Soil scientists warn that acidic farmland is spreading across Bangladesh. Rising acidity is stripping soil of its microbial life, weakening its nutrient base and reducing crop yields. More than 52 percent of all agricultural land now shows signs of acidification, according to a study by Gazipur Agricultural University (GAU).

The study estimates that about 4.6 million hectares are affected, with roughly 3.3 million classed as highly acidic, and the total continues to rise. A 2020 national survey by the Soil Resource Development Institute (SRDI) found that 39.21 million hectares, or 45.67 percent of farmland, were acidic. Data from the agriculture ministry puts current agricultural land at 8.82 million hectares.

Researchers say calcium and magnesium ions are leaching out of topsoil, while aluminium concentrations continue to climb. This is driving soil acidity higher. Iron, manganese, and zinc surge to toxic levels when soil pH drops below 4, blocking plant growth and cutting yields. They note that the share of affected land has grown steadily.

Scientists link the trend to both natural conditions and human activity. Barind, Madhupur, and the hill regions naturally have acidic soils. But other regions face worsening acidity from heavy nitrogen use, particularly urea and ammonia-based fertilisers.

“We’ve seen in a study that nearly two-thirds of Bangladesh’s farmland is now acidic. Northern districts are hit hardest. The region has sandy soil. Those lose calcium and magnesium through leaching, which raises aluminium levels and triggers acidity. Barind, Madhupur, and the hill tracts are naturally acidic. That’s why two-thirds of the country’s land is acidic.” —Dr. GKM Mustafizur Rahman, Vice-Chancellor of Gazipur Agricultural University, and Professor of Environmental Soil Science

Soil acidity is measured by pH, a gauge of hydrogen ion concentration, with 7 considered neutral. Anything below 7 indicates acidity. The lower the number, the more acidic it is. Crop yields hold steady until pH drops to roughly 6, although soil is classified as acidic even when pH drops from 7 to 6.

Several forces push acidity higher. Barind, Madhupur, and the hill regions are naturally acidic because of their geology. Elsewhere, scientists point to human practices. Heavy urea use accelerates acid formation. Monocropping and the steady retreat of organic fertilisers add further stress. Multi-crop land, especially land that hosts three or four cycles a year, tends to be more acidic than single-crop fields.

“Excessive fertiliser use is a major driver of rising acidity. So is intensive cultivation, because the more land is farmed, the more fertiliser it consumes. As acidity rises, soil microbes die off. These microbes supply nutrients to plants, so their loss slows growth and limits production.” —Dr. Amir Muhammad Zahid, Chief Scientific Officer at SRDI’s Dhaka divisional office

He added that high acidity also weakens seed germination and early seedling development.

Data from Global Economy, which tracks agricultural inputs, shows that Bangladesh now applies 391 kilograms of chemical fertiliser per hectare, the highest rate in South Asia. Among Asian countries, only China applies more at 397 kilograms per hectare.

China and Bangladesh record the highest application rates among surveyed nations, with Bangladesh leading all of South Asia in chemical fertiliser input. (Source: Global Economy data)

Bangladesh Economic Review 2024 notes that fertiliser use has risen every year.

Fertiliser use has climbed sharply in Bangladesh. Between fiscal years 2016–17 and 2023–24, consumption rose by more than 35 percent. Farmers applied roughly 4.9 million tonnes in FY 2016–17. By FY 2023–24, the total had reached 6.62 million tonnes. Urea use rose from 2.36 million tonnes to 2.62 million tonnes over the same period, an increase of roughly 11 percent. DAP use surged even faster, more than doubling from 609,000 tonnes to 1.49 million tonnes. MOP use rose 21 percent, gypsum 70 percent, and zinc fertiliser more than 144 percent.

SRDI’s Rajshahi divisional office has launched a potato-cultivation programme to promote balanced fertiliser use. The initiative draws on research to show farmers how to increase yields and reduce input costs.

The institute’s data shows that farmers in the region traditionally applied 50 kilograms each of urea, DAP, and TSP per bigha (1 bigha is approximately 1338 square meters) of potato land. Additionally, they used 100 kilograms of MOP, between 10 and 20 kilograms of gypsum, two kilograms each of zinc and boron, and about 300 kilograms of organic fertiliser. The revised recommendations cut those levels. Farmers are now advised to use 33 to 40 kilograms of urea, 15 to 20 kilograms of TSP or DAP, and 25 to 35 kilograms of MOP per bigha. The guidance also calls for 10 to 15 kilograms of gypsum, 1.5 to 2 kilograms of zinc, and 1 to 1.5 kilograms of boron. It urges heavier organic inputs, including 130 kilograms of vermicompost, 500 to 700 kilograms of organic fertiliser, and 130 to 200 kilograms of dolomite or lime.

“Acidic land is expanding fast. The primary cause is rising nitrogen levels. Farmers rely heavily on urea and DAP. Both contain nitrogen, so they push soil acidity higher. Our survey shows more than 40 percent of farmland is now under acidic stress. We are running awareness programmes to discourage overuse and encourage balanced fertiliser management.” —Dr. Md Nurul Islam, Chief Scientific Officer at SRDI’s Rajshahi office

Multiple studies suggest that nearly 75 percent of Bangladesh’s farmland now lacks natural fertility. Much of the land shows deficiencies in phosphorus, nitrogen, potassium, sulphur, boron, and zinc. SRDI’s study, “Soil Fertility Trends in Bangladesh 2010 to 2020”, also reports a sharp rise in nutrient-deficient zones.

Experts say farmers often respond to nutrient gaps by adding more fertiliser than crops require. Costs rise, soil quality slips, and environmental and health risks build. They recommend focusing on better soil management.

SRDI scientists note that applying dolomite or lime, together with balanced fertiliser use, can lift output of potatoes, pulses, mustard, and vegetables by 10 to 40 percent in areas with severe acidity. Farmers can also lower input costs by 15 to 35 percent.

GAU vice-chancellor Dr. Rahman told Bonik Barta that reduced chemical use and greater reliance on organic fertiliser could ease acidity. “Lime is the most effective treatment,” he said. “Applying one tonne of lime per hectare can raise yields by 20 to 100 percent. On that basis, Bangladesh could add between 5 and 6.5 million tonnes of output.”