Spurious fertilisers are being made secretly at houses and underground factories in different upazilas of the district, said police and officials.
A section of dishonest fertiliser dealers of Bangladesh Chemical Industries Corporation (BCIC) are also allegedly engaged in selling spurious fertilisers.
A group of unscrupulous traders are manufacturing fertilisers rampantly in many houses of Nandangachhi, Shimulia, Baidyanathtala, Faridpur, Gobindapur and Barkatpur villages of Charghat upazila, locals said.
They are selling triple super phosphate (TSP), di-ammonium phosphate (DAP) by mixing smuggled Indian fertilisers with local ones while muriate of potash (MoP) by mixing sand or salt with brick dust and colours, said a number of farmers.
Against this backdrop, the Agriculture Extension Department (AED) has alerted its upazila offices and warned farmers about adulterated fertilisers.
"We asked our staff to remain alert and create awareness among farmers," said Rabindra Kumar Majumder, additional director of Rajshahi regional AED.
He said use of sub-standard and adulterated fertilisers poses threats to the farmlands, environment and health. Finally, it leads to suffering losses by farmers.
Meanwhile, the authorities launched several drives against spurious fertilisers.
On October 25, a mobile court seized 79 sacks of MoP and 60 sacks of NPKS (a mixture of nitrogen, phosphate, potash and sulfate) from the godowns of Ishaq Ali and Zakir Hossain in Bagmara upazila for not having production seal.
On the same day, the authorities arrested Mohammad Bablu while preparing adulterated fertiliser at his house at Baidyanathtola village in Charghat upazila and seized six sacks of MOP from his house.
"Samples of the seized fertilisers were sent to Dhaka for laboratory test. If it is found spurious, its possessors will be punished," said Braja Hari Das, deputy director of Rajshahi District AED.
Durgapur upazila administration fined BCIC dealer Lal Mohammad with Tk 30,000 after some 146 sacks of adulterated MoP fertilisers were seized from his godown on October 6.
In August, the Detective Branch (DB) of Rajshahi Metropolitan Police busted a clandestine spurious fertiliser factory near Rajshahi city and arrested its owner M Waliullah and manager Abdul Alim. They seized 500 sacks of spurious fertiliser from the factory.
Braja Hari said they distributed two types of leaflets describing easy methods of identifying spurious fertilisers and farmers' responsibility in checking the spread of those harmful fertilisers.
The AED sources said they expect potato cultivation on some 40,000 hectares of land this year, some 8,000 hectares higher than last year's, and Boro paddy on some 85,000 hectares of land in the district.
However, several upazila level AED officials wishing anonymity said they apprehend brisk business of adulterated fertiliser this season as there were reports of gross irregularities in recruitment of retailers under the government's new policy for distributing fertilisers at grass-roots level.
"We heard allegations of bribing Tk 20,000 to Tk 50,000 for getting appointed as retailers and we don't not see any visible reason for profit of such amount without malpractice," said an upazila AED official.