Nutrient Replacement Strategies for Hydroponics

Commodities

• Vegetables: greens (lettuces), peppers

Practices

• Production Systems: hydroponics

Levo International, Inc. (Levo) is a 501(c)3 nonprofit with the
main objective to provide food security solutions for families.
Hydroponic agriculture is the main mechanism we use to promote
this objective. Hydroponics is the growth of plants in a
water-based nutrient solution, without the use of soil. We both
run local hydroponic farms and support local growers to start
their own small-scale farms. Hydroponics is a sustainable form of
agriculture which can be used on nonarable land and enables
efficient use of water and fertilizer in a closed loop. High
start-up costs and complexity of operation render hydroponics
inaccessible for many. Our research focuses on developing and
deploying hydroponic systems that are simpler and less expensive
to build and operate.

It is standard practice in hydroponic production to either
regularly replace the nutrient solution or to frequently complete
expensive analysis of the ion content of the nutrient solution
and inject individual nutrient salts accordingly. In a recently
published research project, we produced greens and fruiting crops
in our hydroponic systems without replacement of the nutrient
solution. This approach enables us to conserve water and
fertilizer. This proposed project will enable us to pilot the
implementation of this more sustainable and efficient approach.
Through the proposed research we will gain directly applicable
data about how we can adjust nutrient additions for different
crops, how yields change without replacement of the nutrient
solution and the risk of disease pressure if the nutrient
solution is not replaced.

Our first objective (Obj. 1) is to determine the
concentration of macronutrients over time in nutrient solutions
which are, or are not, replaced. We hypothesize that
macronutrients decrease in a consistent pattern over time and
that measurements of electrical conductivity (E.C.) and total
dissolved solids (TDS), which provide an estimate of the total
concentration of ions in the solution, can be used to estimate
when nutrients should be added.

Our second objective (Obj. 2) is to test the hypothesis that
reuse of nutrient solution decreases the inputs of fertilizer
and water sufficiently that it justifies decreased yields.
To test this hypothesis, we will conduct yield trials at three
different Levo farm locations in which nutrient solutions are
replaced every 3 weeks, or they are not replaced for the duration
of a crop.

Our third objective (Obj. 3) is to record the incidence of
disease over 2 growing seasons in systems described in objective
two. We hypothesize that due to the rapid multiplication and
spread of root rot causal agents such as Pythium, recycling of
the nutrient solution will not lead to greater risk of
disease.