The Application of Controlled Release Urea Mitigates Reactive Nitrogen Losses and Optimizes Nitrogen Management of Summer Maize: A Case Study in the North China Plain
This two-year field study in the North China Plain demonstrates that applying controlled-release urea (CRU) to summer maize significantly enhances yield and nitrogen use efficiency while substantially reducing reactive nitrogen losses through ammonia volatilization, nitrous oxide emissions, and nitrate leaching by synchronizing nutrient release with crop uptake.
Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer
Imagine the North China Plain as a giant, hungry stomach trying to digest a massive meal of summer corn. For years, farmers have been trying to feed this stomach by dumping a huge pile of regular fertilizer (urea) all at once or in two big scoops. It's like throwing a whole pizza at a person who can only eat a slice at a time. The result? The stomach gets overwhelmed, the extra food rots and smells bad (releasing ammonia), or it leaks right through the bottom of the plate (leaching into the ground), while the person still gets hungry later on.
This paper is about a new kind of "smart snack" called Controlled Release Urea (CRU). Instead of a giant, messy pile of food, CRU is like a time-release capsule that slowly drips out nutrients exactly when the corn plant is ready to eat them.
The Big Discovery: The Slow-and-Steady Win
The researchers ran a two-year experiment in Handan, Hebei, to see if this slow-release strategy could fix the mess. They compared three groups:
- The "No Food" Group (CK): No fertilizer at all.
- The "Regular Meal" Group (U): Standard urea, split into two big doses.
- The "Smart Snack" Group (CRU): The special slow-release urea, applied just once at the start.
The results were clear: The Smart Snack group (CRU) grew the best corn. In fact, it produced 8.0% more corn than the Regular Meal group. That's a big deal for farmers! It also made the nitrogen fertilizer work much better. The "agronomic efficiency" (how much extra corn you get for every kilogram of fertilizer) jumped by 34.2%, and the "partial factor productivity" (total corn per unit of fertilizer) went up by 8.0%.
What the "Regular Meal" Got Wrong
The paper explicitly argues against the idea that dumping regular urea is the best way to go. When farmers used the standard urea (U), it acted like a sugar rush followed by a crash.
- The Smelly Leak: Right after they added the regular urea, the soil started screaming with ammonia gas. The CRU group reduced this smelly ammonia loss by 57.4% during the first feeding and 54.4% during the second.
- The Greenhouse Gas Spike: The regular urea caused a massive spike in nitrous oxide (), a potent greenhouse gas. The CRU group cut these emissions by a whopping 68.8%.
- The Deep Leak: The regular urea washed deep into the soil, past where the roots could reach. The CRU kept the nutrients right where the corn needed them, in the top 0–40 cm of soil.
The "Goldilocks" Zone of Soil
Think of the soil as a sponge. With regular urea, the sponge gets soaked in one spot and then the water rushes straight through to the bottom, leaving the top dry later on. The paper found that with CRU, the nutrients were spread out evenly, like a gentle rain.
- In the top layer of soil (0–20 cm), the CRU treatment kept 65.9% more mineral nitrogen than the regular urea.
- In the layer just below (20–40 cm), it held 71.0% more.
- Meanwhile, the regular urea let 27.3% more nitrate leak out of the bottom of the root zone.
The researchers measured this carefully over two years. They found that the CRU treatment didn't just help the corn grow; it also saved money. Even though the CRU fertilizer cost a bit more upfront, the farmers made 12.7% more profit per hectare because they got more corn and didn't have to pay workers to come back and add more fertilizer later.
What the Paper Says About "Why"
The paper suggests that the secret sauce is timing. The CRU releases its nutrients over about 70 days in the field, which matches perfectly with the corn's growth stages.
- The "S-Curve" of Eating: The corn eats slowly at first, then goes into a feeding frenzy during its middle growth stages, and slows down at the end. The CRU capsule opens up just as the corn gets hungry, ensuring the plant never goes hungry and never gets a toxic overdose.
- Breaking the Chain: The study found that when you have too much nitrogen sitting around (like with regular urea), it triggers a chain reaction: it smells bad (ammonia), it creates greenhouse gases (), and it washes away (leaching). The CRU breaks this chain. By keeping the nitrogen levels steady and moderate, it stops these three bad things from happening together.
The Bottom Line
This isn't just a guess; the researchers measured the gas, weighed the corn, and dug up the soil to prove it. They showed that switching to this single-application, slow-release fertilizer is a "win-win." It helps the corn grow taller and heavier (yielding over 12 t/ha in some cases), keeps the air cleaner, stops the groundwater from getting polluted, and puts more money in the farmer's pocket.
In short, the paper concludes that for the North China Plain, the "slow and steady" approach of Controlled Release Urea is a scientifically proven way to feed the corn without wasting the food or polluting the planet. It's a smarter way to farm that balances the needs of the crop, the soil, and the environment.
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