Physical and chemical characterization of pine bark for the production of blueberry (Vaccinium corymbosum L.) in containers

Pine bark (PB), a product of Pinus oaxacana Mirov, is an abundant organic waste in the state of Oaxaca, Mexico. In the last 18 years, about 72,000 t have been generated annually. In Mexico, composted pine bark has not yet been used to make organic substrates. Due to the volume of waste generated, pine bark could be used as a substrate or component of alternative substrate. This work analyzes PB as a sustainable organic substrate for blueberry production in containers. PB was subjected to a controlled composting process for 241 days. The final compost obtained served as the basis for the formulation of four different mixtures that were characterized by analyzing their physical and chemical properties, based on the European regulation-Spanish regulation (UNE-EN). The mixtures were: pine bark + peat moss + expanded clay + vermiculite 30:40:15:15 v/v (CPTAEV2), pine bark + peat moss + expanded clay + vermiculite 30:60:5:5 v/v (CPTAEV3), and pine bark + uncomposted sawdust 80:20 v/v (CPSSC). Each had recommended values of total porosity, aeration capacity and moisture retention capacity - physical properties important to assess the quality of a substrate. Pine bark + peat moss + expanded clay + vermiculite 70:20:5:5 v/v (CPTAEV1), CPTAEV2, and CPSSC mixtures had a proper balance of water and aeration. Regarding readily available water (RAW) and reserve water (RW) parameters, CPTAEV2 and CPTAEV3 mixtures had very appropriate values. Regarding pH, CPTAEV2, CPTAEV3, and CPSSC mixtures had acid values, as required for blueberry cultivation. In regard to electrical conductivity (EC), CPTAEV3 and CPSSC mixtures had values lower than 1 dS m-1, also suitable for cultivation. The cationic exchange capacity (CEC) of CPTAEV2, CPTAEV3 and CPSSC mixtures all had values in the recommended range. The organic matter (OM) had low values and C/N ratio was suitable. Overall, compost and mixtures made from Pinus oaxacana Mirov, exhibited physical and chemical characteristics that meet the conditions for use as growth substrate for production of blueberries in containers.