NUTRIENT DYNAMICS AND pH / CHARGE-BALANCE RELATIONSHIPS IN HYDROPONIC SOLUTIONS

Most commercial hydroponic systems currently require the addition of acid or base to correct plant-induced charge-imbalances in the nutrient solution.
It has been long-known that varying concentrations of NH₄⁺ and NO₃^– in nutrient solutions affects the direction of pH change, as a consequence of H⁺ and anion-equivalent efflux by plants.
A series of experiments with wheat (Triticum aestivum cv. ‘Yecora rojo’) were performed to explore the contribution of other cationic and anionic species to this charge balance relationship over the entire crop cycle (66 days) under tightly regulated (growth chamber) conditions.
Daily nitrogen (N) additions were calculated from optimal tissue nutrient concentrations, and added according to a relative addition schedule based on crop development.
Three balanced electroneutral solutions with varying NH₄⁺:NO₃^– ratios (0:100, 25:75 and 50:50) were used to test the hypothesis that varying the proportion (concentration) of NH₄⁺ and NO₃^– available for plant uptake is the primary contributor to changes in pH in hydroponic nutrient solutions.
The results indicate that this is true for wheat, but K⁺ is also a likely contributor to the overall maintenance of charge balance by plants.
Increasing the proportion of NH₄⁺ in nutrient solutions (to approximately 25%) may be a relatively simple technique that can be used to reduce pH maintenance costs in hydroponic systems, particularly for those crops (e.g. lettuce, tomato and bell pepper) whose crop development cycles under set environmental conditions are well characterized.

International Symposium on Growing Media and Hydroponics

J.D. Lea-Cox, G.W. Stutte, W.L. Berry, R.M. Wheeler

Triticum aestivum ‘Yecora rojo’, ammonium, nitrate, potassium, nutrient film technique

https://doi.org/10.17660/ActaHortic.1999.481.25