自然土壤类型对近50年三江平原农田化过程的影响

The Effect of Soil Types on the Process of Farmland in Sanjiang Plain in Recent 50 Years

土壤、地形等因素对农田的分布有着重要影响。本文基于三江平原1954年～2005年5个时期土地利用数据、土壤数据和DEM，通过使用Rough集理论进行重要性测度计算，发现三江平原农田化过程中，土壤类型的影响要大于地形因子的影响；地形特征中，坡度对农田化过程的影响程度较大，高程与起伏度的影响相当。从土壤类型影响农田化过程的空间分布特征来看，在三江平原农田大幅度扩张期间，农田开发总体呈现出逐渐由松花江上游地区向下游地区过渡的趋势，土壤类型的开发也由分布于地势较高地区的草甸土向地势低洼地区的白浆土、沼泽土变化。从时间变化来看，随着三江平原不断地进行拓荒开发，草地、林地与沼泽湿地被大面积地开发为农田，使得相应的草甸土、暗棕壤、白浆土和沼泽土的农田开发比重越来越大，并且随着上世纪80年代三江平原地区水稻种植面积的增加，白浆土和沼泽土的农田面积比例进一步增大，2000年以后土地垦荒状况基本趋于稳定。

The soil map, DEM and land use maps of 5 periods derived from relief map, MSS and TM images are used to analysis the effect of the natural soil type to the process of farmland in Sanjiang Plain. The importance of different factors to the system made up of the soil type, terrain factors and process of farmland is analyzed based on the Rough Set Theory to indicate that the soil type influenced much more than the terrain factors. From 1954 to 2005, the land use/land cover changed greatly. The area of farmland increased 40 467.33 km^2, while the marsh wetland, forestland and grassland lost 22 831.30 km^2 ,13 691.34 km^2 ,6 143.52 km^2 correspondingly. The main nature soil types of Sanjiang Plain are dark brown soil, meadow soil, lessive, swampy soil and black soil, the sum of whom coved 88.53 % of the area. The meadow soil, lessive, swampy soil and black soil are mainly distributed on the plain while the dark brown soil always appears on the mountain and hilly area. In the process of farmland expansion period from 1954 to 1986, the area of farmland increased from 13 173.70 km^2 to 45 112.78 km^2 with a faster speed than other periods. From 1954 to 1976, the new farmland was reclaimed on the fluvial terra of Songhuajiang River where is widely covered by meadow soil and swampy soil ; from 1975 to 1986, the new farmland was reclaimed on the plain lied in the front of piedmont of the Wanda Mountain where is widely covered by lessive and swampy soil. After 1986, the new farmland emerged shows no obvious spatial distribution pattern. The ratio of the farmland area on one soil type to the area of that soil type reflects the reclamation intensity on different soil types. Up to the year of 2005, the reclamation intensity followed this turn： black soil 〉 lessive 〉 meadow soil 〉 swampy soil 〉 dark brown soil. Till 2005, 78.58 % of the dark soil had been reclaimed for farmland because of the fertileness and vantage location, while only 20.89% of the dark brown soil was reclaimed because reclamation on such soil type is limited by the agriculture technology and protective policy. Then the ratio of the farmland area on each soil type to the whole area of the farmland is analyzed. Meadow soil is one of the main soil types of Sanjiang Plain., and the ratio of farmland area on it is great in every period because its fertility and convenience for agriculture. From 1954 to 2005, the. ratio of farmland on the lessive soil and the swampy soil increased greatly from 15.97% and 2.35% to 24.64% and 13.72% separately, the ratio of farmland on the dark brown soil increased 6.12 percent as well, and the ratio of farmland area to the area of the black soil decreased from 15.97% to 10.72%. Reclamation on the other soil types made the ratio of farmland on the dark soil decreased because of its poor quantity. After the year of 2000, the r reclamation on Sanjiang Plain gets to be stabile.