**2.2. Soil sampling and laboratory analysis**

yield reduction may affect land degradation directly or indirectly. In the twenty-first century, land degradation is considered an important factor affecting food security. The world's agricultural land that is seriously degraded is estimated to have reached up to 40% [2].

Land degradation in Turkey has been mainly in the form of soil erosion, agricultural mismanagement, deforestation, and overgrazing, and is a result of human activities for the last century. The most prominent result of soil degradation in Turkey has been soil erosion, which develops due to the region's climate, topography, soil, and land-use problems. In Turkey, 59% of rangelands, 54% of forest lands, and 71% of agricultural lands are under active erosion threat [3]. Furthermore, an area of 4.2 million ha has lost its productivity partly or completely due to salinity problems [4]. Topographic and climate conditions have made it necessary to combat soil erosion. In Turkey, 24.1 million livestock graze on pastures, but the pastures can no longer provide sufficient roughage for the livestock to feed, and the existing land cover on pasture areas are used intensively. Overgrazing, especially noticeable in Turkey's Mediterranean, Aegean, Southeastern, and Central Anatolia regions, damages vegetation, increases runoff, and promotes erosion. The surface coverage of pasture areas ranges from 15 and 30%. Severe water and wind erosion are visible in those areas. To avoid soil erosion, surface coverage should be increased in the pasture areas where misuse is taking place—an area of 21.7 million ha. The amount of grazing animals and their grazing time must be brought under control [5]. Land use has changed in significant ways over the last 100 years in Turkey due to agricultural expansion. For example, while pasture areas made up about 56.8% (44.2 million ha) of land use in 1940, today they are only 18.6% (14.6 million ha). Most of changes to land use occurred

The main objective of this study is to evaluate soil degradation regarding wheat yield (WY) as affected by deteriorated soil properties in the Çelikli basin, located in North Central Anatolia

This study was conducted in the Çelikli basin, located in Tokat province, which is known as the transitional belt of Turkey. This area is situated between Central Anatolia and Black Sea

as Entisols, Mollisols, and Alfisols according to Soil Survey Staff [6] and are moderately well to well drained with a slope of 2–12% in the majority of the area. The basin is 1041.2 ha and has an average elevation of 1300 m above sea level. Although native land use of the basin was for pasture and forest, over the last five decades, most of the pasture and forest areas were converted to agriculture. The main crop in the cultivated areas is wheat, which is grown under rainfed conditions. Although 14.07% of the basin is available for agriculture, the dry farming area occupies 67.88% of the basin. The main vegetation type in uncultivated areas is degraded pasture with *Graminea*, *Fabaceae*, and *Labiatae* as the dominant species, occupying 24.86% of the basin. The coverage rate in the degraded pasture areas is about 50%. Other features in the area

21′40″E). The types of soil in the basin are classified

on pasture land that was converted to agricultural purposes [3].

06′31″N, longitude 36o

of Turkey.

**2. Materials and methods**

94 Land Degradation and Desertification - a Global Crisis

**2.1. The study area**

regions (latitude 40o

A total of 142 georeferenced soil samples were taken from topsoil (0–0.3 m) and subsoil (0.3– 0.6 m) (**Figure 2**). Organic matter [8], soil pH [9], lime (CaCO3) [10], electrical conductivity (EC) [11], cation exchange capacity (CEC) [12], textural distribution [13], saturated hydraulic conductivity (HC) (Ks) [14], and volumetric water content [15] were analyzed. Erodibility was calculated by a soil erodibility nomograph [16].

Fractions that were greater than 2 mm in diameter were separated and reported as coarse material (CM) [12]. Saturated hydraulic conductivity (Ks) was measured on undisturbed

**Figure 2.** Locations of soil sampling points in the basin.

cores [14]. Soil penetration resistance (PR) was measured with a cone penetrometer at depths of 0–10 and 30–40 cm [17], and the soil-crusting index (CI) was calculated by Eq. (1) using soil organic matter (SOM), clay, and, silt contents [1]:

$$CI = \frac{100SOM \text{(\%)}}{\text{Clay\%} + Silt\%} \tag{1}$$

Wheat yield was measured at sampling sites. Field capacity (*θ*0.33MPa) and wilting points (*θ*1.50MPa) were determined with a pressure plate [14], and plant-available water content (PAWC) was calculated by Eq. (2):

$$PAW = \left(\theta\_{0.33MPu}\right) - \left(\theta\_{1.50MPu}\right) \tag{2}$$


Na , negligible; VL, very low; L, low; M, medium; H, high; VH, very high.

**Table 1.** Indices determined for surface runoff classes in the study area.

Surface runoff was calculated using slope steepness and permeability of the soils (**Table 1**) [18]. Soil loss was calculated by the Universal Soil Loss Equation (USLE) [19] as

$$A = \text{RKLSCP} \tag{3}$$

where A is the soil loss (Mg ha−1), R is the rainfall factor (MJ mm ha−1 h−1 yr−1), K is the soil erodibility factor (t ha h ha−1 MJ−1 mm−1), LS is the topography factor, C is the crop management factor, and P is the management practice factor.
