Cause of Fertilizer Burn

All fertilizer, organic and inorganic contains three primary macronutrients, nitrogen, phosphorus and potassium. These macronutrients mixed with a variety of added micronutrients and other macronutrients help plants develop and grow. However, too much of a concentration of these nutrients can lead to fertilizer burn, which can damage plants, lawns and gardens.

What is in Fertilizer?

Fertilizer contains nitrogen, phosphorus, potassium, baron, copper, iron, magnesium and molybdenum. That long list of ingredients is a mouthful, but the three main nutrients that are important to fertilizer burn are nitrogen, phosphorus and potassium. The other nutrients are considered secondary macronutrients and micronutrients, which are added in limited amounts to most commercial fertilizers. Understanding the difference between organic and inorganic fertilizer is important to determine what nutrients are in your specific fertilizer.

Primary Macronutrients

Nitrogen promotes cell division and leafy green growth, phosphorus helps plants during photosynthesis, take up water and with reproduction, and potassium helps the plant absorb the other two macronutrients. An imbalance of these nutrients in soil can lead to weak plants, poor plant growth and in the case of over fertilization and under fertilization, fertilizer burn.

Organic vs. Inorganic Fertilizer

Organic and inorganic fertilizer contain the same nutrients, but in varying amounts. Inorganic fertilizer contains less of a concentration of macronutrients that cause fertilizer burn. Organic fertilizer is made from decaying matter or organic waste products. These natural methods of extracting nutrients contain less of a concentration per standard 40lb fertilizer bag. Synthetic fertilizer, made in laboratories, often includes micronutrients and secondary macronutrients. The concentration of the nutrients is greater in inorganic or synthetic fertilizer because the concentrations are manmade.

Inorganic Fertilizer Burn

Inorganic fertilizer is the primary culprit for fertilizer burn. Fertilizer replenishes soil with macronutrients; however, soil may already contain these nutrients. Fertilizer burn occurs primarily from too much potassium in soil, but can occur with low levels as well. According to the soil education website by NASA, plants that do not get enough potassium will appear "burned" around the edges. Fertilizer burn also occurs when plants get too much potassium. Potassium works as a salt to plants by helping regulate water intake, when there is too much it makes it hard for plants to take enough water for proper growth.

Organic Fertilizer Burn

Organic fertilizer can burn plants the same way that inorganic fertilizer does. However, the main difference is that organic fertilizer does not contain the same level of nutrients, which means it is very hard to have fertilizer burn from organic fertilizer. Fertilizer burn from organic fertilizer is very rare, but it can happen if too much fertilizer is applied in one or more particular areas.

Soil Testing

Soil testing determines how much fertilizer to apply to your lawn or growing area for proper plant growth. Since all soil is different, it is important to know the nutrients in the soil before applying fertilizer. University-based and private labs test soil samples for a nominal fee. Soil testing should be done at least one-two months before fertilizer application.

Sources:

Personal experience working as the garden supervisor for ACE Hardware and from pursuing a degree in economics with a focus in agriculture

http://soil.gsfc.nasa.gov/soilfert/npk.htm