Application of Principle Component Analysis to Identify the Changes of Soil Properties due to Wastewater Irrigation in Margin Lands of Kashafrood River

Water scarcity is one of the important issues in agriculture, especially in arid and semi-arid regions of Iran. Therefore, the challenge for the agriculture in these areas is to find new sources of water for irrigation. One of the ways that has become more common in recent years is the reuse of wastewater as a secondary source and replaces drinking water. The effects of irrigation with wastewater on physical, chemical and biological properties of soil have been studied by many researchers, which most of them are based on the direct use of untreated wastewater in agricultural land irrigation. In fact, a large amount of wastewater used in the agriculture is indirectly entered into the rivers, and used in the agriculture lands. Irrigation with wastewater may have effects on soil properties such as pH, EC, nutrient content, sodicity, pollutants and etc. In order to determine the effect of irrigation by wastewater on soil properties in May 2015, several points of the Kashafrood River in the north of Mashhad were selected. The studied points were located between 59˚36ʹ- 59˚41ʹ E and 36˚19ʹ- 36˚22ʹ N geographical position. The wastewater is refined in Parkandabad station, and used for irrigation. The samples were taken from a depth of 0-30 cm in each point and three replications were regarded for them. Sampling distance was one kilometer from each other. In general, 15 points were irrigated with wastewater were selected. 12 physical, chemical and biological properties including pH, soil texture, bulk density (BD), dispersible clay (DC), mean weight diameter of aggregates (MWD), sodium adsorption ratio (SAR), organic carbon (OC), available phosphorous (P), available potassium (k), total nitrogen (TN), microbial biomass and base respiration (BR) were measured as a total data set (TDS). According to Liu and Chen the main component with an Eigen value greater than one using the PCA method were chosen as minimum data set (MDS). Within each PC, highly weighted properties were defined as those with absolute values within 10% of the highest weighted loading. When more than one variable was retained in a PC, each was considered important and was retained in the MDS if they were not correlated (r < 0.60). Among well-correlated variables within a PC, the variable having the highest correlation sum was selected for the MDS. Data analysis were performed using SPSS Statistics22 software. The results showed that irrigation with wastewater increased biomass and BR, OC, SAR, K and stability index of soil structure. The parameters of K, TN, pH and MWD have been increased compared to the control, but were not statistically significant. Using PCA, five PCs were obtained, which PC1 and PC2 with Eigen value of 50.6 % were the most important components. The parameters of OC, SAR, TN, pH, BD, MWD, BR and K were chosen as MDS due to be changed as a result of irrigation with wastewater. Then, the correlations between these parameters in two groups of irrigated soils with wastewater and control were investigated. Organic carbon in both soil groups had the highest correlation with the SI. The SAR in both soil groups was negatively correlated with nitrogen and phosphorus. Nitrogen in irrigated soils with control was positively correlated with the SI and OC. The MWD was not correlated with any parameter. PH had shown positive correlation with microbial biomass and OC was positively correlated with BR, TN and SAR in soil controls. Potassium in the irrigated soils with wastewater had the negative and significant correlation with OC, SI, BD and MWD. Microbial respiration had a high positive correlation with SI, OC and TN in irrigated soils, which is due to carbon and nitrogen in the wastewater and causes an increase in its amount compared with the control. The results showed that irrigation with wastewater caused a significant increase in parameters SI, SAR, P, BR, MBC and organic carbon in irrigated soil with wastewater and pH, MWD, TN and K had no a significant difference. On the other hand, the principal component analysis of the two groups of irrigated soils with wastewater and control had two distinct groups indicating that the irrigation with wastewater had a significant impact on the soil properties. According to the principal components analysis, eight parameters including OC, SAR, TN, MWD, BD, pH, BR and K were selected as the most important parameters to study the effects of irrigation by wastewater.