Quanjiu Wang

Mathematical analysis of heat pulse signals for soil water flux determination

[1] Soil water flux is an important parameter in studies of runoff, infiltration, groundwater recharge, and subsurface chemical transport. Heat pulse sensors have been proposed as promising tools for measuring soil water fluxes. To date, heat pulse methods have required cumbersome mathematical analyses to calculate soil water flux from the measured data. We present a new mathematical analysis showing that a simple linear relationship exists between soil water flux and the natural log of the ratio of the temperature increase downstream from the line heat source to the temperature increase upstream from the line heat source. The simplicity of this relationship makes heat pulse sensors an attractive option for measuring soil water fluxes. In theory, this method is valid for fluxes with magnitudes between 10(-4) and 10(-7) m s(-1). The range of measurable fluxes is defined by temperature measurement resolution at the lower end and by the assumptions used in the analysis at the higher end.

Wheat Grain Yield and Yield Stability in a Long-Term Fertilization Experiment on the Loess Plateau

To provide a scientific basis for sustainable land management, a 20-year fertility experiment was conducted in Changwu County, Shaanxi Province, China to investigate the effects of long-term application of chemical fertilizers on wheat grain yield and yield stability on the Loess Plateau using regression and stability analysis. The experiment consisted of 17 fertilizer treatments, containing the combinations of different N and P levels, with three replications arranged in a randomized complete block design. Nitrogen fertilizer was applied as urea, and P was applied as calcium superphosphate. Fertilizer rates had a large effect on the response of wheat yield to fertilization. Phosphorus, combined with N, increased yield significantly (P < 0.01). In the unfertilized control and the N or P sole application treatments, wheat yield had a declining trend although it was not statistically significant. Stability analysis combined with the trend analysis indicated that integrated use of fertilizer N and P was better than their sole application in increasing and sustaining the productivity of rainfed winter wheat.

Modified Green and Ampt models for layered soil infiltration and muddy water infiltration

Soil water infiltration is an important hydrological process at the earths surface. It is connected with both soil water recharge and surface runoff and erosion. While most soil water infiltration models are designed for clean water entering uniform soil profiles, many actual soil profiles consist

A simple model relating soil water characteristic curve and soil solute breakthrough curve

Solute transport through soil may affect groundwater and surface water quality. In recent years, significant attention has been given to prediction of solute transport in soil and groundwater. Solute transport processes are affected by soil pore water velocity distribution. Pore size distribution estimated from water characteristic curves can be used to infer pore water velocity distribution. The objectives of this study were to develop a simple model relating soil water characteristic curves with soil solute breakthrough curves and to evaluate model predictions through comparisons with measured values. Water characteristic and solute breakthrough data for four soil materials were used to evaluate the model predictions. The simple model developed contains two parameters, one relating to pore size distribution and the other to pore connectivity. The coefficient associated with pore connectivity may be set to a constant value for a variety of soil materials. Therefore, there is only one variable parameter in the model. The results of our comparisons indicate that the simple model is useful for relating characteristic curves and solute breakthrough curves. Predicted values are in good agreement with the measured values. This paper provides a simple, approximate method to predict soil solute transport from soil water characteristic curves.

Effects of land use on temporal-spatial variability of soil water and soil-water conservation

Abstract The Loess Plateau of China suffers serious soil erosion primarily resulting from irrational land uses. Soil water plays a critical role influencing vegetation-restoration processes, but varies with temporal and spatial characteristics, of concern to many researchers. However, few studies consider the influence of deep soil water and varied weather patterns in a semi-arid region. Four vegetation types chosen for this study include artificial caragana shrubland, artificial alfalfa grassland, naturally restored vegetation land (Artemisia capillaries, Agropyron chistatum, Heteropapus altaicus Novop, Stipa bungeana, Stipa breviflora griseb and Lespedeza davurica), and bare land. Soil-water content at the top 400 cm depth was monitored continuously from 2004 to 2007 using a neutron probe. Water and wind soil erosion were investigated gravimetrically. Results showed that soil water varied greatly during May through October with different land-use types and annual precipitations. Soil water reached a lower level in both artificial vegetation lands in dry years but recharged with great variation in normal years. Soil water in two other lands tended to have similar changes with less variation as compared with the artificial vegetation lands. Soil water was intensively consumed with depth and continuously decreased in the deeper layers under the two artificial vegetations. The consumption in the artificial caragana shrubland was more intensive, while that in the artificial alfalfa grassland took place at greater depths. The naturally restored vegetation land had less soil-water consumption (close to the level in the bare land) as compared with the artificial vegetation lands. Soil-water content and its variability were increased along the slope with less variation over time. In general, both artificial vegetations effectively reduced the runoff and water-wind soil erosion in the third year after planting, while the naturally restored vegetation consistently showed weak conservation effects in the initial stage.

An Analytical Solution for One-Dimensional Water Infiltration and Redistribution in Unsaturated Soil

Abstract Soil infiltration and redistribution are important processes in field water cycle, and it is necessary to develop a simple model to describe the processes. In this study, an algebraic solution for one-dimensional water infiltration and redistribution without evaporation in unsaturated soil was developed based on Richards equation. The algebraic solution had three parameters, namely, the saturated water conductivity, the comprehensive shape coefficient of the soil water content distribution, and the soil suction allocation coefficient. To analyze the physical features of these parameters, a relationship between the Green-Ampt model and the algebraic solution was established. The three parameters were estimated based on experimental observations, whereas the soil water content and the water infiltration duration were calculated using the algebraic solution. The calculated soil water content and infiltration duration were compared with the experimental observations, and the results indicated that the algebraic solution accurately described the unsaturated soil water flow processes.

Effective raindrop kinetic energy influence on soil potassium transport into runoff

The release and migration of soil chemicals from agricultural lands is both an economic loss and a threat to the quality of surface water and groundwater. Kinetic energy from rainfall is one of the most active factors affecting soil solute transport in runoff. To determine the influence of effective raindrop kinetic energy on soil potassium transfer into runoff, a series of laboratory experiments with different raindrop falling heights and rain intensities was performed. The experimental results indicate that effective raindrop kinetic energy affects soil surface properties and infiltration processes, including infiltration volume and wetting front advance. As effective raindrop kinetic energy increased, the infiltration decreased, the wetted depth decreased, time to initiate surface runoff decreased, and the cumulative amount of runoff increased. The concentration and amount of potassium in runoff increased as effective raindrop kinetic energy increased. There appeared to be a minimum value of raindrop energy to cause splash erosion of soil. The effective depth of interaction (EDI) was calculated, and the results indicated that the EDI increased as effective raindrop kinetic energy increased. Hence effective rainfall kinetic energy influences the whole process of infiltration-runoff-potassium transport, and the amount of potassium in runoff may be decreased by controlling the effective raindrop kinetic energy that reaches the soil surface.

Discrepancy of sap flow in Salix matsudana grown under different soil textures in the water-wind erosion crisscross region on the Loess Plateau

AimsAn accurate understanding about the variation of sap flow and the interaction mechanisms of sap flow with environmental factors is essential when carrying out vegetation restoration projects in areas where rainfall is limited.MethodsA thermal dissipation probe (TDP) measured sap flow of Salix matsudana, growing in typical sandy and loess soils in the same semi-arid watershed on the Loess Plateau, China in 2012 and 2013 from May to October.ResultsSimilar sap flow diurnal variation patterns occurred for both soils but, based on the sap flow, the calculated total transpiration of S. matsudana growing in the loess soil was about five times greater than that growing in the sandy soil due to differences in the sapwood cross-sectional area. Soil texture affected both the vertical distribution of S. matsudana fine roots and the soil water cycle, which led to the S. matsudana growing in the sandy soil being subjected more frequently to drought stress that stunted its growth. In contrast, S. matsudana grew well in the loess soil.ConclusionsSoil texture was the key factor responsible for the discrepancy in the total sap flow of S. matsudana in the study region due to its effect on soil water content. Therefore, if afforestation is planned for this or similar regions, soil texture should be taken into account.

Algebraic model for one-dimensional infiltration and soil water distribution

Soil water infiltration is an important surface hydrological process. Most mathematical models describing soil water infiltration and soil water distribution are complicated. The objective of this paper was to present an algebraic model for one-dimensional transient soil water infiltration. The algebraic model contains three parameters, and the influence of the parameters on the algebraic models was analyzed. A one-dimensional infiltration experiment was performed. Model parameters were determined from the experimental data, and the transient soil water content distributions and the infiltration times were calculated with the algebraic model. The calculated soil water content and infiltration time values were compared with observed data. The results indicate that the model reflects the features of the transient soil water infiltration process.

Influence of 24 annual applications of fertilisers and/or manure to alfalfa on forage yield and some soil properties under dryland conditions in northern China

A field experiment was established in 1984 at Changwu, Shaanxi, China, to determine the long-term effects of three annual fertiliser and/or manure treatments [no fertilisation (CK), application of phosphorus (P) fertiliser alone at 26u2009kgu2009Pu2009ha–1, and application of P fertiliser at 26u2009kgu2009Pu2009ha–1u2009+u2009nitrogen (N) fertiliser at 120u2009kgu2009Nu2009ha–1u2009+u2009animal manure at 75u2009Mgu2009ha–1 (PNM)] to alfalfa (Medicago sativa L.) on forage dry matter yield (DMY) from 1985 to 2008 (24 growing seasons), and some soil properties (moisture content, and concentration of organic matter, total N, total P and available P in soil) in 2001, 2004 and 2006. Compared with the unfertilised CK, application of fertiliser and/or manure resulted in a significant increase of forage DMY in 19 of 24 years, with a maximum DMY usually in the PNM treatment. Cumulative DMY over 24 years (from 1985 to 2008) increased linearly in all three treatments, and it was higher by 22.72u2009Mgu2009ha–1 with PNM and only by 7.78u2009Mgu2009ha–1 with P compared with the CK treatment. Soil moisture contents in deep soil profiles did not differ among treatments in most cases. Soil organic matter, total N, total P and available P in soil increased with fertiliser and/or manure treatments, especially when PNM was applied over a long period. In conclusion, the findings suggest that combined applications of inorganic fertilisers and organic manure to alfalfa can provide substantial benefits in terms of both forage yield and stand longevity, while also improving soil quality on the Loess Plateau of northern China.