A study was conducted to evaluate the effect of soil covering with black oat straw or black plastic on the phosphorus and potassium content as well as biomass production of three cultivars of lettuce in organic system. There were five handling systems for soil covering: without cover, covered with black plastic, covered with laying oats, covered with harvested oats, and covered with oats straw in natural form. Butter head lettuce showed the highest phosphorus content. Soil covering with oat straw promoted higher potassium accumulation and lettuce production in the second year, while soil covering with black plastic promoted lettuce production in first year.
