Soil Acidity

We have taken soil for granted since long. Soil acidification is a major problem in agriculture, affecting 30%–40% of the world’s arable land. Increasing soil pH will automatically increase nutrient availability.

A complete nutrient management plan must include monitoring of pH so that all of the other nutrients can be most efficiently used by the crop. For soils to be highly productive, they must first be in the optimum pH range The proper pH will ensure that all essential nutrients are available for plant uptake. Values under pH 4.5-5.0 can be very damaging to plants .Adjusting soil pH between 6.5 and 7.0 will provide maximum availability of nutrients to the plants.

• Soil pH affects many aspects of crop production, including nutrient availability, potential for metal toxicity, efficacy and degradation of soil-applied herbicides, and nitrogen fixation by leguminous crops.

• Soil pH affects many physical, chemical, and biological reactions necessary for crop yield ,survival and growth.

• Nutrient Transformations and Nitrogen Fixation are restricted in acidic soils, due to reduced activity of the microorganisms which are responsible for these processes.

• Metal Toxicity negatively effects root growth in acidic soils, and is the most important reason for managing soil pH. Certain metals such as Fe, Al and Mn are released into the soil solution when pH becomes acidic. These metals, particularly Al, damage plant roots by interfering with cell division and cell wall formation. It also interferes with the uptake, transport and use of nutrients, including Ca and P.

Soil PH and nutrient uptake by the plant

Main factors affecting soil acidity

• Rainfall and leaching

• Acidic parent material

• Organic matter decay

• Nitrogen Fertilizers

• With an acidic soil (pH4.5) only 30% of Nitrogen (N), 23% of Phosphorus (P) and 33% of Potassium (K) used on the field get absorbed.

Once pH drops to 4.5 the mineralization of the ammonium is slower and nitrate availability reduces. Ammonium sulphate,a nitrogen based fertilizer acidifies the soil three times compared to urea.

Effect of soil acidification by Nitrogen fertilizers

Nitrogen fertilizer

CAN

Urea, Ammonium Nitrate

Ammonium Sulphate Nitrate (ASN) | Diammonium phosphate (DAP)

Ammonium sulfate

Amount of CaO required to compensate the soil acidity caused by 1 kg of Nitrogen considering 50 % utilization