A Method to Reduce Water Evaporation from Soil Using the Absorbent Properties of Organic Wheat Straw

 

Introduction

Water shortage is a problem that already affects every continent and has a great impact on the social and economic sectors of the world. Around 1.2 billion people, more than one-sixth of the world’s population, live in areas of physical water scarcity; 500 million people are advancing toward that situation today. Another 1.6 billion people, more than one-fifth of the world’s population, face economic water shortages. Water insufficiency is among the main problems to be faced by the world in the 21st century.

Farms and their inefficient irrigation systems are major contributors to water shortages across the globe. Farming accounts for 70% of water consumption, and an astonishing 60% of the water diverted or pumped for irrigation is wasted by runoff into waterways or by evapotranspiration. Increasing efficiency in irrigation is an essential step for water conservation. If we can develop a safe, inexpensive additive that can supplement soil, allowing it to hold water for a longer period of time, this will be a practical solution for the worldwide water-shortage problem we are currently facing. There are very few commercially available products that help to increase water retention in soil. Polymer-based products utilizing the molecule polyacrylamide are the only soil-moisture-holding reagents available on the market today. Polymers cost from $2,000 to $3,000 per metric ton, which is far too expensive for developing and arid countries, which account for the bulk of worldwide water need. Due to the chemical nature and cost of this product, farmers are very reluctant to incorporate polymer into their farming. A low-cost, organic, water-holding reagent is urgently needed for water conservation. 

Polysaccharides are polymeric carbohydrate molecules composed of long chains of monosaccharide units bound together by glycosidic bonds. Polysaccharides are an important class of biological polymers. Their function in living organisms is usually either structure- or storage-related. Starch and glycogen are used as storage polysaccharides in plants and animals, respectively. Cellulose and chitin are examples of structural polysaccharides used in plants and insects, respectively. Cellulose is used in the cell walls of plants and organisms such as fungi to provide rigidity. Polysaccharides readily absorb water due to their large numbers of hydroxyl groups, which can form hydrogen bonds with neighboring water molecules.

After researching the current literature, I discovered that wheat straw also contains 35% polysaccharide. Therefore, I hypothesized that wheat straw, an inexpensive organic matter that farmers have easy access to, would allow plants to grow longer in low-water conditions. I compared commercially available polymers to organic wheat straw in order to determine if my prediction was correct. In Phase 1 of the project, I used soil moisture probes to quantitatively measure the effect of soil additives on water retention. In Phase 2 of the project, I used two different types of plants, begonia and cyclamen, to investigate whether or not the absorbent properties of organic wheat straw had a beneficial effect on plant survival.

 

Materials and Methods

 

Materials

  •  90 kg top soil 
  • 4 kg wheat straw
  • 500 g wood chips
  • 1 kg polymer
  • 9 Rieger Begonia plants
  • 9 Cyclamen plants
  • Soil moisture meter
  • 42 6-inch pots
  • humidifier
  • dehumidifier
  • artificial sunlight lamp
 

Experimental Environment

All of the experiments were performed at 21ºC. The humidity level for every experiment was 60%. Each pot received 500 lumens of artificial sunlight.

 

Soil Sample Preparations

Each six-inch pot was filled with two kilograms of topsoil. Each pot received a different sample. There were seven different samples used in the experiment. Topsoil was used as the control in this experiment; 100 g of dextrin and 100 g of polymer were mixed with the topsoil and used as the positive control; 100 g, 150 g and 200 g of cut wheat straw (particles of 1.5 cm) were mixed with topsoil and used as the experimental group. In addition, 150 g wood chip was also used as an experimental group. Each pot was saturated with 200 mL of water at Day 0. No additional watering was performed during the experimental period, which lasted for 21 days. The experimental period was performed three times.

 

Monitoring Soil Moisture

Measuring soil moisture


A soil moisture meter from Zoro Tools was used to measure the soil moisture in this experiment. These measurements were taken at 8 p.m. each day. The probe was inserted into each pot at a three-inch depth in the same location. Soil moisture was measured from four different locations in each pot and recorded. The average of each pot’s four measurements was taken and also recorded. The soil moisture in each pot was monitored for a period of 21 days.

 

Planting the Rieger Begonia and Cyclamen

The next experiment was performed to observe the effect of wheat straw on the growth of plants, applying the results of the soil experiment in a real-life situation. Six-inch pots were used again to store the Rieger begonia and cyclamen plants used in this experiment. Two kilograms of topsoil was used as the control; 150 g of wheat straw mixed with two kilograms of topsoil was used as an experiment group; 100 g of polymer mixed up with 2 kg of topsoil was used as positive control. The plants used in this experiment were Rieger begonia and cyclamen, and they were all of the same size as of Day 0. To saturate each pot, 200 mL of water was used on Day 0. As in the soil experiment, no additional watering was done after Day 0. The soil moisture, number of flowers and plant size were measured and recorded each day for the next 21 days. This experiment was performed three times with Rieger begonia plants and three times with cyclamen plants.

 

Statistical Methods

Analysis of variance (ANOVA) was used in this data analysis. ANOVA provides a statistical test of whether or not the means of several groups are equal, and therefore generalizes the t-test to more than two groups. Doing multiple two-sample t-tests would result in an increased chance of committing a Type 1 error. The ANOVA statistical program in Microsoft Excel was used to perform all of the statistical analysis for this experiment.

 

Results

 

Effects of Water-Retaining Reagents on Soil Moisture

The effect of wheat straw on soil moisture was studied in three concentrations: 100 g, 150 g and 200 g, along with 150 g wood chip, dextrin and polymer. These results indicated that the three concentrations of wheat straw, 150 g wood chip, polymer and dextrin all had significantly greater soil moisture levels compared to the control after Day 10 (Table 1 and Figure 1). Twenty-one days after the initial watering on Day 0, the soil moisture in the pots containing the wheat straw concentrations, wood chip and two positive controls (polymer and dextrin) remained at moisture levels of 3.8 to 4.8. These moisture levels are also plant growth friendly. This experiment also indicates that there was no significant difference between the wheat straw, wood chip and the two positive controls in soil water retention.

Figure 1: The x-axis represents the time in days and the y-axis represents the soil moisture on a scale of 1 to 10. This bar graph shows that the three concentrations of wheat straw, 150g wood chip, polymer and destrin yield significantly higher soil water retention results than the control. 


Time (Days) Topsoil

Top Soil + 

Dextrim

(100g)

Top Soil +

Polymer

(100g)

Top Soil +

Wheat Straw

(100g)

Top Soil +

Wheat Straw

(150g)

Top Soil +

Wheat Straw

(200g)

Top Soil +

Wood Chips

(150g)

F- value P- value
0

10.00

±0.00

10.00

±0.00

10.00

±0.00

10.00

±0.00

10.00

±0.00

10.00

±0.00

10.00

±0.00

N/A N/A
3

10.00

±0.00

10.00

±0.00

10.00

±0.00

10.00

±0.00

10.00

±0.00

10.00

±0.00

10.00

±0.00

N/A N/A
6 9.67±0.26 9.67±0.26

10.00

±0.00

10.00

±0.00

10.00

±0.00

10.00

±0.00

10.00

±0.00

N/A <0.05
9 7.33±0.19 8.33±0.17

10.00

±0.00

9.78±0.58

10.00

±0.00

10.00

±0.00

9.33±0.48 36.05 <0.001
12 5.33±0.21 6.67±0.10 9.33±0.48 8.33±0.37 9.33±0.48 9.67±0.58 8.00±0.00 54.09 <0.001
15 3.33±0.21 4.64±0.17 8.00±0.00 7.33±0.58 8.00±0.00 8.33±0.58 6.77±0.57 71.54 <0.001
18 2.00±0.00 3.33±0.10 6.33±0.37 5.57±0.38 6.33±0.38 6.87±0.57 4.78±0.57 62.12 <0.001
21 0.67±0.17 1.67±0.17 4.00±0.00 3.77±0.35 4.33±0.58 4.77±0.67 3.77±0.33 44.71 <0.001

Table 1: This table shows the moisture level results for the seven different reagents used in the experiments. Statistical analysis was done using a one-way ANOVA test for each time point.

 

Dosage Response Curve of Wheat Straw on Soil Water Retention

 

The three concentrations of wheat straw are shown in comparison with the control in this curve. The results (Figure 2) indicated that all three concentrations of wheat straw significantly increased moisture levels compared to regular topsoil. The results also showed a significant increase in soil moisture levels for concentrations of 150 g and 200 g compared to 100 g of wheat straw. However, there was no statistical difference between the moisture levels of 150 g and 200 g of wheat straw. As a result, 150 g of wheat straw was chosen for future experiments.

Figure 2: The x-axis represents the time in days and the y-axis represents the soil moisture on a scare of 1 to 10. This dosage response curve shows that the three different concentrations of wheat straw have significantly higher soil moisture levels than the control.

Figure 2: The x-axis represents the time in days and the y-axis represents the soil moisture on a scare of 1 to 10. This dosage response curve shows that the three different concentrations of wheat straw have significantly higher soil moisture levels than the control.


 Effect of Polymer and Dextrin on Soil Moisture in Comparison with Wheat Straw

Experiments have indicated that 150 g of wheat straw and the two positive controls yield significantly higher soil moisture levels than the control (Figure 3). As with 150 g and 200 g concentrations of wheat straw, there was no significant difference between the soil water retention of wheat straw and polymer. Both wheat straw and polymer retained significantly more moisture than the dextrin; hence, 150 g of wheat straw and polymer was chosen to be used in the Rieger begonia and cyclamen experiments.

Figure 3: The x-axis represents the time in days and the y-axis represents the soil moisture on a scale of 1 to 10. This curve shows that wheat straw, polymer, and dextrin all retain more water in the soil when compared to the control.

Figure 3: The x-axis represents the time in days and the y-axis represents the soil moisture on a scale of 1 to 10. This curve shows that wheat straw, polymer, and dextrin all retain more water in the soil when compared to the control.


 

Effect of Wheat Straw on the Soil Water Retention of Rieger Begonia Plants

The results shown in Figure 4 indicate that both the wheat straw and polymer groups contained significantly greater soil moisture levels. The soil moisture level of the control group declined rapidly; by Day 10 of the experiment, the soil had already dried up in the control group. Meanwhile, both the wheat straw and polymer groups remained at comfortable, plant-growth-friendly moisture levels. By Day 20, the soil moisture levels of the wheat straw and polymer samples were still at levels of 1.5 and 3.5, respectively.

Figure 4: The x-axis represents the time in days and the y-axis represents the soil moisture on a scale of 1 to 10. This graph shows that both wheat straw and polymer significantly increase water retention in the soil compared to the regular topsoil.


 

Effect of Wheat Straw on the Growth of Rieger Begonia Plants

 

In these photos, 1A is the control group; 2A is the wheat straw group; 3A is the polymer group. These pictures show that the Rieger begonia plant begins to die off after day 7 in the control group; the wheat straw and polymer groups are still growing strong at day 7 and remain healthy even until day 21.

In these photos, 1A is the control group; 2A is the wheat straw group; 3A is the polymer group. These pictures show that the Rieger begonia plant begins to die off after day 7 in the control group; the wheat straw and polymer groups are still growing strong at day 7 and remain healthy even until day 21.


The results of the experiments regarding the growth of the Rieger begonia plants are shown in Figures 5 and 6. In figure 5, the number of flowers and the dimensions of the plants were significant larger in the wheat straw and polymer groups compared to the control group. In Figure 6, results indicated that the Rieger begonia plants were significantly healthier and stronger in the 150 g wheat straw group compared to the polymer group. The Rieger begonia plant began to die after Day 10 in the control group, while the Rieger begonia plants in the wheat straw and polymer groups continued to grow consistently until Day 16 and began to die after Day 21.

Figure 5: The x-axis represents the time in days and the y-axis represents the number of flowers the plant has. This bar graph shows that the number of flowers is significantly higher in both the wheat straw and polymer groups when compared to the control. 


Figure 6: The x-axis represent the time in days and the y-axis represent the dimension by in3. This graph shows that the dimensions of the plant increase when wheat straw and polymer are used as supplements to the soil, whereas the dimensions of the control plant decreased significantly. However, the begonia plant grew healthier and larger in the wheat straw group.


 

Effect of Wheat Straw on the Soil Water Retention of Cyclamen Plants

The results shown in Figures 7, 8 and 9 correspond to the effect of 150 g of wheat straw on soil water retention in cyclamen plants. These results indicate that wheat straw and polymer can help to retain water in the soil of cyclamen plants for a significantly longer amount of time than the control group. The soil moisture levels for wheat straw and polymer remained between 2 and 3 after the 21 days of the experiment. In the control group, the soil moisture level was already at 0 within 10 days of the experiment.

Figure 7: The x-axis represents time in days and y-axis represents soil moisture on a scale of 1 to 10. This bar graph shows that the wheat straw and polymer supplements significantly increase soil water retention when compared to the control. 


Figure 8: The x-axis represents the time in days and the y-axis represents the number of flowers. This bar graph shows that the cyclamen plant grows much better with wheat straw and polymer groups than with the control. The number of flowers is also significantly higher in the wheat straw group when compared to the polymer group. 


Figure 9: The x-axis represent the time in days and the y-axis represents the dimensions of the cyclamen plants by in3. This bar graphs shows that the cyclamen plants grow better and stronger in the wheat straw and polymer groups. The results also show that the cyclamen plant grows significantly bigger in the wheat straw group than in the polymer and control group.


 

Effect of Wheat Straw on the Growth on Cyclamen Plants

Cyclamen

Experiments also demonstrate that cyclamen plants grew better in the wheat straw group compared to the polymer and control groups. The number of flowers and the dimensions of the plant were significantly larger in both the wheat straw and polymer groups when compared to the control group (Figure 7, 8 and 9). In the control group, the water-sensitive cyclamen plants were dying by Day 7; meanwhile, the cyclamen remained healthy and strong for two weeks in the wheat straw and polymer samples. These conditions continued 20 days into the experiment for the wheat straw and polymer groups.


 

Discussion

Wheat straw is an agricultural by-product; farmers have quick access to it. Wheat straw is cheap as well, costing only $60 to $80 per metric ton.  This project demonstrates that wheat straw has great water-holding capacity in soil. This project demonstrates that wheat straw has the same water-retention capabilities as commercial polymer, which costs about $2,000 to $3,000 per metric ton. Wheat straw is a natural and organic product that will help improve soil quality by introducing more organic matter into soil. Wheat straw can also help to control sediment in soil and prevent soil erosion.

In the Rieger begonia and cyclamen studies, research results showed that plants were healthier in the wheat straw group. This is possibly a result of the fact that wheat straw is an organic matter and can be used as fertilizer as well.

By mixing 7.5% wheat straw into soil, water retention in soil could be enhanced by 10 to 15 days. If farmers can adapt this method into their growing of crops, we could save more money and water in the world.

 

Conclusions

This research has indicated that wheat straw can significantly enhance soil water retention. Wheat straw can help to keep plants alive for three weeks without watering. Wheat straw can also help in the growth of these plants, making them healthier and stronger. Wheat straw is a great candidate for farmers to use when planting crops to save money and water.

Possible sources of error in my experiment could be fluctuations in temperature and humidity, or accidental uneven distribution of water to the samples. Fortunately, none of these predicaments occurred. However, I could have increased the sample size to reduce the possibility of committing a statistical error.

In future studies, more experiments using wheat straw could be conducted directly in crop fields where farmers grow their plants. More studies can be done on the effect of wheat straw on crop plants such as vegetables, fruits and grains. I am also interested in testing the effectiveness of wheat straw in a porous bag, which could allow for increased convenience in applying wheat straw to the soil.

 

Bibliography

“2012 Guidelines for Water Reuse.” U.S. Environmental Protection Agency, Sept. 2012. PDF.

Acín-Carrera, M., et al. “Impacts of Land-Use Intensity on Soil Organic Carbon Content, Soil Structure and Water-holding Capacity.” Soil Use and Management. British Society of Soil Science, 2013. Web. 14 Oct. 2013.

Brown, Lester. “The Real Threat to Our Future Is Peak Water.” The Guardian, 7 July 2013.Web. 21 Sept. 2013.

“Coping with Water Scarcity: Challenge of the 21st Century.” United Nations Food and Agriculture Organization, 22 March 2007. Web. 23 Sept. 2013. PDF.

Flett, Adam. “How Much Does It Cost to Water This Tree?” My Minnesota Woods. University of Minnesota Department of Forest Resources, 9 Jan. 2009. Web. 14 Oct. 2013.      

“Running Dry.” The Economist, 18 Sept. 2008. Web. 15 Oct. 2013.

Vengadaramana, Jashothan A. “Effect of Organic Fertilizers on the Water-Holding  Capacity of Soil in Different Terrains of Jaffna Peninsula in Sri Lanka.” Scholars Research Library. Journal of Natural Product Plant Resources 2.4 (2012): 500-503. Web. 24 Sept. 2013.

“Water Scarcity: International Decade for Action.” United Nations News Centre. Web. 21 Sept. 2013. PDF.