Tillage and plant residues influence soil attributes and, consequently, soil quality. Therefore, suitable management and maintaining the stability of soil structure is important. This study was performed to evaluate the effects of tillage systems on soil quality during a 4-year crop rotation (wheat, canola, wheat and tomato) at the Agricultural Research Center of Khorasan Razavi province (Iran) from 2011 to 2015. The study was conducted as a randomized complete block design in a factorial arrangement with 3 replications. For this purpose, conventional tillage (CT), minimum tillage (MT) and no-tillage (NT) systems together with three rates of plant residues (0, 1,500, and 3,000 kg ha-1) were applied annually after harvesting. Soil quality was determined by using the integrated quality index (IQI) and Nemoro quality index (NQI) based on total data set (TDS) and minimum data set (MDS). In total, 23 physical, chemical, and biological soil characteristics were considered as TDS and 7 out of these were selected as MDS for use in the principal component analysis (PCA). Soil quality in different tillage treatments was determined and the most appropriate indices and effective characteristics for soil quality assessment were selected. Correlation coefficients between IQITDS and IQIMDS (r= 0.69) and between NQITDS and NQIMDS (r= 0.76) showed that NQI was a better indicator for assessing soil quality. The NQITDS provided a more accurate and comprehensive assessment of soil quality. However, using MDS reduced the cost and time with proper precision. Soil quality in MT and NT treatments was more desirable than the CT system, and the addition of plant residues improved the soil quality. According to the results of NQITDS, IQITDS, and IQIMDS, soil quality in the NT system with 3,000 kg ha-1of plant residues and the MT system with 1,500 and 3,000kg ha-1 of plant residues were more favorable than other soil tillage treatments. Soil characteristics that decreased soil quality in the conventional tillage were soil structure, macro and micronutrients, while in conservation tillage it was micronutrients, especially Zn.

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