The Disadvantages of Inorganic Nitrate & Phosphate Fertilizers

Plant Needs

• Plants use nitrogen to build proteins and enzymes. Nitrogen is a key component in chlorophyll, the pigment that gives plants their color and is responsible for photosynthesis. An ample supply of nitrogen in the soil promotes high yields of fruits, vegetables and seeds. Phosphorus is also important for photosynthesis as well as vigorous growth, abundant blooms and strong roots.

Nitrate

• Even though over three-quarters of the atmosphere is made up of nitrogen, most plants cannot use atmospheric nitrogen and rely on ammonium (NH4+) and nitrate (NO3-) in the soil for their supply of nitrogen. The nitrogen cycle turns the nitrogen from the air and from other organic sources of nitrogen such as manure and decomposing plant wastes into usable ammonium and nitrate in the soil. To increase the amount of ammonium and nitrate in the soil quickly, farmers and gardeners often add nitrate forms of inorganic fertilizers such as ammonium nitrate and calcium nitrate.

Nitrate Fertilizer Problems

• Nitrate fertilizers move through the soil in water. Excessive rainfall and irrigation send the fertilizer deeper into the soil away from the root zone and may enter groundwater, causing contamination. When rain and irrigation water hit the nitrate fertilizers sitting on the surface of the soil, the reaction causes some nitrogen loss to the atmosphere. Heavy watering and rainfall also wash away excess surface nitrate fertilizer, contaminating waterways.

Phosphate Fertilizer

• To make inorganic commercial phosphate fertilizers, fossilized remains of ancient marine life are combined with sulfuric acid to produce phosphoric acid, which is then heated to remove water. The superphosphoric acid produced is about 72 to 76 percent phosphate and contains orthophosphate and polyphosphate. Orthophosphate is the form of phosphorus readily taken up by plants. The polyphosphate converts to orthophosphate in the soil.

Phosphate Fertilizer Problems

• Phosphate fertilizers bind to soil particles quickly, preventing leaching and runoff. However, when phosphate fertilizer is not properly applied, and the fertilizer hits hard surfaces like driveways, roadways and pavements, it is washed away with rainwater that drains into lakes and rivers. This phosphorus pollution promotes the overproduction of algae, which depletes the waterways of oxygen, killing the native wildlife.