The effect of biochar addition on plant major nutrient uptake in hydroponic systems

The effect of biochar addition on plant major nutrient uptake in hydroponic systems

Farming is a vital part of people’s lives worldwide. New methods for increasing agricultural productivity, such as aquaponics and aeroponics can be costly and slow to implement. Whereas conventional approaches tend to use more fertiliser to increase productivity, significantly impacting the environment and human health.

This study examines if the ancient technology of hydroponics, can benefit from the addition of biochar (BC) in its growth media. Measurements included effects on pH, electrical conductivity (EC), and macronutrients, coupled with the effects on plant chlorophyll, photosynthesis, dry weight, leaf area, height and nutrient contents.

Prior to selecting coconut shell biochar (CSBC), the CSBC was applied at four rates (0, 5, 25, and 50%) using two types of growth media (washed river sand and peatmoss). Initial tests used a largely inert growth media to eliminate as many variables in the system under test. Later column tests used CSBC mixed with more commercially representative mixtures of sand and peatmoss.

Tests were initially conducted at a small laboratory scale, then under temperature-controlled conditions in a glasshouse, before making final observations with a small farm trial. Throughout these tests, CSBC’s effects on pH, EC and macronutrients (nitrate, phosphate, potassium, calcium, magnesium and sulphate) retention and release were monitored. In the Glasshouse tests, CSBC’s effect on the previously optimised parameters were measured for the two irrigation solutions (hydroponic nutrient solution and pure water). Plant physiochemical characteristics (nitrate, phosphate, potassium, calcium, magnesium, sulphate, leaf area, plant height, dry weight, photosynthesis, and chlorophyll) were monitored, with a commercial SCADA package used to control the system.

As CSBC rates increased pH increased and EC decreased, most nutrient retention increased, except for potassium and magnesium, e.g. the highest release of nutrients (56 - 60 mg.L-1) was from the control (0% BC) whereas the lowest was from the 25-50% BC (100 - 108 mg.L-1). For commercial usage it was determined that the 5 - 10% BC rate showed the most positive combination of effects on plant growth and nutrient sorption/desorption.