Soil management practices can have negative or positive effects on soil quality. Our objective was to assess the effect of long-term agricultural practices by evaluating selected soil physical and chemical properties. Soil samples were collected from two depths (0 to 15 and 15 to 30 cm) within a native pasture and an adjacent agricultural field that was being used for three different crop rotations. Soil quality was quantified using aggregate stability, bulk density, soil texture and available water content as physical properties and pH, electrical conductivity, organic matter and available phosphorus as chemical properties. The farmland soils were functioning at 71 and 70 per cent of their full potential at the 0-to 15-and 15 to 30-cm-depth increments, respectively, whereas those from the pasture were functioning at 73 and 69 per cent, respectively. The assessment showed substantial loss in soil organic carbon following 50 years of farmland cultivation. Tillage and fertilizer applications were presumably the primary reasons for weaker spatial dependence within farmland at the 0-to 15-cm depth. Grazing was postulated as the main reason for weaker spatial dependence within the pasture soils at the 15-to 30-cm depth. Overall, we conclude that 50 years of cultivation has not caused soil quality to decline to a point that threatens sustainability of the agricultural fields.Notes: CV, coefficient of variation; ns, not significant; TOC, total organic carbon; BD, bulk density; EC, electrical conductivity; SQI, soil quality index. a Significant at the 0·01 level. b Significant at the 0·05 level.

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Current agricultural practices and their impacts on the sustainability of crop production can be evaluated by simple and reliable soil structure assessment tools. The study was conducted to determine the effects of long‐term (2006–2017) tillage systems on structural quality of a clayey soil using the visual evaluation of soil structure (VESS) and classical field and laboratory measurements. A field experiment with seven tillage systems, representing both traditional and conservation tillage methods, was conducted on a clayey soil in the Cukurova region, Turkey. Soil samples from 0–10, 10–20 and 20–25 cm depths were analysed for mean weight diameter (MWD), porosity and organic carbon. Penetration resistance (PR) was determined in each treatment plot. The VESS scores (<2) of upper 0–5 cm indicated a good structural quality for all tillage systems. The VESS scores were positively related to PR and MWD and negatively to macroporosity (MaP) and total porosity. In reduced and no‐till systems, poorer soil structures were observed in subsurface layers where firm platy and angular blocky structures were defined. Mean VESS score (3.29) in 20–25 cm depth where PR was 3.01 MPa under no‐till indicated a deterioration of soil structural quality; thus, immediate physical interventions would be needed. Lower VESS scores and PR values under strategic tillage which was created by ploughing half of no‐till plots in November 2015 indicated successful correction of compaction caused by long‐term no‐till. The results suggest that the VESS approach is sensitive and useful in distinguishing compacted layers within the topsoil.

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Information on the spatial distribution of plant nutrients is a prerequisite to predict their behaviour and to monitor the fertility in a watershed. This study was conducted to evaluate variations of plant available potassium (PAK) and non-exchangeable potassium (NEK) of a watershed with different land use and parent materials. Eight hundred soil samples were taken from 0-30 and 30-60 cm depths across the Kazova watershed of 20 656 ha in size. Average PAK was 152.8 mg/K kg in surface layers and 167.2 mg/kg in subsurface layers. NEK was 925 mg K/kg in surface and 167.2 mg K/kg in subsurface layers. All forms of K were the lowest in soils formed over serpentinite. Soils in pastures had the highest PAK and NEK. Both K forms were positively related to clay content. Spatial variability patterns of PAK and NEK were similar and consistent at both soil depths. The variation in parent material and land use is considered as the main cause for large variations of potassium forms.

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Soil salinity is a major land degradation process reducing biological productivity in arid and semi-arid regions. Therefore, its effective monitoring and management is inevitable. Recent developments in remote sensing technology have made it possible to accurately identify and effectively monitor soil salinity. Hence, this study determined salinity levels of surface soils in 2650 ha agricultural and natural pastureland located in an arid region of central Anatolia, Turkey. The relationship between electrical conductivity (EC) values of 145 soil samples and the dataset created using Landsat 5 TM satellite image was investigated. Remote sensing dataset for 23 variables, including visible, near infrared (NIR) and short-wave infrared (SWIR) spectral ranges, salinity, and vegetation indices were created. The highest correlation between EC values and remote sensing dataset was obtained in SWIR1 band (r = -0.43). Linear regression analysis was used to reveal the relationship between six bands and indices selected from the variables with the highest correlations. Coefficient of determination (R2 = 0.19) results indicated that models obtained using satellite image did not provide reliable results in determining soil salinity. Microtopography is the major factor affecting spatial distribution of soil salinity and caused heterogeneous distribution of salts on surface soils. Differences in salt content of soils caused heterogeneous distribution of halophytes and led to spectral complexity. The dark colored slickpots in small-scale depressions are common features of sodic soils, which are responsible for spectral complexity. In addition, low spatial resolution of Landsat 5 TM images is another reason decreasing the reliability of models in determining soil salinity.

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