedling growth over a 30-day period (Musokwa, 2020).
Thirty days after sowing, seedlings at the 7-9 leaf stage were subjected to water deficit conditions across four gravimetric soil water content (SWC) levels The pots for drought treatment were weighed daily until they reached target weights corresponding to 30%, 25%, 20%, and 15% SWC The SWC was calculated using the formula: \$\theta_g = \frac{W_{water}}{W_{1soil}}\$ (Paul Voroney, 2019), where \$W_{water}\$ is the mass of water in the soil sample and \$W_{1soil}\$ is the mass of 15 kg of dry soil in the sample, with values of \$\theta_g\$ expressed as a percentage.
- Plant height was measured at each 15 days until the end of the drought stress treatment
- Number of leave: Counting from the first true leaf to the final leaf
- SPAD chlorophyll readings were measured by using portable chlorophyll meters (SPAD-502, Minolta, Japan)
-Leaf area was calculated using the following equation:
The leaf area of a plant can be calculated using the formula \$\text{Leaf area} = n \times (a \times L \times W)\$, where \$L\$ represents the average length of the leaves, \$W\$ denotes the average width at the widest part of the leaves, \$n\$ is the total number of green leaves, and \$a\$ is a correction coefficient Research indicates that for corn, the value of \$a\$ is approximately 0.75 (Yao et al., 2010).
After harvest the leaf area and primary root length of the samples were measured
- Primary root length: Lengthiest part of primary root (RL)
- Number of primary roots (NPR)
For dry weight measurements, samples were placed in oven at 90°C until the dry mass samples unchanged and then the samples were weighed
- Number of kernels per ear (KE)
- Soil preparations: Grind, soil solarization, remove plant debris, weed and large clods
- Sowing: seed direct sowing, hole sowing
- Fertilizer was applied per plant according to (QCVN 01 56 :2011 /BNN PTNT) in the following procedure:
*Top-dressing: Two application times
- First time when maize at 4-5 leave stage
- Second time when maize at 7-9 leave stage
* When maize at 4-5 leave stage, apply the first top dressing combine with
* When maize at 7-9 leave stage, apply the second top dressing combine with soil plowing and gathering to prevent maize falling
- Pest managements: control and management according to the procedure of Hanoi Plant protection department, applying pesticide only when the pest density reaches the economic threshold
The experiments utilized a complete randomized design (CRD) to ensure reliable results Each treatment's outcomes represent the means of at least three replications, accompanied by standard deviation (SD) Statistical analysis was conducted using analysis of variance (ANOVA) at a significance level of P ≤ 0.05, followed by Duncan’s multiple range test, employing IRRISTAT 5.0 software and Microsoft Excel for data evaluation.
RESULTS AND DISSCUSSION
Effect of water deficit conditions on growth traits of four maize varieties
4.1.1 Effect of water deficit conditions on plant height of four maize varieties grown in the vinyl house
The height of a plant's stem is crucial for transporting minerals from the roots to the leaves and organic matter in the opposite direction, reflecting the plant's dry matter accumulation and vegetative development While plant height is influenced by the genetic traits of different varieties, it is also affected by external conditions and cultivation techniques Monitoring plant height can help assess the impact of soil water content on the growth of various maize varieties An experiment examining the effects of different soil water levels on the height of four maize varieties—CP111, LCH09, NK7328, and NK4300—has yielded significant results, as detailed in the accompanying table.
Table 4 1 Effect of water deficit conditions on plant height of four maize varieties
Silking Stage Harvested Varieties CP111 93.5 ab 151.8 a 166.9 a 170.4 a ab b b b
Table 4.1 reveals a significant difference (P