Rising soil acidity threatens crop production in Bangladesh

Soil is a very important natural resource. It is the source of food and habitat for most of the world's organisms. Agricultural Bangladesh does not have much natural mineral resources. As a result, the livelihood of most people in this country is dependent on agriculture. And the main basis of agricultural work is soil resources. This soil resource is more precious than the gold associated with the destiny of most of the people of this country. But unfortunately, it is true that the soil environment and soil fertility are under threat due to various reasons. Besides, food prices are expected to increase by 30 percent in the next 25 years due to soil degradation. Seventy five percent of Bangladesh's total agricultural land has lost its fertility.

One of the many problems in crop production is soil acidity. The total cropland in Bangladesh is about 85 lakh 86 thousand hectares. Out of this, about 2 lakh 78 thousand hectares of land is highly acidic (pH value below 4.5) and about 36 lakh 44 thousand hectares of land is more acidic (pH value 4.5 to 5.5). Soil acidity is increasing due to unplanned use of chemical fertilizers. A study by the Soil Resources Development Institute (SRDI) found that in 2010, about 2.5 million hectares of land were very strongly acidic (pH <4.5) and about 3.7 million hectares were strongly acidic (pH 4.5-5.0) across the country in 2010.As seen in the 2020 survey, highly acidic land increased to 2.78 million hectares and 3.64 million hectares to strongly acidic land. Besides, in 2010, the soil of 0.30 million hectares of land was deficient in both calcium and magnesium.

The 2020 study showed that the cultivated land in very low to low calcium and magnesium status is about 2.10 and 1.05 million hectares which is 24.53% and 12.31% of the total cultivated land of Bangladesh respectively. Excessively acidic soils are deficient in phosphorus, calcium, magnesium and molybdenum and excess in Aluminum, iron and manganese, stunting crop growth and reducing yield. Most of the soil in the Barend and Madhupur average areas of Bangladesh including the hilly areas of greater Rangpur, Dinajpur, Sylhet, Chittagong are very acidic to highly acidic. As a result, the desired yield of cultivated crops is not being achieved in all these regions. In order to obtain the desired level of yield, it is necessary to take necessary steps to reduce excessive and high acidity of such soil.

Soil Acidity or pH: The strength of hydrogen ions in soil is called soil pH. Soil pH is a measure of soil acidity or alkalinity. If the soil acidity/alkalinity is not balanced, plants cannot take nutrients from the soil in the right amount even if there is sufficient amount of nutrients in the soil. Therefore, if any nutrient deficiency symptoms appear, the first thing to check is whether the pH of the soil is correct. Soil pH is measured on a scale of 1 to 14. If the soil has too many hydrogen ions, the pH will be low and the mixture will be acidic and if the hydrogen ion level is low, the soil will be alkaline. When the pH is around 7, the mixture is neutral and when the soil pH rises above 7, the soil becomes alkaline.

This availability of pH is very important. This is because it affects the availability of various nutrient ions in the fertilizer. Ensuring favourable soil conditions is necessary for good crop production. These nutrients are readily available to crops if the soil pH is between 5.6 and 7.3, i.e., mildly acidic to mildly alkaline soils. Soils with this pH value are favourable for the growth of soil micro-organisms, which increase the availability of essential nutrients for crops. In Bangladesh, especially in the northern part of the soil, there is a deficiency of calcium, magnesium and other alkaline elements, which is one of the reasons for the increase in soil acidity.

How Soil Acidity Increases: First, Acid rain plays a major role in lowering soil pH. Acid rain water has a pH of around 5.7, which is acidic in nature. This water mixes with the soil and lowers the pH of the soil making it acidic. Secondly, the carbon dioxide (CO2) emitted by the plant as a result of root respiration increases the amount of carbolic acid (H2CO3) in the soil, which lowers the soil pH and makes the soil acidic. Thirdly, plants absorb ions (NO3?, NH4+, Ca2+, H2PO4-) from the soil to carry out their various biological functions, which creates an imbalance of mineral ions in the soil. As a result, the soil becomes acidic in nature. Fourth, the application of chemical fertilizers changes the pH of the soil because the main component of chemical fertilizers is ammonium (NH4+) which reacts with the ions present in the soil to form nitrate (NO3) and hydrogen ions (H+) are released in the soil, as a result the soil pH decreases and the soil becomes acidic.

Treatment of Acidic Soils: Retention of water in the paddy field brings the acidity under control within three weeks. Applying fresh ash of wood ash or chaff to the soil reduces the effects of aluminium poisoning. Adequate application of organic fertilizers of good quality is beneficial. If the soil pH is less than 5.5, it is absolutely necessary to treat the soil with lime. The recommended dose of Dolochun in more acidic soils is 04 kg per decimal or 400 kg per acre or 1000 kg per hectare. It cannot be increased or decreased in any way. After applying Dolochun to a land once, there is no need to apply Dolochun again for three years. Before applying Dolochun to any land, the total Dolochun should be divided into two equal parts according to the recommended dosage. Half the amount of Dolochun should be sprinkled in north-south direction while the soil is fertile.

The remaining half amount of Dolochun should be sprinkled along east-west or horizontally. Along with the application of Dolochun, it should be mixed well with the soil by cross-cultivation and a ladder. After at least 7 days the land should be planted with necessary tillage and ladders or planting of trees. Sowing seeds immediately after application of Dolochun may reduce the rate of seed germination or inhibit root and stem growth of germinated plants. If the land is dry or there is less juice, then the rule of using Dolochun is that Dolochun should be applied transversely as needed on vacant land. Then it should be levelled with a ladder by ploughing. With light irrigation should be done. Then after at least 7 days, the land should be sown or planted with the necessary tillage and ladder.

Finally, soil acidity is closely related to soil health. Sustainable soil management is essential to ensure food security. Agriculture in Bangladesh is now transitioning from subsistence agriculture to commercial agriculture. In this situation, it is essential to reduce soil acidity and protect soil biodiversity. Maintaining soil fertility through this is vital for the future agricultural production of the country. Therefore, it is the need of the hour to take necessary initiatives in this regard.

The writer is Principal Scientific Officer, Soil Resources Development Institute, Ministry of Agriculture, Regional Laboratory, Faridpur