[Image above] Researchers found that fertilizers based on iron oxide nanomaterials may promote better soybean growth than some traditional fertilizers. Credit:United Soybean Board, Flickr (CC BY 2.0)
Just like humans, plants require a well-rounded diet to grow big and strong. And because plants get their nutrients from the soil in which they are grown, farmers are constantly researching ways to ensure the fertility of the soil, for example, by harnessing established techniques such ascrop rotationand the ever-evolving science offertilizers.
Fertilizers are chemical or natural substances that are added to soil to increase its fertility. While most fertilizers contain the three basic plant nutrients—nitrogen, phosphorus, and potassium—some fertilizers also contain certain “micronutrients,” such as zinc and other metals, that are necessary for plant growth.
Iron fertilizers are one type of micronutrient fertilizer that requires more research. To date,iron chelatesare commonly used as iron fertilizers. “Chelate” refers to the pincer-like way in which an iron ion is encircled by a larger organic molecule, usually a ligand, which prevents the iron from oxidizing and thus improves its uptake by the plant.
While iron chelates are significantly more effective and efficient than nonchelated iron fertilizer sources, they can have negative effects on the environment, either directly or indirectly. For example, some studies have found that certain iron chelatesincrease soil pH and can cause phytotoxicity in sensitive speciesand can causestress to soil microorganisms.
Developingalternative iron chelatesis one way to improve iron fertilization. However, fertilizers based on nanomaterials is another approach that is gaining traction.
The use of nanotechnology in fertilizer developmentremains relatively lowcompared with nanomaterials in pharmaceutical research. The research that does exist, however,is encouraging.
Of the studies that have explored iron-based nanomaterials,somepublishedreportsfound that foliar application of iron-based nanomaterials—which involves applying liquid fertilizer directly to the leaves as opposed to in the soil—can lead to greater plant growth than conventional iron chelates.
“Given these promising findings and the known sensitivity of soybean to [iron] deficiency, future intensive investigation into the mechanisms of action and optimization of efficacy is warranted,” researchers write in arecent paper.
The researchers come from Jiangnan University in China, along with colleagues from the Chinese Research Academy of Environmental Sciences, the Connecticut Agricultural Experiment Station, and the University of Massachusetts Amherst. In their new study, they investigate the effects of variously sized iron oxide nanomaterials (γ-Fe2O3) on the development, gain, and plant nutritional value of soybeans.
The nanomaterials in this study were sorted into three categories: small (4−15 nm), medium (8−30), and large (40−215 nm). Examination of the foliarly treated soybeans revealed that those treated with the small iron oxide nanomaterials exhibited the greatest enhancement on growth, yield, and nutritional quality. In addition, these soybeans outperformed ones treated with a conventional iron fertilizer of an equivalent iron dose.
The researchers attribute the good performance of the small iron oxide-based fertilizer to a modulation of the nitrogen fixation process, or the mechanism by which atmospheric nitrogen is assimilated into organic compounds. They identify three mechanisms in particular that are modulated:
- 小的氧化铁纳米材料增强碳assimilation in nodules, thus supplying more energy for nitrogen fixation.
- The small iron oxide nanomaterials activate nodule antioxidative systems, with subsequent elimination of excess reactive oxygen species.
- The small iron oxide nanomaterials upregulate synthesis of cytokinin and downregulate synthesis of ethylene and jasmonic acid in the nodule, which promotes nodule development and delays nodule deterioration.
“These findings offer significant insight for understanding the potential of γ-Fe2O3NMs [nanomaterials] as a high efficiency and sustainable agricultural amendment,” the researchers write.
They conclude by saying future studies should focus on optimizing material chemistry properties and application regimes to maximize sustainable benefit, “particularly under scenarios related to a changing climate (e.g., increased temperature, drought, salinity, light intensity) that will maximize abiotic oxidative stress.”
The paper, published inACS Nano, is “Foliar application with iron oxide nanomaterials stimulate nitrogen fixation, yield, and nutritional quality of soybean” (DOI: 10.1021/acsnano.1c08977).