Effects of Biochar-Nitrogen Interaction on Soil Nitrogen Transformation and Cucumber Growth in Facility Cultivation

Continuous cropping and long-term excessively using nitrogen fertilizers in facilities vegetables has led to the imbalance of nitrogen conversion in soil and plants. A pot experiment was conducted to investigate the effects of biochar on soil and plant nitrogen transformation in cucumber under simulated different nitrogen contents in facility cultivation. Eight pot treatments: no nitrogen (N0), 100 kg·hm^-2 of nitrogen (N100), 150 kg·hm^-2 of nitrogen (N150), 200 kg·hm^-2 of nitrogen (N200), and which with the addition of 5% biochar named BN0, BN100, BN150, BN200. The results showed that BN100 (100 kg·hm^-2 N + 5% biochar) significantly increased the soil nitrogen transformation and the growth of cucumber. Specifically, the nitrate reductase, GOGAT activity, and the nitrate nitrogen absorption of cucumber roots were enhanced. It also elevated soil pH by 0.43 units and increased urease, neutral protease, nitrite reductase (NIR, and NR activities by 136.63%, 23.95%, 18.4%, and 12.1%, respectively. The relative abundance of nitrogen metabolism-related microorganisms such as Nitrospira and Sphingomonas were increased. The nitrification, nitrogen fixation, the contents of nitrate nitrogen and nitrite nitrogen in soil were increased. These changes collectively improved soil nitrogen transformation and ultimately promoted cucumber plant growth. This study reveals the potential role of biochar in regulating soil nitrogen transformation and facilitating plant growth.