A study looked at different types of organic fertilizers for growing lettuce in soil. The best results were seen with a mix of organic and inorganic fertilizer, which increased lettuce production by over 300%. Biological fertilizers also increased production, but using only organic fertilizer decreased production. All types of organic fertilizers reduced nitrate levels in lettuce and lowered levels of harmful metals like mercury, lead, and chromium. They also increased the levels of sugar and vitamin C in lettuce, but had varying effects on amino acids.