Enhancing Vegetative Growth of Quinoa and Soil Properties under Water Shortage through Targeted Organic Amendments

The scarcity of water resources is considered a major threat and challenge for agriculture. Water limitations could strongly affect the growth and development of many crops including quinoa, a nutrition-rich, climate-resilient crop that is gaining attention globally. Organic amendment application has been reported as a suitable option to mitigate the detrimental impacts of water shortage on soil and plant growth. In this context, two experiments were conducted on Chenopodium quinoa “Titicaca”; in the first experiment, we investigated the effect of different organic amendments, namely woodchips biochar (Bw), vineyard pruning biochar (Bv), and vermicompost (V), applied (alone and mixed) at 2% soil dry weight, on soil properties and the plant biomass of quinoa subjected to a water stress period during vegetative development. Among organic amendments tested, Bw and Bw+V increased plant biomass on average by 15%, while Bv and Bv+V reduced the plant biomass by 62% compared to nonamended soil (C). A significant reduction in soil pH was observed with Bw (7.61), while BV increased pH (8.04) compared to C (7.76). The Bw and Bv also reduced soil bulk density (BD) (1.19 g/m3 and 1.13 g/m3, respectively) compared to C (1.28 g/m3). As Bw performed better in the first experiment, the second experiment assessed only Bw at different doses, i.e., 0%, 2%, and 4% under water shortage by restoring only 50% evapotranspiration losses, when soil water content reached the 50% of available water content. Considering the Bw rates, the plants treated with Bw2% showed 34% and 19% more biomass and 36% and 66% more panicles than Bw0% and Bw4%, respectively. The Bw2% decreased the soil pH (7.79 versus 7.85) and electrical conductivity (286 versus 307 μS/cm) compared to Bw0%, which was not different from Bw4%. No differences were observed in BD between Bw0% and Bw2% (on average 1.28 g/m3), while BD decreased in Bw4% (1.06 g/m3). The findings of both experiments highlighted that the appropriate type and dose of biochar could improve soil properties and help quinoa plants to grow better under water-limited conditions.