Soil Nutrient Mining

Soil Nutrient Mining strictly described as deterioration in soil physical, chemical and biological properties. It occurs through a combination of lowering of soil organic matter and loss of nutrients. Crop production has been based on the use of plant nutrients already contained in the soil.

In Bangladesh, soil nutrient mining is mainly due to exploitation of land without proper replenishment of plant nutrients in soils. The problem is enhanced by intensive landuse without appropriate soil management. The problem is more acute in areas where HYV crops are being cultivated using low and imbalance doses of mineral fertilisers and little or no organic recycling. Because of increase in the cropping intensity and cultivation of modem varieties of crops, the net removal of nutrients (nitrogen- N, phosphorus- P, potash- K, sulphur- S) in areas under intensive cultivation ranges between 180 and 250 kg/ha/yr. Most of the soils under highland and medium highland situations are low in fertility level where especially N, P, K, S and Zn are deficient. Recently, deficiencies of magnesium (Mg), boron (B) and molybdenum (Mo) are also being found in some areas of Rangpur, Nilphamari, Kurigram, Gaibandha, Dinajpur, Panchagarh, Thakurgaon, Gazipur districts and barind tract. These areas of low fertility or nutrient mining comprise about 60% of the total cultivable land areas (mainly intensively cropped areas) of the country.

Of the total nutrients used in Bangladesh agriculture nitrogen alone constitutes about 80% while the use of P and K is limited to about only 6.0 and 6.6 percent respectively. Data show that the use of TSP fertilisers has remarkably fallen to 72.629 tons in 1996-97 from 215.061 tons in 1980-81, but again increased to 592 tons in 2010-11. By this time the use of DAP has also increased which is used as a source of nitrogen and phosphorus. Among the fertilisers which are in use in agriculture, urea is at the top of the list. The consumption ratio of N : P : K was 17 : 1 : 1.85 in 2010 which 8 : 3 : 1 in 2000 but the recommended dose of fertilizer is at the ratio of 2 : 1 : 1.2. Thus an imbalance condition is existing in nutrient balance in soil. [Muslem Uddin Miah]