Research conducted by the SRDI shows an acute deficiency of nutrient nitrogen in most arable lands and various degrees of deficiency of nutrients like phosphorus, potash, sulphur, boron and zinc.

The SRDI attributed the deficiency to persisting production of the same crop in the same lands, intensification of cropping, cultivation of modern crop varieties without required land and soil tests and unbalanced use of chemical fertilisers.

The depletion of nutrients, especially nitrogen, has resulted in comparatively low production of crops and consequent rise in production cost.

About 5.7 million hectares of land suffer from sulphur and zinc shortage, and 5 million hectares from shortage of organic matters, SRDI scientists said.

The country has 12.31 million hectares of land, of which 7.85 million hectares are arable.

"The process of nutrient depletion started mainly in the early eighties when cultivation of high-yielding variety (HYV) of rice began," said a principal scientific officer at the SRDI.

"Farmers cultivate two or three crops a year in the same lands but do not use nutrients properly due to ignorance or poverty. So, the deficiency of nutrients is escalating," he added.

The SRDI put the average per hectare nutrient depletion at 300 kg a year. This shortfall is partly replenished in the natural process from air and floodwaters but it continues.

Plants need 16 nutrients -- 13 from soil and 3 from air -- to grow properly.

To produce six tons of rice per hectare, 108 kg of nitrogen is needed, 18 kg of potash, 120 kg of phosphate and 11 kg of sulphur.

Application of 100 kg of urea fertiliser in one hectare replenishes 45 kg of nitrogen. To replenish other nutrients, various types of fertiliser should be applied properly, the researchers said.

Deficiency of sulphur and organic matters has been detected in croplands mainly in Panchagarh, Thakurgaon, Dinajpur, Kurigram, Gaibandha, Naogaon, Joypurhat, Bogra, Chapainawabganj, Jamalpur, Netrakona, Tangail, Gazipur, Meherpur, Magura, Chandpur, Sherpur, Mymensingh, Kishoreganj, Comilla and Jessore.

Zinc shortage has been found in croplands mainly in Rajshahi, Natore, Pabna, Meherpur, Chuadanga, Kushtia, Rajbari, Faridpur, Shariatpur, Gopalganj, Jhenidah, Magura, Jessore, Narail, Comilla, Barisal, Brahmanbaria, Satkhira, Khulna, Bagerhat, Noakhali and Chandpur.

Meanwhile, the SRDI has prepared a Land and Soil Resources Using Manual for the 460 upazilas of the country, said its Director Monirul Haq.

"Crop production can be increased at least by 10 percent if fertiliser is used properly," he said.