Korea is located in the humid temperate climatic zone, affected by the influence of both continental and oceanic air masses. National average annual rainfall is about 1,300 mm, ranging from about 980 mm (Daegu-si) to about 1,440mm (Jejudo).
About 50 ~ 60 percent of annual rainfall occurs during the summer months; July to September, with occasional typhoons. During the summer, although the ambient temperature is high (mean temperature; 20 ~ 25 oC), and crop canopies are thick, the precipitation exceeds the potential evapotranspiration because of concentrated heavy rainfalls. As a result, the base saturation ratio is rather low in the majority of soils. With the exception of some soils developed from alkaline rocks containing large proportion of calcium and/or magnesium carbonates, it typically results in a low soil pH.
Temperatures in the spring and autumn are mild (mean temperatures of 10~15oC) and winter months are rather cold (monthlymean temperature of -5~2oC), particularly in the central and northern regions. During winter, spring and autumn, the rainfalls are much smaller than in the summer. Despite these seasonal differences, the amount of precipitation and the potential evapotranspiration, remain similar all throughout the year because of the lower ambient temperatures in the drier seasons.
Korea is a mountainous country. More than two-thirds of the country is occupied by mountains with steep slopes. Plains are subdivided into inland plains, coastal plains and the plains in the narrow valleys. The plains had been under intensive use for agricultural productions.
The high relief of the land coupled with the heavy downfalls of rain in the summer, affects the characteristics of Korean soil very profoundly. Erosion of soils has been intensive throughout the country for a long time, particularly where the population density was high. In olden days, people in the rural areas used to rely upon the mountains for their fuel and composts for farming. Exploitation of forest vegetations by the people increased soil erosion to such an extent that there are very few mature soils in the country. Continued erosion, has not allowed soil development to occur.
The parent materials of Korean soils are part of about ten recognized geologic systems from different geological time series. Dominant rock types include granitic gneiss (32.4%), granite (22.3%), schist (10.3%), limestone of the Chosun series (Cambrian-Ordovician: 10.1%). The former three geologic systems are present in about 60%, of the land area and are known as acidic rocks.
The fact that the rainfall exceeds the potential evapotranspiration (PET), coupled with the abundance of acidic rocks, results in the wide occurrence of acidic soils in the country. The limestones of the Chosun Group are alkaline, thus the soils derived from these rocks tend to be neutral or slightly alkaline. These soils are only found near Gangwon-do. Some areas contain sandstone bedrock which results in coarse-textured soils. However, even among the soils derived from the same parent rock, textures can vary depending upon the location in the soil catena. Soils developed in higher places tend to be coarse due to severe loss of fine particles by erosion. The soils developed at the locations where soil erosion is not severe tend to be fine-textured..
In Korea, vegetation was not a major factor influencing the soil characteristics even in the mountains. In the past, with the exception of remote areas, forests were heavily used resulting in extremely low soil fertility due to exploitation by humans. During the last three decades or so, mountains in the country have become green because the exploitation forests has stopped as electricity and fossil fuels became widely available in rural areas.
The wide use of chemical fertilizers also contributed for this change. With the convenient fertilizers in their hands, farmers did not need to go to mountains to collect the grasses to make compost. If these trends continue, vegetation in the forests may exert noticeable influence on soil formation in the future. To this point in time, it appears that the influence of vegetation on the characteristics of Korean soils is generally not significant when compared to those of climate, topography and humans.
Undoubtedly time is a very important factor affecting the characteristics of soils. The older the soil, the more mature the soil. Distinct soil horizons reflect the history of the soil. As mentioned earlier, due to unique rainfall patterns and topographical conditions (e.g. mountains with steep slopes) soils in the highland are eroded severely, while soils lying in low land frequently receive new parent material. Either of these conditions does not result in long periods of stability necessary for soils to mature.
It follows that, with the exception of some locations, time is a minor factor in the development of soils in Korea.
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Korean Soils
