Extraction optimization and quality evaluation of humic acids from lignite using the cell-free filtrate of Penicillium ortum MJ51.

Bio-solubilization of lignite is a promising technology to transform coal into humic acids (HAs) which are broadly used in agriculture. In this work, HAs were extracted from lignite using the cell-free filtrate (CFF) of Penicillium ortum MJ51. The extraction method was optimized using response surface methodology (RSM) based on the interactive effects of nitric acid concentrations, coal loading ratio, extraction temperature and time as input factors, and the absorbance of HAs at 450 nm wavelength as the output response. Under optimized conditions (lignite pretreated with 4.7 N HNO3, coal loading ratio of 4.9%, temperature of 77.3 °C and time of 8.6 hours), the absorbance at 450 nm peaked at 70.28, and the concentration and extraction yield of HAs were 31.3 g L-1 and 63.9%, respectively, which were dramatically higher than those observed for traditional biological methods (0.7 g L-1 and 14.1%, respectively). The qualities of HAs produced under optimized conditions were evaluated and compared with those extracted by the conventional chemical method. The optimized process resulted in better HA quality indices, including lower molecular mass; higher nitrogen; less aromatic carbon; more aliphatic and carboxylic carbon; and higher bioactivity for promoting plant growth. Moreover, the anti-flocculation ability was improved, thereby supporting its applicability in agriculture. Extraction of HAs from lignite using the CFF of P. ortum MJ51 provides a novel technological approach for the efficient conversion of lignite to bio-active HAs.

Mitigation of ammonia volatilization and nitrate leaching via loss control urea triggered H-bond forces.

Excess nitrogen (N) fertilizer applied to crops, which discharges to the environment, principally through denitrification, runoff, leaching, and volatilization, results in a waste of resources and pollution. Here, a high-performance loss control urea (LCU) was prepared by adding a loss control agent (LCA) with high thermal stability, large specific surface area, and good water retention capacity complex (6%) to traditional urea (94%). The existence of hydrogen bonds between LCA and N source for LCU in the presence of water enhanced N source adsorption capacity, where adsorption between LCA and NH4+-N was strongest, for urea and NO3--N was weakest. In a laboratory experiment, cumulative losses of NH3 volatilization from soils treated with N application rates of 80, 160 and 240 kg N ha-1 were 14.8, 18.1, and 24.2% for urea, respectively, and 10.1, 12.7, and 17.5% for LCU. Simulated rapid and long-term leaching experiments showed that, compared with urea, LCU reduced N leaching loss within 30 d, and delayed long-term N leaching loss. Hydrogen bonds in LCU effectively controlled NH3 volatilization and N leaching loss. This type of LCU may optimize supply of N in soils and increase adsorption and utilization of N in crops.

[Effects of nitrogen application rate on soil enzyme activities in wheat rhizosphere].

This paper studied the effects of nitrogen application rate on the soil enzyme activities in the rhizosphere of wheat cultivars Lankaoaizao 8, a large spike genotype, and Yumai 49-198, a small spike genotype, under high yield condition. The results showed that the enzyme activities in rhizosphere soil had similar changing trends with wheat growth. The protease, urease and dehydrogenase activities in rhizosphere soil increased with wheat growth, maximized at heading stage, jointing stage, and heading stage, respectively, and decreased thereafter. Catalase activity increased with wheat growth, and peaked at maturing stage. At the same growth stage, the protease, catalase and dehydrogenase activities in rhizosphere soil of the two cultivars increased with increasing nitrogen application rate and peaked at 180 kg N x hm(-2). Urease activity also increased with increasing nitrogen application rate, and the maximum activity was observed at 360 kg N x hm(-2).