Lei Tingwu

Run off-on-out method and models for soil infiltrability on hill-slope under rainfall conditions

The soil infiltrability of hill-slope is important to such studies and practices as hydrological process, crop water supply, irrigation practices, and soil erosion. A new method for measuring soil infiltrability on hill-slope under rainfall condition with run off-on-out was advanced. Based on water (mass) balance, the mathematic models for soil infiltrability estimated from the advances of runoff on soil surface and the water running out of the slope were derived. Experiments of 2 cases were conducted. Case I was done under a rainfall intensity of 20 mm/h, at a slope gradient of about 0° with a runoff/on length (area) ratio of 1: 1. Case II was under a rainfall intensity of 60 mm/h and a slope of 20° with a runoff/on length (area) ratio of 1: 1. Double ring method was also used to measure the infiltrability for comparison purposes. The experiments were done with soil moisture of 10%. Required data were collected from laboratory experiments. The infiltrability curves were computed from the experimental data. The results indicate that the method can well conceptually represent the transient infiltrability process, with capability to simulate the very high initial soil infiltrability. The rationalities of the method and the models were validated. The errors of the method for the two cases were 1.82%/1.39% and 4.49%/3.529% (Experimental/Model) respectively, as estimated by comparing the rainfall amount with the infiltrated volume, to demonstrate the accuracy of the method. The transient and steady infiltrability measured with double ring was much lower than those with this new method, due to water supply limit and soil aggregates breaking down at initial infiltration stage. The method can overcome the short backs of the traditional sprinkler method and double ring method for soil infiltraility. It can be used to measure the infiltrability of sloped surface under rainfall-runoff-erosion conditions, in the related studies.

Experimental Investigation of Water Use Efficiency under the Mixed Cropping System of Corn with Grasses

A new cropping system of corn mixed with grasses was advanced to make full and efficient use of water and to easy environmental problems in grain and forage feed production practices. Field experiments were conducted to investigate the water use efficiency under this newly suggested model of corn-grasses mixture cropping system at the Farming Mechanization Experimental Station of China Agricultural University. Six treatments with 2 replicates were arranged as: bare field, corn only, rye only, alfalfa only, rye-corn mixture and alfalfa-corn mixture. Lysimeters were used to measure different components of water consumption in the crop fields for water use efficiency estimation with water balance equation. From the yields and water consumption of crops under different treatments, combined water use efficiency of corn and grasses were estimated. The results showed that WUEs in the mixed cropping fields of corn-grasses were much higher than those in the fields where only corn or grass was grown. Averaged WUE was 3.71 kg/m3 from the corn and rye mixture fields, 30% higher than that from the plots where only corn or rye was grown. Averaged WUE was 4.55 kg/m3 from the alfalfa and corn mixture fields, 60% higher than that from the fields where only corn or alfalfa was grown. Under the same conditions of irrigation, yields from the rye and corn mixture plots were increased by 33%, as compared with those from the fields where only corn or rye was grown. And the yields from alfalfa and corn mixture fields were 61% higher than those from the fields where only corn or alfalfa were grown. The experimental results also indicated that corn and alfalfa mixture cropping is better than corn-rye mixture system.

Meltwater erosion process of frozen soil as affected by thawed depth under concentrated flow in high altitude and cold region

Changes in thawed depth of frozen soil caused by diurnal and seasonal temperature fluctuations are commonly found in high altitude and latitude regions of the world. This is of great importance in terms of its impact on hydrologic and erosion processes. There is a need for experimental data to improve our knowledge and modeling of the phenomenon. Laboratory experiments were conducted in Beijing to assess the impacts of thawed depth, slope gradient, and flow rate on soil erosion by concentrated meltwater flow over underlying frozen soil layer. Flumes were filled with soil collected from watershed deposited sediments before being saturated and frozen. After the soil was completely frozen, flumes were taken out of storage to thaw the frozen soil from top to designed depths. Meltwater was simulated with a tank filled with ice cubes to supply water flow at approximately 0 °C. The erosion experiments involved four thawed depths of 1, 2, 5, and 10 cm, three slope gradients of 5°, 10°, and 15°, and three flow rates of 1, 2, and 4 L/min, with seven rill lengths of 0.5, 1, 2, 3, 4, 5, and 6 m. Sediment-laden water samples were collected at the lower end of the flume for determination of sediment concentration which showed that it increased exponentially with rill length to approach a maximum value. The sediment concentrations were closely correlated with thawed soil depth, flow rate, and slope gradient. Shallower thawed depths produced more sediments than thick thawed depths. However, the effect of flow rate on sediment concentration was not as great as slope gradient, which declined with increases in slope gradient. Results from these experiments are useful for understanding the effect of thawed depth on erosion process in thawed soils subject to freezing and for estimating erosion model parameters.