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Sunflower Plant Growth with Minimal Water Requirements Report

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Updated: Aug 20th, 2020

Research Question

How does the type of plant affect the growth rate when using minimum water requirements?

Background Knowledge

The Middle East region has arid and semi-arid climatic conditions that are characterized by water scarcity and high temperatures that result in high evaporation rates (Beaumont, Blake & Wagstaff 2016). Additionally, the loose soils and desert winds contribute to air pollution when the soil is blown into the air leading to respiratory illnesses (Anderson et al. 2012; Lelieveld et al. 2014). The loose soils are also prone to soil erosion leading to the loss of soil nutrients.

Increasing plant cover has been reported to be a viable solution to the problem of soil erosion and air pollution by soil. However, given the issue of water scarcity, it is necessary to find plant species that can thrive with minimum water requirements. Therefore, this investigation seeks to find the most suitable plant that can thrive with minimal water requirements to survive the harsh climatic conditions of the Middle East. The availability and growth of such a plant will not only conserve the soil and its nutrients but will also protect the society from respiratory disorders associated with inhaling soil particles in the air.

Various plant species are adapted to growing in different climatic conditions. An example is sunflower plant Helianthus annuus, which is well suited to growing in warm climates (SFGATE 2016). The plant is also known to do well in areas that allow it to have a minimum of six hours of direct sunlight every day. The growth rates of other plants related to Helianthus annuus was determined to determine the best plant species that can survive warm climates with minimal water requirements.


It was hypothesized that the sunflower plant (Helianthus annuus) would grow fastest and have the highest biomass.

Significance or Manipulation of Variables

Independent variable

The independent variable was the type of plant. Different plants have varying water requirements depending on their inherent adaptations to survive under varying climatic conditions. The type of plant was manipulated by using seeds from five different plants. The independent variable did not have units of measurement. However, the five seed types were obtained from a group of closely related plants of the order Asterales.

Dependent variable

The dependent variable was the plant growth rate. The rate of plant growth is a useful indicator of the growth conditions that favor the development of a plant. The rate of growth was measured consistently using the biomass (dry weight) of the plants at the end of the experiment. The biomass was measured in grams.

Controlled variables

The controlled variable in this experiment was water. The amount of water was kept constant by using a measuring cup to provide the plants with a specified amount of water once a day. Water is useful for the germination of seeds and the growth of plants. In the germination process, water is taken up by imbibition to break the seed coat and activate hydrolytic enzymes that catalyze the physiological processes necessary for germination (Bradbeer 2013).

During the growth of the plant, water is necessary for transpiration and evaporation. The walls of plant cells permit the accumulation of water to develop turgor pressure. Turgor pressure plays a vital role in the rigidity and mechanical stability of non-woody plants such as the five species from the order Asterales that were used in this experiment. Mechanical stability is beneficial in normal plant processes such as growth, anchoring, gaseous exchange, and transport of substances (Jones 2013).

Water is also used as a raw material alongside carbon dioxide to manufacture food through the process of photosynthesis in the presence of sunlight. The objective of the study was to determine whether plant type affects growth rate when using minimum water requirements. Therefore, it was necessary to regulate the amount of water on the bare minimum to identify the impact of plant type on growth rate under similar water conditions. Failing to control the amount of water would not highlight the impact of minimum water requirements.

Uncontrolled variables

The uncontrolled variables were temperature, humidity, and wind speed. The variations in temperature and wind were not taken into consideration. It is known that temperature affects the rate of evaporation by heating up water molecules and helping them vaporize. High wind speed increases the rate of evapotranspiration by carrying away water droplets from the surface of the plant thus affecting the rate of water loss in a plant. The rate of evapotranspiration is lower on a humid day than on a dry day because the saturation of the atmosphere with moisture reduces the diffusion gradient thus slowing down the rate of water loss from the plant to the atmosphere.


Five types of plant seeds: Zinnia (Zinnia Elegans), Cosmos (Cosmos bipinnatus), Sunflowers (Helianthus annuus), Dahlias (Dahlia pinnata), and Vinca (Vinca diformis) were obtained. Appropriate amounts of soil were measured and put into 25 pots. Five seeds of one plant seeds were then placed in every five pots by placing one seed per pot. The plants were watered once a day with a specific amount of water for all the plants for one month. At the end of the study, the plants were harvested and washed. The clean plants were placed on a tray and allowed to dry for six hours in an oven set to a temperature of 60 degrees. The dry mass of the dried plants was then obtained by measuring the weight of each plant. The findings were recorded in Table 1.

Justification of Method Used

The sampling was done to include related plants since water requirements tend to vary in different plants. For example, trees have different water requirements from shrubs and so on. Therefore, it was necessary to have related plants to reduce the variations associated with distantly related plants.

Five seeds from each plant type were used to provide replicates and increase the validity of the methods. The use of replicates helps to ascertain the reproducibility and validity of the experiment by confirming that the observed results are not due to chance occurrences. Additionally, using replicates makes it possible to apply statistical methods of data analysis and ensure that the findings are generalizable to the population. The plants were grown in a field after which the biomass data were collected in the laboratory. This experiment was a fair test because all plants were accorded similar treatment regarding the amount of water during growth and processing to obtain the biomass.

Risk Assessment and Ethical Considerations

The study did not have any ethical considerations or associated risks. No additional chemicals (such as fertilizers) were used in the process, which could contain substances known to have deleterious health effects. However, proper standards of handling and disposing of plants were followed throughout and after the experiment.

Data Collection


The mean biomass of each plant species was calculated by finding the average of the five biomasses. For example, the mean biomass for sunflower was calculated as follows:

  • (0.15+ 0.11+ 0.1+ 0.19+ 0.12)÷5=0.67/5

Mean biomass=0.134g

Analysis of Variance (ANOVA) was used to compare the means of the five plant species at α=0.05. The findings of the ANOVA computations and the means are summarized in Table 2.

Processed Data Tables

Table 1: The biomass of the five plant species and the mean biomass for each species.

Plant Species Biomass (g)0.134 Mean Biomass (g)
Sunflower: A 0.15
B 0.11
C 0.1
D 0.19
E 0.12 0.134
Zinnia: A 2.69
B 2.1
C 1.36
D 1.63
E 1.27 1.81
Cosmo: A 0.02
B 0.02
C 0.02
D 0.02
E 0.03 0.022
Dahlia : A 0.03
B 0.04
C 0.01
D 0.03
E 0.02 0.026
Vinca: A 0.02
B 0.03
C 0.03
D 0.03
E 0.02 0.026

Table 2: ANOVA Output.

Source of Variation SS df MS F P-value F crit
Between Groups 12.40714 4 3.101784 44.59662 0.00000000108349276784 2.866081
Within Groups 1.39104 20 0.069552
Total 13.79818 24

From the ANOVA output, Fcal is greater than Fcrit. Therefore, we reject the null hypothesis and conclude that the groups are significantly different.

Graphs and Charts

Mean biomass for the five plant species.
Figure 1: A graph of the mean biomass for the five plant species.


The plant growth rate of the plants was highest in Zinnia elegans (1.81g) followed by Helianthus annuus (0.134g). The lowest growth rate was observed in Cosmos bipinnatus (0.022g). Dahlia pinnata and Vinca diformis had the same growth rate as 0.026g. The findings did not support the hypothesis that sunflower (Helianthus annuus) would have the highest growth rate. The differences in growth rates as indicated by the differences in means between the different plants was significant implying that the water needs of the plants were different. All the five plants were shrubs from the order Asterales. Zinnia Elegans is native to drylands of the Southern parts of America (Chicago Botanic Garden 2016).

Plants require water for evapotranspiration, which is the term used to denote crop water needs. Plants use their roots to absorb water from the soil and eliminate it through the leaves and stems through the process of transpiration. In addition, water has the tendency to escape from open surfaces through the process of evaporation, which occurs in plants from the soil and exposed plant surfaces such as the stem and leaves. The units millimeters per day, millimeters per month, or millimeters per season are used to express and quantify the water needs of plants. The crop water needs are determined by the climate, type of crop, and stage of growth (Elliot et al. 2014).

Plants require more water on a hot, dry day than on a cloudy and cool day due to the impact of temperature on the rate of evapotranspiration. Some crops require more water than others, for instance, sugarcane has higher water needs than wheat. Plants also need more water in advanced stages of development than in the early stages due to an increase in the number of physiological processes like reproduction and the increased size of the plant. The differences in the observed water needs of the plants could be attributed to the type of plant because all climatic conditions were kept constant. Additionally, all plants were at the same stages of development.


Zinnia Elegans had the highest growth rate and minimal water requirements of the five plants with mean biomass of 1.81g followed by the sunflower plant (Helianthus annuus) with biomass of 0.134g. Dahlia pinnata and Vinca diformis were third with a growth rate of 0.026g while Cosmos bipinnatus had the lowest growth rate (0.022g). These findings point to the conclusion that the type of plant played an important role in the growth rate when using minimum water.

Conclusion in Environmental Context

Growing Zinnia elegans in arid areas would use minimal water resources to alleviate the problem of soil erosion and air pollution.

Evaluation of Method Used

The method was reliable because related plants were used to reduce the variations of plant water needs that occurred in different plants. The replication of the groups also increased the validity of the study. However, the effects of temperature, humidity, and wind speed on the water needs of plants were not considered. The experiment could be improved by accounting for the impact of wind speed, humidity, and temperature on plant water needs. Future studies could look into the exact water needs of the plants by growing the seeds with varying water quantities to determine the lowest amount of water that supports the satisfactory growth of the plants.


From the findings of the investigation, Zinnia elegans is best suited to growing in warm climatic conditions. Therefore, this plant can be grown to provide plant cover, minimize soil erosion and air pollution. The advantage of growing Zinnia Elegans for plant cover is that a high rate of growth is observed with minimal water input due to the heat and drought tolerance of the plant (Chicago Botanic Garden 2016). The plant is also low maintenance thus does not require extensive resources. However, the downside of using Zinnia Elegans for cover plants is that it affected by excess water, which leads to the development of a disease called powdery mildew.


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Beaumont, P, Blake, G & Wagstaff, J M 2016, The Middle East: a geographical study, Routledge, London.

Bradbeer, J W 2013, Seed dormancy and germination, Springer Science & Business Media, New York.

Chicago Botanic Garden 2016, . Web.

Elliott, J, Deryng, D, Müller, C, Frieler, K, Konzmann, M, Gerten, D, Glotter, M, Flörke, M, Wada, Y, Best, N & Eisner, S, 2014, ‘Constraints and potentials of future irrigation water availability on agricultural production under climate change,’ Proceedings of the National Academy of Sciences, vol. 111 no. 9, pp. 3239-3244.

Jones, H G 2013, Plants and microclimate: a quantitative approach to environmental plant physiology, Cambridge University Press, Cambridge.

Lelieveld, J, Hadjinicolaou, P, Kostopoulou, E, Giannakopoulos, C, Pozzer, A, Tanarhte, M, & Tyrlis, E 2014, ‘Model projected heat extremes and air pollution in the eastern Mediterranean and Middle East in the twenty-first century,’ Regional Environmental Change, vol. 14 no. 5, pp.1937-1949.

SFGATES 2016, Web.

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