Evaluation of electrical conductivity and pH in a nutrient solution with recirculating system in rose crop

Soilless culture systems with drainage recycling require continuous monitoring of electrical conductivity (EC) and pH, which are basic indicators of the chemical state of the solution that determine the extent to which recycling of nutrients is possible. These indicators are influenced by the physical, chemical, and microbiological properties of the substrates, as well as evapotranspiration, substrate temperature, and the stage of plant development. A rose crop cv. ‘Charlotte’ was established in three different substrates composed of mixtures of coconut fiber (CF) and burned rice husk (BRH). An automatic drainage recycling system was implemented with three percentages of nutrient recycling (0, 50, and 100%) to record the changes in EC and pH over 8 weeks of cultivation. This bifactorial experiment was carried out under a split-plot design in randomized complete blocks, where the main plot corresponded to the recycling percentage factor and the subplot to the substrate factor. The EC was significantly higher when recycling the nutrient solution in the following substrates: 35% BRH and 65% CF (35BRH) and 65% BRH and 35% CF (65BRH) at 1, 2, and 3 weeks after pruning (WAP). It was also higher for 100% BRH (100BRH) and 65BRH at 7 and 8 WAP. At 6 WAP, recycling at 50% and 100% had a significant effect on the EC values independent of the substrate. This could be caused by the release of ions and higher water retention, typical of CF, and the high adsorption of ions by the BRH. For pH, the trend was acidification, which was significant for the 100BRH treatment without recycling between 0 and 4 WAP. This could be related to changes in the absorption of ions such as NO3- and the activity of nitrifying microorganisms facilitated by the properties of the CF.