Nitrate Leaching & Nitrogen Lost to Drainage
Tracks nitrate
“Real reviews from real users decide this tool's public rating.
Nitrate is highly mobile and washes below the root zone with drainage — estimate the fraction lost from your applied N, drainage and water-holding capacity, and protect groundwater.
Nitrate leaching risk
Next: split N and avoid heavy irrigation to cut nitrate leaching; here ~16 kg N risks moving below the root zone — schedule lighter, more frequent waterings.
Leach fraction = drainage ÷ (drainage + soil water capacity). Sandy soils with low capacity leach far more; cover crops mop up residual nitrate over winter.
Nitrate leaching — key facts
- Nitrate
- negatively charged, highly mobile
- Driver
- drainage vs water-holding capacity
- Leached
- applied N × leaching fraction
- Retained
- applied N − leached
- Cost
- wasted fertiliser, polluted water
- Reduce
- split doses, match to need
- Cover crops
- mop up residual nitrate
- Privacy
- Runs in your browser; nothing uploaded
Don't feed the drainage water
Nitrate is the nitrogen form crops use most, but it's negatively charged so the soil can't grip it — it dissolves freely and goes wherever the water goes. When rain or irrigation pushes drainage water below the root zone, it carries nitrate with it, wasting fertiliser you paid for and polluting groundwater. The fraction lost rises with drainage relative to the soil's water-holding capacity: the more water passes through versus what the soil can store, the more nitrate is flushed away.
This tool gives the leaching fraction, nitrogen leached, nitrogen retained and residual N from your applied nitrogen, drainage and water-holding capacity. Use it to time and size applications, judge irrigation, and see how much nitrogen actually stays for the crop. Pair it with the Irrigation Water Nitrogen Credit, Urea Volatilization Loss and Fertilizer Split Dose tools for a full nitrogen plan.
Cut fertiliser waste
See how much applied N is washing away.
Protect groundwater
Keep nitrate out of aquifers and rivers.
Time applications
Avoid fertilising before heavy drainage.
Judge irrigation
Over-watering drives nitrate below the roots.
Frequently Asked Questions
What is nitrate leaching?+
Nitrate is the form of nitrogen plants take up most, but it carries a negative charge so the soil can't hold it — it dissolves in soil water and is highly mobile. When drainage water moves down past the root zone, it carries nitrate with it. That nitrogen is lost to the crop, wastes fertiliser money, and can pollute groundwater and rivers.
How is the leaching fraction calculated?+
The fraction of nitrate lost rises with drainage relative to the soil's water-holding capacity. The more water drains through compared with what the soil can store, the larger the share of dissolved nitrate flushed below the roots. The calculator turns your drainage and water-holding-capacity figures into a leaching fraction, then applies it to your applied nitrogen.
Why is nitrate so prone to leaching?+
Soil colloids carry negative charges, which hold positively charged cations but repel negatively charged nitrate. So unlike ammonium or potassium, nitrate stays free in the soil water and moves wherever the water moves. Any rainfall or irrigation beyond what the soil can hold drives it downward, out of reach of roots.
What does the residual N output mean?+
Residual N is the nitrogen left in the root zone after leaching — the applied nitrogen minus what's leached. It's the pool still available to the crop. A high leaching fraction leaves little residual N, signalling that you've fed the drainage water rather than the plant and may need to adjust timing or rate.
How do I reduce nitrate leaching?+
Match nitrogen rate to crop need, split applications so less sits exposed before uptake, avoid fertilising before heavy rain or excess irrigation, use cover crops to mop up residual nitrate, and improve soil organic matter and water-holding capacity. Anything that cuts drainage relative to capacity, or shrinks the free nitrate pool, lowers leaching.
Does irrigation increase leaching?+
Over-irrigation is a major driver — water applied beyond the soil's holding capacity drains through and flushes nitrate with it. Irrigating to refill the root zone without overshooting, and scheduling to crop demand, keeps drainage and therefore leaching low. The Irrigation Water Nitrogen Credit tool also helps you account for N already in your water.
Why does leaching matter beyond the field?+
Leached nitrate ends up in aquifers and surface water, where it raises nitrate levels in drinking water and fuels algal growth and eutrophication. Cutting leaching protects both your fertiliser budget and the wider environment, and in many regions it's increasingly regulated — so managing it is good agronomy and good compliance.
What inputs does the calculator need?+
Applied nitrogen (kg/ha), the drainage water depth, and the soil's water-holding capacity. From these it derives the leaching fraction and reports the nitrogen leached, the nitrogen retained, and the residual N. Use realistic seasonal drainage figures for the most meaningful estimate.
How precise is the estimate?+
It's a sound planning estimate. Real leaching also depends on the nitrate concentration at the time water moves, soil structure and preferential flow, temperature and microbial activity. Treat the result as guidance for timing and rate decisions rather than an exact loss figure, and re-run it as conditions change.
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