Effects of biochar amendment on rhizosphere soil available nitrogen and crop growth

Biochar acts to improve soil quality, increase soil fertility, and promote plant growth, with its efficacy depending on the biochar type. In a pot experiment with a 2% application rate, we investigated the effects of corn stover biochar (CSB), grapevine branch biochar (GBB), and their mixtures (in ratios of 1:1, 3:1, and 1:3) on soil nitrogen availability and the growth of tobacco (Nicotiana tabacum L.).The results showed that biochar increased total nitrogen (TN), ammonium nitrogen (NH4+–N), nitrate nitrogen (NO3−–N), microbial biomass nitrogen (MBN), and dissolved organic nitrogen (DON) contents compared to the control group. Furthermore, compared with non-rhizosphere soil, biochar primarily increased the nitrogen content in the rhizosphere soil. Linear regression analyses indicated that biochar effected the accumulation of both NH4+–N and NO3−–N in the rhizosphere soil, but its effect on non-rhizosphere soil was not significant. The non-rhizosphere soil maintained overall soil available nitrogen by converting DON to NO3−–N. In addition, biochar increased the activities of nitrogenase, urease, and nitrate reductase. Based on this, biochar significantly enhanced tobacco growth by improving soil nitrogen availability, resulting in peak nitrogen content, aboveground dry weight, and underground dry weight of 4.56%, 87.82 g, and 25.39 g, respectively. Overall, the treatment group (CSB : GBB = 1:1) was most effective in increasing soil nitrogen as well as promoting tobacco growth.