Essay: Crop physiological response to different EC and pH adjustments

The aim of this research to deduce the different outcomes of the usage of typical aquaponic low EC-high pH conditions compared to high EC-low pH conditions on crop growth, yield and crop quality in an ebb-and-flood system.

Introduction

In a growing population, more food is being in demand. Thus, more productive ways of producing food is becoming an important topic to be able to feed the world.
Small-scale hydroponic and aquaponic crop production is getting more common everyday due to its convenience and economical growth. A lot of people switch to hydroponic grown crops due to its health benefits. Producers around the world use hydroponic nutrient solutions that have an electrical conductivity (EC) between 1 and 3 dS m−1 and a pH range of 5.5 to 8.[2] The varitity in this approach brings questions. As everyone wants to get the highest amount of yield from their production, farmers want to know whether high or low pH levels in their nutrient solutions are better for their yield. In this experiment, by using two different levels of pH(high & low) the question will be answered.

Hypothesis
Crops provided with high EC-low pH solutions are more likely to yield more crops compared to those provided with low EC-high pH solutions.
Connection between scientific problem and research question
The dependence on synthetically produced mineral nutrient solutions are causing concerns in the hydroponic food production industry as they are not sustainable enough due to the fact that overuse of them may contribute to greenhouse gas emissions and eutrophication of surface waters.[2] Aquaponics which is the integration of aquaculture and hydroponic plant production in a closed-loop system where synthetic fertilizers and water disposal are almost completely eliminated can be the solution. In aquaponics, nutrients in fish effluent are filtered and used by plants in a recirculating closed-loop hydroponic system. Aquaponics also reduces the water waste by decreasing the need for complete water exchange.[3]

Solution pH in aquaponic systems is a compromise between bacterial and plant demands. While optimum pH level for bacterial transformation of ammonia to nitrite is 8.5, plant nutrient uptake for many crop species is optimized near pH 6.0. As a result of aquaponic systems is managed around pH 7.0 to provide enough nitrification without having a significant effect on the plant uptake potential of essential nutrients in solution.[4] Even though there are a lot intakes in hydroponics nutrient strength(EC) and pH have the strongest impact on the crop yield.

EC(Electrical Conductivity) of the water solution is dependent on the amount of minerals it may contain. These minerals are NO3 -N, PO4 -P, K, SO4-S, Ca, Mg, B, Fe, Mn, Zn, Cu, Mo. [5] The EC and pH levels of solutions are inversely proportional to each other due to the fact that the minerals that increase the electrical conductivity are mainly bases.

Safety, Environmental and Ethical Issues
Write the safety rules, ethical rules and rules that you should pay attention to during the experiment. These rules must be written in a table.
The plants should be supplied with required amount of water(250ml of water changed 3 times a week) and nutrient solution(added after each change).
Plants should be provided with enough light which is provided with 4 light bulbs of 400lm.
The water waste should be filtered.
The plants should be checked at least 4 times a day to make sure everything is running properly.

Variables and Impact on experiment

Variables How the Variable will be Controlled and Changed Impact on the Study
Independent Variable(s) pH Level of the water In the experiment, two different nutrient solutions with two different values of pH have been used which are pH 5.8 0.1 (high EC–low pH solution) and pH 7.20.1(low EC–high pH solution). The high EC–low pH solution was made by adding 975mg of Peters Professional Hydroponic Special to 1 liter of water and the low EC–high pH solution was made by adding 240mg of Peters Professional Hydroponic Special to 1 liter of water.
The study is testing the impact of different pH levels on crop yield, therefore, two different solutions are going to have different impacts on the crop yield.
Dependent Variable(s) Crop yield The crop yield will be measured by measuring the height of the crop. The height of the plant will be measured for 2 months(60 days) after every 5 days since day 1. The crop yield will be the main measure of this experiment as it is going to determine whether the hypothesis is right or not.
Controlled Variable(s) Place, temperature, lightning, oxygen level
The experiment was done in Ankara, Turkey(39.9334° N, 32.8597° E; elevation = 850 meters) in March of 2020. Greenhouse temperatures were maintained at 27.5 2.5◦C during the day and 22.5 2.5◦C at night. 4 400lm white light bulbs was used during day and night to supply light. The air in the greenhouse was directly supplied from outside. These variables might have an impact of uncertainty on the experiment in the case of a change.

Materials
Potassium Hydroxide
HANNA Instruments Ph Meter
Pots
Peat-based soilless mix
4 x 400lm white light bulbs
5kg of coco coir media
high EC–low pH solution(pH 5.8 0.1)
low EC–high pH solution(pH 7.20.1)
Phosphoric Acid

Write all the glass materials, all chemical materials and other materials you use in the experiment in a table. Pay attention to uncertainties of the beaker, burette…
Method
Plants were grown in a coco coir media and fertigated via the ebb and flow method four to six times per day for ten minutes at a time, depending on crop growth stage and estimates of evaporation. Seeds were planted in a peat-based soilless mix in seeding trays and transplanted into coco coir and netted pots when at least one leaf was fully emerged.
Solution pH in each experimental unit was tested two times weekly and adjusted up as needed with potassium hydroxide or adjusted down as needed with phosphoric acid or acetic acid.
this approach does not capture the true essence of an aquaponic system, it does allow for the mechanistic isolation of the effects of nutrient solution pH and EC on vegetable crop physiology, which is the objective of this study. A similar “mimic” approach has been successfully used to isolate the effect of pH on nitrification rate in aquaponic systems.
Nutrient solution EC (dS m−1 ) was sampled from each experimental unit with a HANNA Instruments EC/pH meter immediately after mixing new nutrient solutions and immediately prior to emptying old nutrient solutions. Plant height was measured from the base of the stem to top of the newest, fully-emerged leaf when extended vertically.
Crops were harvested as needed, as often as two times per week, depending on crop. Number and fresh mass of marketable and non-marketable leaves (kale), sprigs (basil), and fruit (tomato and pepper) were recorded at each harvest interval.

Plant height is predicted with the equation[6]:

Height= A/(1+〖exp〗^(((x_0-log⁡(DAP)/b)) )

DAP: Days after planting
A: Parameter representing the upper asymptote
xo: the inflection point of the curve
b: scale parameter

Write the method in a list with using passive sentences.
Analysis
Raw Data
Use your raw data collected in the raw data section.
Processed Data
This section is where you process your experimental data
Evaluation
Conclusion
In this section, interpret your process data and graph.
Evaluation
In this section, write your comments about your experiment on the basis of your bibliography and scientific theories to see if your hypothesis has been verified.
Limitations and Weakness and Improvements
Explain how to improve deficiencies by specifying limitations and weaknesses in your method in the experiment.
Strengths
Defend your hypothesis by specifying the strengths of your experiment and method
Further Investigations
For further research, make suggestions about how you can improve your experiment and what other research you can connect with.

Bibliography

[1]Lind, Olle. “Organic hydroponics – efficient hydroponic production from organic waste streams.” (2017).
[2] Hashida, S., Johkan, M., Kitazaki, K., Shoji, K., Goto, F., Yoshihara, T., 2014.
Management of nitrogen fertilizer application, rather than functional gene abundance, governs nitrous oxide fluxes in hydroponics with rockwool. Plant Soil 374, 715–725.
[3] Rakocy, J.E., Masser, M.P., Losordo, T.M., 2006. Recirculating Aquaculture Tank Production Systems: Aquaponics—Integrating Fish and Plant Culture. SRAC Publication No. 464.
[4] Tyson, R.V., Simonne, E.H., White, J.M., Lamb, E.M., 2004. Reconciling water quality parameters impacting nitrification in aquaponics: the pH levels. Proc. Fla. State Hortic. Soc. 117, 79–83.
[5] Resh, H.M., 2012. Hydroponic Food Production: A Definitive Guidebook for the Advanced Home Gardener and the Commercial Hydroponic Grower. CRC Press, Boca Raton, FL, USA.
[6] Paine, C.E.T., Marthews, T.R., Vogt, D.R., Purves, D., Rees, M., Hector, A., Turnbull, L.A., 2012. How to fit nonlinear plant growth models and calculate growth rates: an update for ecologists. Methods Ecol. Evol. 3, 245–256.

2020-3-30-1585591879