Soil Wealth ICP team member Camilla Humphries has been working with Doug Chamberlain from Grown Smart Produce in Carabooda, Western Australia, around 50km north of Perth, to set up a demonstration site trial for the project focusing on plant health and nutrient use efficiency of hydroponic cucumbers.
Doug would like to improve the nutrition in the current hydroponic system to receive premium value for his cucumbers and also improve water use efficiency in the system.
The demonstration site aims to improve plant health and nutrient use efficiency by applying the required inputs in alignment with optimum EC and pH levels through the fertigation system. This will require close monitoring of the hydroponic system over the 8-10 week growth cycle for the cucumber crop, including performing regular EC and pH tests and changing the nutrient inputs based on the test results, and monitoring nutrient deficiency/toxicity symptoms over time.
Grown Smart Produce also asked for direction on irrigation scheduling to maintain runoff between 20-30% in the intensive cucumber hydroponic system.
Initial insights
Sap, plant dry tissue and hydroponic water tests have been conducted at various stages of the demonstration site trial, including at planting, harvest and post-harvest.
The desirable pH range for the emitters is 5 to 6.2. Over the plant growth cycle, pH fluctuated and plateaued at an average pH of 6.5 in the weeks leading up to harvest in November 2024.
The desirable EC range is 1.5-2.5 mS/cm for the emitter nutrient solution. Over the plant growth cycle, EC fluctuated from planting in September 2024 until mid-October 2024 when it started to stabilise at the desirable range for the remainder of the growth cycle.
The hydroponic water test by AgVita Analytical showed a slightly higher than optimal EC of 2.92 dS/m, indicating excess salt in the solution.
Sap tests taken in September 2024 showed that ammonium levels were too high at 660 ppm indicating that the ammonium concentration in the nutrient solution was too high. It was recommended to use different forms of nitrogen based fertilisers such as potassium nitrate and calcium nitrate to boost calcium levels and support fruit growth via potassium. At the time of the second sap test in November 2024, ammonium levels had dropped to 6.6 ppm and nitrate levels had increased from 2080 ppm to 4374 ppm, which was in the desirable range.
At harvest a plant dry matter (tissue) test indicated that calcium, boron and magnesium levels were in the desirable range. Despite the brix levels being good, potassium levels were low. Potassium supports fruit growth and regulation of transpiration.
Stay tuned for further results from the demonstration site later in 2025.
