County-level Arable Land Grading Test Based On Grading Control Unit

The main task of Third National Land Survey and Evaluation of Arable Land,taking the province as a unit,is to comprehensively update the results of arable land grading and create a special database of arable land grading on the basis of improving the parameter system and the existing data of Investigation and Evaluation of Arable Land Grading,then in summary to form the national results of arable land grading gradually.Among them,improving the existing basic data of Investigation and Evaluation of Arable Land Grading puts forward higher requirements for the accuracy of Grade Evaluation of Arable Land Quality in China.It is necessary to check and ensure the accuracy of the original grading results,and form the grade control unit map,and then control the arable land map of Third National Land Survey.This study based on the realistic work needs of the investigation and evaluation of arable land grading in Third National Land Survey,starting from the aspects of gathering results and the index areas of grading factors,drawn up two kinds of grade control unit maps,which are Polygon Merging Method and Grading Factors Map Superposition Method.For the sake of verifying the feasibility of the programming of grade control unit map,selecting Wen County,a typical plain county-level city,carry out the Rationality Analysis of Factor Selection and Indicator Value Verification and the trial calculation of grading based on its results of grading in 2016 to form the grade control unit map,and then carry out the trial calculation of the grading of arable land polygon in Third National Land Survey.It provides reference and technical support for Evaluation of Arable Land Quality Grade in Third National Land Survey.The main conclusions are as follows:(1)The index values of grading factors based on the interpretation of soil map are credible.According to the existing soil census results in Wen County,there are some inconsistencies between the surface soil texture attribute values in the database of grading and the interpretation results in some regions.After investigation,it is confirmed that the database of grading lacks the currency,which need to be corrected.(2)Correcting the results of arable land quality grade in 2016 is the precondition for the accuracy of arable land grading in Third National Land Survey.Firstly,the results of arable land grading of Wen County in 2016 were tested,and it was found that there were historical errors in the calculation,which needed to be corrected to form an accurate reference basis for grading.Secondly,it was found that the attribute values of grading factors are not in conformity with the realistic situation,and needed to be corrected to ensure the accuracy of arable land quality grade.(3)It is necessary to carry out trial calculation to discuss the applicability of the parameter system in Investigation and Evaluation of Arable Land Grading in Third National Land Survey.The new light-temperature productivity potential index and productive ratio given in the draft of third National Land Survey Office on the parameter system have far more influence on the quality of arable land than the adjustment of grading factors index value.Utilizing the adjusted parameter system to carry out the trial calculation and find the grade is reduced by one grade.Therefore,it is necessary to demonstrate the applicability of light-temperature productivity potential index and productive ratio coefficient in County level.(4)The programs of grade control unit is feasible.Polygon Merging Method and Grading Factors Map Superposition Method can realize the control of arable land grading in Third National Land Survey.The quality of arable land in Wen County Grading Control Unit is 6-7 grade,and the quality of arable land in Third National Land Survey is 5-6 grade,the distribution of the grade has spatial consistency,spanning only one grade.