Effects of the Dicranopteris linearis root system and initial moisture content on the soil disintegration characteristics of gully erosion

Benggang erosion is caused by a special type of gully erosion in southern China that seriously endangers the local ecology and environment.In this study,typical Benggang collapsing-wall soils were used as the study area to investigate the effects of different initial moisture contents and dicranopteris linearis root weight densities,as well as their interactions on disintegration in orthogonal test method.The results showed that the rate of soil disintegration decreased as a linear function of the initial moisture content.The soil disintegration rate tended to rise and then fall as the root weight density increased,reflecting an optimum root weight density of 0.75-1.00 g/100 cm3.The incorporation of dicranopteris linearis roots was most effective for soil consolidation in the shallow layers of soil.In addition,the disintegration rate of the collapsing-wall soils increases as the soil layer deepened.The dicranopteris linearis root system and initial moisture content had an interactive effect that was more pronounced in deeper soils.However,the combined effect of these processes was always dominated by the initial moisture content.Moderate initial soil moisture content(0.20-0.24 g/g)and the addition of a high root density in dicranopteris linearis(0.75-1.00 g/100 cm3)were the optimal combinations that reduced the disintegration rate.In conclusion,maintaining a suitable natural moisture content in collapsing-wall soils and taking measures that use plants to consolidate soil can effectively prevent and control the occurrence of Benggang erosion.The results of this study provided further insight into the factors that influence soil disintegration and offered a scientific basis for soil erosion management in the southern China.

Effects of initial soil moisture content on soil water and nitrogen transport under muddy water film hole infiltration

Film hole irrigation has been widely adopted as an effective water-saving irrigation technology in the arid and semiarid areas of China.To investigate the effects of initial soil moisture content(θ0)on soil water and nitrogen transport characteristics under muddy water film hole infiltration,the laboratory experiments were conducted with muddy water film hole infiltration,using five initial soil moisture content treatments.The models for describing the relationships between the cumulative infiltration(I(t))and infiltration duration(t);the relationship among the horizontal and vertical migration distances of the wetting front(Fx,Fz),θ0 and t,were established.The results showed that the initial soil moisture content had a significant effect on I(t),Fx,Fz and moisture content distribution in the wetted body.The change of I(t)over t conformed to Kostiakov model.With the increase ofθ0,the infiltration coefficient(K)gradually decreased.NO-3-N was mainly distributed in the range of the wetting radius of 15 cm,while NH+4-N was mainly distributed in the range of the wetting radius of 8 cm.This study can provide a theoretical basis and technical support for film hole irrigation.

Isothermal diffusion of water vapor in unsaturated soils based on Fick’s second law

In arid regions, water vapor diffusion predominates the total water migration in unsaturated soil, which significantly influences agriculture and engineering applications. With the aim of revealing the diffusion mechanism of water vapor in unsaturated soil, a water vapor migration test device was developed to conduct the water vapor migration indoor test. The test results demonstrate that the characteristics of water vapor diffusion in unsaturated soil conformed to Fick’s second law. A mathematical model for water vapor diffusion under isothermal conditions in unsaturated soil was established based on Fick’s law. Factors including the initial moisture content gradient, initial moisture content distribution, soil type and temperature that affect the water vapor diffusion coefficient were analyzed. The results show that there was good agreement between the moisture content calculated by the mathematical model and obtained by the indoor experiment. The vapor diffusion coefficient increased with increasing initial moisture content gradient and temperature. When the initial moisture content gradient is constant, the vapor diffusion coefficient increases with the increase of matrix suction ratio in dry and wet soil section. The effect of soil type on the water vapor diffusion coefficient was complex, as both the moisture content and soil particle sizes affected the water vapor diffusion.

Characterization of Okra Convective Drying, Influence of Maturity

An experimental study for the drying kinetics of whole okra was carried out. In the study, different ages were considered by taking into account influence of okra maturity on its convective drying. The 2D moisture evolution inside the product and its maturity were evaluated by fitting experimental data versus drying time. The water effective diffusion coefficient of okra at different maturity states was gotten by the experimental model using Fick’s second law. A parametric study was carried out in the ranging of okra age from 2 to 7 days at 60℃, both fruits gathered on the same plant to avoid divergences due to okra varieties that can induce difference on physical structure and the chemical composition. It was found from the experimental results that okra maturity has important influence on its behaviour during convective drying. At 2, 3, 4, 5 and 7 days old, the drying effective time was respectively 780, 1000, 1155, 850 and 750 min. Effective diffusivity of the okra in this order of age was 1.38 × 10-10, 6.09 × 10-11, 1.23 × 10-11, 8.98 × 10-11, and 1.05 × 10-10 m2/s in the present study, while the average initial moisture content was respectively 12.27, 9.00, 7.53, 5.97 and 4.92 Kgw/Kgdm.

Study on drying rate in contact drying with flexible screen

The moisture contents (MC) of popular veneers were tested in Composition Board Laboratory of Northeast Forestry University by contact drying with flexible screen. The influence factors considered included temperature, initial moisture contents (IMC), and veneer thickness. Veneer-drying laws under different hot press conditions were analyzed. The results showed that the drying rate increased with temperature rising. 160°C was considered to be more efficient than 140°C and 180°C because excessive high temperature has no significant contribution to drying rate. IMC had significant effect on drying rate. The veneer with high IMC had a higher drying rate at above fiber saturation point (FSP) and a lower drying rate at below FSP, compared to the veneer with low IMC. Average drying rate also varied with thickness in power law.

Temperature characteristics of wood during microwave treatments

In order to investigate the temperature characteristics of wood during microwave(MW) treatments,optical fiber sensors were used to measure wood(Pinus sylvestris L. var. mongolica Litv.) temperatures. The results show that the development of internal temperatures in wood basically includes two patterns during the process of MW treatment. The first may be divided into three phases: warming, constant temperature, and a sharply rising phase. The second pattern may be divided into two phases: warming, and constant temperature. The maximum temperature(MT) and rate of temperature increase(RTI)rose as the microwave power increased. The initial wood moisture content decreased while the period of constant temperature fell. Temperatures varied in different positions in the wood. The order of MT and RTI levels were the upper surface, center, bottom surface and the end point.Along the direction of wood thickness, the closer the monitoring point was to the generator, the faster the temperature increased. The MT and RTI of the end point was a minimum value because of the rapid removal of steam.