Signs Your Soil Has Too Much Nitrogen

Originally posted on Men's Journal | By Emily Fazio | Last updated Aug 5, 2024 9:28 AM ET

Organic nitrogen is important for plant growth, but too much of it can cause a range of problems. Over-fertilization, improper composting, or runoff from nearby agricultural areas can all contribute to excess of chemical nitrogen in your soil. Here are some signs that your soil might be showing symptoms of nitrogen toxicity, either due to improper use of synthetic fertilizers or other sources of nitrogen:

1. Excessive Leaf Growth

One of the most obvious signs of nitrogen leaching is lush, green foliage with very few flowers or fruits. Plants rely on soil fertility to grow leaves, but as an expression of nitrogen stress, plants may grow tall and leafy but without producing the flowers, fruits, or vegetables you expect — it'll be a noticeable crop response. This can be particularly problematic in flowering plants and crops where the primary goal is crop yield, not just foliage.

2. Weak, Leggy Plants

While nitrogen field studies show that it can promote leaf growth, the increase in nutrient uptake can cause plants to become weak and leggy. The stems may be thin and unable to support the weight of the foliage, making plants prone to falling over or breaking. This weakness is often due to the plants putting too much energy into growing leaves at the expense of developing strong stems and plant roots.

3. Delayed Flowering and Fruiting

If the quantity of nitrogen released is too high during the spring, it can delay the flowering stage and fruiting processes. Plants with high nitrogen levels may take longer to bloom, or they may produce fewer flowers and fruits. This delay occurs because the plants are focusing their energy on producing foliage rather than reproductive structures.

4. Increased Pest and Disease Problems

Excess nitrogen can make plants more susceptible to pests and diseases. The lush, tender growth that results from too much nitrogen is often more attractive to pests and can be more prone to fungal infections and other diseases.

How to Fix Nitrogen-Heavy Soil

If you suspect your soil has too much nitrogen, don't worry—there are several steps you can take to balance your soil nutrients and promote healthy plant growth.

Stop adding nitrogen fertilizers. Switch to balanced or low-nitrogen options if fertilization is still necessary for other nutrients. Also, be mindful of the nutrients your soil gets in the late summer — it's different than the springtime!
Incorporate high-carbon materials. Add things like sawdust, straw, or shredded leaves, to the soil. These materials help to balance the nitrogen by promoting microbial activity that breaks down excess nitrogen.
Plant nitrogen-absorbing crops. Certain plants, known as "nitrogen-hungry" crops, can absorb excess nitrogen from the soil. Consider planting crops like corn, broccoli, cabbage in your garden, or fast-growing grasses in your lawn. All will help balance the levels of nitrogen in the soil.
Increase soil drainage. Incorporate organic matter and improve how you irrigate. Good drainage helps to promote nitrogen loss and wash away other soluble nutrients from the root zone.
Monitor soil pH. High nitrogen levels can lead to acidic soil conditions. Regularly test your soil's pH and adjust it as needed with lime or sulfur to maintain a balanced pH level.
Use mulch. Applying mulch around your plants can help to moderate soil temperature and moisture, which can aid in the reduction of nitrogen levels over time.
Compost wisely. When adding compost to your soil, make sure it's well-decomposed and balanced in nutrients. Avoid compost that's too rich in nitrogen, such as fresh manure.

Can soil testing help identify nitrogen levels?

Yes, soil testing is an excellent way to determine nutrient levels, including nitrogen. Testing can provide a precise measurement and help guide your amendments to balance the soil. Testing soil is important, and you might even find that some areas of your yard have alkaline soil if they haven't been routinely fertilized.

Does air temperature affect soil nitrogen levels?

Indeed, the temperature does affect soil health! Here's how:

Microbial Activity: Warmer temperatures increase microbial activity, enhancing nitrogen processes. Extreme heat can inhibit it.
Nitrogen Volatilization: High temperatures boost nitrogen loss as ammonia, especially from urea-based fertilizers.
Decomposition Rates: Warmer conditions speed up organic matter decomposition, releasing more nitrogen.
Plant Uptake: Higher temperatures promote plant growth, increasing nitrogen uptake. Cooler temperatures reduce this.
Soil Moisture: Warmth reduces soil moisture through evaporation, impacting nitrogen availability.
Nitrification and Denitrification: Moderate to warm temperatures speed up these nitrogen conversion processes.

How long does it take to correct nitrogen levels?

The time required to balance soil nitrogen depends on the severity of the excess and the methods used. It can take a few months to a growing season to see significant changes.

This article first appeared on Men's Journal and was syndicated with permission.

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