Effects of reducing nitrogen ferilizer combined with biochar on the yield and quality of wheat and carbon sequestration and emission reduction in Northern Xinjiang of China

Numerous research endeavours have been conducted to explore the application of biochar as a means to enhance soil fertility and augment crop productivity in agricultural regions, but there is a lack of quantitative research and in-depth analysis on whether the application of biochar in farmland of irrigation area of Northern Xinjiang can increase production, sequester carbon and reduce emission. Hence, this study aimed to conduct a thorough assessment to ascertain the possible applicability of biochars in the ecosystems of agriculture irrigated in oasis regions. A field experiment was herein conducted in a spring and winter wheat rotation system from April 2021 to July 2022 with 7 treatments: the conventional application of nitrogen (N1: 300 kg/hm²), the reduction of nitrogen fertilizer by 15% (N2: 255 kg/hm²), the reduction of nitrogen fertilizer by 30% (N3: 210 kg/hm²), a single application of biochar (B: 20 t/hm²), the conventional application of nitrogen combined with biochar (N1B), the reduction of nitrogen fertilizer by 15% combined with biochar (N2B), and the reduction of nitrogen fertilizer by 30% combined with biochar (N3B). The effects of nitrogen fertilizer and biochar on soil organic carbon pool, soil respiration, wheat quality and yield were studied, with the aim to explore the potentiality of stable yield, carbon fixation and emission reduction of biochar application in the farmland of the Northern Xinjiang irrigation area. The results showed that compared with applying conventional nitrogen fertilizer alone (N1), the application of biochar resulted in an increase in soil total organic carbon (SOC), active organic carbon (AOC), carbon pool management index (CPMI), wheat yield, wheat quality as well. The soil AOC content was 1.44 g/kg in the treatment that 15% nitrogen fertilizer reduction combined with biochar(N2B), which was 30.91% higher than that in N1. Meanwhile, the SOC content was higher than that in N1. When it comes to the wheat yield, the spring wheat yield was 8 301.35 kg/hm², and the winter wheat yield was 10 784.76 kg/hm² in N2B, with an increase of 22.12% and 36.17%, respectively when compared with N1. As it for the wheat quality, the sedimentation value of protein (dry base) , gluten (wet base) and Zeleny increased under the treatment of 15% reduction of nitrogen fertilizer combined with biochar (N2B) in 2022, while there was no significant difference among the 2021 treatments. The cumulative soil CO₂ emission under other treatments was higher, except for biochar treatment in 2021 and 2022, and nitrogen reduction by 15% (N2) treatment alone in 2022. In a word, the effect of carbon sequestration and emission reduction in farmland soil and the yield and quality of wheat were better, when applied with 255 kg/hm² nitrogen fertilizer and 20 t/hm² biochar, which could be suggested as an ideal fertilization scheme to optimize the combination of nitrogen fertilizer and biochar in the wheat field of irrigation area in the northern Xinjiang.