Fertilizers are used to replace nutrients used from the soil by plants in the landscape and garden. When used properly, fertilizers are a useful tool for improving garden conditions. Mismanaged fertilizer applications, however, may pollute the ground water, water located beneath the soil surface between soil pores and in large rock fractures in the subsoil.
Phosphorous and Nitrogen Runoff
Phosphorous is a macronutrient found in almost all store-bought fertilizers. Inorganic fertilizer contains phosphorous that does not move readily in soil, according to the University of Minnesota. Soil erosion from floods, drought or wind may move soil that contains phosphorous into drains that lead to ground water. Nitrogen is of greater concern. It is not tightly held by soil and easily becomes a part of water runoff, making it a mobile nutrient.
Phosphorous when released into water supplies causes the growth of algae. Ground water that rises and becomes part of a lake or stream may cause algae to grow at an accelerated rate, causing oxygen levels to drop and fish and wildlife to die. Nitrogen in ground water that rises and pollutes proper water supplies can cause nitrogen poisoning. Excessive amounts of nitrogen in water supplies may cause methemoglobinemia in infants, which is the inability to process oxygen properly.
A soil test is recommended to determine the amount of fertilizer required for a lawn or garden, says the University of Wisconsin. Soil tests determine the nutrient content of the soil as well as the soil pH, or acidity. Choosing the correct fertilizer according to its nutrient contents prevents the leaching of excess nutrients not used by plants in the lawn.
Applying fertilizer correctly prevents the pollution of ground water supplies. A drop spreader is recommended for fertilizer application to prevent fertilizer pellets or material from being thrown into nearby water or gutters, which may wash into ground water supplies. Any fertilizer that is on the street or sidewalk requires quick cleaning to prevent it from spreading. Grass clippings require sweeping from the street as well to prevent fertilizers in the clippings from polluting.
Erosion and Irrigation
Controlling erosion of soils helps prevent the pollution of ground water supplies. Prevent dried soil from being washed off by covering it with crops or by regularly irrigating. Carefully apply water to plants to prevent flooding and soil runoff. Sloped sites require frequent watering at a shallow depth to prevent runoff.