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Since the 1950s, heavy plowing of Mollisols, combined with a lack of organic matter intake, has resulted in severe soil degradation in northeast China. The use of biochar in combination with fertilizer is a sustainable method of improving soil quality. In this paper, we conducted field experiments to explore the response of the stability mechanism of the soil aggregate, the dynamic properties of organic carbon, and changes in the microbial community structure to biochar. The biochar input levels were C1, C2, and C3 (9.8, 19.6, and 29.4 Mg C ha -1 , respectively), while the nitrogen (N) fertilizer rates were N1/2 (300 kg N ha -1) and N (600 kg N ha -1). Results indicated that biochar combined with N fertilizer effectively increases soil carbon storage and aggregates stability (P<0.05). And C2N treatment increased the aggregate contents of the >2 mm and 0.25–2 mm fractions by 56.59 % and 23.41 %, respectively. The phospholipid fatty acid (PLFA) analysis revealed that microbial community structure was effectively improved with biochar combined with N fertilizer application (P<0.05). The F/B ratio increased by 25.22 % and the gram-positive (Gm +) to gram-negative (Gm -) ratio by 4.65 % under the C2N1/2 treatment. This study concluded that the response of Mollisols to biochar is primarily determined by the interplay of aggregate, organic carbon, and microorganisms. Therefore, the use of biochar combined with N fertilizer might mitigate soil degradation of Mollisols under an optimal application ratio, but the underlying mechanism still requires further exploration. This study will provide a scientific basis for the conservation and sustainable utilization of Mollisols resources. [ABSTRACT FROM AUTHOR]

Microscopic differences in soil pore water velocity cause hydrodynamic dispersion of solute transport. By analogy, thermal dispersion should be considered in soils where water and heat flow occur simultaneously. Few published data are available regarding thermal dispersion in soils. In this study, we investigated thermal dispersion influences on heat transport in saturated soils with one-dimensional water flow. A new soil container was developed to eliminate wall flow influences on saturated water flow. An inverse model was applied to obtain the thermal dispersion coefficient ([[lambda].sub.d]) by fitting the conduction-convection-dispersion (CCD) model to soil temperature change as a function of time from heat-pulse measurements. Thermal dispersion became significant when the water flux was higher than a threshold value. In the studied water flux range, the maximum contribution of hydrodynamic dispersion to effective heat conduction [[lambda].sub.d]/([lambda].sub.d] + [lambda].sub.0])' where [lambda].sub.0] is the bulk thermal conductivity] was 6, 9, and 12% in a sand, a silt loam, and a sandy clay loam, respectively. A power function relationship was established between [lambda].sub.d] and the soil water flux density ([J.sub.w]): [lambda].sub.d] = [kJ.sub.w.sup.0.9], where k is a coefficient related to soil texture. Experimental evaluation indicated that, compared with the conductionconvection model, the CCD model performed better in describing the temperature change vs. time data from heat-pulse measurements. Abbreviations: CCD, conduction-convection-dispersion. doi: 10.2136/sssaj2008.0251

Since the 1950s, heavy plowing of Mollisols, combined with a lack of organic matter intake, has resulted in severe soil degradation in Northeast China. The use of biochar in combination with fertilizer is a sustainable method of improving soil quality. In this paper, we conducted field experiments to explore the response of the stability mechanism of the soil aggregates, the dynamic properties of organic carbon, and changes in the microbial community structure to biochar. The biochar input levels were C1, C2, and C3 (9.8, 19.6, and 29.4 Mg·ha-1, respectively), while the nitrogen (N) fertilizer rates were N1/2 (300 kg·ha-1) and N (600 kg·ha-1). The field test showed that the C2N treatment increased the aggregate contents of the > 2 mm and 0.25–2 mm fractions by 56.59 and 23.41 %, respectively. The mean weight diameter increased by 41.53 %, while the geometric mean diameter increased by 21.62 %. The organic carbon content of large aggregates shows a greater increase, with an average of 28.14 %. The phospholipid fatty acids analysis revealed that bacteria (B) were the most prevalent organisms in the soil, followed by fungi (F). The C3N treatment increased the F / B ratio by 36.46 %, whereas the C3 treatment increased the gram-positive (Gm+)/gram-negative (Gm−) ratio by 19.67 %. We concluded that the response of Mollisols to biochar is primarily determined by the interplay of aggregates, organic carbon, and microorganisms. Based on the sequestration of SOC and the sustainability and stability of the ecosystem, we selected the optimal ratio for biochar and N fertilizer application and provide a scientific basis for the sustainable utilization of Mollisols resources. [ABSTRACT FROM AUTHOR]

This study is focused on the determination of exterior convective heat transfer coefficient for low-rise residential buildings. The convective heat transfer coefficient is an important parameter in building heat transfer analysis and building energy simulation. While there are many open literature studies based on either laboratory measurement or field testing, researchers have used different sources of wind data, testing conditions and building types, and therefore an applicable correlation especially for low-rise residential buildings is somewhat missing. In this study, a new calculation model is applied that comprehensively considers the influence of sky temperature, ground temperature as well as view factors. Several correlations are developed for both the convective heat transfer coefficient and the ground temperature, and an appropriate sky temperature model is selected. Based on the test data, an ASHRAE formula is also used to estimate the local wind speed using the free stream wind speed. The results of this study will provide new correlations of the convective heat transfer coefficient that can be used for low-rise residential buildings in the energy simulation process. [ABSTRACT FROM AUTHOR]

Tidal marshes play an important functional role in removing nitrogen (N) pollution before delivery to coastal and ocean systems; however, little is known about their removal capacity as N2O gas emissions from different plant species. To evaluate the effects of N inputs on N2O emissions from tidal marshes, we measured N2O fluxes from native (Cyperus malaccensis) and invaded (Spartina alterniflora) tidal marshes in the Min River estuary, and fertilized with exogenous N at the rates of 0, 21 and 42 g N m−2 yr.−1, respectively. S. alterniflora invasion did not significantly influence N2O emissions from the C. malaccensis marsh under natural conditions, but under N addition conditions, the invasion of S. alterniflora decreased N2O emissions, primarily owing to its stronger N uptake capacity. Exogenous N had significant positive effects on N2O fluxes in both native and invaded tidal marshes. Moreover, significant temporal variability of N2O fluxes was observed after N was gradually added to the native and invaded marshes. Within 3 h of N addition, N2O fluxes were significantly higher in plots receiving N additions relative to controls. After 8 days, few significant differences were found between treatments. Moreover, electrical conductivity, pH and oxidation-reduction potential at different soil depths were not significantly affected by N addition. Considering N addition showed extremely high positive effects on N2O fluxes at the hours scale, the overall increase of N2O emissions from wetlands in response to N addition may be significantly underestimated. To better assess the global climatic role of salt marshes that have been affected by N addition, the short-term temporal variability of N2O emissions should receive greater attention. [ABSTRACT FROM AUTHOR]

Heat-pulse technique (HPT) has shown promise for predicting soil water flux (Jw). This study evaluated the accuracy of HPT in predictingJwin packed saturated columns of quartz, sand, silt loam, and sandy clay loam.Jwwas predicted using the maximum dimensionless temperature differences (MDTD), ratio of downstream to upstream temperature increases (Td/Tu), and an improvedTd/Tumethod. Results indicated thatJwpredictions had a good linear relationship with measurements (R2 > 0.93). The HPT underestimatedJwto varying degrees, and the underestimations increased asJwincreased and soil texture became fine. TheTd/Tumethod outperformed theMDTDand the improvedTd/Tubecause of its higher accuracy, fewer parameters, and simpler calculations. TheMDTDexhibited the poorest performance. In coarse-textured soil materials (e.g. quartz and sand),Jwpredictions by theTd/Tumethod were most accurate, and even with highJw(up to 72.4 μm s−1), relative errors still remained within 9.8%. However, in fine-textured soil materials,Jwwas underestimated significantly by 16.9% in silt loam and by 23.3% in sandy clay loam. The lowerJwlimits were 1.0, 2.3, 2.4, and 4.0 μm s−1for quartz, sand, silt loam, and sandy clay loam, respectively (P > 0.05). [ABSTRACT FROM AUTHOR]