Irrigation Water & Nitrogen Credit
Credits nitrate
Enter nitrate-N, water depth applied and area to get the free nitrogen your irrigation or groundwater supplies — so you can cut the fertiliser N you apply.
Irrigation water N credit
Next: credit ~30 kg N/ha (≈ 65.2 kg urea-eq) against your fertiliser plan, then test the water again seasonally as nitrate levels drift.
Assumes nitrate-N is plant-available; 1 ppm over 1 mm depth ≈ 0.01 kg N/ha. Have your irrigation water lab-tested for nitrate to get a reliable ppm figure.
Water nitrogen credit — key facts
- N supplied
- nitrate-N × depth(mm) × 0.01
- Units in
- ppm (mg/L) and mm applied
- 1 ppm·mm
- 0.01 kg N/ha
- Nitrate → N
- divide nitrate by 4.43
- Urea is
- ≈ 46% N
- Time it
- irrigate to crop demand
- Re-test
- season start and on change
- Privacy
- Runs in your browser; nothing uploaded
The fertiliser already dissolved in your water
Every time nitrate-rich irrigation or groundwater hits the field, it carries plant-available nitrogen — free fertiliser most growers never count. Across a full season of irrigation that nitrogen can add up to a real fraction of the crop's needs, yet it's routinely ignored, so fertiliser is applied on top and money runs straight into the soil. Crediting the water means measuring its nitrate, working out the nitrogen it delivers, and subtracting that from the bag.
This tool gives the nitrogen per hectare, the total nitrogen across the field, and a urea equivalent from your nitrate-N test, the depth of water applied and the area. Use it to trim your nitrogen programme, avoid over-fertilising from already-rich sources, and protect water quality. Pair it with the Fertilizer (NPK), Nutrient Balance and Nitrate Leaching tools for a full nitrogen plan.
Spend less on N
Deduct free nitrogen the water already brings.
Use the right units
Nitrate-N in ppm, water depth in mm.
See urea saved
Credit translated into bags you can skip.
Protect water
Avoid piling N onto already-rich sources.
Frequently Asked Questions
What is a nitrogen credit from irrigation water?+
Many irrigation and groundwater sources carry dissolved nitrate, which is plant-available nitrogen. Crediting it means counting that nitrogen as part of the crop's supply and subtracting it from the fertiliser you apply. It's essentially free fertiliser delivered every time you irrigate — ignoring it means over-applying N and wasting money.
How is the nitrogen supplied calculated?+
N supplied (kg/ha) = nitrate-N (ppm) × depth applied (mm) × 0.01. The constant comes from the unit maths: 1 ppm is 1 g/m³, and 1 mm of water over a hectare is 10 m³, so 1 ppm over 1 mm gives 0.01 kg/ha. For example 10 ppm nitrate-N applied as 200 mm of irrigation supplies 10 × 200 × 0.01 = 20 kg N/ha.
Is the water test nitrate or nitrate-N?+
It matters a lot. Labs may report nitrate (NO₃⁻) or nitrate-nitrogen (NO₃-N). Nitrate-N is what this formula needs. If your result is given as nitrate, divide by about 4.43 to convert to nitrate-N before entering it. Mixing the two up overstates the credit by more than four times, so check the units on the report.
Why convert the credit to a urea equivalent?+
Most growers buy nitrogen as urea (about 46% N), so a credit in kg N/ha is easier to act on as the bags of urea it replaces. The urea-equivalent output translates the nitrogen the water supplies into the fertiliser you can leave in the shed, making the saving concrete at purchase time.
Does the whole credit really count?+
Nitrate in water is immediately plant-available, so under good timing most of it counts toward the crop. But some can leach below the roots if you irrigate heavily before the crop needs it, or be lost if water is applied off-season. Time irrigation to crop demand to capture the most of the credit.
How often should I test the water?+
Nitrate in groundwater and surface sources changes with season, rainfall, and surrounding land use, so test at least at the start of the season and again if you notice a change in source or unusually lush or pale crops. Several tests across the year give a more reliable average concentration to credit.
Can high nitrate water be a problem?+
Yes. Very high nitrate water can over-supply nitrogen, causing lush growth, lodging, delayed maturity or quality problems, and it raises environmental and drinking-water concerns. Crediting it properly and cutting applied N keeps the crop balanced and avoids piling more nitrogen onto an already rich source.
Does it work for any area or water unit?+
Yes — enter nitrate-N in ppm (mg/L), the depth of water applied in mm, and the area in your preferred unit. The tool returns nitrogen per hectare, the total nitrogen across the area, and the urea equivalent. Convert volumes to a depth in mm over the field first if you meter water by volume.
How accurate is the credit?+
The chemistry is exact, so accuracy depends on your inputs: a representative water test in the right units and a realistic seasonal depth applied. Treat it as a sound planning figure, re-test periodically, and adjust applied nitrogen on the basis of crop appearance and soil tests as the season unfolds.