The slope of gradient has an important role in land conservation and land suitability. The composition of the developed soil, structure, biomass, density of the plant community is strongly influenced by the slope (Albaba, 2014). Large slopes are a serious threat to land degradation (Andrian, Supriadi, & Marpaung, 2014) when linked to land conservation. The greater the slope of the slope will automatically increase the surface runoff, so the greater the energy of the surface water (run-off) (Martono, 2004), as a result, a lot of soil grains are carried away by these currents. This condition clearly disturbs the plants above it, thus affecting plant growth and productivity (Nadal-Romero, Petrlic, Verachtert, Bochet, & Poesen, 2014).
The ideal depth of soil effectiveness in the field is difficult to find because of the influence of dredging on the surface soil by bauxite mining activities, however, in some, places it can still be found and can be measured in several places. For adjacent soil drainage with water drainage both in and in the soil, the drainage in (internal) is influenced by the size of the grain (texture). The bigger the grain or coarser the texture of the soil, the better the deep drainage. External drainage is influenced by the slope of the slope, the more sloping the slope the better the outer drainage.
Soils that have poor drainage are marked with the surface layer and the soil at the bottom layer has a gray color with spots due to water stagnation on the surface of the soil (Abd-Elmabod et al., 2017). Poor drainage affects the reduction of nitrogen (N), which is needed by plants (Stout & Schnabel, 1994). Soil that is moderately well drained is characterized by the absence of yellow, brown, or gray spots on the top and bottom layers. Soil that has good drainage is marked from the top layer to the bottom layer and has a bright color and does not have yellow, brown, or gray spots.
Soil sensitivity to erosion (soil erodibility) in the study area ranges from 0.21 to 0.63 (in terms of erosion sensitivity is moderate to very high). Soil erosion sensitivity (soil erodibility) is only one of several components/factors that influence erosion. Other factors are climate, slope length and slope, land cover (land cropping), and land management. Soil erodibility variations were significantly influenced by the thickness of the biological layer, soil mass density, organic matter content, plant litter density, and root mass density (Wang, Liu, & Zhang, 2011). Based on the results of the field survey, it is known that the rock and gravel content ranges from 0.01–90%. Rocks and gravel have an influence on land capability, namely inhibiting plant growth. Plants do not develop properly because of the distribution of rocks and gravel in the soil layer and on the land surface.
For the threat of flooding to occur during one month of the year, the land is always inundated by floods for more than 24 hours. The threat of flooding or inundation is caused by deep drainage and poor surface drainage. The infiltration and percolation processes are hampered due to the presence of soil texture or the size of the soft soil grains, meanwhile, the surface grinding is also hampered due to the flat to gentle slope.
Water availability capacity has a very important role. High water availability capacity is very beneficial for soil density, soil permeability, and soil strength and structure. High soil density, high soil strength, low permeability, massive non-granular soil structures, and blocks reduce water capacity thereby limiting plant roots (Uhland, 1951) and root distribution over the entire soil mass. The ability of soil to provide water is needed by plants. In general, in a lot of open land conditions in ex-mining areas, the ability of the soil to store water is greatly reduced. However, an assessment of the capacity of water availability is necessary to determine the capacity of the land.
In areas where it rains frequently and supplying the land with more water, available water capacity is not very important. However, the condition of the former mining area which is wide open where the falling water becomes runoff and with high heat causes high evaporation, the falling rain is not sufficient to supply groundwater. However, in areas where crops emit more water than the amount provided by rainfall, the amount of available water that the soil can provide is very important. Water is needed to support the needs of plants.
Soil properties that affect water are soil texture and organic matter. Soil that has a fine soil texture has a high to very high water storage capacity and vice versa. Rock fragments reduce the capacity of available water in direct proportion to their volume unless the rock is porous. Soil that has a fine texture can bind more water. This is because soils with fine textures have a larger surface area than coarse-textured soils. Bulk density plays a role by controlling the pore spaces that hold the available water. In areas where it rains every day and supplies the soil with as much or more water than the plants remove, the available water capacity is not that important. However, the condition of the former mining area which is widely open, where the water that falls a lot becomes runoff and with high heat causing high evaporation, the rain that falls is not enough if it is only used as a supply factor for groundwater availability.
In areas where plants emit more water than the amount supplied by rainfall, the amount of available water that the soil can provide may be very important. This water is needed to sustain crops between rainfall events or irrigation periods. Soil effectively supports the root environment of the plant against periods of water deficit.
Soil properties that affect water are soil texture and organic matter. Soil that has a fine soil texture has a high to very high water storage capacity and vice versa. Rock fragments reduce the capacity of available water in direct proportion to their volume unless the rock is porous. Soil that has a fine texture can bind more water. This is because soils with fine textures have a larger surface area than coarse-textured soils. Bulk density plays a role by controlling the pore spaces that hold the available water.