Potassium-enriched biochar-based fertilizers for improved uptake in radish plants

Biochar-based fertilizers (BBFs) enriched with potassium (K) can increase the efficiency of K use by plants. This study evaluated the effect of a new K-enriched sewage sludge biochar in the pellet and granule forms, applied at full and reduced application rates, compared with a conventional K fertilized control (KCl), on soil chemical attributes, nutrition and relative chlorophyll content (SPAD index) of radish plants grown in a greenhouse. Both BBF forms (granule and pellet) showed good performance in supplying K and other nutrients to the plants. On average, BBF in the granule form increased the concentration of K in radish sap by 30% compared to BBF in the pellet form and KCl. Even when applied at half the recommended rate (174 kg ha −1 of K), BBFs were efficient in supplying K and other nutrients to the plant. BBF in the pellet form increased the tuber dry mass, which was on average 150% higher than KCl and BBF in the granule form. In general, the results of the present study indicate that the better supply of K promoted by the BBF also contributed to higher SPAD index values in the radish crop. More studies should be carried out to better understand the effect of BBF on the performance of crops with different cultural cycles (short and long).