Effects of compost fertility on the growth, yield, and nutrient content of lettuce (Lactuca sativa)

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 and pesticidal sources that are allowed in agriculture to sources derived by plant and animal products or directly mined. Compost is a renewable organic resource that is capable of providing fertility and microbiome diversity to soil and soilless culture thereby reducing the need for inorganic fertility and pesticidal sources. In this study, the efficacy of a one-time application of several different composts to lettuce were evaluated after six weeks based on lettuce yield and nutrient content. Composts varieties including: food scrap, home, dairy manure, yard trimmings, and microbially inoculated were mixed at 30% (volume based) with an 85:15 peat perlite blend. Composts in general appeared to have decreased in nutrients at approximately 4 weeks after potting. Dairy manure compost produced among the highest yields for the compost treated lettuce and did not exhibit deficiency related disease. However, all compost treated lettuce had lower yields and foliar nutrient concentrations than the controls. While compost does provide fertility, it may not be enough to sustain the nutrient demand of crops. Therefore, multiple applications of compost or supplementation with a different fertility source is recommended.