If you’ve ever stood in a field at dawn, watching dew glisten on rows of corn or tomato vines heavy with fruit, you know fertilizers aren’t just synthetic white bags or granular pellets—they’re the quiet workhorses feeding 7.8 billion people on this planet. For 12 years, I’ve been a fertilizer supplier, and I’ve spent just as many late nights driving down muddy country roads, sitting across from farmers over cold coffee, arguing with extension agents, and even debating fellow suppliers at industry conferences: what really happens when fertilizer hits the soil, and how does it shape the water quality in the rivers, streams, and aquifers that we all depend on? It’s easy to reduce this to a black-and-white story—fertilizer = bad water—but as someone who sells products that grow food for my own nieces and nephews, I know it’s far more nuanced, a dance between science, practice, and care that every player in agriculture is still learning to navigate. Fertilizer
Let’s start with the basics. Fertilizers, whether the organic ones I source from composting operations and livestock farms or the synthetic ones I blend to precise nutrient ratios, aren’t just random chemicals. They’re made of three core nutrients plants need to grow: nitrogen, phosphorus, and potassium, plus a handful of micronutrients that keep crops healthy. Nitrogen builds leafy growth, phosphorus fuels root development and fruit production, and potassium helps plants fight off drought and disease. For decades, farmers have relied on these nutrients to boost yields, and rightfully so—without fertilizer, global crop production would drop by nearly half, according to the Food and Agriculture Organization (FAO), leaving billions without enough to eat. But here’s the catch: plants don’t absorb every drop of fertilizer we apply. Only about 30 to 50 percent of the nitrogen from synthetic fertilizers makes it into the harvested crop, and phosphorus is even less efficient, with many crops taking up just 10 to 25 percent of what’s spread on fields. The rest? It doesn’t just disappear. It moves. That movement is where water quality gets affected.
When it rains, or when farmers irrigate their fields with well or surface water, excess nutrients don’t stay trapped in the soil. They can run off across the field’s surface, carried by sediment that’s washed into nearby ditches, streams, and lakes. Or they can leach deeper into the ground, seeping through porous rock to reach aquifers that supply drinking water to millions of people. Both pathways have distinct, well-documented effects on water quality, and they’re the ones that make fertilizer a target for environmental groups and regulators alike.
Phosphorus, for example, is a big part of the surface runoff problem. Phosphorus binds tightly to soil particles, so when sediment erodes from tilled fields (a common practice in conventional farming before cover crops became standard), phosphorus rides along for the ride. Once it reaches a lake or slow-moving river, it becomes a fertilizer for algae. That’s how harmful algal blooms—those bright green, sometimes scummy mats that can turn a recreational lake into a closed, toxic space—form. Last summer, I drove 200 miles to a lake in western Ohio that had been closed for three months because of a microcystin bloom, a toxic byproduct of algae that can make humans and pets sick. A local farmer I talked to there, a third-generation corn grower named Tom, told me he’d cut his phosphorus application by 20 percent that year, but his fields were on a slope that drained straight into the lake. “It doesn’t matter how much I put on,” he said, “the rain takes what it wants.” That’s the frustrating truth of runoff: it’s as much about how and when you apply fertilizer as how much you use. Excess phosphorus isn’t just bad for water—it’s a waste of money for farmers, too, since they’re paying for nutrients that end up in the water instead of their crops.
Nitrogen is the bigger culprit for leaching and groundwater contamination, though, and that’s the one that ends up in drinking water. Unlike phosphorus, nitrogen is highly mobile; it doesn’t stick to soil particles easily, so it can move with water through the ground until it hits an aquifer. When nitrogen breaks down in soil, it turns into nitrate, a compound that’s especially dangerous for infants and pregnant people. The EPA sets a maximum contaminant level of 10 milligrams per liter of nitrate in drinking water, because high levels can cause methemoglobinemia, or “blue baby syndrome,” a rare but serious condition that reduces the blood’s ability to carry oxygen. I’ve seen this firsthand in rural parts of Iowa, where many small towns rely on private wells or shallow aquifers. A few years ago, a group of families in a town I won’t name tested their well water and found nitrate levels three times the legal limit. The local extension agent traced it back to overapplication of nitrogen on neighboring corn fields, where farmers had applied extra fertilizer hoping to boost yields during a dry year, not realizing that dry soil would hold the nitrogen until heavy rains came and washed it down.
But here’s the part that most people outside agriculture don’t talk about: these effects aren’t inevitable. For nearly a decade, I’ve been working with farmers to adjust how they use fertilizer, and I’ve seen firsthand that when done right, fertilizer can support both crop growth and water quality. The first key is precision agriculture. Modern tools like soil testing, drone mapping, and variable-rate application let farmers apply only the exact amount of nutrients a field needs, not a blanket “one size fits all” dose. I recently started partnering with a group of agronomists who come to our supplier for training on soil testing; last year, one of their customers cut his nitrogen use by 18 percent while increasing his corn yield by 5 bushels per acre. That’s not just good for water—it’s good for farmers’ bottom lines, too, because they’re not wasting money on excess fertilizer.
Another game-changer is timing. Applying fertilizer right before a heavy rain or during a time when crops aren’t actively growing is a surefire way to lose nutrients to runoff or leaching. That’s why we’ve pushed farmers in our region to switch to split applications: applying small amounts of fertilizer throughout the growing season, when crops are actually taking up nutrients, instead of dumping it all at planting time. We also emphasize edge-of-field practices—planting cover crops like rye or clover between main crops, which hold soil and excess nutrients in place, or installing buffer strips of grass along streams that catch runoff before it reaches surface water. Last year, I drove to a farm in Illinois that planted a 30-foot buffer strip along his creek; he told me that last spring, when a heavy rainstorm washed sediment off his corn fields, the buffer caught 80 percent of it, and the stream below stayed clear even as neighboring creeks were muddy.
Organic vs. synthetic fertilizer is another line that gets blurred all too often. A lot of people assume organic fertilizer is harmless for water quality, but that’s not always true. Manure, for example, is a great source of nitrogen and phosphorus, but if it’s applied at the wrong rate or timing, it can lead to the same runoff and leaching problems as synthetic fertilizer. I’ve had conversations with organic vegetable farmers who’ve had their crops shut down because of E. coli in irrigation water, traced back to improperly managed manure fields. The key isn’t the source of the fertilizer—it’s how it’s managed.
Regulation has a role to play here, too, but I’ve seen how one-size-fits-all rules can hurt small farmers without actually improving water quality. A few years ago, a state in our region tried to ban all synthetic nitrogen application after harvest, a rule that would have hurt small vegetable farmers who plant cover crops in the fall and rely on nitrogen to get those crops established. After working with the state’s agriculture department to show them data on split applications and cover crops, we helped adjust the rule to allow targeted applications for cover crops, striking a balance between environmental protection and farmer needs.
As a fertilizer supplier, I know I’m part of the problem for some people’s frustration with agricultural runoff. It’s not easy to look at a blue-green algal bloom on a lake and think about the fertilizer that grew your grocery store bananas or bread. But I also know I’m part of the solution. Over the last five years, my team and I have invested in low-solubility synthetic fertilizers that release nutrients slowly, matching the rate at which crops absorb them, cutting runoff by up to 40 percent. We also offer free soil testing for small farmers, something most big suppliers don’t do because it’s not as profitable. Last year, we started a program to train local farmers on nutrient management planning, bringing in agronomists at no cost, because I believe that if farmers succeed, and water stays clean, we all win.
The truth is, fertilizer is a necessary tool for feeding the world, and its effect on water quality depends less on the fertilizer itself and more on how we use it. It’s about choosing the right product for the soil, applying it at the right time and rate, and pairing it with practices that keep nutrients where they belong—on the crops, not in the water. I’ve seen the damage that poor fertilizer management can do: a lake closed for months, families drinking water that needs treatment, farmers wasting money on nutrients that never help their crops. But I’ve also seen the good: a farm that cuts costs while growing more food, a stream that’s clear enough for kids to fish in, a farmer who can look at their fields at the end of the season and know they’ve done right by their land and their community.
If you’re a farmer looking to improve your nutrient management, or a stakeholder working to balance agriculture and water quality, I’m here to talk. We can work together to find solutions that work for your fields and for the water that matters to all of us.
Copper(II) Sulfate References
- Food and Agriculture Organization of the United Nations. (2022). World Fertilizer Trends and Outlook to 2025. Rome, Italy.
- U.S. Environmental Protection Agency. (2021). Nutrient Pollution: A Threat to Our Waters. Washington, D.C.
- Sawyer, J. E., et al. (2019). Precision nutrient management: Reducing environmental impact while improving crop productivity. Journal of Environmental Quality, 48(3), 567–582.
- United States Department of Agriculture. (2020). Cover Crop Practices and Water Quality Benefits. Washington, D.C.
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