,

Institute of Geography, Henan Academy of Sciences, Zhengzhou 450052, China

Abstract As the existing cultivated land quality evaluation index system is unable to accurately evaluate the quality of cultivated land after land remediation, a modified land use coefficient method was established in this study to calculate the land use coefficient of cultivated land after land remediation. An evaluation index system was first established for the land utilization level of cultivated land in the remediation areas. After that, the land utilization level index before and after the remediation was evaluated separately. The ratio of the two was used as the correction factor to correct the original land use coefficient. The corrected land use coefficient was used to evaluate the quality of cultivated land. The quality evaluation and verification of the land remediation areas in Yuzhou City were conducted. It was found that the land use coefficient corrected by the modified method was more consistent with that calculated by production method 5 years after the project acceptance. It suggests that the modified land use coefficient method reflects the impact of land remediation on the quality of cultivated land, and it is more suitable compared with the production method for the quality evaluation of cultivation land in remediation areas.

Key words Land remediation, Cultivated land quality, Agricultural land grading, Land use coefficient, Yuzhou City

1 Introduction

Land remediation is an effective measure to improve land use conditions and improve the quality of cultivated land[1]. In recent years, domestic scholars have carried out a lot of research around land remediation[2-8]. From the perspective of the impact of land remediation on the quality of cultivated land, a variety of evaluation methods and index systems have been established[9-13]. With the spread of the application of agricultural land grading results, many scholars have begun to study the grading methods of agricultural land to evaluate the quality of cultivated land in the land remediation areas[14-18]. Some scholars have proposed a variety of modified methods for agricultural land grading systems and results[19-25]. Because the evaluation systems are difficult to unify, the compatibility of the evaluation methods and the comparability of the evaluation results are not satisfactory. At the same time, due to the diversity of natural conditions and utilization level of cultivated land in China, in order to ensure the comparability of grading results across the county, the agricultural land grading methods mainly highlight the factors that have a greater impact on the quality of cultivated land. The construction of comprehensive land remediation projects not only has an impact on the natural quality grade of cultivated land, more importantly, it will bring significant improvements to the utilization level of cultivated land. The evaluation factors in the original agricultural land grading methods cannot accurately and sensitively reflect the positive improve effect of land remediation behavior on the quality of cultivation land. At the same time, in the quality evaluation system of agricultural land grading methods, the land use coefficient is used to reflect the utilization level of cultivated land. The calculation method of land use coefficient in theRegulationforGradationonAgricultureLandQuality(GBT28407-2012) (hereafter referred to as theRegulation) is the production method, that is, the ratio of the crop yield of the evaluated unit to the highest yield of the index areas is the land use coefficient. However, it was found through investigation that effectiveness of land remediation cannot be quickly realized after the competition of the project[26]. After the remediation project is completed, it often takes several years for the grain output to gradually reach the optimal output after remediation, and the output after the completion of the inspection does not represent the actual production. The land use coefficient calculated according to the method in the currentRegulationcannot scientifically reflect the land utilization level of cultivated land after remediation. Calculating the land use coefficient by the production method is not reasonable for the cultivated land in the remediation areas.

Aiming at the grading results of cultivated land quality and the characteristics of land remediation projects in Henan Province, the modified land use coefficient method was established in this paper to calculate the land use coefficient after the construction of the land remediation areas. The factors influencing the impact of land remediation projects on the utilization level of cultivated land such as the concentration, flatness, irrigation and drainage conditions, and road accessibility were used as the correction factors of the land utilization level, and the land utilization level correction evaluation index system was established to revise the land use coefficient and grade the quality of cultivated land. This method can more accurately evaluate the impact of land remediation projects on the improvement of cultivated land quality. It is verified that the modified method established in this study is more reasonable than the original production method. The research results can provide technical reference for the compilation of technical specifications for the evaluation of cultivated land quality after land remediation in Henan Province.

2 Overview of remediation areas and source of data

2.1OverviewofremediationareasTaking the land remediation projects completed in Yuzhou City in 2012 as an example, the quality of the cultivated land after land remediation in the project area was evaluated. Yuzhou City is located in the central part of Henan Province, in the transition zone between the Funiu Mountain and the Yudong Plain, and at the junction of the Huanghuai Plain and the hilly area of the western Henan. Its surface landforms are complex, including mountain, hill, plain,etc. The terrain is high in the northwest and low in the southeast. Yuzhou City belongs to northern warm temperate continental monsoon climate zone, with annual average temperature of 14.4℃, average annual precipitation of 650 mm. The standard farming system is winter wheat-summer maize, two seasons a year.

The project areas are located in the Fanpo Township and Xiaolu Township in the south of Yuzhou City. The two project areas are non-adjacent. The construction contents of the two remediation projects were land leveling, farmland water conservancy construction and field road construction. The location of the project areas was shown in Fig.1. The total cultivated land area of two remediation projects was 2 286.64 ha. In one project area, the area of cultivated land was 1 516.05 ha, and the soil type was dominated by meadow cinnamon soil. Before the implementation of the project, the average grade of the cultivated land was 8. In the other project area, the area of cultivated land was 770.59 ha, and the soil type was dominated by podzolized chernozem. Before the construction of the project, the average grade of the cultivated land was 9. As the two areas are large in size and belong to two different townships, the landforms, soil, surface water and other natural conditions and land use conditions are different. The original quality of the cultivated land was also different between the two project areas. Therefore, the cultivated land in the two project areas was evaluated separately in this study.

Fig.1Locationoflandremediationprojects

2.2SourceandprocessingofdataThe collected information includes the following three categories. First, database and maps: the complemented and improved database results of quality grade of cultivated land of Yuzhou City in 2011; annual update results of quality grade of cultivated land of Yuzhou City in 2015; land use change survey database of Yuzhou City in 2015; land use status map, land consolidation planning map, topographic map,etc. in the project areas; soil testing and formula fertilization pilot data of Yuzhou City in 2012. Second, text information: planning and design report and planning and design change report of the land remediation projects in the project areas; statistical yearbooks of Yuzhou City from 2010 to 2013. Third, field survey data: (i) according to the annual upgrade of quality grading results of the cultivated land in Yuzhou City, combining the land use characteristics and topography, a total of 28 plots were arranged, 16 in Piece I and 12 in Piece II, and the information about the land utilization level such as field irrigation and drainage, production cost, field leveling, and road accessibility was obtained through questionnaires in October 2012; (ii) the input and output of typical plots of 575 administrative villages in the county was surveyed on October 2012; (iii) the production of the 28 plots in 2017 was surveyed in June 2017. The location of the plots was shown in Fig.2.

Fig.2Locationofplotsinlandremediationprojectareas

3 Research methods

3.1ResearchideasWith the widespread application of agricultural land grading results and their annual update in land and resources management, the agricultural land grading method has also become a commonly used method for the evaluation of cultivated land quality[27-28]. In this study, based on agricultural land grading method, the modified land utilization level method was established, which not only retains the natural grading method of the agricultural land grading method to ensure the comparability of evaluation results but also adds the concentration degree, flatness, irrigation and drainage conditions and road accessibility that produce impact on the land utilization level into the system. Through the correction of land use coefficient, the change of cultivated land quality brought about by land remediation is accurately reflected.

3.2UpdatingofcultivatedlandnaturalqualitygradingintheprojectareasThe factors included in the original cultivated land quality grading are surface soil texture, organic matter content, irrigation guarantee rate, soil pH, topographic slope, barriers layer depth, profile configuration, and drainage conditions. By analyzing the construction methods of each land remediation project and its impact on the factors for grading of cultivated land natural quality, the property-unchanged stable factors and property-mutated variable factors were determined.

The remediation contents in the two project areas included land leveling, irrigation and drainage engineering, water conservancy construction, field road construction, and farmland protection engineering. The implementation of land leveling and water conservancy construction improved the topographic slope, irrigation guarantee rate and drainage conditions, which are variable factors. The remaining five factors were not influenced by the above four land remediation contents, and they are stable grading factors. The attribute values of the variable grading factors were updated according to the acceptance data of the projects and the field survey data, and the attribute values of the stable factors were as same as those before the remediation.

After the updating of variable grading factors, the natural quality grade index of the project areas after remediation was calculated according to the following formulas:

(1)

Rij=αtj·CLij·βj

(2)

Ri=∑Rij

(3)

whereCLijrepresents the natural quality score of the designated crop in the cultivated land quality evaluation unit;irepresents the code of the cultivated land quality evaluation unit;jrepresents the code of the designated crop;krepresents the code of certain grading factor;mrepresents the number of grading factors;fijkrepresents the value (0-100) of thek-th grading factor of thej-th designated crop in thei-th cultivated land quality evaluation unit;ωkrepresents the weight of thek-th grading factor;Rijrepresents the natural quality grade index of thej-th designated crop in thei-th cultivated land quality evaluation unit;atjrepresents the light-temperature (climate) production potential index of thej-th crop;βjrepresents the yield ratio coefficient of thej-th crop; andRirepresents the natural quality grade index of thei-th cultivated land quality evaluation unit.

3.3Determinationoflandusecoefficientcorrectionsystemintheprojectarea

3.3.1Determination of land use correction factors. The land remediation area will improve the natural quality of cultivated land through the comprehensive management of field, water, road, forest and canal. At the same time, it will also affect various factors affecting the change of land use coefficient of cultivated land quality, thereby improving the utilization level of cultivated land. In order to accurately evaluate the quality level of cultivated land after land remediation, it is necessary to construct a land utilization level evaluation index system to determine the land utilization level of the project area before and after the remediation and to calculate the land use coefficient of the project area based on the modified method that is based on the comparison of land utilization level before and after the remediation.

3.3.2Determination of weights of correction factors. The Delphi method was used to determine the weights of the factors.

3.3.3Calculation of land use correction coefficient. After the determination of the cultivated land utilization level evaluation correction factor system, grading and scoring rules of correction factors, and weights of correction factors, the correction coefficient of cultivated land utilization level for land remediation was calculated according to the following formulas:

(4)

(5)

(6)

3.4Upgradingofcultivatedlandnaturalqualitygradeintheprojectarea

3.4.1Calculation of land use coefficient after land remediation. According to the changes in the land utilization level index before and after the land remediation, combing the land use coefficient before the land remediation, the land use coefficient after the land remediation was calculated according to the following formula:

(7)

3.4.2Evaluation of cultivated land utilization level. After the cultivation of land use coefficient, the utilization grade index of each plot after the land remediation was calculated according to the formula in the agricultural land grading procedure. The formula was as follows:

(8)

Yi=∑Yij

(9)

whereYijrepresents the utilization grade index of thej-th crop in thei-th cultivated land quality evaluation unit; andYirepresents the utilization grade index of thei-th cultivated land quality evaluation unit.

4 Evaluation results

4.1WeightsandscoringrulesoflanduselevelevaluationfactorsinlandremediationregionsThrough consultation with relevant experts in local agriculture, water conservancy,etc., combined with existing research results and project area information, the factors that have a greater impact on land utilization level in land remediation projects were selected, including water source type, irrigation method, drainage method, road accessibility, field flatness, field concentration, and density of forest nets. The description, weights and scoring rules of the factors were shown in Table 1.

Table1Weightsandscoringrulesoflandutilizationlevelevaluationfactorsinlandremediationareas

Evaluation indexWeightIndex characteristics and grading standards ScoreWater source type0.10Surface water100Groundwater80Natural precipitation60Irrigation method0.18Water-saving irrigation100Pipe irrigation80Canal irrigation70No irrigation50Drainage method0.15Natural drainage100Artificial drainage60Road accessibility0.15Good, well-equipped with road system, and easy to produce100Moderate, with roads that have not yet formed a sound system80Poor50Field flatness0.16The field is flat and regular, which facilitates mechanical farming100The field is relatively flat and regular, which does not affect mechanical farming80The field is flat but not very regular, which has little effect on mechanical farming60The field is neither flat nor regular, which makes mechanical farming difficult to be achieved40Field concentration0.18Degree 1, the area of more than 80% of the fields is larger than the countys average100Degree 2, the area of 60% to 80% of the fields is larger than the countys average90Degree 3, the area of 40% to 60% of the fields is larger than the countys average80Degree 4, the area of 20% to 40% of the fields is larger than the countys average60Degree 5, the area of less than 20% of the fields is larger than the countys average40Forest net density0.08≥80%10060%-80%8030%-60%60<30%40

4.2EvaluationresultsofcultivatedlandqualitygradeintheremediationareasBased on the survey results of the 28 plots in the project areas, combined with the land use status of Yuzhou City, the planning and design of the project areas and the acceptance report, the utilization level index value before and after the land remediation was calculated. The representative area weighed average algorithm was used to calculate the utilization level index before and after the land remediation, and the correction coefficient of utilization level after the land remediation was calculated. Combined with the utilization coefficient of each cultivated land quality evaluation unit in the project areas before land remediation, the utilization coefficient of each cultivated land quality evaluation unit in the project areas after land remediation was calculated. Finally, the average of the utilization coefficients of the project areas before and after the remediation was calculated by weighed average method (Table 2).

Table2Landusecoefficientafterlandremediationbythemodifiedlandusecoefficientmethod

Code of project areaBefore land remediationWheatMaizeUtilization level indexBefore remediationAfter remediationUtilization levelcorrection coefficientUse coefficient after land remediationWheatMaizePiece I0.750.7671.8084.001.170.8770.889Piece II0.630.7568.2084.001.230.7500.877

4.3Evaluationoflandutilizationlevelafterlandremediation

Based on the results shown in Table 2, the utilization grade index after the construction of the two projects was calculated. As shown in Table 3, the utilization grade index of the two project areas was increased by 182.26 and 204.89 points, respectively, and the utilization grade was both increased by one grade. By comparing the utilization grade index calculated by the production method and modified utilization level index method, it could be found that the utilization grade index calculated by modified utilization level grade method was improved compared with that calculated by production method.

Table3Changeinlandutilizationgradeafterlandremediation

Code of projectareaBefore land remediationGradeindexGradeAfter land remediationOriginal gradingproduction methodModifiedmethodChange in grade indexOriginal gradingproduction methodModifiedmethodChange in gradeOriginal gradingproduction methodModifiedmethodPiece I1 526.8981 565.691 709.1538.80182.26-+1Piece II1 377.8291 425.261 582.7147.44204.89+1+1

4.4AccuracyverificationofevaluationresultsThrough the survey in 2017, it was found that the production area in the project areas was basically stable in the past two years, and it could be considered that it had reached the normal level. As shown in Table 4, five years after the completion of the project, the crop yield increased significantly compared with that before land remediation. The project areas are located in Fanpo Township, which has the best cultivated land quality in the southeast of Yuzhou City, the yield per unit area of wheat and maize increased by about 1 500 kg/ha compared with that before land remediation. According to the evaluation of cultivated land quality in Henan Province in 2017, the highest yields of wheat and maize were 10 060 and 11 020 kg/ha, respectively. Using the calculation formula of land use coefficient in theRegulation, the land use coefficients of wheat and maize after land remediation were calculated.

According the results shown in Table 2 and Table 4, the following figure was drawn (Fig.3). As shown in Fig.3, the calculation results of the utilization level index method were highly consistent with those of the production method when the project areas reached the normal production level. The land use coefficients calculated by the crop yield in the acceptance year were low. It could be concluded that the utilization level index method was suitable for the calculation of cultivated land use coefficient after land remediation, and the cultivated land utilization grade calculated by this method was more in line with the actual conditions of cultivated land in the project areas after land remediation.

Table4Cropyieldandlandusecoefficientsbeforelandremediation,intheacceptanceyearandin2017

YearYield∥kg/haMaizeWheatLand use coefficientMaizeWheatBefore land remediation6 7507 5000.7180.714In the acceptance year of 20126 7507 5000.7180.7142017 8 2509 0000.8210.816

Fig.3Landusecoefficientscalculatedbythemodifiedlandusecoefficientmethodandtheproductionmethod

5 Conclusions

The comprehensive land improvement project not only affects the evaluation factors of quality of cultivated land. More importantly, it will bring about a significant increase in the utilization level of cultivated land. In the existing agricultural land grading method, the production method is used to calculate the use coefficient of cultivated land, which is used to reflect the utilization level of cultivated land. After the land is remediated, it often takes several years for the grain output to gradually rise to a stable state. The output at the acceptance does not represent the actual output of the land. Therefore, it is not reasonable to use the production method to evaluate the quality of cultivated land in the land remediation project areas.

In this study, the modified land use coefficient method was established to calculate the land use coefficient of cultivated land in the land remediation project areas. The land remediation project areas in Yuzhou City that were accepted in 2012 were selected for cultivated land quality evaluation. The project has been completed for five years and its output has basically reached a stable state. The verification showed that the evaluation results of the modified land use coefficient method were highly consistent with those of the production method when the output reached a stable state. It suggests that the modified land use coefficient method is able to reflect the impact of land remediation projects on the quality of cultivated land, and compared with the production method, it is more suitable for the quality evaluation of cultivated land in the land remediation project areas.