Impacts on soil quality from long-term irrigation with treated greywater

Abstract

Drought condition in many places leads to the imperative use of greywater for irrigation. There is a serious concern on the impact of such prolonged uses on soil sustainability. The objective of this study was to evaluate the long-term impacts of greywater irrigation on soil electrical conductivity (EC) and other soil quality parameters in field conditions. Six locations were monitored in this study where home gardens have been irrigated with treated greywater for 2 years. Results showed a general reduction in EC levels of soil samples along all depth intervals at all locations. The average soil EC before greywater irrigation was 0.97 dS/m and decreased to 0.41 dS/m, which may be due to the use of greywater as well as the rainwater effect. The reduction in soil EC and irrigation water quantity shows positive correlation (correlation coefficient r = 0.64). Calcium precipitation might also have a major role in soil EC reduction. Soil calcium content was 81 mg L−1 before using treated greywater and decreased to 43 mg L−1 after 2 years of treated greywater usage, which might have been caused by calcium carbonates (CaCO3) precipitation. The results of other soil chemical analyses clearly show that using treated greywater for irrigation has reduced the concentration of organic matters, K, Cd, Pb, P, Mg, Cl, Na, exchangeable sodium percentage, and sodium adsorption ratio after 2 years of application. Zn concentration increased from 11 to 15 mg L−1, and soil pH became slightly higher from 7.6 to 7.8.