窒素肥料は、作物の成長を助け、収穫量を増やすことができるため、農地で広く使用されています。

READING

Nitrogen fertilizers are widely used on farmland because they help crops grow and can increase yields. However, plants do not absorb all of the nutrients that farmers apply. When more nitrogen is added than crops can use, some of it remains in the soil and can be carried away by rain. Water moving across fields or through the ground may then transport this excess nitrogen into rivers, lakes, and coastal waters. As a result, areas far from the original farmland can receive unusually high levels of nutrients, especially after heavy rainfall or during seasons when fields are left bare.

Too much nitrogen in water can cause serious environmental and economic problems. High nutrient levels can trigger rapid growth of algae, which may block sunlight and later consume large amounts of oxygen as they decompose. When oxygen levels fall, fish and other aquatic organisms can decline or disappear from affected areas. This can reduce catches for fishing communities and damage ecosystems that support tourism and recreation. Water utilities may also face greater difficulty and expense when polluted rivers or lakes are used as drinking-water sources. In this way, fertilizer runoff can affect both natural systems and people who depend on clean water.

One response is to manage fertilizer use more precisely so that farmers apply only the amount crops are likely to need. Vegetated buffer strips can also be maintained along waterways to capture nutrients before they reach streams or lakes. These measures can reduce pollution, but they have limits. The correct amount of fertilizer varies with soil, weather, and crop conditions, making precise decisions difficult. In addition, setting aside land for environmental protection can reduce the area available for production. Farmers may therefore face lower income or higher management costs even when the measures improve water quality.