Bioponic Cultivation Using Chicken Droppings to Produce Lettuce Plants (Lactuca sativa rz) Uncontaminated by Trace Metals

Abstract

Anthropogenic activities have denatured aquatic, terrestrial, and aerial environments throughout the world in general, and in Lubumbashi in particular, where market garden soils have become uncultivable for many plants. Thus, bioponics could be an effective means of producing uncontaminated vegetables in soilless cultivation, not only reducing the amount of fertilizer used and limiting contamination of agricultural produce but also achieving higher yields than in open-ground cultivation. The overall objective of this study was to implement a new bioponic technique for producing liquid fertilizer from chicken manure and utilize it in the organic hydroponic cultivation of lettuce (Lactuca sativa var. Lucrecia) installed on floating raft systems. To achieve this, two types of trials were conducted. The first was aimed at determining the quantities of organic matter to be used in the formulation of nutrient solutions. The second trial aimed to determine the optimal nitrogen concentration to be provided for hydroponic plant growth. Mineralization and/or anaerobic digestion of chicken manure were conducted for 7 days in 200 L barrels. For the first trial, nutrient solutions were created from three different concentrations of chicken manure (0.35%, 3.5%, and 7% dry matter—D.M.). These solutions were then used in bioponic rafts where total ammonia nitrogen (TAN) concentrations were fixed at 150 mg/L. For the second trial, D.M. was fixed at 2.5% for each tested modality, but TAN concentrations varied among them (i.e., 60, 90, and 120 mg/L TAN concentration). Modalities with low D.M. concentration (0.35%) and those with low TAN concentration (60 mg/L) resulted in higher yields than bioponic modalities receiving high concentrations of dry matter or TAN, respectively, for trials 1 and 2. Although the reference chemical solutions generate the greatest yields, bioponic systems operating with chicken manure present a good alternative for the cultivation of vegetables in developing countries with heavily contaminated soils. Indeed, bioponics allows for the production of vegetables in large quantities from animal waste, which does not pose health risks for human consumption. Local vegetable species commonly grown in Lubumbashi should be tested under hydroponic conditions.