The impact of threshold levels on soil quality indicators in some orchards and paddy fields in the Marvu'ak region, Lorestan province

The present study aimed to compare Integrated and Nemoro soil quality indicators and investigate the impact of determining or not determining critical limits in scoring fuzzy and sigmoidal functions in apricot orchards and paddy fields near the Maru’ak dam in Dorud city, Lorestan province. A total of 20 sites, including 10 apricot orchards and 10 rice fields, were selected for soil sampling. Samples were collected from a depth of 0 to 30 cm, and 16 soil and land properties were identified for the total dataset (TDS). Gravel content, bulk density, texture, salinity, acidity, calcium carbonate percentage, organic carbon, and available nutritional elements including phosphorus, potassium, iron, manganese, zinc, and copper, were measured from laboratory. Slope percentage were also obtained by field observation and google earth software. Principal component analysis was utilized for weight assignment and minimum dataset (MDS) selection. Scoring of soil properties was carried out using fuzzy functions with specified threshold levels for each land use, as well as sigmoid functions without threshold limits. Subsequently, the integrated and Nemoro quality indicators were calculated and classified. Based on the results, soil acidity, available iron, available potassium, and available magnesium were identified as MDS and the most important factors controlling soil quality in the region. For both TDS and MDS, the integrated quality index values were greater than 0.6 (indicating high quality), and the Nemoro quality index values were less than 0.4 (indicating moderate quality). This shows that there is a difference in soil quality evaluation when using various indices. Upon comparing the results, it was found that the MDS indices had similar evaluation to the TDS indices. This indicates that specific properties could be utilized in place of the overall soil properties. Furthermore, the results indicated that the absence of threshold limits in sigmoid functions did not accurately represent the conditions of iron pollution in paddy fields, resulting in slightly higher indices than in orchards. This indicates that establishing threshold limits can greatly impact how results are interpreted and how management strategies are developed. Therefore, experts and researchers must conduct additional research to establish standardized threshold limits for soil characteristics in regions of Iran where such limits are currently lacking.