When I hear the terms sustainable agriculture and innovation, I automatically think about hydroponics. Requiring up to 95% less water, 99% less land, and virtually no pesticides compared to conventional farming methods, and growing in exponentially less amount of time, this relatively new technology is taking the world by storm and can quite possibly be our next big solution to ending world hunger.
However, while placing an emphasis on sustainability as well as creating demand for their products, hydroponic growers are making big transitions towards using organic fertilizers as opposed to conventional chemical blends containing minerals needed by plants such as nitrogen, phosphorus, and potassium. Nonetheless, chemical fertilizers tend to have several negative environmental impacts since mining of these nonrenewable minerals involves the heavy usage of fossil fuels and chemically treated fertilizer water can end up leaching these minerals and degrading ecosystems. Organic fertilizers however, can be cheaply made from readily available bio waste such as a “tea” made from seaweed extract, vermicompost, or hydrolyzed fish emulsion. Essentially, it would be turning already existing food waste into food for our food.
Although organic fertilizer sounds like a perfect solution, experiments have shown that yield in hydroponic crops grown with organic fertilizers is lower than that of their conventional counterparts. This is often attributed to the development of a viscous biofilm formed in organic hydroponic reservoirs. Rich in bacteria and pathogens that cause plant diseases such as root rot, these microbes floating around are also competing with crops for resources often depriving root zones of oxygen. On a macroscopic level, the thick, gunky biofilm tends to clump on roots and can even end up clogging hydroponic systems.
Eliminating this biofilm has proved to be difficult since finding a disinfectant strong enough to kill off pathogens without harming the plants is no easy task. Few studies have been conducted on this topic and most are inconclusive. Scrolling through the internet, I found that hydroponic hobbyists often recommend using hydrogen peroxide as a treatment, though application techniques and dosage are never consistent and there are few testimonials of this method proving success.
Last year, when I was working in the Controlled Environment Agriculture labs at Cornell University, I designed and conducted an experiment testing the use of hydrogen peroxide in conjunction with both conventional and organic hydroponic fertilizers. In this study, three different treatments consisting of a control, 1.25 mL/L, and 2.5 mL/L of hydrogen peroxide were added to aerated 4-L reservoirs that were fertilized with either organic (4-1-1) or inorganic nutrients (21-5-20), both applied at 150 mg·L-1 N. Three replicates for each treatment and each fertilizer were prepared resulting in a total of eighteen reservoirs with one head of oakleaf lettuce being grown in each.
The results of this trial showed that when added to conventional fertilizers, doses of 1.25 mL/L and 2.5 mL/L of hydrogen peroxide stunted the growth of or killed the heads of lettuce. However, when applied to organic fertilizers, the lettuce yield matched that of the conventionally fertilized control. Though some biofilm visibly persisted, no diseases developed in the organically fertilized root zones and the lettuce clearly thrived since typically, organically fertilized hydroponics yields noticeably less than that of its conventionally fertilized counterpart. Though I have only tested this with oakleaf varieties of lettuce, I believe that exploration of similar methods can be applied to other hydroponically grown crops from microgreens to even peppers and tomatoes in order to reduce crop disease stemming from the buildup of pathogenic biofilm found in organically fertilized reservoirs and to increase the efficiency of organic hydroponics making it competitive with conventionally fertilized hydroponics while lessening its carbon footprint.
As we globally move forward in agricultural innovation, I strongly believe that hydroponics has a large place in our future. As a sustainable, efficient, and simple way to grow crops, discovering out how to eliminate pathogens found in organic hydroponic biofilm will help us fully optimize the use of this technology that can help us feed the world without biting the hand that feeds us: Planet Earth.
Vanessa Lau, USA