| China is amongst the countries suffering serious water and soil losses, especially in the arid and semi-arid areas including the Loess Plateaus.In arid and semiarid climate areas, water and soil losses are dominant reasons for poor harvest and degradation of land and ecological environmental systems. Soil crust, a common phenomenon for many soils worldwide, plays an important role in water and soil losses. Soil seals and crusts can significantly reduce soil infiltration rate and subsequently lower the utilization of water resources, increase runoff, and induce heavier soil erosion. The objectives of this study were: i) to understand the mechanism of applying polyacrylamide (PAM) to control crust formation, to increase infiltration and reduce soil erosion; and ii) to quantify the dynamics of soil erosion processes with rare earth elements (REE) tracers.Experiments were conducted with rainfall simulation under laboratory conditions. Experimental soil used in this study was from Inner Mongolia, typical loess sampled from top layer of cultivated soils. The bulk density was 1.2 g cm-1. The soil contents about 60% of silts and about 15% of clays. A slope adjustable flume of 3 by 8 m was subdivided into 15 mini-flumes of 0.2 by 8 m. The experiments involved three different rainfall intensities (50, 100, and 150 mmh-1); four slopes (8.74%, 17.63%, 36.4% and 46.63%), four (%???) soil surface treatments (one control and three PAM coverage rates: 80%, 60%, 40%). And 8 REE elements: Dy, La, Sm, Yb, Ce, Eu, Nd and Tb were applied in sections upon the slope. Each individual experiment run was divided into two consecutive storms. After the first storm, the soil was set for 24 h before the second rainstorm. Three replicates were adopted for each individual experimental treatment.A corn field experiment was conducted at Qingshuihe near Huhehot, Inner Mongolia. The experiment fields, with slope of 5% to 7%, were consisted of eight adjacent rectangle plots sized about 10 by 16 m. The experiment applied four soil surface treatments (one control and three PAM coverage rates: 80%, 60%, 4%). After corn seeds were planted, granular PAM mixed with loess soil was spread to cover the soil surface. Two replicates were adopted in the experiments.Scanning electric microscope (SEM) photographs were used to examine the structure of surface soil experienced a rainstorm, for the purpose of understanding the mechanism of soil crusting. It approved that soil crusting consists of depositional crust and structural crust. The curves of infiltration with time revealed four stages of crust formation. Crust significantly reduces soil infiltration rate and subsequently lowers the utilization of water resources, and increase runoff, which induce heavier soil erosion.PAM treatment can prevent the disintegration of soil aggregates, even improve thestructure of soils and prevent crust formation. PAM, with high viscosity, can significantly increase water infiltration. Analyses were made to relate infiltration rates with PAM coverage and describe impacts of PAM application on infiltration.Experimental results showed that the soils treated with PAM had better and stabile properties. PAM is able to cohere strongly the soil particles at the surface to form bigger aggregates, therefore to significantly increase infiltration and reduce soil erosion. Analyses were made to relate soil erosion with PAM coverage and describe impacts of PAM application on soil erosion.The cornfield experiment showed that PAM could significantly reduce runoff and increase infiltration of rainwater and increase soil water content. Corns planting in the soils treated with PAM were taller and more vigorous, with higher mass produced.The REE tracing of dynamic processes of soil erosion revealed soil erosion mechanism in details. The occurrence and development of soil erosion along slope were showed clearly. From the changes in soil erosion upon the slope, the dynamic processes of runoff and soil erosion along slope was analyzed.With REE to trace the processes of... |
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