*3.2.3. Surface runoff and soil loss*

Surface runoff was low in 83.51% of the basin soils and moderate to high in 16.49%. In spite of low runoff, a considerable siltation was observed in Çelikli pond, which was attributed to highintensity rainfall causing high water erosion.

The mean predicted annual soil loss was 7.66 tons ha−1 for Çelikli basin. Total soil loss for basin is approximately 8028.42 tons per year with 86.91% of the loss occurring from agricultural areas (73.56% of total land area). Pasture and shrublands contribution to soil loss was 9.51 and 3.58%, respectively. When soil loss was considered in terms of soil depth in the basin, the mean soil loss tolerance values [40] were around 4.5 tons ha−1, which may be accepted as the threshold

level of the basin. In the basin, the agricultural areas are mainly converted from forest and pasture. According to USDA land capability classification, most of the agricultural land-use areas fall under classes VI and VII [24]. In these areas, conventional tillage should not be used. Due to limitations of slope and depth, these areas are mostly suitable for rangeland, pasture, wildlife habitat, or forestland. Although only 14% of the basin is suitable for cultivation, currently 68% of the entire basin is used for agriculture. Surface runoff and soil erosion maps of the study area (**Figure 4e** and **f**) reveal that the area has high potential for erosion, suggesting that measures should be taken to lessen soil erosion in the area.

Globally, soil erosion is responsible for 84% of soil degradation, 56% of water erosion, and 28% of wind erosion [41]. Soil erosion removes the nutrient-rich topsoils. It was pointed out that soil loss by erosion is a widespread global problem and has adverse effects on natural ecosystems such as agriculture, forests, and rangelands [42, 43]. Its effect is accepted as one of the prime environmental problems, impacting water availability, energy, and biodiversity. It causes several environmental damages such as nutrient loss, sedimentation, pollution, and flooding thus impacting productivity and sustainability of the soils [44].

#### *3.2.4. Plant-available water content*

Soil in the study area is generally low in PAWC (**Table 4**). Approximately 50% of the soil had PAWC values of <100 mm, and the PAWC values in the area varied (**Figure 4d**). This implies that the stored water in the soil cannot meet the plant water requirement during the summer months (from June to August) as per calculated daily evapotranspiration for reference crop of 6.4–6.8 mm in Tokat province [45].

Plant-available water content is generally considered as one of the most critical properties of soils, especially in the dry farming regions [46]. In semiarid regions, precipitation is generally scarce in summer, and evapotranspiration needs are not met due to low and improper distribution of the precipitation. Plant-available water content is a limiting factor for the rooting depth [47–49]. The amount of rainwater stored in the soil depends on water-holding capacity of soil in effective rooting depth. The remaining water moves beyond the plant-root zone. Thus, the amount of water held by the soil may be critical in dryland areas.

#### *3.2.5. Other soil properties*

Physical and chemical soil properties of the topsoil and subsoil with 142 and 115 sampling points, respectively, showed a moderate to high variability. Coarse material exhibited greatest variation in topsoils and P content in subsoils. The soil properties were inconsistent in the coefficient of variation by depth. Values of CV for soil properties of EC, pH, K, Zn, Fe, Mn, and CEC were relatively uniform by depth and this could be attributed to the similarity in the distribution of clay in topsoil and subsoil as these variables are mainly controlled by soil clay content and types of clay.


level of the basin. In the basin, the agricultural areas are mainly converted from forest and pasture. According to USDA land capability classification, most of the agricultural land-use areas fall under classes VI and VII [24]. In these areas, conventional tillage should not be used. Due to limitations of slope and depth, these areas are mostly suitable for rangeland, pasture, wildlife habitat, or forestland. Although only 14% of the basin is suitable for cultivation, currently 68% of the entire basin is used for agriculture. Surface runoff and soil erosion maps of the study area (**Figure 4e** and **f**) reveal that the area has high potential for erosion, suggesting

Globally, soil erosion is responsible for 84% of soil degradation, 56% of water erosion, and 28% of wind erosion [41]. Soil erosion removes the nutrient-rich topsoils. It was pointed out that soil loss by erosion is a widespread global problem and has adverse effects on natural ecosystems such as agriculture, forests, and rangelands [42, 43]. Its effect is accepted as one of the prime environmental problems, impacting water availability, energy, and biodiversity. It causes several environmental damages such as nutrient loss, sedimentation, pollution, and

Soil in the study area is generally low in PAWC (**Table 4**). Approximately 50% of the soil had PAWC values of <100 mm, and the PAWC values in the area varied (**Figure 4d**). This implies that the stored water in the soil cannot meet the plant water requirement during the summer months (from June to August) as per calculated daily evapotranspiration for reference crop of

Plant-available water content is generally considered as one of the most critical properties of soils, especially in the dry farming regions [46]. In semiarid regions, precipitation is generally scarce in summer, and evapotranspiration needs are not met due to low and improper distribution of the precipitation. Plant-available water content is a limiting factor for the rooting depth [47–49]. The amount of rainwater stored in the soil depends on water-holding capacity of soil in effective rooting depth. The remaining water moves beyond the plant-root zone. Thus,

Physical and chemical soil properties of the topsoil and subsoil with 142 and 115 sampling points, respectively, showed a moderate to high variability. Coarse material exhibited greatest variation in topsoils and P content in subsoils. The soil properties were inconsistent in the coefficient of variation by depth. Values of CV for soil properties of EC, pH, K, Zn, Fe, Mn, and CEC were relatively uniform by depth and this could be attributed to the similarity in the distribution of clay in topsoil and subsoil as these variables are mainly controlled by soil clay

that measures should be taken to lessen soil erosion in the area.

flooding thus impacting productivity and sustainability of the soils [44].

the amount of water held by the soil may be critical in dryland areas.

*3.2.4. Plant-available water content*

102 Land Degradation and Desertification - a Global Crisis

6.4–6.8 mm in Tokat province [45].

*3.2.5. Other soil properties*

content and types of clay.
