Environmental Impacts of Indiscriminate Use of Fertilizers
Fertilizers contaminate the soil with impurities, which come from the raw materials used for their manufacture. Mixed fertilizers often contain ammonium nitrate (NH4NO3), phosphorus as P2O5, and potassium as K2O. Further, over use of NPK fertilizers reduce quantity of vegetables and crops grown on soil over the years.
Pollution by Indiscriminate use of Urea
Since Urea is more subsidized in comparison to the P and K fertilizers, there is much more use of Urea and this brings in nitrogenous pollution. The nitrogen from fertilizers and manures are eventually converted by bacteria in the soil to nitrates. These nitrates can be leached into the groundwater or be washed out of the soil surface into streams and rivers. High nitrate levels in drinking water are considered to be dangerous to human health.
Pollution by indiscriminate use of Phosphorus
Phosphorus cannot be readily washed out of the soil, but is bound to soil particles and moves together with them. Phosphorus can therefore be washed into surface waters together with the soil that is being eroded. The phosphorus is not considered to be dangerous, but it stimulates the excessive growth of plants and this process is called eutrophication. These algae eventually die and decompose, removing the oxygen from the water which in turn kill the fish. Further, the The Arsenic, Lead and Cadmium present in traces in rock phosphate mineral get transferred to super phosphate fertilizer.
Since the metals are not degradable, their accumulation in the soil above their toxic levels due to excessive use of phosphate fertilizers, becomes an indestructible poison for crops.
Indiscriminate use of Potassium
Potassium, the third major nutrient in fertilizers, does not cause water quality problems because it is not hazardous in drinking water and is not a limiting nutrient for growth of aquatic plants. It is tightly held by soil particles and so can be removed from fields by erosion, but generally not by leaching. However, too much use of Potassium inhibits the absorption of other nutrients, which leads to the symptoms caused by the deficiency of these nutrients.
It also reduces the protein content of wheat, maize, grams, etc., grown on that soil. The carbohydrate quality of such crops also gets degraded. Excess potassium content in soil decreases Vitamin C and carotene content in vegetables and fruits. The vegetables and fruits grown on overfertilized soil are more prone to attacks by insects and disease.