Conversion of quinoa and lupin agro-residues into biochar in the Andes: An experimental study in a pilot-scale auger-type reactor

Abstract

In the last decades, the cultivation of quinoa and lupin became an important source of income for Andean farmers due to the demand for high nutrient-density foods from the Global North. The increase in the cultivation intensity caused by this exogenous demand led to the overexploitation of local ecosystems and a decrease in soil fertility. As an alternative to recover and improve soil quality, this work uses a pilot-scale auger pyrolysis reactor, implemented in the Andes, to assess the conversion of the agro residues generated in the post-harvesting processes of quinoa and lupin into biochar for soil amendment. Following the European Biochar Certificate guidelines, the pyrolyzed quinoa stems can be classified as biochar while the pyrolyzed quinoa husks can be classified as pyrogenic carbonaceous material. Both can be used for soil amendment considering their molar ratios (H/Corg, O/Corg) and carbon content. It was not possible to carbonize lupin stems and seedcases. Despite the altitude (2,632 m.a.s.l), the CO concentration during the carbonization of quinoa stems and husks were 1,024.4 and 559 mg/Nm3, this last, near the European eco-design standard of 500 mg/Nm3. A subsequent SWOT analysis showed the need to explore low-cost and low-complexity pyrolysis reactors that allow the decentralized conversion of agro residues at the farm-scale. The development of local standards to regulate the production and use of biochar is also essential to grant the safety of the processes, the quality of the products, and mobilize funds that allow implementation at relevant scales.

Upcycling post-harvest biomass residues from native European Lupinus species: from straws and pod shells production to nutritive value and alkaloids content for ruminant animals

“…In this study, the production, nutritive value, and alkaloid content were assessed separately for straw and pod shells. Regardless of location, the combination of straws and pods per variety accounted for 63.5-74.3% of total aerial biomass harvested (grains, straws, and pod shells), agreeing with the biomass residues of L. angustifolius and L. mutabilis Sweet, also known as Andean lupin, which accounted, respectively, for 71.0 and 87.5% of total harvest (46,47,51). The overall results here presented suggest a poor adaptation of the early cultivar L. angustifolius 'Tango' to the specific climatic conditions of both studied locations during the agronomic year of 2018/2019.…”

“…In 2021, European lupin production accounted for 391,342 tons, corresponding to 28.7% of the world production yield (13). Although scarce data exist on the agroresidues generated during lupin seed harvest and post-harvesting processes, it has been estimated that 7 tons of biomass residues are produced per ton of seed (46). Unlike cereal straws, lupin biomass residues (e.g., stalks, stubbles, straws, pod shells, husks) are traditionally left in the fields and burned in open fires and/or incorporated in the soil to promote carbon and minerals content (47).…”

“…Under this rationale, we anticipate that the biomass residues obtained from lupin grain harvest may be valorized if collected, stored, and used as fodder for ruminants in periods of feed scarcity. On the other hand, as legumes are harvested some centimeters off the ground, the stalks and stubbles that remain in the field could be further incorporated into the soil or processed as soil amendment (46), along with the root biomass that contributes to promote the soil OM and nutrient content (50). This holistic approach addresses the quest for biomass for soil amendment and animal feeding, pointing out the need to sustainably balance biomass demands (4).…”