The world has experienced uncertainties, in various aspects at the global level, which impose challenges to our humanity. Among them all, hunger and climate changes could directly threat the future existence of human being, let alone humanity. To guide us through these challenges, the United Nations has proposed that 17 critical Sustainable Development Goals need to be achieved by 2030. Amongst, "Zero Hunger" and "Climate Action" are the two goals closely related to agriculture. Undoubtedly and quite naturally, they go hand by hand – a successful agriculture that conquers hunger needs to be sustainable in the long run. For this very reason, we are constantly searching for an ideal climate-smart agriculture: more output for less input.

The reality, of course, is less than ideal. While some global collaborations are of significant help in fighting hunger in some regions, competitions are almost inevitable due to disparities in financial situations, natural resources, technology accessibility, cultural norms, government policies and etc. Nevertheless, such a reality should not stop us from collaborations in all aspects. It is especially imperative for scientists to share our knowledge so we can attain the goals set by UN.

While breeding of crop varieties and/or crop gene engineering have been proven as the most impactful biotechnology in modern agriculture, an improvement in agricultural practices also plays a significant role. Among them, fertilization is one with a long history. It is commonly understood that traditional fertilizer application alone cannot resolve the contradiction between food security and greenhouse gas emissions. It promotes crop production but increases greenhouse gas emissions at the same time, and vice versa. Therefore, simply put, new types of fertilizers are needed to resolve this contradiction. Our study suggests nano iron is a promising one.

Transmission electron microscope image (left) and diffraction of x-rays analysis (XRD) (right) of Fe₃O₄ nanoparticles 

Nano iron, as a new generation of fertilizers, has gradually been applied in crop production. The starting point of current researches on nano iron fertilizers often focuses on the physiological needs of plants. In recent years, the prominent importance of iron in the biogeochemical cycling of soil ecosystems has gradually been revealed. However, there are few reports on the overall impact of nano iron fertilizer on the entire agricultural ecosystem, especially lacking in long-term tracking studies. This understanding can help us to develop nano-enabled strategies for a climate-smart agriculture.

The picture of the four-year nano iron oxide fertilization experiment

From our four years of long-term experiments in rice fields, we found that with supplemental nano iron oxide application increased crop yield (recently published in Nature Sustainability (https://doi.org/10.1038/s41893-024-01334-6)). More interestingly, it is accompanied by a reduction in the greenhouse gases emission and an increase in soil carbon sinks. An investigation of the underlying mechanism indicates that, nano iron oxide fertilizer affects the carbon-nitrogen cycling process and microbial community of rice soil. By doing so, it reduces the emissions of methane and nitrous oxide in rice fields. Consequently, more carbon and other nutrients are retained in the soil over the years, leading to an improvement of soil fertility. The chemical structure of nano iron oxide facilitates the fixation of ammonia nitrogen in the soil, thus reduces ammonia volatilization in rice fields (for “Climate Actions”). The fixed nitrogen is released later as nutrients for plant growth – another factor responsible for a better crop yield (for “Zero Hunger”). We expanded our comparative analysis to the whole span of nano iron oxide strategy: from its production to transportation and finally to field application. There is still a sizable benefit in its climate effect. 

A conceptual framework showing that Fe₃O₄ nanoparticles (FeONPs) fertilization can close the gap between climate regulation and food security trade-offs in rice ecosystems. Specifically, FeONPs can decrease methane (CH₄) and nitrous oxide (N₂O) emissions by inhibiting soil enzyme activities involved in soil carbon cycling and stimulating Feammox process. For promoting soil fertility and crop yield, FeONPs can enhance carbon sequestration by decreasing the ratio of oxidases to hydrolases and meantime hold more N nutrient in paddy soils by decreasing ammonia volatilization via the entrapment of nanoparticles.

Undoubtedly, this nano iron oxide strategy will not be practically viable unless it is financially beneficial. Thanks to the higher crop yield, the extra income under current market is more than enough to cover the costs of nano iron oxide strategy. Looking forward, considering the increasing grain prices in markets and even higher yields (due to better soil fertility), we can only expect the financial future of such strategies to be more and more attractive. 

In all, excitement is an understatement when our study revealed the aligning benefits in lower greenhouse gas emission and higher crop yield when nano iron oxide is applied as a supplemental fertilizer in experimental rice fields. The future of this agriculture practice is even brighter in achieving the goals set by the United Nations.

Youzhi Feng, Nanjing Forestry University

Linghao Zhong, The Pennsylvania State University at Mont Alto

Shiying He, Jiangsu Academy of Agricultural Sciences