Nitrate content of lettuce (Lactuca sativa L.) after fertilization with sewage sludge and irrigation with treated wastewater.

摘要

A romaine-type lettuce (Lactuca sativa L.) was cultivated over 3 crop seasons (spring 2005, spring 2006 and autumn-winter 2006) in six 36 m2 plots in Alcazar de San Juan, Spain. A drip irrigation system was used to water all plots: 5 plots with drinking water and 1 plot with wastewater from the activated sludge system of a wastewater treatment plant (WWTP). 1 drinking water-irrigated plot was not fertilized (control). 5 different treatments were applied to the soil: 3 organic mixtures (sewage sludge, sewage sludge mixed with pine bark and municipal solid waste with composted sludge) and a conventional fertilizer were applied to the 4 plots irrigated with drinking water. The last plot was irrigated with treated wastewater. The treatments were tested for their effect on plant growth and nitrate concn. in vegetable tissue. An increase in fresh wt. of lettuce was linked to the dosage of sewage sludge. The highest nitrate level was observed in the sewage sludge treatment in all crops and seasons, although, in general, all values were below the max. limits established by the European Commission for nitrate content in fresh romaine lettuce. In the 3rd crop season, a significant increase in nitrate content was observed in lettuce from organic treatments. Nitrate concn. in lettuce from irrigated treated wastewater was higher than control, although significant differences were not found.