Organic acids to adjust pH of chicken manure extract for fertilization of potted coriander

Abstract

Fertigation solutions with high pH are a challenge in organically certified greenhouse production. We investigated how organic and inorganic acids affected pH of a fertigation solution derived from certified organic chicken manure extract (CME) in a 23-day pot experiment with coriander (Coriandrum sativum L.). The pH was adjusted to 6.0 using four organic acids: apple vinegar (CAV), citric acid (CCA), redcurrant juice (CR) and lactic acid water (CAW); and using inorganic sulfuric acid to adjust pH to 6.0 (CIN6.0), 6.5 (CIN6.5) and 7.0 (CIN7.0). CME without pH adjustment (C) and an inorganic fertigation treatment with a pH of 6 (IN) served as controls. Nutrient status, pH and oxygen concentration of the growing medium, and biomass yield parameters of coriander were measured. The pH of CME fertigation solutions increased by 0.9–1.4 units within seven days. CME lowered concentrations of NO3, Ca, Mg and B, increased concentrations of NH4, P, K, Cl, Na and Fe, and electrical conductivity (EC) in the growing medium solutions compared to IN. Most macro- and micronutrients concentrations in shoots (except N, K and Mg) were higher when coriander was given CIN6.0 compared to CME with organic or no pH-adjustment. Oxygen concentration was lower in CME than IN treated pots at 7 cm depth. Organic acids failed to efficiently control the pH of CME fertigation solutions, reduced nutrient availability and resulted in lower root score and a 29–41% lower coriander biomass than IN. Despite inefficient pH control, organic acids did not reduce coriander biomass compared to inorganic acids.