[Effects of enhanced-efficiency nitrogen fertilizers on nitrous oxide emissions from cotton field under plastic mulched drip irrigation in Xinjiang,China]. / 高效氮肥对新疆膜下滴灌棉田土壤氧化亚氮排放的影响.

The effect of enhanced-efficiency nitrogen (N) fertilizers on emissions of nitrous oxide (N2O) from the grey desert agricultural soils of Xinjiang is uncertain. In this study, the enhanced-efficiency fertilizers, polymer-coated urea (ESN), and stabilized urea with urease and nitrification inhibitors (U+I) were compared to conventional urea (U) for N2O emissions from cotton under plastic mulch drip irrigation near Urumqi, Xinjiang. ESN was added once at planting but the other treatments were added multiple times with drip irrigation during the growing season. Gas samples were collected and analyzed twice per week during the growing season, using the static chamber-chromatography methodology. The results showed that generally, ESN significantly increased soil cumulative N2O emissions during the growing season by 47%-73% compared to other treatments. In the first four months after fertilization, soil ammonium (NH4+-N) and nitrate (NO3--N) concentrations under ESN treatment were generally higher than under other treatments. Thereafter, NH4+-N and NO3--N concentrations under all treatments gradually decreased to similar levels. ESN all added at planting was likely responsible for high NH4+-N and NO3--N concentrations and highest N2O emissions. The U+I treatment reduced soil N2O emission by 9.9% in comparison with U, whereas the difference was not statistically significant. In addition, soil NO3--N contents of the U+I treatments were generally lower than those of the ESN and the U treatments. The cumulative N2O emissionsover the growing season ranged from 300 to 500 g N2O-N·hm-2, generally lower than emissions reported for other agricultural ecosystems. Drip irrigation successfully kept moisture conditions below levels for appreciable N2O emissions. Multiple applications of N via drip irrigation seemed to be effective to lower emissions than all N applied at planting. Therefore, for cotton field under plastic mulch drip irrigation in arid land of Northwest China, the benefit of enhanced efficiency N ferti-lizers on N2O mitigation is limited.

[Content and evolution characteristics of organic carbon associated with particle-size fractions of grey desert soil under long-term fertilization].

Physical fractionation technique was used to analyze the content, distribution, and temporal evolution of organic carbon associated with particle-size fractions of grey desert soil under long-term (1990-2007) fertilization. Compared with no fertilization, a combined application of manure and chemical fertilizers increased the organic carbon associated with particle-size fractions significantly, with the highest increment (0.34 g x kg(-1) x a(-1)) in sand. Following also increased the organic carbon associated with clay and silt significantly. Straw return to cropland only maintained the organic carbon content in different particle-size fractions, while long-term application of chemical fertilizers was not beneficial to the organic carbon increase in particle-size fractions. Coarse silt and coarse clay had the highest distribution rates of organic carbon (27.9% and 27.1%, respectively), being the important fractions in sequestrating organic carbon. When manure was applied with chemical fertilizers, the organic carbon in sand was significantly increased by 119.4%, while that in fine silt and coarse clay was significantly decreased by 40.3% and 37.9%, respectively, which resulted in the increase in the ratio of particulate organic carbon content (W(POC)) to mineral-associated organic carbon content (W(MOC)), and improvd soil carbon property. Long-term application of manure combined with chemical fertilizers was the best mode to increase the organic carbon content in particle-size fractions and improve the fertility of grey desert soil.

[Determination of trace Hg element in gas by CVAAS with single optical path].

Since the anthropogenic emissions of mercury into environment were mostly entering the atmosphere through flue gas, continuous monitoring of mercury in the flue gas was significant for mercury emission control. A bench scale test rig was set up for the measurement of mercury through both wet chemical method and CVAAS (cold vapor atomic absorption spectrometry) with single optical path. The concentration of Hg in absorbent solution was determined by Hydra AA mercury analyzer. The concentration of Hg in gas was calculated in terms of wet chemical testing results, which showed a stable rate of permeation device. Hg atom absorption signal intensity was detected and analyzed in comparison with the test results of wet chemical methods according to Beer-Lambert law. Experimental data well agreed with the theory analysis, which indicated that the single optical path was suitable for the determination of trace Hg element in pure gas. Further research work should aim at the improvement of system adaptability and anti-jamming ability. To reduce the intensity fluctuation of mercury lamp, another spectral line could be detected simultaneously. Interference from surroundings, e.g. dust in gas or spot on the quartz surface, could be eliminated by optoelectronic coupling.