Biochar can enhance potassium availability during cyclamen cultivation

This study examined the feasibility of using biochar in soilless substrates as a substitute for mineral components and as an additive to buffer peat acidity and increase cation exchange capacity. Two different substrates were studied: a control mix composed of peat and perlite (80:20%, v/v) and a biochar mix, composed of peat and biochar (80:20%, v/v). To evaluate the role of biochar in the dynamic of plant available potassium, two levels of starter potassium fertilization were used (0 and 150 mg K L(‑1) substrate). A randomized trial was conducted in a commercial greenhouse, where 132 pots were filled with the control mix and with the biochar mix; then one young plant/pot of Cyclamen persicum Mill. 'Halios' was transplanted and cultivated for 150 days. Special attention was paid to the effect of biochar on potassium and other nutrients dynamic in pore water during the first phases of plant growth and in the substrate at the end of the cultivation. Cyclamen morphological properties (leaf number, plant height, flower number, fresh and dry biomass of aboveground) were surveyed at an early crop growth and at the end of the experiment. Biochar increased K, P and Mg concentrations in the pore water up to 16 days after transplanting. At 75 d, the growth of cyclamen was 30% enhanced by biochar, with statistically significant increases in fresh and dry weight. Leaf and flower numbers, and mineral content of leaves were not influenced by biochar and starter K addition. At the end of the cultivation, there was no more noticeable effect of biochar on cyclamen quality and leaf nutrient contents. Chemical analysis of the substrates showed that biochar was able to induce an increase in water extractable K (+23%) and in CAT (calcium chloride and DTPA) extractable K (+36%) in respect to control medium. Moreover, the significant interaction between biochar and starter potassium fertilization suggested that biochar can preserve potassium from leaching, being able to store potassium fertilizer in a plant available pool. These results demonstrated that biochar can be considered a good substitute for perlite in growing media, acting at the same time as a sink and a source of potassium available for plants.