alfalfa fertiliser and yield calculator
A tonne of alfalfa removes about 28 kg of nitrogen, 6 kg of phosphate and 24 kg of potash from the field. Replacing offtake is the starting point for any nutrient plan. A legume with very high potash removal; a hay crop strips potassium fast.
- Phosphate product rate
- 156.5 kg/ha
- Potash product rate
- 480.0 kg/ha
- Nitrogen removed by the crop
- 336.0 kg N/ha
- Phosphate removed
- 72.0 kg P2O5/ha
- Potash removed
- 288.0 kg K2O/ha
- Nitrogen product for the whole area
- 55.652 tonnes
- Phosphate product total
- 6.261 tonnes
- Potash product total
- 19.200 tonnes
- Seed for the whole area
- 0.800 tonnes
- Expected harvest
- 480.0 tonnes
- Applied nitrogen per tonne of yield
- 40.00 kg/t
Show the working
- Area = 40
- Target yield = 12
- Nitrogen content of your product = 34.5
- Phosphate content = 46
- Potash content = 60
- Nutrient use efficiency = 70
- Seed rate = 20
- Expected harvest = 12 * 40 = 480
- Nitrogen removed by the crop = 12 * 28 = 336
- Phosphate removed = 12 * 6 = 72
- Potash removed = 12 * 24 = 288
- n_applied = 336 / (70/100) = 480
- Nitrogen product rate = 480 / (34.5/100) = 1391.3
- Phosphate product rate = 72 / (46/100) = 156.522
- Potash product rate = 288 / (60/100) = 480
- Nitrogen product for the whole area = 1391.3 * 40 / 1000 = 55.6522
- Phosphate product total = 156.522 * 40 / 1000 = 6.260 87
- Potash product total = 480 * 40 / 1000 = 19.2
- Seed for the whole area = 20 * 40 / 1000 = 0.8
- Applied nitrogen per tonne of yield = 12 > 0 ? 480 / 12 : 0 = 40
Values are shown to six significant figures here; the arithmetic itself runs on exact fractions and is only rounded where a number is printed.
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The formula
- nutrient removed = yield x removal rate per tonne
- product rate = nutrient required / nutrient content of the product
- nitrogen is adjusted for use efficiency because losses are unavoidable
Removal rates are typical published figures and vary with variety, season and whether the straw or residue is taken off.
This replaces what the crop takes. A proper plan also accounts for soil indices, manure history and any legume in the rotation.
Phosphate and potash build or deplete a soil reserve rather than being used in-season, so a below-index soil needs more than removal.
A legume with very high potash removal; a hay crop strips potassium fast.
alfalfa nutrient removal
| Nutrient | Per tonne of crop | At 12 t/ha |
|---|---|---|
| Nitrogen (N) | 28 kg | 336 kg/ha |
| Phosphate (P2O5) | 6 kg | 72 kg/ha |
| Potash (K2O) | 24 kg | 288 kg/ha |
Frequently asked
How much nitrogen does alfalfa need?
It removes about 28 kg of N per tonne of crop, so a 12 t/ha crop takes off roughly 336 kg/ha. Applied rates are higher because not all of it is taken up.
Where the numbers come from
- Nutrient removal figures follow the usual published offtake tables; check against local recommendations.