Fertilizers acidify soils

Crop yield drops, plant biodiversity is impacted as a whole  

By Salonie Chawla
Published: Friday 30 April 2010

SOILS, too, must endure acidity. Each plant and soil life form has a particular soil pH it is used to. Any change can lead to complications in the organism’s metabolism. For example, decrease in pH modifies the top soils—a major source of crop nutrients.

J H Guo from the China Agricultural University in Beijing and his team used two countrywide surveys, comparisons of individual sites and long-term monitoring-field data sets to evaluate changes in soil pH. Soil pH declined significantly from the 1980s to the 2000s in the major Chinese crop production areas. Average decline for was between 0.13 and 0.80. The places followed intensive agriculture using large amounts of nitrogen fertilizers.

Acidity increased more in soils growing vegetables which need more fertilizers than soils cultivating cereals. Compared to 1981, grain production increased 54 per cent by 2007. During this time nitrogen fertilizer consumption increased 191 per cent.

Nitrogen cycling releases 20 to 221 kilomoles of hydrogen ion per hectare (ha) per year. This is much higher than the acid deposition (0.4 to 2.0 kilomoles of hydrogen ion per ha per year) through processes like acid rain. Acidification by human activities such as nitrogen fertilization is at least 10 to 100 times greater.

“Optimal nutrient management strategies can significantly reduce nitrogen fertilizer rates without decreasing crop yields,” the researchers wrote in the study published in Science on February 19. “Fertilization based on nitrogen management practices is one of the most urgent requirements for sustainable agriculture in China and in other developing regions worldwide”, they added.

India faces a similar problem. “There are 100 million ha suffering from acidity. About 25 million ha are in critical condition and 12 million ha need immediate attention,” P D Sharma, ICAR Assistant Director General (Crop Science Division) told Down To Earth. The problem is evident in hilly areas and coastal regions and the Deccan area. ICAR is developing approaches to counter it. Soil liming— addition of lime to soils is one.

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