Are biochar and hydrochar adequate materials as growth medium constituents? A summary of the research carried out at UPV

Abstract

[EN] Biochar and hydrochar are produced by charring organic matter through pyrolysis and hydrothermal carbonization, respectively. Biochar has been tested extensively in agricultural soils. Nevertheless, both materials have scarcely been tested as soilless growth medium constituents. We have conducted studies on the properties and behaviour of biochar [forest waste (BCH-FW) and olive mill waste (BCH-OMW)] and hydrochar [forest waste (HYD-FW)] as growth medium constituents under different culture conditions. We have grown ornamental, forest and vegetable species. We have conducted assays on seed germination, cutting rooting and plantlet growth under nursery conditions, and tomato growth under commercial conditions. The materials proved useful for growth medium formulation. However, they were not good performers as sole constituents, because they posed specific problems depending on the material. BCH-FW was alkaline and its major problem was the large particle size that some batches presented, which caused low retention of water and nutrients leading to low plant performance. Nevertheless, good results were obtained for seed germination, cutting rooting and plant survival. BCH-OMW was alkaline and highly saline, and as a result was phytotoxic to plants. This was a drawback for seed germination and young plant growth, but not for adult plants and saline-tolerant species such as tomato. HYD-FW was highly hygroscopic and showed high microbial activity, emitting large amounts of CO2. Under these conditions, the low O2 pressure in the rhizosphere led to a decrease in plant performance.