Effects of weed management strategies on quality and enteric pathogen contamination of organic lettuce

Kurzfassung

Quality requirements for raw edible produce like lettuces include nutritional value and hygienic quality. Organic lettuce is often considered to cause a potential health risk for immunocompromised individuals due to assumed pathogen transfer from organically manured soils into lettuce heads (Lactuca sativa, var. capitata). The effect of different weed management strategies (rotary tiller, mouldboard plough combined with flame weeding, plastic mulch and straw layer, resp.) on pathogen transfer from fresh and composted farm yard manure were assessed in four field experiments in 2006 and 2007. Results gave no hint on any pathogen transfer given by the assumed pathways (contaminated soil particles transported by mechanical tools and/or splash effect of rain drops). Nitrate contents in lettuce were low ranging from 269 mg/kg to 828 mg/kg in fresh matter respectively. A new method for measuring leaf tissue firmness is being developed by using an artificial denture. Substantial negative effects of manure on lettuce quality were not recorded.