The contribution of chemical fertiliser to raising Bangladesh's farm output is undeniable. Since the Green Revolution, fertiliser has brought notable success in food production. But applying either less or more fertiliser than needed harms agriculture, and unbalanced fertiliser use is now one of the biggest challenges facing the country's farming. In many cases farmers use too much urea or nitrogen fertiliser but do not apply enough phosphorus, potash, sulphur, zinc, boron and other nutrients. This upsets the soil's nutrient balance and in the long run puts farm production, the environment and public health at serious risk.

At least 17 essential nutrients are needed for normal crop growth and development. Nitrogen, phosphorus and potassium are known as the primary nutrients, while sulphur, calcium, magnesium, zinc, boron, iron and other micronutrients are just as important. Maximum yield is possible only when all the nutrients a crop needs are present in the right proportions. If one nutrient is in excess or deficit, normal plant growth is hindered. In agronomy this is called Liebig's law of the minimum: the nutrient in shortest supply sets the limit on production.

The greatest damage from unbalanced fertiliser use is to the soil. Applying urea alone for years reduces soil organic matter and creates shortages of other essential nutrients. Organic matter in most of Bangladesh's farmland has already fallen below the desired level. Excess nitrogen increases soil acidity, harming soil structure and biodiversity. The soil's water-holding capacity falls and its physical, chemical and biological properties deteriorate. Land that once gave high yields gradually loses productivity, so farmers must use even more fertiliser to grow the same amount, creating a vicious cycle.

Many farmers believe more fertiliser means a bigger harvest. In reality the opposite is true. Excess nitrogen makes stems and leaves grow too much but can reduce grain yield. In rice, too much urea makes plants more likely to lodge. In vegetables, excess nitrogen promotes leaves rather than fruit. A shortage of potash or zinc leaves fruit small and of poorer quality. Unbalanced nutrition reduces flowering and fruit set, leaves grain unfilled and lowers market value, so farmers miss out on the profit they expected.

Plants that get balanced nutrition resist disease better. Unbalanced fertiliser use weakens them and raises the risk of disease and pest attack. Excess nitrogen produces soft tissue that becomes attractive food for insects, and disease increases in rice, wheat, maize and vegetables under such conditions. Farmers then have to use more pesticide, raising production costs and creating new risks for the environment and public health.

The effects of unbalanced fertiliser use are not confined to the field; they spread across the whole environment. Excess nitrogen and phosphorus are washed by rain into canals, beels, rivers and ponds, causing abnormal algal growth known as eutrophication. This depletes oxygen in the water and kills fish and other aquatic life. Beneficial soil microbes, earthworms and other organisms also decline; since they play an important role in maintaining fertility, their loss reduces the soil's natural capacity to regenerate. Excess nitrogen also releases nitrous oxide, a powerful greenhouse gas that further accelerates climate change.

Another serious effect of excessive and unbalanced fertiliser use is a rise in harmful residues in food. Excess nitrogen can cause nitrate to accumulate, especially in leafy vegetables. In the human body this nitrate can be converted into nitrite and pose various health risks. Long-term consumption of contaminated food can particularly harm children, pregnant women and the elderly. If nitrate pollution of groundwater increases, safe drinking water can also become scarce. Fertiliser use is therefore not only a matter of farm production but closely tied to protecting public health.

With fertiliser prices rising steadily, farm production costs are also going up, and using more fertiliser than needed becomes a direct financial loss. Farmers often think more fertiliser will bring a bigger yield, but excess fertiliser may instead cut yields, so they spend more without getting the profit they expected. At the same time, more pests and diseases raise the cost of pesticides, increasing overall production costs and reducing profitability.

An important point in plant nutrition is the interaction between nutrients. If one nutrient is deficient, the crop cannot take up others properly even when they are plentiful. For example, without enough phosphorus the efficiency of nitrogen falls, and a shortage of potash weakens a plant's water management and disease resistance. A desired yield cannot be achieved by applying more of only one nutrient; each must be applied in balanced, scientific doses.

Several effective steps are urgently needed to tackle unbalanced fertiliser use:

• Test the soil at regular intervals to know its real nutrient status, and follow fertiliser recommendations based on the results.
• Not just urea: ensure TSP, MoP, gypsum, zinc, boron and other nutrients are applied as needed.
• Increase organic matter by returning cow dung, compost, vermicompost, green manure and crop residues to the soil.
• Ensure integrated use of chemical and organic fertilisers to maintain long-term soil health.
• Train farmers in modern nutrient management, soil testing and fertiliser application technology.
• Expand soil sensors, digital soil maps, GPS-based fertiliser management and ICT-based farm services.

The future of Bangladesh's agriculture depends not on using more fertiliser but on using it in the right doses and in balance. Unbalanced fertiliser use destroys soil fertility, lowers yield and quality, increases pest and disease attacks, pollutes the environment, endangers food safety and public health and costs farmers money. The call of the hour is "not more fertiliser, but the right fertiliser". If soil testing, balanced nutrient management, more organic matter and modern technology can be ensured, agriculture will be more productive, environmentally friendly and sustainable. There is no alternative to balanced fertiliser use for healthy soil, safe food and profitable farming. Unbalanced fertiliser use is a silent danger to agriculture, the environment and public health.

Source: Jagonews24. First published in Bengali on The Agro News.