The Studies Of Farmland Grading In Longhai Base On GIS

According to Procedures and Rules for Farmland Grading and Regulations for Technological Operations of Farmland (Cultivated Land) Grading ofFujian Province, The paper made an comprehensive and deep investigation on LongHai city's farmland and then selected 110 sample plots to continue following research. The research obtained the first-hand data of farmland grading factors and then compared them with the data getting from the Second National Land Survey (1978). By using the software ARCMNFO and ARCVIEW, the paper graded the farmland according to two sets of data respectively. This paper tries to explore the feasibility of using the data of the Second National Land Survey to the current research by comparing and analyzing two sets of grading results,The investigation shows that though past 20 years, the organic matter content, drainage condition and the thickness of cultivation horizon of Longhai city's farmland have changed obviously. However its topsoil texture, soil profile structure, irrigation assurance, thickness of soil horizon (dry land), elevation, slope degree and soil erosion degree changed within a small extent.Grading results shows that the grading result by the data of the Second National Land Survey differs greatly from that of the current research data. If only the organic matter content or the thickness of cultivation horizon using the data of the Second National Land Survey and the current research data, the grading result has greatly difference. If grading land based on only topsoil texture factor using the data of the Second National Land Survey and the current research data, the differences of the two grading results could be regarded as reasonable error only if we set grading interval on 200 , When grading by only the factor as irrigation assurance, drainage condition or soil profile structure using the data of the Second National Land Survey and the current research data, to make the differences within the extent of reasonable error, the grading interval should be set on 100. Considering the erosion degree, elevation and slope degree of the Second National Land Survey differs little from that of the current research, itsdata can be used as the grading factors.After the research, the paper regards that, to set the grading interval on 150 is a good choice when grading land. By this way, only 18.2% example plots' grading results got by two sets of data differ and the grade result has 6 classes, which can improve the accuracy of grading result by the data of the Second National Land Survey. The paper concludes with the recommendation of using 150 as the grading interval.