Demand for gasification biochar is expected to increase, owing to the bioenergy requirements of a sustainable society. Here, we assessed the applicability of gasification biochars from cedar wood (W) and rice husk (R) for the agricultural soil amendment and compared their ability in enhancing soybean yield in two consecutive cropping cycles. The pot experiment included four treatments: F0 (control 1), without both nitrogen fertilizer (Nfer) and biochar, F (control 2), using only Nfer, W–F, using W with Nfer, and R–F, using R with Nfer. Both gasification biochars had higher pH, CEC, and greater nitrogen retention than the soil. In the first cropping cycle, the W application showed an immense impact on some soil physical properties, including bulk density reduction (12%) and water-holding capacity increment (25%) while the R amendment significantly increased exchangeable K (45%) and soil pH. In addition, other changes in soil chemical due to W and R applications included enhancement of available phosphorus (P, 8–14%) and reduction of ammonium content (12–21%). After two consecutive cropping cycles, W–F indicated the largest content of soil available P and the highest soil pH. Ultimately, the co-application with Nfer of W and R had the same significant impact on soybean yield compared with control 1 in the first and two consecutive cropping cycles. In addition, the W application specifically recorded a significantly higher soybean yield than control 2 in the first and two cropping cycles, unlike the R amendment.
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