1. The Influence of Biochar on Hydroponically Grown Chinese Water Spinach Jake Pinkus University of Vermont
Results
Abstract
Hypothesis
Chinese Water Spinach (CWS), or Ipomea aquatica, is an Asian vegetable mainly grown for its crispy stalks and leaves. CWS requires very unique waterlogged growing conditions. Waterlogged soils pose distinctive pH and nutrient concerns for CWS farmers, often subjecting farmers to decreased yield. Biochar, an ancient Amazonian charcoal-like soil amendment, has been known to fix these issues in dry conditions, but not waterlogged. In order to investigate this, two ebb-and-flood systems were set up in The University of Vermont main campus greenhouse. The control ebb-and-flood system contained pure LECA balls as a substrate, while the experimental ebb-and-flood contained 25% (by volume) of biochar and 75% of LECA. Both systems contained twelve CWS plants grown from seed. Plant parts (stems/leaves) were harvested monthly over a period of three months. After the third consecutive regrowth, stem weight in biochar plots decreased by 29% (p=.041). Leaf area decreased in biochar plots by 25% during all three trials (p=.047), and leaf weight decreased by 32% (p=.021). Electrical Conductivity (EC) in the ebb-and-flood system containing biochar was 14% higher than in the control (p=.031), however pH was not different between the two ebb-and-flood treatments over time.
After the third consecutive regrowth, stem weight in biochar plots decreased by 29% (p=.041) (Fig. 5). Leaf area decreased in biochar plots by 25% (Fig. 9) during all three trials (p=.047), and leaf weight decreased by 32% (p=.021) (Fig. 6) . Electrical Conductivity (EC) in the ebb-and flood system containing biochar was 14% higher than in the control (p=.031) (Fig. 10) , and pH was not different between the two ebb-and-flood treatments over time. Stem and leaf dry weights grew similarly the first two regrowth trails, but biochar significantly decreased the third trial (Fig. 5&6).
H0: Biochar has no effect on hydroponically grown Ipomea aquatica
H1: Biochar increases the yield of hydroponically grown Ipomea aquatica.
H2: Biochar decreases the yield of hydroponically grown Ipomea aquatica
Figure 5.
Figure 6.
Methods
Seeds of CWS were sown on 9/11/16 in foam Oasis® cubes and kept in a fog chamber in a greenhouse for sixteen days until plants reached 1st true leaf stage. A total of 24 plants were selected and transferred out of the fog, twelve for each treatment (Fig. 4). The biochar treatment contained 25% biochar (by volume), while the control contained only LECA. The control consisted of 10 gallons of LECA (porous clay balls traditionally used in hydroponics), while the biochar treatment consisted of 7.5 gallons of LECA with 2.5 gallons of biochar. Pelletized soft-wood biochar was used (Fig. 2)
Two separate ebb-and-flood systems were used, one for the control and one for the biochar treatment. pH and EC were measured on a weekly basis to determine how or if biochar effected the fertilizer solutions. The fertilizer was a 50:50 blend of Jack's All Purpose fertilizer and Jack's Dark Weather Plus Magnesium LX in tap water to yield a 150 ppm solution. This solution was completely replaced in the ebb-and-flood reservoirs every seven days.
Greenhouse temperature was maintained at 24C (day) and 18C (night).
An electric timer was used to control the flow of the fertilizer solution, turning it off at night, and pumping the solution every two hours during the day.
Unlike most crops, Ipomea aquatica was coppiced and allowed to regrow. Every four weeks, plants were cut just above the root, only leaving one node to regrow (Fig. 3). At harvest, plants were individually bagged after stem length was measured and leaves were counted and run through a Li-COR Leaf Area Meter. Leaves and stems were then dried at 50C for 2 days and dry weights were recorded.
Chinese Water Spinach
Chinese Water Spinach (Ipomea aquatica) is a traditional East Indian leaf crop, grown for its long, crisp, hollow stems. Water Spinach has been a staple in Asia, traditionally used in stir dry dishes and eaten raw. Water Spinach is a unique crop due to its preferred wet growing conditions. CWS grows best in swamp-like conditions, making it an important crop for farmers with these usually unfavorable growing conditions. CWS has been a staple in Asia, traditionally used in stir dry dishes and eaten raw.
Figure 7.
Figure 8.
Biochar
Biochar is a charcoal-like product primarily known for its agricultural success in the Amazon basin. It’s success is attributed to several key factors:
Organic Matter: Biochar is a product of the pyrolysis of organic materials (i.e. crop residue, woodchips, etc). The pyrolysis process burns the material at ~700C without the presence of oxygen, only leaving behind Carbon. Biochar, today, remains one of the cheapest and most direct forms of organic matter.
CEC: Cation Exchange Capacity ties in closely with Organic Matter (OM). CEC is the ability of a soil to stop and hold certain nutrients in the soil, which would have otherwise leaked into groundwater. The ability for a soil/system to hold these nutrients is crucial to proper crop growth.
Biological Activity: An extensive amount of pore space lends itself to hosting high levels of biological activity. (Fig. 1)
Many studies have examined biochar's use in traditional field crops, but never under waterlogged conditions that Chinese Water Spinach thrives in. This study was designed to address this.
Figure 9.
Figure 10.
Conclusion
Chinese Water Spinach grown in an ebb-and-flood system preferred the control to the biochar treatment. This result may be due to a variety of factors collected during the experiment. Most importantly, we believe that the biochar withheld or prevented CWS from up taking nutrients due to an overall higher Electrical Conductivity. A more in depth study could involve looking at the biochar to determine the total salts (fertilizer) they took out of circulation. Also, whether plants used biochar as a nutrient source while in a hydroponics system.
Figure 1. Structure of Biochar
Acknowledgments
Figure 2. Pelletized soft-wood biochar
Mark Starrett (Advisor), Alan Howard UVM Statistician (academic computing services), Isaac Roach, Paige Casio, Tom Doubleday, Andrew Lyman, Owen Dumais, Paul Saaman, and David Heleba.
Figure 3. Root structure of Ipomea aquatica in biochar
Figure 4. Twelve Ipomea aquatica in ebb-and-flood