by Ron Alexander
For decades, conversations about fertilizers and soil amendments have focused on a single concern: keeping nutrients out of our waterways.
That’s an important goal—but it’s also one that is often oversimplified.
Nutrients such as nitrogen and phosphorus are essential for healthy plant growth, yet their movement through soil depends on far more than simply how much is applied. Soil texture, organic matter, microbial activity, moisture, and the form in which nutrients are supplied all influence whether nutrients remain available to plants or become an environmental concern.
Understanding these relationships helps landscape (and turf) professionals make better decisions that support both plant health and water quality.
Plants Require Nutrients—The Goal Is Using Them Wisely
Nitrogen, phosphorus, and potassium are among the nutrient’s plants required in the greatest quantities.
Without them, landscapes cannot establish and grow properly, and crops cannot be produced in appropriate quantities.
The objective isn’t eliminating nutrients from landscapes—it’s ensuring they’re available when plants need them while minimizing unnecessary losses to the environment.
Nutrient Movement Is More Complicated Than Many People Think
One common misconception is that nutrient management is simply a matter of applying less fertility.
In reality, nutrient movement depends on many interacting factors, including:
- Soil texture and structure
- Organic matter content
- Soil pH
- Rainfall
- Biological activity
- The chemical form of the nutrient
Two sites receiving the same application rate may experience dramatically different nutrient behavior depending on their soil and other climatic conditions.
Healthy Soil Is One of the Best Nutrient Management Tools
Improving soil health can actually help reduce nutrient loss.
Healthy soils:
- Hold more water
- Improve moisture infiltration and aeration
- Reduce runoff
- Support beneficial microorganisms
- Possess a higher cation exchange capacity (so, increase nutrient retention)
- Improve root development
Instead of viewing biosolids-based products solely as nutrient sources, they should also be viewed as tools that improve the soil’s ability to retain and cycle nutrients naturally (soil builders).
Organic Matter Helps Keep Nutrients in the Root Zone
Organic matter provides one of the greatest benefits to nutrient management.
As organic matter increases, soil develops a greater capacity to hold positively charged nutrients through a property known as **cation exchange capacity (CEC).**
Higher CEC means nutrients are less likely to be lost before plants can use them.
Organic matter also improves soil structure, allowing rainfall to infiltrate rather than run off the surface carrying nutrients with it. Further, organic matter also holds moisture which is a key method of reducing nutrient loss, as much of them are dissolved in water.
Nitrogen and Phosphorus Behave Very Differently
Although they’re often discussed together, nitrogen and phosphorus move through soil in different ways.
Nitrogen
Nitrogen—particularly nitrate (NO3)—is relatively mobile.
Because it dissolves readily in water, it can move through sandy soils or be lost through leaching if applied in excess. Further, it is negatively charged, like organic matter and clay particles, making it less likely to be bound in the soil.
For this reason, slow-release nitrogen sources often provide environmental and agronomic advantages. A large volume of the nitrogen in biosolids and compost products is in ‘organic’ form, bound within the organic matter that carries it.
Some of the nitrogen is also in ammoniacal (NH4) form, making it easy to bind with clay in soils (especially when incorporating it into the soil following application), but also readily volatilized into the atmosphere when left on the soil surface.
Phosphorus
Phosphorus behaves very differently.Rather than moving freely through soil, phosphorus readily binds to soil particles and minerals such as iron, aluminum, and calcium.
As a result, the amount of phosphorus contained in a soil amendment is not necessarily the amount immediately available for plant uptake—or for movement into nearby waterways. Phosphorus in chemical fertilizers are prone to be more mobile.
Slow-Release Nutrients Offer Important Advantages
Many recycled organic soil amendments contain nutrients in forms that become available gradually through microbial activity.
Rather than releasing nutrients immediately after application, these materials rely on natural biological processes to mineralize the nutrients over time.
This gradual release better matches plant demand while reducing the potential for rapid nutrient loss.
Soil Biology Is Part of the Nutrient Cycle
Healthy soils contain billions of microorganisms that perform critical functions.
They:
- Break down organic matter
- Cycle nutrients
- Improve soil aggregation
- Support root growth
- Help suppress certain soil-borne diseases
These biological processes regulate when nutrients become available, creating a more natural and efficient nutrient cycle than relying solely on highly soluble fertilizers.
Not All Soil Amendments Behave the Same
Organic amendments differ significantly depending on how they’re produced.
Fresh organic materials, composts, biosolids-based products, and other recycled organics each contain different:
- Carbon-to-nitrogen ratios
- Nutrient concentrations
- Organic matter stability
- Rates of nutrient release
Understanding these differences is far more useful than assuming all organic amendments perform the same way.
Modern Testing Provides Better Answers
Historically, nutrient management often relied on measuring total nutrient content.
Today, newer testing methods can evaluate how much phosphorus is actually water-extractable—or more immediately available—rather than simply reporting the total amount present.
These methods provide a much better understanding of how recycled organic amendments are likely to perform in the field.
Carbon Is Becoming Increasingly Important
One of the biggest shifts in soil science is recognizing the importance of carbon.
And adding stabilized organic matter does far more than add some nutrition and help to cycle it.
It also:
- Improves soil structure
- Increases water-holding capacity
- Supports microbial communities
- Builds long-term soil health
- Improves climate resilience
These benefits often work together to improve nutrient efficiency while reducing environmental risk.
Practical Steps to Reduce Nutrient Loss
Landscape professionals can significantly reduce nutrient movement by following several best management practices:
- Test soils before making nutrient applications.
- Choose slowly-release nutrient sources when appropriate.
- Incorporate soil amendments (organic matter) into the soil whenever practical.
- Avoid overapplication.
- Match nutrient applications to plant needs.
- Maintain healthy vegetation to reduce erosion.
Good nutrient management begins with healthy soil rather than simply applying more fertilizer.
The Future of Nutrient Management
As research continues, nutrient management is becoming more sophisticated.
Rather than focusing only on how much nitrogen or phosphorus a product contains, researchers increasingly evaluate:
- Nutrient availability
- Release rates
- Soil interactions
- Organic matter content
- Biological activity
- Water movement
- Long-term soil health
This more complete understanding allows landscape professionals to balance environmental protection with successful plant establishment.
Healthy soils are not simply better growing media—they are one of our most effective tools for protecting water quality and resisting climate change, while creating resilient landscapes.
*Ron Alexander is a horticulturist, author, educator, and one of North America’s leading experts on compost, recycled organics, and manufactured soils. With more than 40 years of experience consulting with landscape architects, municipalities, manufacturers, and the green industry, he has helped advance the science and practical application of compost and organic soil amendments. Ron has contributed to numerous books and authored hundreds of technical publications and is a frequent speaker on soil health, sustainable landscapes, compost utilization, and soil amendment technologies.*
