Zink oxide leads to sustainable crop growing

NANOPARTICLES of zinc oxide can help plants absorb native phosphorus from soil, reducing the amount of phosphorous fertilisers needed, leading to a more sustainable agricultural industry.

Engineers from Washington University in St Louis, US have been experimenting with mung bean plants which absorb approximately 42% of the phosphorus applied to the soil. The excess phosphorus runs off into the water streams, causing certain species of algae to grow out of control and damage aquatic ecosystems, a process known as soil leaching.

The team created zinc oxide nanoparticles from a fungus found at the plant’s root, in a new environmentally benign process that avoids using harmful chemicals as in existing methods. The nanoparticles help the plant take up nutrients and the zinc increases the activity of three enzymes in the plant which mobilise native soil phosphorus into a form which the plants can use.

When the team applied the zinc nanoparticles to the leaves of the mung bean plant, it increased its phosphorus uptake by around 11%, allowing it to absorb 53% of the applied phosphorus. The nanoparticles were applied to the leaves instead of the root in order to avoid direct contact with the soil; this ensured the plant was being fed and led to better nutrient uptake.

They also found that the nanoparticles increase the activity of the three enzymes responsible for phosporous mobilisation from 84% to 108%. This means less phosphorus is required in fertiliser to sustain the plant’s growth over its life as the plant can absorb more of the naturally-occurring phosphorus found in soil.

Research scientist Ramesh Raliya said: “When the enzyme activity increases, you don't need to apply the external phosphorus, because it's already in the soil, but not in an available form for the plant to uptake. When we apply these nanoparticles, it mobilises the complex form of phosphorus to an available form.”

Approximately 82% of the world's phosphorus is used as fertiliser, and is in limited supply. Raliya says if farmers continue to use fertilisers at current rates, the supply will be depleted in around 80 years.

The team hopes to deploy the nanoparticle method in developing countries where farmers are using a lot of phosphorus, and are dependent on the US for phosphorus exports.

“If this crop can grow in a more sustainable manner, it will be helpful for everyone,” added Raliya.

Agric Food Chem, DOI: 10.1021/acs.jafc.5b05224