Improving soil quality, sustaining high crop yields and conservation environment are the main goals behind soil quality assessment. Soil quality indexes (SQI) serve as efficient decision tools for agriculture managers, scientists and policy makers to choose appropriate management practices for sustaining land and yield quality. The aim of this study was to evaluate soil quality by using three common SQI models: additive, weighted and principal component analysis (PCA). Seventy-two soil samples were collected during two years (2016 and 2017) from three walnut orchards in Erbil Province, Iraq. SQI values varied from low (<0.5) soil type in location 2 (Malakan village), low (0.35) to moderate (0.72) in location 3 (Choman District) and from low (0.32) to high (0.83) soil type in location 1 (Shaqlawa District). According to weighted SQI, the highest main contribution percentage root growth capacity (RGC) 35% and the lowest contribution percentage storage water capacity (SWC) 3% were estimated in the Malakan location. Results indicate that the PCA-SQI model is more convenient for selected soil indicators to minimum data set (MDS) than additive and weighted SQI for evaluating soil quality.

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