Enhancing crop production and carbon sequestration of wheat in arid areas by green manure with reduced nitrogen fertilizer.

Green manure with appropriate amount of chemical nitrogen fertilizer can increase crop yield, but also aggravate soil carbon emissions. However, it is unclear whether incorporation of green manure into the cropping pattern with reduced nitrogen amount can alleviate this situation and enhance carbon sequestration potential. So, a field experiment with split-plot design was set up in 2018 of northwest China, and studied the effects of nitrogen reduction on crop productivity, carbon emissions, and carbon sequestration potential in 2021-2023. The main plots were two cropping patterns, including multiple cropped green manure after wheat harvest (W-G) and fallow after wheat harvest (W). Three nitrogen application levels formed the split-plots, including local conventional nitrogen amount (N3, 180 kg ha-1), nitrogen amount reduced by 15% (N2, 153 kg ha-1) and 30% (N3, 126 kg ha-1). The results showed that W-G increased grain yield of wheat and energy yield of wheat multiple cropped green manure pattern. The multiple cropped green manure after wheat harvest with local conventional nitrogen amount reduced by 15% (W-GN2) had the significant increasing-effect, and increased grain yield of wheat by 9.6% and increased total energy yields by 39.3% compared to fallow after wheat harvest with local conventional nitrogen amount (W-N3). Relative to W-N3, W-GN2 did not significantly increase carbon emissions of wheat season, and increased total carbon emissions of cropping pattern by 11.1%. Compared to multiple cropped green manure after wheat harvest with local conventional nitrogen amount (W-GN3), W-GN2 decreased carbon emissions by 5.8% in wheat season and decreased by 3.9% in the whole cropping pattern. Therefore, W-GN2 gained high carbon emission efficiency based on grain yield, and were 9.9% and 11.2% higher than W-N3 and W-GN3, respectively. In addition, W-GN2 enhanced soil total nitrogen, carbon, and organic carbon contents, compared with W-N3, thus increasing soil carbon sequestration potential index (net primary productivity/carbon emissions). We conclude that multiple cropped leguminous green manure after wheat harvest with local conventional nitrogen amount reduced by 15% can enhance crop productivity and carbon sequestration potential of farmland in arid areas.

Structural Characterization and Molecular Simulation of Baoqing Lignite.

The molecular structure of Baoqing lignite was analyzed by ultimate analysis, Fourier transform infrared spectroscopy, X-ray diffraction spectroscopy, 13C solid-state nuclear magnetic resonance, and X-ray photoelectron spectroscopy. The results revealed that the aromaticity of Baoqing lignite is 27.64%, and the aromatic structure mainly contains benzene and naphthalene. The aliphatic structure consists of alkyl side chains and cycloalkyl. Oxygen atoms are present in phenol, ether, carbonyl, and carboxyl groups; nitrogen atoms are chiefly in pyridine and pyrrole; sulfur atoms mainly exist in sulfoxide sulfur. The molecular structure model of Baoqing lignite was constructed based on experimental data, and the molecular formula is C184H199O50N2S. The molecular configuration was optimized by adopting the M06-2X basis set in the framework of density functional theory. Moreover, the simulated FTIR spectrum was in good agreement with the experimental spectra, proving the accuracy of the molecular structure. The molecular model of Baoqing lignite contains a majority of aliphatic structures and aromatic rings with a poor condensation degree. Moreover, the aromatic layers irregularly arrange in space.