Soil-based zeolite and metal oxide nanomaterial application alters reactive nitrogen losses and lettuce (Lactuca sativa L.) growth

Abstract

Excessive nitrogen fertiliser use has resulted in reactive nitrogen losses to the environment through gaseous N emissions, like N₂O, resulting in agriculture being a major anthropogenic source of N₂O gas emissions globally. Using engineered nanomaterials to deliver reactive nitrogen can aid in more efficient nutrient delivery to crops, maximising yield and crop quality, while minimising reactive losses to the environment. ZSM-5-15, a nano-zeolite, increased cumulative N₂O emissions by 134% when applied in combination with a 50% dose of conventional nitrogen fertiliser. This is theorised to be through ion exchange of ZSM-5-15's extra-framework NH₄⁺ ion load being released, allowing nitrifying microbes to act on the newly released NH₄⁺ and increase N₂O emissions. BEA-19, a similar zeolite to ZSM-5-15 but with a slightly altered Si : Al ratio, size and charge, causes no increase in N₂O emissions. While ZSM-5-15 increases reactive N emissions it also drives improved lettuce growth, with 13% more biomass accumulation compared to a half dose of conventional fertiliser. Ce_0.75Zr_0.25O₂, a nano-metal oxide, improves growth by 6% and maintains the nutritive quality of lettuce, with higher Zn, Cu, Mg, K, Fe and Mn contents, without increasing N₂O emissions. Nano-Ce_0.75Zr_0.25O₂ transforms in soil to form CeO₂ and Ce_0.9Zr_0.1O₂, leaching Zr⁴⁺ ions some of which form ZrCl₄. These compounds may then act on lettuce roots and soil microbes independently. These results indicate how nanomaterials may impact reactive nitrogen emissions through effects on soil microbial communities.