Studies on the Percolation Control of Paddy Field Reclamation in the Desertificating Area

The case of eastern edge of Maowusu desert

Abstract

In order to clarify the possibility of paddy fields reclamation in the desertificating area of Maowusu desert in China, two soil samples were made experiments in percoration control of paddy field reclamation in laboratory. One was at Yulin of the progressively desertificating area, and the other was sampled at Lantian of the southen edge of the Loess Plateau.
A well developed system of soil pores that had been produced by plant roots, named as “pore system formed by roots” was observed in Yulin samples by means of the x-ray stereoradiography using contrast medium. The permeability coefficient of undisturbed soil samples were so high that the countermove against excessive percolation will be necessary for paddy field reclamation in this area.
The results of permeabilty tests of compacted soils showed that the permeability coefficients are lower than 10^-6--7 cm/s, Lantian sample which has hight clay content is the same permeability characteristic of compacted soil with Japan's volcanic ash soil and Kanto loam, but Yulin sample which has high fine sand content is somewhat different with Japan's.
We also obtained the following results: the soil for plow layer which contains lower than 9.5% clay content can not be reclaimed to paddy field by puddling ; and the soil for plow layer which contains higher than 6.0% clay content is necessary for Crushing and Compaction Method in this area. It is possible to reclame paddy field by puddling in Loess Plateau becauce the soil clay content gradually increases from the north to the south.