Comparison of organic water-soluble fertilizer efficacy on Lactuca sativa (lettuce)

In the last decade, the consumer demand for organic produce has increased 500% causing a surge in the development of organic farms. The constraints of organic farming limits the number of fertility sources that are allowed in agriculture to sources derived by plant and animal products or directly mined. The manner in which organic fertilizers are produced often leads to variation in the fertilizer product which affects the reproducibility of crop plants. In this study, three organic fertilizers were applied to lettuce (Lactuca sativa) alongside a conventional fertility source standardized to 100 mg L^‑1 N for six weeks to determine the efficacy of each organic fertility type. The organic fertility sources provided all plant-essential nutrients but varied significantly in their ability to sustain lettuce growth. The all-purpose organic fertilizer had an inhibitory effect on lettuce growth which was likely due to an excess of copper. The fish emulsion, though capable of supporting lettuce growth, produced a low yield. Fulvic acids produced a yield that was comparable to a conventional treatment. In conclusion, when standardized to the same rate of N, organic fertility sources may not support yields equal to conventional sources of fertility.