Effects of urea solution concentration on soil hydraulic properties and water infiltration capacity.

Elucidating the effect of fertigation on soil hydraulic parameters and water-solute transportation is fundamental to the design of farmland irrigation systems and their sustainable utilization. Few studies have focused on soil hydraulic parameters or water infiltration characteristics or how they are influenced by urea solution concentration. In this study, the clay loam and sandy loam in Yangling District of Shaanxi Province, China, were used as test soil, and experiments involving seven urea solution concentrations (0.2, 0.4, 0.6, 0.8, 1, 3, and 5 g/L) and a control treatment (0 g/L) were conducted to explore the influence of the various urea solution concentrations on soil hydraulic parameters and water infiltration characteristics. The results indicated that the cumulative infiltration and wetting front migration depth increased with urea solution concentration, as accurately estimated using the Kostiakov model and a power function, respectively. In addition, the coefficients of the Kostiakov model and the power function increased with urea solution concentration. Treatment with multiple concentrations of urea solution resulted in an increase in the volume of macro pores in the soil but a reduction in the volume of mesopores and micro pores in the soil, leading to increases in the saturated water content, saturated hydraulic conductivity, soil water diffusivity, and infiltration capacity and a reduction in the water-holding capacity of the soil. The effect of urea solute potential on the inhibition of soil water movement is small, and this inhibitory effect is far weaker than the improvement effect of the urea solution on soil structure, and hence enhance the soil water infiltration capacity. Our results increase the understanding of soil hydrological mechanisms and may be usefully applied for improving the management of fertigation.

[Effects of attapulgite addition on soil evaporation and crack characteristics]. / å‡¹å‡¸æ£’åœŸæ·»åŠ å¯¹åœŸå£¤è’¸å‘åŠè£‚ç¼ç‰¹å¾çš„å½±å“.

Water is one of the most important factors limiting vegetation recovery and agricultural development in arid and semi-arid areas. The reduction of ineffective soil evaporation can improve soil water use efficiency. As a kind of clay mineral, attapulgite (ATP) plays a critical role in limiting soil evaporation due to its hydrophilicity and adsorption. In this study, three typical soils with different textures (dark loessial soil, cultivated loess soil, and sandy soil) were selected from the arid and semi-arid area of the Loess Plateau, and five ATP additions (0%, 1%, 2%, 3% and 4%) were set for conducting soil evaporation experiments under natural conditions using micro-evaporators to investigate the effects of ATP addition on different soil evaporation processes and the characteristics of evaporation surface cracks. The results showed that the cumulative evaporation and evaporation loss ratio of the same soil decreased with the increases of ATP addition when the ATP addition was <3%. When ATP was added at 3%, the cumulative evaporation and evaporation loss ratio of dark loessial soil and sandy soil decreased, while those of cultivated loess soil increased. When ATP was added at 4%, the cumulative evaporation decreased and the evaporation loss ratio increased for dark loessial soil, the cumulative evaporation increased and the evaporation loss ratio decreased for sandy soil, and the cumulative evaporation and evaporation loss ratio decreased for cultivated loess soil. The average cumulative evaporation of different soils followed an order of dark loessial soil > cultivated loess soil > sandy soil. Soil water content of ATP treatment was consistently higher than that of control throughout the whole evaporation process in the same soil. Simulations of cumulative evaporation versus the square root of time indicated that the amount of water released from the ATP-treated soil samples at the end of evaporation was higher than that of the control. After the addition of ATP, the crack area density of dark loessial soil and cultivated loess soil increased significantly, and the crack area density of sandy soil increased with the increase of ATP addition. The crack area density of all three soils reached the maximum at 4% of ATP addition. In summary, ATP addition of 3% could minimize the ineffective evaporation of soil water.

Characteristics of pulsed runoff-erosion events under typical rainstorms in a small watershed on the Loess Plateau of China.

The pulsed events of rainstorm erosion on the Loess Plateau are well-known, but little information is available concerning the characteristics of superficial soil erosion processes caused by heavy rainstorms at the watershed scale. This study statistically evaluated characteristics of pulsed runoff-erosion events based on 17 observed rainstorms from 1997-2010 in a small loess watershed on the Loess Plateau of China. Results show that: 1) Rainfall is the fundamental driving force of soil erosion on hillslopes, but the correlations of rainfall-runoff and rainfall-sediment in different rainstorms are often scattered due to infiltration-excess runoff and soil conservation measures. 2) Relationships between runoff and sediment for each rainstorm event can be regressed by linear, power, logarithmic and exponential functions. Cluster Analysis is helpful in classifying runoff-erosion events and formulating soil conservation strategies for rainstorm erosion. 3) Response characteristics of sediment yield are different in different levels of pulsed runoff-erosion events. Affected by rainfall intensity and duration, large changes may occur in the interactions between flow and sediment for different flood events. Results provide new insights into runoff-erosion processes and will assist soil conservation planning in the loess hilly region.

Effects of rainfall intensity and slope gradient on runoff and sediment yield characteristics of bare loess soil.

Soil erosion is a universal phenomenon on the Loess Plateau but it exhibits complex and typical mechanism which makes it difficult to understand soil loss laws on slopes. We design artificial simulated rainfall experiments including six rainfall intensities (45, 60, 75, 90, 105, 120 mm/h) and five slopes (5°, 10°, 15°, 20°, 25°) to reveal the fundamental changing trends of runoff and sediment yield on bare loess soil. Here, we show that the runoff yield within the initial 15 min increased rapidly and its trend gradually became stable. Trends of sediment yield under different rainfall intensities are various. The linear correlation between runoff and rainfall intensity is obvious for different slopes, but the correlations between sediment yield and rainfall intensity are weak. Runoff and sediment yield on the slope surface both presents an increasing trend when the rainfall intensity increases from 45 mm/h to 120 mm/h, but the increasing trend of runoff yield is higher than that of sediment yield. The sediment yield also has an overall increasing trend when the slope changes from 5° to 25°, but the trend of runoff yield is not obvious. Our results may provide data support and underlying insights needed to guide the management of soil conservation planning on the Loess Plateau.

Spatio-temporal variation of erosion-type non-point source pollution in a small watershed of hilly and gully region, Chinese Loess Plateau.

Loss of nitrogen and phosphorus in the hilly and gully region of Chinese Loess Plateau not only decreases the utilization rate of fertilizer but also is a potential threat to aquatic environments. In order to explore the process of erosion-type non-point source (NPS) pollution in Majiagou watershed of Loess Plateau, a distributed, dynamic, and integrated NPS pollution model was established to investigate impacts of returning farmland on erosion-type NPS pollution load from 1995 to 2012. Results indicate that (1) the integrated model proposed in this study was verified to be reasonable; the general methodology is universal and can be applicable to the hilly and gully region, Loess Plateau; (2) the erosion-type NPS total nitrogen (TN) and total phosphorus (TP) load showed an overall decreasing trend; the average nitrogen and phosphorus load modulus in the last four years (2009-2012) were 1.23 and 1.63 t/km(2) · a, respectively, which were both decreased by about 35.4 % compared with the initial treatment period (1995-1998); and (3) The spatial variations of NPS pollution are closely related to spatial characteristics of rainfall, topography, and soil and land use types; the peak regions of TN and TP loss mainly occurred along the main river banks of the Yanhe River watershed from northeast to southeast, and gradually decreased with the increase of distance to the left and right river banks, respectively. Results may provide scientific basis for the watershed-scale NPS pollution control of the Loess Plateau.

Application of modified export coefficient method on the load estimation of non-point source nitrogen and phosphorus pollution of soil and water loss in semiarid regions.

Chinese Loess Plateau is considered as one of the most serious soil loss regions in the world, its annual sediment output accounts for 90 % of the total sediment loads of the Yellow River, and most of the Loess Plateau has a very typical characteristic of "soil and water flow together", and water flow in this area performs with a high sand content. Serious soil loss results in nitrogen and phosphorus loss of soil. Special processes of water and soil in the Loess Plateau lead to the loss mechanisms of water, sediment, nitrogen, and phosphorus are different from each other, which are greatly different from other areas of China. In this study, the modified export coefficient method considering the rainfall erosivity factor was proposed to simulate and evaluate non-point source (NPS) nitrogen and phosphorus loss load caused by soil and water loss in the Yanhe River basin of the hilly and gully area, Loess Plateau. The results indicate that (1) compared with the traditional export coefficient method, annual differences of NPS total nitrogen (TN) and total phosphorus (TP) load after considering the rainfall erosivity factor are obvious; it is more in line with the general law of NPS pollution formation in a watershed, and it can reflect the annual variability of NPS pollution more accurately. (2) Under the traditional and modified conditions, annual changes of NPS TN and TP load in four counties (districts) took on the similar trends from 1999 to 2008; the load emission intensity not only is closely related to rainfall intensity but also to the regional distribution of land use and other pollution sources. (3) The output structure, source composition, and contribution rate of NPS pollution load under the modified method are basically the same with the traditional method. The average output structure of TN from land use and rural life is about 66.5 and 17.1 %, the TP is about 53.8 and 32.7 %; the maximum source composition of TN (59 %) is farmland; the maximum source composition of TP (38.1 %) is rural life; the maximum contribution rates of TN and TP in Baota district are 36.26 and 39.26 %, respectively. Results may provide data support for NPS pollution prevention and control in the loess hilly and gully region and also provide scientific reference for the protection of ecological environment of the Loess Plateau in northern Shaanxi.

Assessment of herbicide transport and distribution in subsurface environments of an orange field.

The demand for assessing both the variability of risk areas and the intensity of pollutant load rates on pesticide transferring to waters in China has been increasingly vigorous in recent decades. Therefore, to explore the transport of linuron with rainfall and irrigation in canopy-soil systems, an integrated pesticide transport modeling system has been selected and verified for simulating the three-phase linuron environmental fate in an orange field of the Three Gorges Reservoir (TGR) area. Results demonstrate that spatio-temporal distributions of linuron in surface soil primarily depend on its properties, rainfall, irrigation, and its applications; the peak levels of linuron in subsurface and deep soil are closely related to the cumulative and delayed effects. The findings may be used for policy supporting of soil-water-crop-pesticide management in an agricultural field of the TGR area.

[Texture variation of CC 5052 aluminum alloy slab from surface to center layer by XRD].

For improvement of the processing and gaining uniformity texture structure and performance of direct chill cast CCAA 5052 aluminum alloy band after first hot rolling with different reduction, the material was annealed at 454 degrees C and then cold rolling with different reduction was conducted, the texture at surface, quarter and center layer of the sample was tested and examined by X-ray diffraction method, the data calculated using special software and the difference of texture at surface, quarter and center layer was analyzed. There existed an elevated gradient of intensity from surface layer to center layer after cold rolled with less than or equal to 40% reduction, The main texture of beta is stronger mainly due to transformation from remainder exposure, while the goss and remainder is infirm, the state of texture at each layer is close to each other after cold rolling with reduction high than 56.1%.

[Texture variation of DCAA 5052 aluminum alloy slab at difference position through thickness by XRD].

For improvement the processing and gaining uniformity texture structure and performance the thickness direction of direct chill cast DCAA 5052 aluminum alloy band after first hot rolling with different reduction, the material was annealed at 454 degrees C and then cold rolling with different reduction, we test and examined the texture at surface, quarter and center layer of the sample by use X-ray diffraction method, we calculated the data by use special software and analyses the difference texture at surface, quarter and center layer. The intension gradient of beta texture was along the direction from surface to center layer gradually enhance at different reduction sample. For beta texture, the intension gradient was along the direction from surface to center layer gradually reduce, the volume fraction gradually augment and the intensity gradually were almost equal with the cold rolling reduction increased from 0% to 90%.

[Mathematical simulation of point source average infiltration depth under film hole irrigation].

By using RETC and SWMS-3D software, the point source infiltration characteristics of several typical soils under film hole irrigation were simulated, with the infiltration characteristics and related affecting factors analyzed. One simplified point source infiltration model with the parameters opening film hole rate, film hole diameter, soil clay particle content, and soil bulk density was established, and tested by infiltration experiments with the typical soils from Loess Plateau. It was shown that the infiltration coefficient under film hole irrigation increased with increasing opening film hole rate and decreased with increasing film hole diameter and soil clay particle content, while the infiltration index decreased with increasing opening film hole rate and soil clay particle content. This model could simply and accurately reflect the point source infiltration characteristics under film hole irrigation, and credibly determine the infiltration coefficient and index.