Development of a low-tech bioponic method using mineralized chicken and goat droppings to produce lettuces

Bioponics is a form of hydroponics that uses organic materials as fertilizers. This method appears to be an excellent alternative method for growing vegetables in areas with soils that are polluted, degraded or unsuitable for agriculture. It avoids the use of mineral chemical fertilizers, which are often expensive or inaccessible in more remote regions or in developing countries. Trials have been conducted since 2020 to develop a low-tech method for producing bioponic nutrient solution from chicken and goat manures. This research is done as part of the SWIM project in collaboration with Oxfam and AFAD, which aims to develop innovative and sustainable farming methods in Sahrawi refugee camps, located in Algeria (Sahara desert). Manures first underwent a microbial “digestion”, before being used as nutrient solutions to grow plants. This digestion was done in two stages: (1) first an anaerobic fermentation stage of 7 days, resulting in nutrient rich solutions, (2) followed by an aerobic mineralization stage of 21 days, via oxygenation of the solutions. Between the two, solutions were filtered and diluted based on the total mineral nitrogen concentration. The 1st trial tested a concentration of 65 mgN/L for chicken and goat manure solutions, while the 2nd trial tested two different concentrations for a chicken manure solution: 65 mgN/L and 140 mgN/L. The resulting solutions were then used on lettuce (Lactuca sativa) in bioponics, and compared to a conventional chemical solution. In term of yields, in the 1st trial, goat feces based solutions resulted in lettuces of about 50% of the fresh yields obtained with a chemical solution, while this percentage reached 70% on average for the chicken feces solution. In the 2nd trial, the two solutions of different concentrations resulted in yields similar to those with a chemical solution. In term of lettuce quality, manure based solutions overall resulted in lettuces of better nutritional quality than that of the chemical, i.e. leaves with lower nitrate concentration, and higher Ca, Mg, Fe, Mn and Zn concentrations. At the microbiological level, all lettuces were safe for consumption. These trials show that it is possible to grow quality lettuces in bioponics with a simple and low-tech method using manures. Chicken manures appear to be more suitable as fertilizers, in comparison to goat feces. However, the quantities of fertilizers used for the bioponic solution must be controlled to avoid mineral losses. Trials are carried out in refugee camps in Algeria to test and adapt the method to the local context. More generally, the principles of this technique can be developed in a more high-tech way and on a larger scale, notably as a way of recovering agricultural wastes and/or processing livestock effluents, which can be source of pollution.