As a part of the agricultural developments of Paraguay, the soil survey of alluvial lowland in the northwestern area of Lake Ypoa (aout 60 km to the south of Asuncion, the area is 52,000 ha) was carried out. This project area belongs to the subtropical climate zone, and has dry and wet season. The annual average temparature is 22.7℃, and the annual rainfall is 1,420 mm. The Soils of this area were classified into five of soil types, acceding to the observation of soil profiles and the results of soil analysis. Except for V-Type, the another types were inmature soils and they had very weakly developed profiles. I, II, IV-Types had a hard pan under the surface soil. The pan had been preventing air and water movement, and drainage of surface water during wet season. Further, the pan influenced the chemical properties of soils. Their surface soils showed acid reaction, but subsoils showed neutral or weakly alkali reaction and had a large amounts of exchangeable bases. II-Type showed high electoric conductivity in subsoil, because of a large amounts of exchangeable sodium. IV-Type had surface water through the year, differed from I and II Types by the changes of microtopography. III-Type had low clay contents compared with the another soil types, and didn't have the hard pan. It showed acid reaction in all horizons. The dominant clay minerals of I, II, III and IV-Types were Montmorillonite and Illite, and a little amounts of kaolin mineral was contained. V-Type had some cracks in the mollic A horizon at least two or three centimeter wide to a depth of about fourty centimeter during dry season, and a large amounts of clay, exchangeable bases and Montmorillonite as a dominant clay minerals in all horizons. Acceding to the Soil Taxonomy I, II, III and IV-Types were classified into Haplaquent and V-Type was Pelludert. On the other hand acceding to the FAO/UNESCO system, they were classified into Eutric Gleysols, pellic Vertisols respectively.
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