Abstract
Reinforcing and optimizing sustainable food production is an urgent contemporary issue. The depletion of natural mineral resources is a key problem that is addressed by recycling mined potassium and phosphorus, and nitrogen, whose production depends on very high energy input. A closed-loop approach of fertilizer use asserts the necessity for efficient management and practices of organic waste rich in minerals. Human-derived urine is an underutilized yet excellent source for nitrogen fertilizer, and, in this study, processed urine fertilizer was applied to greenhouse soilless cultivation of lettuce (Lactuca sativa L.) cv. Grand Rapids. Biomass increase, biometric parameters, soil plant analysis development (SPAD) index, minerals, and organic acids content of lettuce were analyzed. From eight different urine fertilizer products generated, K-struvite, urine precipitate-CaO, and the liquid electrodialysis (ED) concentrate supported the growth of lettuce similar to that of commercial mineral fertilizer. ED concentrate application led to the accumulation of potassium (+17.2%), calcium (+82.9%), malate (+185.3%), citrate (+114.4%), and isocitrate (+185.7%); K-struvite augmented the accumulation of magnesium (+44.9%); and urine precipitate-CaO induced the highest accumulation of calcium (+100.5%) when compared to the control, which is an added value when supplemented in daily diet. The results underlined the potential of nitrogen- and phosphate-rich human urine as a sustainable source for the fertilization of lettuce in soilless systems.
Highlights
The natural resources on Earth are the driving factor of humans’ welfare
The results showed that urine derivatives (UDs) were suitable for integration in future complete growing cycles and could be a component for creating a circular cultivation method whereby nutrients were recycled and reused for the production of food
The accumulation of PO4 and Mg in lettuce treated with K-struvite corroborated with the results reported by Ryu and Lee [36], while these elements were abundant in lettuce leaves
Summary
The natural resources on Earth are the driving factor of humans’ welfare. The linear exploitation of these resources is currently scrutinized and requires a strenuous redesign [1].The urgency entails a new vision concerning resources’ overconsumption and losses. The natural resources on Earth are the driving factor of humans’ welfare. In the view of circular agriculture, a resource is detained within the system through recycling and reuse [1]. Food production systems and our consumption customs are unsustainable; to render it sustainable, implementations are propounded to reinforce it and optimize it through the concept of a circular economy [2], especially with a continuous population growth that drives an expansion in agricultural activity to emulate the pace [2,3,4]. Global food production has been thriving through extrinsic inorganic fertilizers administration, such as nitrogen (urea and ammonium nitrate), phosphorus, and potassium [5,6,7]
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