To the untrained eye all nanofertilizers may look the same.
This makes sense, a fertilizer that measures less than 100 nanometres wide (1,000 times thinner than a human hair) is invisible to the naked eye. So rather than looking the same, a nanoparticle for crop nutrition is invisible from a human perspective.
But to the informed fertilizer supplier, nanofertilizers are definitely not the same.
In general, there are three main types of nanofertilizers:
· Nanoscale coating fertilizers are bulk fertilizers that have been given a coating of nanoparticles to aid delivery, delay release, slow down release, or to add an additional nutrient at a nanoscale.
· Nanofertilizers are nanoparticles of nutrients that are applied directly onto plants or into the soil. Each particle measures less than 100 nm in size, which makes it easier for crop uptake.
· Nanoscale additives are traditional, bulk fertilizers that have had nanoparticles of nutrients added to them.
Nanoscale nutrients are top-down produced by physically making macroscale nutrients smaller; or bottom-up produced by chemically manufacturing nanosized particles.
A further development of nanofertilizers involves the encapsulation of nanoparticles inside nanoporous materials. This method has been found to significantly reduce nitrogen loss by regulating nutrient release, which in turn further enhances plant uptake.
Porous nanomaterials include:
1. Ammonium charged zeolites, which boost the solubility of phosphate minerals and therefore availability to crops.
2. Graphene oxide films, a carbon-based nanomaterial often used for the slow release of potassium nitrate.
3. Nanocalcite (CaCO3-40%) with nano SiO2 (4%), Fe2O3 (1%), and MgO (1%). A combination such as this improves plant absorption of calcium, magnesium, and iron, as well as boosting phosphorous uptake with micronutrients zinc and manganese.
These nanoporous materials can also contain soil and plant friendly microorganisms (biofertilizers).
Whatever form of nanofertilizer is used, they each possess advantages over conventional fertilizers, both economically and environmentally.
Conventional fertilizer production is a major emitter of greenhouse gases into the atmosphere. Additionally, bulk fertilizer uptake into plants can be incredibly inefficient. A 2019 study reporting that, “… nitrogenous fertilizers have efficiency of only 45–50%, while the corresponding figure for phosphorous fertilizers has been reported to be only 10–25%.”
Nutrients that are not absorbed by plants can remain in soils, making them toxic to soil friendly bacteria, or are washed out into streams and rivers causing eutrophication that kills wildlife. Additionally, ammonia from fertilizer can pass off as vapour from the soil into the atmosphere.
Alternatively, nanofertilizers are crop nutrition products that have been proven to increase plant health and crop yields.
Data sourced from a variety of studies (Zheng et al, Mandeh et al, Manikandan et al, Zhang et al, Zhao et al, Zebarth et al, Rathnayaka et al, Yang et al, & Kim et al has found that the application of nanofertilizer enhances seed germination rate and seedling growth, as well as boosting photosynthetic activity.
Other studies have found that nutrients supplied in a nanoparticle form can suppress disease and aid plant defence pathways, such as combating phytopathogens through the production of reactive oxygen species.
Ultimately, as the nanotechnology journal AzoNano explains, “Nanomaterials improve the productivity of crops and efficiently regulate the delivery of nutrients to plants and targeted sites, guaranteeing the minimal usage of agrochemicals.”
But crucially for farmers, “Nanomaterials can increase crop yield by increasing fertilizer nutrient availability in soil and nutrient uptake by plants.”