On the Potential of Biochar Soil Amendments as a Sustainable Water Management Strategy

Biochar has been put forward as a potential technology that could help achieve sustainable water management in agriculture through its ability to increase water holding capacity in soils. Despite this opportunity, there are still a limited number of studies, especially in vulnerable regions like the tropics, quantifying the impacts of biochar on soil water storage and characterizing the impacts of biochar additions on plant water composition. To address this critical gap, we present a case study using stable water isotopes and hydrometric data from melon production in tropical agriculture to explore the hydrological impacts of biochar as a soil amendment. Results from our 10-week growing season experiment in Costa Rica under drip irrigation demonstrated an average increase in volumetric soil moisture content of about 10% with an average moisture content of 25.4 cm(3) cm(-3) versus 23.1 cm(3) cm(-3), respectively, for biochar amended plots compared with control plots. Further, there was a reduction in the variability of soil matric potential for biochar amended plots compared with control plots. Our isotopic investigation demonstrated that for both biochar and control plots, there was a consistent increase (or enrichment) in isotopic composition for plant materials moving from the roots, where the average delta O-18 was -8.1 parts per thousand and the average delta H-2 was -58.5 parts per thousand across all plots and samples, up through the leaves, where the average delta O-18 was 4.3 parts per thousand and the average delta H-2 was 0.1 parts per thousand across all plots and samples. However, as there was no discernible difference in isotopic composition for plant water samples when comparing across biochar and control plots, we find that biochar did not alter the composition of water found in the melon plant material, indicating that biochar and plants are not competing for the same water sources. In addition, and through the holistic lens of sustainability, biochar additions allowed locally sourced feedstock carbon to be directly sequestered into the soil while improving soil water availability without jeopardizing production for the melon crop. Given that most of the expansion and intensification of global agricultural production over the next several decades will take place in the tropics and that the variability of tropical water cycling is expected to increase due to climate change, biochar amendments could offer a pathway forward towards sustainable tropical agricultural water management.