Basic tests for automatic nutrient monitoring for hydroponic crop production system

Background: Recently around the world, the global climate change caused the decrease in the food production. Besides this, traditional farming and amount of cultivable land are also decreasing. As an alternative to these problems, more attention is paid to the plant factory. Automated nutrient sensing and control for plant factory (e.g., closed hydroponic system) would allow more efficient use and management of nutrients for crop production. An attempt has been taken to test the components along with the nutrient management system for plant factory.

Methods: The nutrient management system was divided into two parts - sensing and controlling part. First, a data acquisition code was made using Lab View 2011. Using NI USB 6009 device, performance of EC, pH, NO3 and K ion selective electrodes were checked by measuring the correlated components in standard and real-time nutrient solution. A mixing algorithm was developed to control the individual solution volume to be supplied depending on their concentration in the mixing tank.

Results: The EC, pH, NO3 and K sensors were tested in a standard solution of 3, 4, 100 mg L-1 and 10 mg L-1. Standard deviations after calibration and regression between before and after calibration were 0.189, 0.245, 1.371, 1.400 and 0.902, 0.885, 0.829, 0.861 for EC, pH, NO3 and K sensors, respectively. After rinsing the standard error reduced to 16.69% and 42.16% for NO3 and K ISE sensors, respectively.

Discussion: Errors occurred due to signal drift and bio-film formation in the sensors head. Signal processing algorithm would be developed to remove these errors.

Conclusion: An ISE-based, computer-controlled nutrient maintaining system would be a viable technique for improving accuracy and precision application of nutrient solutions in a plant factory crop production system.