Assessment Of Cultivated Land Quality And The Spatial-temporal Variation In The Region Of Three-river Plain

Three-river(Heilong River,Songhua River and Wushuli River)Plain is rich in cultivated land and natural conditions,which is one of China's major grain producing areas.Due to long-term overuse,this area has suffered by soil erosion and soil degradation and quality decline of cultivated land.These have affected this region's food production.Based on widely collecting the data of cultivated land investigation in 1982 and 2012,using the methods of AHP,Delphi and GIS,this study evaluated and graded the cultivated land quality in 1982 and 2012 in this region by constructing the same evaluation index system of cultivated land assessment in order to analyze the spatial-temporal variation of cultivated land quality.The changes of cultivated land quality in this region have been discussed in past 30 years.The main results were as follows:1.The quality evaluation system of cultivated land was esTablelished,including 13 indices in 4 classes of nature condition,land management,soil physical and chemical properties,soil profile feature.The methods of AHP and Delphi were used to evaluate cultivated land quality in Three-river Plain in 1982 and 2012.2.According to the standards of the Ministry of Agriculture,applying to the method of cumulative frequency curve,the cultivated land quality was classified by ten grades,showing that the area of these grades with the order of Grade 3>Grade 5>Grade 4>Grade 2>Grade 1>Grade 6>Grade 7>Grade 8>Grade 9>Grade 10 in 1982,while Grade 5>Grade 3>Grade 1>Grade 7>Grade 6>Grade 2>Grade 4>Grade 10>Grade 8>Grade 9 in 2012.3.In general,the quality of cultivated land in this area was high.Meanwhile,the qualities of cultivated land in Hegang,Shuangyashan,Jiamusi and Jixi were higher than that in other areas,and the qualities of cultivated land in swamp soil and albic soil were higher than that of other soils.During the past 30 years,the quality of cultivated land showed a decreasing trend,and the percentages of grade 1 to grade 6 were reduced,while others was increased.4.There were differences in soil nutrients variation,affecting the quality of cultivated land.Among them,pH showed a small variation with an average decreased 0.51.Organic matter,available phosphorus and available potassium showed a medium variation with an average of organic matter decreased 2.53 g/kg,an average of available phosphorus increased 14.96 mg/kg and an average of available potassium decreased 93.94 mg/kg.