Soil desiccation in the Loess Plateau of China

Soil desiccation usually takes place below the depth of soil affected by rainfall infiltration (about 1–3 m) with relatively low water content, and is one kind of particular hydrological phenomena in semi-arid and semi-humid regions of the Loess Plateau in China. This desiccation results from the excessive depletion of deep soil water by artificial vegetation and long-term insufficient rainwater supply, which is difficult to disappear with land use change. Due to the influence of global warming during 1950–2000, large-scale vegetation rehabilitation aggravated water scarcity and led to soil desiccation in the deep soil layer in the Loess Plateau. From southeast to northwest, soil desiccation becomes more intensive with lower water content and bigger range in depth due to drier climate and lower water holding capacity. The range of soil desiccation has a close relationship with root distribution of plant, and its intensity varies with the types and ages of vegetation. The climate drought, soil properties and soil water cycle characteristics might be the precondition for the occurrence of soil desiccation, and artificial vegetation with improper type and exorbitant productivity could have accelerated this process in range and intensity. Soil desiccation has obviously negative effects on water cycle in soils, greatly reduces the anti-drought capacity of plants, and heavily influences the growth and natural succession of vegetation. In order to reduce the range, intensity, and negative effects of soil desiccation, proper types of vegetation should be selected according to rainfall and soil water conditions, and the control of vegetation density and productivity should be considered together with soil-water conservation measures.     

A multiple regression approach to assess the spatial distribution of Soil Organic Carbon (SOC) at the regional scale (Flanders,Belgium)

Estimates of the amount of Soil Organic Carbon (SOC) at the regional scale are important to better understand the role of the SOC reservoir in global climate and environmental issues. This study presents a method for estimating the total SOC stock using data from Flanders (Belgium). More than 6900 SOC measurements from the national soil survey (database ‘Aardewerk’) are combined with a digital land use map and a digital soil map of Flanders. The spatial distribution of the SOC stock is studied in its relation to factors such as soil texture, soil moisture (drainage class) and land use. The resulting map with a resolution of 15 m consists of different classes forming a combination of these environmental factors. The results show that the lowest SOC amount (kg m^? 2) is stored under cropland whereas the highest amount is found under grassland. Regarding the effect of soil properties, a significant correlation between SOC stock and depth of the ground water table is observed. Sandy loam soils stock the lowest SOC amount (kg m^? 2), whereas clay soils retain the highest SOC amount. First, the mean SOC amounts of the land use–soil type classes are calculated and assigned to the corresponding cells in order to obtain a total SOC stock with its spatial distribution for Flanders. Then, a multiple regression model is applied to predict the SOC value of a particular land use–soil type class on the map. This model is based on the observed relationships between SOC and land use–soil type characteristics, using the entire dataset. The first approach does not allow to obtain a (reliable) SOC value for all land use–soil type classes due to a lack of samples in some classes. A major advantage of the regression model approach is the attribution of class specific SOC values to each land use–soil type class, regardless of the number of observations in the classes. Consequently, by applying the model approach instead of the mean approach, the area for which a reliable SOC estimate could be obtained increased by 8.1% (from 9420 km² to 10179 km²) and the total predicted SOC stock increased by 10.1% (from 88.7 ± 5.6 Mt C to 97.6 ± 1.1 Mt C).     

Soil salinity reduction and prediction of salt dynamics in the coastal ricelands of Bangladesh

Field experiments were conducted in moderately saline and saline soils during the 1996 dry and wet seasons and the 1997 dry season to document salt dynamics and establish their relationship with local hydrology. Topsoil (0–15 cm) salinity in the dry season varied from 4.0 to 9.0 dS m⁻¹ in moderately saline soils at Mirzapur and from 5.0 to 12.0 dS m⁻¹ in saline soils at Barodanga. In wet season, the corresponding figures were from 1.5 to 2.5 dS m⁻¹ and from 2.0 to 3.0 dS m⁻¹, respectively. Dry season cropping significantly reduced topsoil salinity at both the research sites. Overall peak salinity in non-plowed cropped lands was 25–38% lower than that of fallow lands, and in plowed cropped lands it was about 30–40% less than the non-plowed cropped lands.Multiple linear and non-linear regression models were developed to predict topsoil salinity of the fallow land for both moderately saline and saline soils by using daily rainfall and evaporation as independent variables. The prediction level was not significantly improved when a non-linear model was employed in place of linear model. Therefore, a linear model may be used to predict topsoil salinity of the coastal ricelands of Bangladesh.     

Effects of Pseudomonas fluorescens and fertilizers on the reproduction of Meloidogyne incognita and growth of tomato

A 60-day glasshouse experiment was conducted to assess the influence of two strains of Pseudomonas fluorescens (GRP3 and PRS9), organic manure, and inorganic fertilizers (urea, diammonium phosphate (DAP), muriate of potash and monocalcium phosphate) alone and in combination on the multiplication of Meloidogyne incognita and growth of tomato. Pseudomonas fluorescens GRP3 was better at improving tomato growth and reducing galling and nematode multiplication than PRS9. Organic manuring resulted in less galling and nematode multiplication than occurred with DAP. However, DAP was found better in reducing nematode multiplication and improving plant growth than urea. Muriate of potash was the inorganic fertilizer least effective in reducing galling and nematode multiplication. Pseudomonas fluorescens GRP3 with organic manure was the best combination for the management of M. incognita on tomato but improved management of M. incognita can also be obtained if DAP is used with the GRP3 strain of P. fluorescens.     

Interrelations of yield,evapotranspiration, and water use efficiency from marginal analysis of water production functions

The study uses the concepts of marginal water use efficiency (MWUE), and elasticity of water production (EWP) to reveal the dynamic interrelations of crop yield (Y), seasonal evapotranspiration (ET), and water use efficiency (WUE) based on the functional relation of an ET production function (ETPF). When the ETPF is linear, the changing trend of WUE with ET is directly affected by the intercept of the function, and the EWP will be numerically equivalent to a yield response factor (K_Y) when ET reaches maximum ET (ET_m). When the ETPF is quadratic, the ET needed to maximise WUE is less than the ET for maximum yield (Y_m), and the ET value that occurs at maximum WUE equals the arithmetic square root of the ratio of the intercept of the function to the coefficient of function quadratic term. The interrelationships of Y, ET, and WUE are demonstrated using a quadratic ETPF developed for maize from data obtained in a field experiment.     

Application of fuzzy logic-based modeling to improve the performance of the Revised Universal Soil Loss Equation

This paper discusses the application of fuzzy logic-based modeling to improve the performance of the Revised Universal Soil Loss Equation (RUSLE). An analysis of over 1700 plot-years of data, taken from more than 200 plots at 21 sites in the U.S., showed that soil erosion was not adequately described merely by the multiplication of five RUSLE factor values in all cases. The fuzzy logic-based modeling approach was to make the RUSLE's structure more flexible in describing the relationship between soil erosion and other factors and in dealing with data and model uncertainties without requiring any further information. The approach used in this study consisted of two techniques: multi-objective fuzzy regression (MOFR) and fuzzy rule-based modeling (FRBM). First, MOFR was applied to small subsets of RUSLE factor values to derive the relationship between soil loss and the rainfall erosivity factor within each subset of data. These MOFR models, considered as single fuzzy rules, were in turn linked together in a FRBM framework to form a fuzzy rule set. Then the fuzzy rule set was applied to compute the soil loss prediction corresponding to each combination of RUSLE factors. The model efficiency [Journal of Hydrology (Amsterdam) 10 (1970) 282] of the fuzzy model on a yearly basis was 0.70 while the RUSLE's was 0.58. On an average annual basis, the model efficiency was 0.90 and 0.72 for the fuzzy model and the RUSLE, respectively.     

猪活动区域多孔介质模型及其阻力系数的CFD模拟

旨在尝试将躺卧姿势下的猪体简化成不同几何形状以求取其阻力系数,并分析它们的差异性。本研究采用校核过的CFD模型,模拟探究了简化猪模型、半椭球模型、椭球模型和半圆柱模型4种不同躺卧猪模型对猪群区域在X、Y和Z3个垂直方向上阻力系数的影响,分析了4种模型对猪栏内气流以及压力分布的影响。结果表明,椭球模型的惯性阻力系数相比半椭球模型与半圆柱模型更加接近简化猪模型,其在X、Z和Y方向上的惯性阻力系数与简化猪模型之间的相对误差分别为-4.0%、-12.2%和14.7%,并且气流与压力分布基本一致。因此,采用椭球模型代替简化猪模型进行建模计算不仅能保证准确度还能有效提高计算效率。