Low use efficiency of conventional agrichemicals is a significant impediment to global food security, particularly given the 60-70% increase in food production is needed by 2050 to support the projected population. Further confounding these efforts is climate change, which is forcing crop cultivation under more marginal conditions. The low efficiency of nitrogen and phosphorus use represent perhaps the most significant shortcoming of conventional agriculture, wasting tremendous resource inputs and directly causing significant environmental damage. We are exploring nano-enabled strategies to increase the efficiency and precision of macronutrient application. For nitrogen, efforts have focused on enhancing biological nitrogen fixation (BNF) to reduce use and increase yields. BNF relies on select prokaryotic species fix N2 to NH3; these species form symbiotic relationships with legume roots. Enhancing BNF could reduce resource inputs for ammonia fertilizer production and subsequent greenhouse gas emissions. In fact, excessive synthetic nitrogen use likely limits BNF activity. We have demonstrated that nanoscale MoS2, Fe3O4, and NiO modified with sucrose, chitosan, and/or silica can enhance BNF by precision delivery, targeted release, increased photosynthesis, and stress protection. For phosphorus, nanoscale biopolymer-based strategies have been investigated to control availability, including nutrient embedding in nanocellulose-based hydrogels that are modified with hydrophobic shells to tune release. Separately, different forms of nanoscale or conventional phosphorus have been blended with polymers such as polycaprolactone, chitosan, starch, and pectin to control availability. Another project is investigating citrate-stabilized amorphous calcium phosphate nanoparticles that are doped with micronutrients as a fertilizer. In all cases, phosphorus materials were used in plant-growth studies, with significant findings including up to 90% decreases in nutrient leachability/run-off, increased in planta phosphorus, and increased bioavailability of residual soil P. This work collectively demonstrates that nanotechnology-based solutions increase fertilizer use efficiency and crop yield, which is critical to combatting global food insecurity in a changing climate.
