Effects of using wastewater on soil chemical properties under drip

Introduction

The increasing growth of world's population has made the agricultural activities to be synchronized with it in order to increase supplying nutritional materials. Nevertheless, successive droughts in recent years have led the farmers living in dry lands to exploit fresh water resources to its utmost extent in the countries which possess dry lands. Hence, regarding the problem of fresh water shortage in the dry lands and arid areas, the utilization of wastewater can be considered as an alternative approach for irrigation. Also, it can be positively justified through economic as well as environmental issues. In addition, wastewater can be considered as a source rich in mineral and organic materials for fertilizing soil. A plethora of studies have demonstrated that the utilization of wastewater for irrigation enjoys a direct impact on the soil characteristics.

Thereby, the PH level of soil in the lands irrigated with wastewater is significantly lower than the lands irrigated with normal water. Many studies have reported the reduction of soil acidity in the conditions of wastewater irrigation because of the increase in organic materials, the formation of acid intermediate materials and gases such as H2S (Mojiri, 2011). Moreover, the salinity level of soils irrigated with wastewater is higher than normal soils. The results of a number of studies, also, demonstrated an increase in the nitrogen, phosphor, as well as potassium levels in soil; however, the changes in the level of heavy metals have a direct correlation with the years of wastewater irrigation (8 and 11). 

Carrying out their study on the impact of municipal wastewater of Ahvaz (in Iran) on soil hydraulic properties, Hanifloo and Moazed (2007) concluded a significant increase in the saturated hydraulic conductivity coefficient and permeability of the soil surface in comparison to irrigation with Karoon river (in Ahvaz) water. Furthermore, Heidarpour et al. (2007) investigated the influence of refined wastewater on the chemical properties of soil such as electrical conductivity, sodium, calcium, magnesium soluble, nitrogen, phosphorus and potassium, in both surface and subsurface irrigation. The results of the study showed that the utilization of subsurface irrigation causes an increase in electrical conductivity, sodium, and magnesium soluble within the surface level of soil. 

Nevertheless, the changes in the parameters of soil texture, true density, porosity and water penetration are not reported to be significant. Besides, Rezapour et al. (2012) scrutinized the reaction of physical and chemical properties of soil after a long period of irrigation with wastewater in the semi-dry land. They concluded that the utilization of wastewater for irrigation causes the increase of 80 percent hydraulic conductivity, 350 percent of organic Carbon, 100 percent of Nitrogen, and 300 percent of Potassium. Another study carried out by Karimzadeh et al. (2012) indicated that the utilization of wastewater for irrigation causes the reduction of hydraulic conductivity of soil and the increase of soil weight.

Meli et al. (2002) investigated the influence of municipal wastewater on the chemical and microbiological properties of soil in the semi-dry lands. Their study implicated that the utilization of municipal wastewater causes the fertilization and productivity of soil. In another study, Aiello et al. (2007) investigated the impact of refined wastewater on soil properties through exploiting drip irrigation. 

They concluded that the utilization of wastewater causes an increase in the pollution level of microbes as well as a reduction in the porosity and hydraulic conductivity in the soil surface. Furthermore, Zu et al. (2010) evaluated the long-term distance influence (i.e., 20 years) of refined wastewater on agricultural soils. They demonstrated that the utilization of wastewater results in the reduction of PH but a five-percent increase in the heavy metals within the surface. 

In their study, Sacco et al. (2012) scrutinized the seasonal changes in the physical properties of soil under different conditions of irrigation for rice plants. In addition, Blum et al. (2012) investigated the changes in the soil properties of a cane farm after irrigation with refined wastewater within a two-year timeline. They concluded that such changes were significantly much more severe in the first year rather that the second year in terms of chemical properties. SauDakoure et al. (2013) assessed the irrigation impact of industrial wastewater on soil properties. They reported a disorganized soil structure and unsuitable soil physical conditions after irrigation with wastewater. Moreover, Papadopoulos et al. (2014) investigated the organic materials which positively influence the quality of soil physical properties. 

Kerman province enjoys the average annual rainfall of 145 mm and evaporation of 1700 mm; also, this province which is located in Iran suffers from severe limitations in terms of water resources. One of asymmetrical water resources in Kerman is the municipal sewage-processing and wastewater refinery system which was established in 2007. Thereby, more than 20 thousand subscribers has exploited from its refined water. It has been predicted that this refinery system will be exploited to its utmost potential which is 38.5 million cubic meters annually until 2026 (Asdi et al, 2010).

 Hence, considering the aforementioned issues, we can exploit from the municipal sewage-processing and wastewater refinery system, especially in dry and semi-dry lands. In addition, in case this refined wastewater is utilized for farmlands, one can pave the way for saving water, reducing the costs of supplying water, as well as minimizing soil fertilizer consumption. Also, the physical and chemical properties of soil irrigated with refined wastewater in Kerman can be considered as one of the innovations of the present study.

 Meanwhile, no similar study with respect to physical and chemical analysis of the soil in this has been carried out. The present study aims to investigate the refined municipal wastewater of Kerman (in Iran) on the chemical characteristics of soil within the framework of the two methods of drip and furrow irrigation in comparison to well-water irrigation.