The combined effects of treated wastewater irrigation and plastic mulch cover on soil and crop microbial communities

Global water scarcity necessitates the use of treated wastewater (TWW) for various purposes, including agricultural irrigation, yet this water may introduce various contaminants to the soil and crops. Therefore, application of TWW irrigation was sanctioned by barriers (drip irrigation and plastic mulch) to reduce risks to consumers; however, barriers’ effect on soil health is controversial. We hypothesized that the combination of TWW irrigation with plastic mulch barrier would alter the soil microbial community (bacteria and protists), while TWW irrigation alone would have a negligible effect. To test our hypothesis, we compared the response of soil and crop (cucumbers and melons) microbiomes to water qualities (TWW and potable water (PW) applied by drip irrigation in combination with plastic mulch during two growing seasons. The abundance, diversity, composition, and predicted functions of the water, soil, and crop microbial communities were analyzed in 230 samples, concomitant to monitoring the physicochemical parameters. TWW had significantly higher nutrients and salinity than PW but did not differ in pH. TWW-irrigated soils were significantly more saline than PW-irrigated soils, particularly under plastic cover, but all other physiochemical parameters were similar. The microbial communities significantly differed between water qualities, yet these differences did not carry to the irrigated soils or crops, regardless of the use of plastic mulch. Moreover, limited migration was detected between communities in the different matrices. Our results imply that short-term irrigation with TWW and the use of plastic mulch has negligible impact on soil and crop microbiomes.