Investigation of the Soil Quality Indices in Irrigated Wheat Farms of Nazarabad Region in West of Alborz Province

Awareness of the physical, chemical and biological quality of soil in agriculture and natural resources is essential for optimal land management and achieving maximum economic productivity. Soil has various functions, including crop production ability, carbon storage, water retention, nutrient cycling, water filtering and etc. Thereby, the quality of soils can be taken into consideration depended on the purpose of their use. The soil quality indices are often regional; therefore, a set of indices cannot be used consistently to determine soil quality in all areas. In this study, the Nemero Soil Quality Index (NQI), the Weighted Additive Soil Quality Index (SQIw), and the Additive Soil Quality Index (SQIa) were determined using the total data set (TDS) and minimum data set (MDS) and the impact of properties affecting the soil quality and the yield of irrigated wheat were investigated, in Nazarabad region.

This study was carried out in 26000 hectares of Nazarabad agricultural lands, known as an area with irrigated farms in western Alborz province. The Nazarabad area was sub-divided into a network consisting of 95 squires of 1650 m × 1650 m. The surface soil (0-30 cm) was sampled from the farms located in the middle of each squire (9+5 soil samples from 95 farms) and the irrigated wheat was sampled from 32 farms. Then, soil physical properties including sand, silt, and clay percentages, soil structural stability (MWD), bulk density (BD), particle density, soil porosity (F), field capacity (FC) and permanent wilting point (PWP), available water (AW), saturated hydraulic conductivity (Ks) and soil chemical properties including salinity (EC), pH, organic matter (OM), equivalent calcium carbonate (TNV), available phosphorus )p < sub>ava(, available potassium )Kava(, sodium absorption ratio (SAR) and soil microbial respiration (SMR) were measured. Effective properties on soil quality were selected using SPSS 24 by principal component analysis method (PCA). For this purpose, components with Eigen values greater than one were selected and in each component, properties with high loading coefficient up to 10% lower than the highest loading coefficient were selected MDS affecting soil quality. Then, the Nemero Soil Quality Index (NQI), the Weighted Additive Soil Quality Index (SQIw) and Additive Soil Quality Index (SQIa) were determined using TDS and MDS. For validating soil quality indices, the correlation between the yield of irrigated wheat and NQI, IQIa and IQIw indices were determined in MDS and TDS.

The results showed that the correlation between the soil quality indices (NQI, SQIw and SQIa( using total data set and MDS were significant (p <0.01). In addition, a significant correlation was observed between methods of MDS and TDS in IQIw (r=0.76), IQIa (r=0.73) and NQI (r=0.68) indices. According to the results, there was a significant correlation (p <0.01) between the yield of irrigated wheat and IQIw (r=0.68), IQIa (r=0.67) and NQI (r=0.62) using MDS method; and using total data set method this correlation was 0.61, 0.58 and 0.58, respectively. The results indicated that using NQI, SQIw and SQIa indices based on MDS, 42, 57 and 57% of the study area were in very high quality category and 29, 25 and 24% were in high quality category, respectively. However, using NQI, SQIw and SQIa indices based on TDS, 16, 16 and 18% of the study area were in very high quality class and 42, 39 and 45% were in high quality class, respectively.

The results showed that in Nazarabad region, the yield of irrigated wheat was affected by texture, p < sub>ava, B, SAR, Bd and TNV. There was no significant difference between IQIw and IQIa and NQI indices. In addition, the correlation between soil quality indices based on MDS and total data set was significant, and the correlation between the yield of irrigated wheat and the soil quality indices was stronger while using MDS rather than the use of TDS. Therefore, the use of MDS is more appropriate due to better results and fewer properties and less cost. According to the results obtained from Nazarabad region using NQI and SQIw indices, nearly 82% and 72% of the area are in the very high and high quality class, about 6% and 8% are in the moderate quality class and about 7% are in very low and low quality class, respectively. The studied area is less restricted in terms of physical properties such as soil texture and bulk density. Consequently, due to the high quality of soils in Nazarabad region, it is possible to improve the yield of wheat by proper management.