PAU field experiment finds several problems with nano urea

A two-year field experiment on the efficacy of nano urea by scientists from Punjab Agricultural University (PAU) has found a substantial decrease in rice and wheat yields when compared to conventional nitrogen (N) fertiliser application. A decline in grain nitrogen content, which is essential for protein production, was also observed.

There was a 21.6 per cent decrease in wheat yield and a 13 per cent decrease in rice yields with the use of nano urea, the researchers found. The study was done in 2020-21 and 2021-22 by Rajeev Sikka, senior soil chemist and Anu Kalia, assistant professor, nanoscience, at PAU. 

Nano liquid urea was launched in June 2021 by the Indian Farmers and Fertiliser Cooperative (IFFCO), which claimed a 500-millilitre spray bottle of nano urea can substitute a full 45-kilogramme bag of the conventional fertiliser. The central government has heavily promoted the fertiliser since its development.

Urea is one of the most concentrated nitrogenous fertilisers, which readily converts to ammonia in the soil — an essential macronutrient for plant functions. Nano urea contains nitrogen “in the form of granules that are a hundred-thousand times finer than a sheet of paper,” according to IFFCO.

The fertiliser is a foliar spray, meaning it should only be used once leaves arrive on the crops. 

The field experiment was conducted for two consecutive years at the research farms of Department of Soil Science, PAU Ludhiana. The scientists did a foliar spray treatment comprising 50 per cent N application to soil, along with two sprays of nano urea as per IFFCO-recommended protocol. 

Along with the decrease in yield, there was also a 17 and 11.5 per cent decrease in grain N content of rice and wheat, respectively, with the combined application of nano urea and N to to soil. 

A decrease in grain N content reflected a lowered protein content. This, the scientists say is worrisome for India where these two cereals form the staple food source for protein and carbohydrates and low protein content will deplete the protein energy requirements of the population. 

“Therefore, even if 100 per cent use efficiency is achieved by this nano formulation, the requisite nitrogen nutrient could not be provided to the growing crop compared to nitrogen provided by 45 kg of conventional urea,” said Sikka. 

Moreover, the cost of nano urea formulation was 10 times higher than that of granular urea and will add to the cost of cultivation for farmers. 

Last year, a four-part report by Down To Earth looked into how nano liquid urea performed on the field and found spraying the fertiliser was spiking input costs for farmers with no noticeable results.

The PAU field experiments also revealed that the above ground triller biomass and root volume were reduced after nano urea application, thus resulting in less root biomass addition after the crop harvest.

The lower root volume indicated a decreased available root-surface area that can culminate to lowered N and other nutrient uptake processes by the root. 

In terms of yield, the scientists also pointed out that the magnitude of its reduction increased in the second year, indicating that the decrease in yield can be sequential, meaning the production may lower year after year if the application of nano urea is continued. 

“The soil pool of nitrogen is limited and is diminishing, so year after year, if you follow foliar spray with nano urea and do not replenish the soil with nitrogen, the reduction would be sequential,” Sikka said.  

The study was also published in the January issue of the monthly journal of PAU. 

It seems the claim of obtaining grain yields equivalent to the recommended dose of conventional urea with IFFCO nano urea will require further long-term field evaluation for at least 5-7 years, said Sikka, adding that so far, the results are not encouraging and the use of IFFCO nano urea cannot be recommended for rice and wheat.