Response of seedling growth and nutrient characteristics to biochar, fulvic acid and nitrogen form of Pinus kesiya var. langbianensis

To explore the effects of coffee shell biochar, fulvic acid (FA) and N form on the growth and nutrient status of Pinus kesiya var. langbianensis seedlings for providing scientific theoretical basis for the directional cultivation of strong seedling. Using L₉(3⁴) orthogonal design, experiments were carried out with biochar supplemental level (0, 25, 50 g/L), FA concentration (0, 0.8, 1.6 g/L) and N form (no nitrogen, nitrate nitrogen, ammonium nitrogen). A total of 9 treatments were used. The effects of factor levels and their combinations on the growth and nutrient characteristics of P. kesiya var. langbianensis seedlings were analyzed. Coffee shell biochar, FA and N significantly promoted the seedlings growth (P < 0.05). High, ground diameterand biomass increased first and then decreased with the increase of biochar, and the growth of seedlings was the best at 25 g/L biochar. Biochar supplemental decreased N content of seedlings, but increased P and K content. With the increase of biochar, K content increased synchronously, but P content increased first and then decreased. FA application significantly increased height, biomass, N and P contents of seedling. N addition promoted the growth of seedlings and increased the contents of N and P. The growth and P content of seedlings treated with ammonium nitrogen were significantly higher than that of nitrate nitrogen, and ammonium nitrogen significantly increased the P content, while nitrate nitrogen had no significant effect on the P content (P≥0.05). Positive interaction effects between FA and N were observed on height and N content of seedling. Range of effect degree of each factor on seedling growth was coffee shell biochar > N > FA. Correlation analysis showed that seedling height, BD and biomass increased synergistically, and growth parameters were significantly correlated with P content (P < 0.01), that indicating P was a limiting element for seedling growth. Coffee shell biochar, FA and N promote seedling growth by enhancing the absorption of N, P and K. The optimal treatment is 25 g/L biochar and 0.8 g/L FA combined with ammonium nitrogen, and it is recommended to supplement P fertilizer appropriately during the production process.