How Does Nitrogen Leach Out of Lawn Soil?

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Nitrogen leaves lawn soil mainly when nitrate dissolved in soil water moves downward past the grass roots. Once it is below the root zone, the plant cannot use it. The question of how does nitrogen leach out of lawn soil matters for two reasons: lawn color depends on nitrogen staying in reach of the roots, and nitrate that moves past the root zone can reach groundwater. This guide explains the mechanism using two university sources. One is a field study of lawn turf in southern New England. The other is a University of California extension publication on how nitrogen moves in turfgrass systems. It also marks where those sources stop.

Quick answer

• Nitrogen leaches when it is in the nitrate form. Nitrate is not held by soil particles, so it moves with the water that drains through the soil.
• In a three-year New England lawn study, annual nitrate losses were 16.8 percent of the nitrogen applied for ammonium nitrate, 1.7 percent for a polymer-coated sulfur-coated urea, and 0.6 percent for an organic product.
• In that study, losses happened mainly from late fall through early spring.
• The University of California source recommends watering fertilizer in right after application, avoiding heavy irrigation soon after fertilizing, and using slow-release sources on sand or very leachable soils.

How the leaching process works

Lawn nitrogen starts as several forms. Fertilizer may supply ammonium, which soil particles can hold, or nitrate, which they do not. Organic nitrogen in thatch and clippings also breaks down over time into ammonium and then nitrate. The University of California publication by Gibeault and co-authors explains the key point directly: when nitrogen is in the nitrate form, “it is not bound to soil or organic colloids.” Because it stays dissolved in the soil water, it “is mobile and can be taken up by turfgrass and other plant roots, or it can move from the immediate turfgrass system by leaching or runoff.”

That means leaching is a water problem as much as a fertilizer problem. Nitrate needs a downward flow of water to carry it past the roots. If irrigation or rain adds more water than the soil can hold within the root zone, the excess drains down and takes dissolved nitrate with it. If the grass is actively growing and the soil holds water near the roots, the plant and soil microbes can take up most of the nitrate before it moves far.

The same publication describes a second pathway that does not involve leaching. Ammonia can be lost to the air through volatilization when it is not dissolved in water quickly. This guide focuses on leaching, but it is useful to know that fertilizer loss can happen in more than one direction.

What the New England field study measured

Guillard and Kopp (2004), published in the Journal of Environmental Quality, set up a field experiment on a turf typical of southern New England lawns. The research compared four treatments over three years: ammonium nitrate, a polymer-coated sulfur-coated urea, an organic product, and a nonfertilized control. Each plot was supplied with a total of 147 kilograms of nitrogen per hectare per year. Percolate was collected with zero-tension lysimeters, which capture water that has drained below the root zone.

The flow-weighted nitrate concentrations in the percolate were 4.6, 0.57, 0.31, and 0.18 milligrams per liter for ammonium nitrate, the coated urea, the organic product, and the control. After correcting for losses in the control, the average annual nitrate leaching losses were 16.8 percent of the nitrogen applied for ammonium nitrate, 1.7 percent for the coated urea, and 0.6 percent for the organic product. Those numbers show that the fertilizer form made a large difference in how much nitrogen left the root zone.

The authors also found a seasonal pattern. In their words, “NO3–N leaching losses from lawn turf in southern New England occur primarily during the late fall through the early spring.” Their recommendation follows from the data: “lawn turf fertilizers should be formulated with a larger percentage of slow-release N than soluble N.”

The abstract gives the main results, but it is a summary. This guide relies on the abstract text and does not describe the full methods in the article.

What the California review adds

The University of California publication, titled “Movement of Nitrogen Fertilizer in a Turfgrass System,” reports a separate study at the Turfgrass Research Project in Riverside. The turf was a mature sward of mixed Kentucky bluegrass and perennial ryegrass on Hanford fine sandy loam with neutral soil pH. Irrigation was scheduled from evapotranspiration estimates. Leachate was collected from suction lysimeters, which draw soil water through a ceramic cup placed in the soil.

The study compared granular urea, sulfur-coated urea, and blood meal, along with an untreated check. Urea produced the highest nitrate concentration in the leachate, and it peaked “10 to 14 days following fertilizer application.” The June peak with urea was about 3 parts per million nitrate higher than the tap water used for irrigation. The publication states that sulfur-coated urea “resulted in significantly less leaching of nitrate than urea during urea peak leaching times.” Blood meal showed the lowest potential for nitrate leaching among the sources tested.

The review also draws a broader conclusion. “Most nitrogen applied to turfgrass usually stays in the turfgrass system,” the authors write, because surface organic matter supports microbes that hold and recycle nutrients. They say there “appears to be little chance of downward movement of nitrogen, other than on pure sand with immature turf present.” That statement is useful for setting expectations: for a healthy, mature lawn on ordinary soil, leaching may be small, but the risk rises on sand and on young turf.

Timing and soil type

Both sources point to timing. The New England study found losses concentrated in the cooler months, from late fall through early spring. The California study found that nitrate in leachate peaked roughly two weeks after urea was applied. Together, these results suggest that a lawn is most exposed when fertilizer is applied shortly before a period of heavy water movement through the soil.

Soil type matters too. The University of California publication recommends that growers “use low nitrogen rates or slow release sources on sands or very leachable soils.” It also cites a Washington State study on sand putting greens, where nitrogen leaching was higher in the first year than in the second. In that study, pure sand leached more nitrogen than a sand-peat mix, and frequent, moderate applications gave the lowest losses in the first year. The publication says leaching in the second year was greatly reduced, which the authors linked to more extensive rooting, more thatch, and more organic matter in the root zone.

The cited putting-green research is a different turf system from a home lawn. Its main lesson for a typical lawn is that a young stand on loose sand has less capacity to hold nitrogen than an established stand in loam, so timing and rate matter more in that case.

Practical ways to reduce leaching

The sources support a short list of practices. None of them requires special equipment, and they follow directly from the mechanism described above.

• Water fertilizer in soon after application. The University of California publication recommends watering in fertilizer immediately after application so it moves into the root zone rather than sitting on the surface.
• Choose slow-release nitrogen. The New England study found that coated and organic sources lost far less nitrogen than ammonium nitrate. Slow-release products make nitrogen available to the grass over a longer period.
• Use lower rates on sand. On sand or very leachable soils, the publication advises low nitrogen rates or slow-release sources.
• Avoid overirrigation after fertilizing. The same publication advises avoiding over-watering closely after fertilization, since excess water is what carries nitrate down.
• Apply when roots can use it. The publication recommends applying nitrogen when the turf roots can take it up and when soil nitrate is expected to be low.

Applying these practices together is a reasonable approach, but the sources do not give a single schedule that fits every lawn. The right timing depends on local climate, rainfall, soil texture, and grass species, and the sources do not rank these factors against one another.

For more on how to check and adjust soil conditions that affect water movement, see how to check soil moisture and how to make garden soil better.

How we chose

The two sources were selected because they measure nitrogen movement directly rather than describing it in general terms. The New England study reports leachate concentrations and loss percentages, and the California publication reports leachate sampling over time. Both come from university research or extension programs. Both are old enough to be well established, which means they describe turf practices that have not changed much, but the fertilizer products on store shelves today may differ from the ones studied.

The New England work is available to this guide only as a repository abstract. The California publication was read in full as extracted text. Neither source was checked for updates after its publication date, so the findings should be read as the state of published research as of the sources’ dates.

What we could not verify

The two sources do not answer every question about nitrogen loss from lawns. The gaps below should be kept in mind when applying the findings to a specific yard.

What the sources do not say

• The sources do not give a clay-soil comparison. The California publication mentions sands and very leachable soils, but it does not quantify leaching on heavy clay.
• The New England figures come from southern New England and three years of data. They do not establish loss rates for other climates or for lawns in drier regions.
• The California leaching samples came from a single site in Riverside and a 1990 study period. The publication does not give a general loss percentage for all lawns.
• The sources do not state a single safe nitrogen rate per square foot for home lawns. Rate recommendations depend on grass type and local conditions, and those are outside the sources reviewed here.
• The sources do not evaluate whether leached nitrate causes drinking water problems at typical lawn application rates, so this guide makes no claim about that.

Readers who need local guidance should check their state university extension service, since soil and rainfall patterns vary by region.

Frequently asked questions

Does nitrogen always leach out of lawn soil?

No. The California publication states that most nitrogen applied to turfgrass usually stays in the turfgrass system, and that leaching is small for mature turf on ordinary soils. Leaching is more likely when nitrate is present, when water moves downward through the soil, and when the soil is sandy.

Which lawn fertilizer loses the most nitrogen to leaching?

In the New England study, ammonium nitrate lost the most. Its average annual nitrate leaching loss was 16.8 percent of the nitrogen applied, compared with 1.7 percent for the coated urea and 0.6 percent for the organic product. The California study also found urea produced the highest leachate nitrate concentrations.

When is nitrogen most likely to leach from a lawn?

The New England study found losses occurred mainly from late fall through early spring. The California study found nitrate in leachate peaked about 10 to 14 days after urea was applied. Both sources suggest that timing relative to heavy water movement matters.

Do sandy soils lose more nitrogen than loam?

The sources indicate that sands and very leachable soils carry a higher risk. The California publication recommends low rates or slow-release sources on those soils, and it reports higher leaching from pure sand than from a sand-peat mix in the putting-green study. The sources do not provide a direct comparison with loam or clay under the same conditions.

Can overwatering a lawn cause nitrogen leaching?

Overwatering can increase leaching because nitrate moves with drainage water. The California publication advises avoiding overirrigation closely after fertilizing and avoiding runoff. The sources do not give a specific watering depth or schedule that prevents leaching.

Sources

• Guillard, K., and Kopp, K. L. (2004). Nitrate leaching from lawn turf receiving different nitrogen fertilizers. Journal of Environmental Quality 33:1822-1827. Utah State University repository abstract, https://digitalcommons.usu.edu/psc_facpub/538/ (opened 2026-10-27).
• Gibeault, V. A., Yates, M., Meyer, J., and Leonard, M. (1998). Movement of Nitrogen Fertilizer in a Turfgrass System. California Turfgrass Culture, Vol. 48, Nos. 1 and 2, University of California Cooperative Extension, https://turfgrass.ucr.edu/media/337/download (opened 2026-10-27).