Harmful Effects of Fertilizers

The long-term use of fertilizers has been shown to have detrimental effects on soil structure and overall soil health that leads to erosion. Farmers commonly report that the long-term use of synthetic fertilizers leads to soil compaction and poor tilth.

Living Soil

Healthy soil is made up of minerals, air, water and organic matter. Mineral particles are broken down into sand, silt and clay. When we speak of soil texture we are referring to the proportions of these three mineral parts that are present. Soil structure refers to the ability of soil particles to clump together to form aggregates. Good soil structure can be demonstrated by how easily it crumbles in your hand. Both soil texture and structure determine how well soil holds air and water. The final element of healthy soil is organic matter in various stages of decomposition and the presence of a large, diversified population of soil organisms that help decomposition and the recycling of nutrients.

How Plants Use Nutrients

In the natural environment plants don't take in fertilizer directly but rely on microorganisms to convert nutrients into compounds the plants can absorb. Bacteria break down organic matter and minerals, while mycorrhizae (my-cor-ry'-zee) fungi live on plant roots, increasing the uptake of water and nutrients. They also produce hormones and antibiotics that enhance growth and fight disease.

Commercial fertilizers can be a valuable resource when used in moderation. The exuberant use of commercial fertilizer upsets the natural balance of soil when applied incorrectly.

Nitrogen Fertilizers

Excessive use of nitrogen stimulates the growth of bacteria and the decomposition of organic matter, but this eventually leads to an imbalance of the nitrogen-carbon ratio. With little carbon available, the bacterial population shrinks and soil texture declines.

Sodium Buildup

Sodium, a component of most chemical fertilizers, accumulates and combines with carbonic acid to form sodium carbonate. This substance causes the soil to assume a cementlike hardness that affects drainage, friability and aeration. Fertilizers that contain a high salt content include potassium nitrate (muriate of potash), ammonium nitrate and sodium nitrate.

Alkalinity

Certain fertilizers can affect soil alkalinity. Repeated use of calcium nitrate, di-ammonium phosphate, ammonium sulfate or aluminum sulfate will make the soil more alkaline, while monoammonium phosphate (ammo-phos) or sulphate of ammonia will make it more acidic. A pH reading that is too high or low will make essential nutrients unavailable.

Solution

Fertilizers can be a great benefit when used sparingly to correct an acute deficiency. A boost of nitrogen after a period of wet weather can be helpful. Consider diluting water-soluble fertilizers by half and apply twice as often. Organic sources such as manure and compost are a better choice for planned yearly applications.

References

• Sustainable Soil Management