*2.3. Evaluation Method*

#### 2.3.1. Clarity of Evaluation Object

The "Land Use Status Classification" (GB/T 21010-2007) defines sandy land as land with a surface covered by sand and basically without vegetation. Low vegetation coverage and bare sandy soil on the surface can be perceived through the surface morphology of the land, which is an intuitive and realistic reflection of land degradation. This study defined the existing sandy land as visible sandy land and defines other land use types except the existing sandy land, and its soil texture is sandy soil as invisible sandy land (Figure 2).

All visible and invisible sandy land was considered as the object of investigation and evaluation of sandy land suitable for cultivation. According to the survey results of land use change in Hangjin Banner in 2013, the land use type of sandy land (land type code: 126) was extracted on the geographic information system (GIS) platform as the spatial range of dominant sandy land. The extraction process includes two aspects: one is the extraction of sandy soil. According to the analysis of soil types in Hangjin Banner, the sandy soil types in the soil map were extracted, including mobile aeolian soil, semifixed aeolian sand, fixed aeolian sand, sandy chestnut calcium soil, sandy fluvo-aquic soil, and sandy light brown calcium. There are 9 soil types in total: soil, sandy brown calcium soil, and sandy flood silt soil. The second is the extraction of invisible sandy land. With the help of the spatial superposition function of GIS, the superposition of the obtained sandy soil and the land use types outside the sandy land is the recessive sandy land. For the existing cultivated land, all are considered invisible sandy land (Figure 3).

**Figure 3.** Type and spatial distribution of sandy land in Hangjin Banner.

2.3.2. Construction of the Evaluation Index System

Based on the natural and socioeconomic conditions of Hangjin Banner and combining existing research, this study constructed an evaluation index system for limiting factors of suitable arable sandy land in arid and semiarid regions. Evaluation indicators include land use type and vegetation coverage [31], irrigation conditions [32], ecological conditions [33], and soil properties [34,35] (Table 1).


**Table 1.** Limited evaluation index system of appropriate tillage sandy land.

#### 1. Land use types

The type of index of land use was based on the idea of protective development of sandy land suitable for cultivation and identifies the land use types suitable for cultivation in sandy land. For the purpose of ecological protection, forestland, grassland with high and medium coverage, swamp, and other lands should be regarded as ecological land and should not be reclaimed, while sandy land, saline-alkali land, tidal flats, and other grasslands with irrigation conditions and soil improvement conditions should be evaluated as suitable sandy land.

## 2. Vegetation coverage

In the "Classification of Land Use Status" (GB/T21010-2007) issued by the Ministry of Land and Resources, the vegetation coverage of sandy land and other grasslands in land use types has not been clearly quantified. Through field investigation and the superposition of land use status and vegetation coverage in the internal industry, it was found that there is very-low-coverage vegetation, low-coverage vegetation, and medium–high-coverage vegetation in the grassland and sandy land in the land use status map. For vegetation with different coverage degrees in sandy land, according to the classification of desertification degree in "Technical Regulations for Monitoring Desertification Land" (GBT24255-2009), vegetation coverage ≤ 10% is extremely low vegetation coverage, belonging to mobile sand dunes, and 10% ≤ vegetation coverage ≤ 30% is low-coverage grassland, belonging to semifixed dunes.

#### 3. Ecological conditions

Ecological land plays an important role in ecological security, was used directly or indirectly by humans or other organisms, and mainly plays the role of maintaining biodiversity and the regional environment. The nature reserves, parks, water sources, and tidal flats with an area of more than 100 hm<sup>2</sup> designated by governments are ecological land. Scenic spots, revolutionary sites, cultural heritage reserves, and scenic tourist areas are special human and ecological lands that also need to be protected. Therefore, suitable arable sandy land in these protected areas should not be developed.

#### 4. Irrigation conditions

Water is a necessary condition for plants to synthesize carbohydrates for photosynthesis. During the growing season of crops, the soil must have a certain amount of water supply before it can mature. Soil moisture comes either from natural precipitation or from irrigation. The annual precipitation in Hangjin Banner was between 140 and 340 mm, and the interannual variation is large, so it was impossible to meet the basic requirements of agricultural water demand through natural rainfall. Therefore, taking irrigation conditions as a restrictive index for the development and utilization of sandy land in Hangjin Banner, sandy land without irrigation conditions is not suitable for reclamation.

#### 5. Degree of salinization

Saline-alkaline soil is a general term for soils that contain a certain number of soluble salts and make crops unable to grow and are divided into saline soils and alkaline soils. Among them, saline soil contains a large amount of soluble neutral salt, and the PH value is not very high; alkaline soil contains a large amount of alkaline soluble salt, and the PH value is very high, greater than 9.0. Hangjin Banner has no alkaline soil, only salt, which can be improved by leaching the salt with fresh water. This fresh water could be from water irrigation and precipitation, especially in areas with better drainage systems. However, severe salinization leaching salt improvement consumes more water and costs too much, which is not suitable for arid and semiarid regions. Therefore, severe salinization is classified as unsuitable sandy land.
