Characterization of Biochar Produced from Greenhouse Vegetable Waste and Its Application in Agricultural Soil Amendment

The main objective of the current work is to evaluate the effect of adding biochar obtained by pyrolysis of a mixture of greenhouse waste to agricultural soil, measuring its effectiveness as an amendment. A mixture of broccoli, zucchini, and tomato plant residues was pyrolyzed in a lab-scale reactor at 450 °C, obtaining a biochar yield of 35.6%. No carrier gas was used in the process. A thorough characterization of the biochar obtained was performed, including elemental and proximal analysis, density, pH, electrical conductivity, cation exchange capacity, surface area, and metal content. Since the raw material had a high percentage of ash (approximately 20%), the resulting biochar contained around 50% inorganic matter, with potassium and calcium being the major metals detected (10–11%). This biochar had a 29% fixed carbon content, a high heating value of 11.5 MJ kg−1, a cation exchange capacity of 477 mmol kg−1, and an electrical conductivity of 16 mS cm−1.The biochar was mixed with greenhouse soil and fertilizer to form a substrate to grow bean seeds, the crop selected for the study. Different experiments were carried out, varying the biochar, fertilizer, and soil percentages. By adding 0.5% biochar to a substrate containing 1% fertilizer, the bean production was increased by 24.5%. It is worth noting that by adding only 0.5% biochar to soil, the bean production reached higher values than when adding 1% fertilizer. Biochar produced from the studied biomass improved the productivity of agricultural soils. The avoidance of selective collection by farmers as well as the non-use of carrier gas in the pyrolysis process made the implementation of the pyrolysis system in situ easier. Consequently, this research has great potential for practical application in modest agricultural areas.