Nutrient uptake of vegetable crops and calculating fertilizer requirements
The nutrient uptake of vegetable crops are used to determine very rudimentary fertilizer recommendations if you have nothing else to go by. A lot of purists will be up and arms of these guideline tables, but none of them can come up with a simple method of determining fertilizer recommendations that an average non-scientific farmer can use as a guideline. So many growers are in the dark and their applications can be out with 500 % with a significant result in loss in income. This table provides a very basic guideline to start with.
How to use the nutrient uptake table
Using the table is extremely easy, no complicated maths required :). Let’s assume a grower wants to plant determinate tomatoes. We need to know what the potential yield will be. A good thumbsuck based on the grapevine and other growers is good enough. On average one should achieve 100 t/ha of tomatoes. That includes marketable and unmarketable tomatoes. It also assumes that you will apply good disease and insect management to achieve the yield. Just fertilizing will not guarantee that you will harvest a crop.
To calculate N, P and K we do the following;
Nitrogen (N):
- yield × uptake = N fertilizer requirement.
- 100 t/ha × 2.5 kg/ton = 250 kg N/ha application for the whole season
Phosphorus (P):
- yield × uptake = P fertilizer requirement.
- 100 t/ha × 0.75 kg/ton = 75 kg N/ha application for the whole season
Potassium (K):
- yield × uptake = K fertilizer requirement.
- 100 t/ha × 3 kg/ton = 300 kg N/ha application for the whole season
| Crop | Yield (t/ha) | N Uptake (kg/ton yield) | P Uptake (kg/ton yield) | K Uptake (kg/ton yield) |
|---|---|---|---|---|
| Artichoke (Jerusalum) | 27 | 2.5 | 0.5 | 3 |
| Artichoke globe | 6.5 | 2.5 | 0.5 | 3 |
| Asparagus | 0 | 2.5 | 0.5 | 3 |
| Baby carrots | 40 | 2.5 | 0.5 | 3 |
| Baby marrows | 10 | 2.5 | 0.5 | 3 |
| Beetroot | 25 | 5 | 0.7 | 7 |
| Brinjal | 20 | 2 | 0.25 | 2.4 |
| Broad beans | 12 | 25.5 | 2.6 | 15.3 |
| Broccoli | 15 | 2.5 | 0.5 | 3 |
| Brussels sprouts | 18 | 109 | 11.2 | 111.8 |
| Butternut | 22 | 2.5 | 0.5 | 3 |
| Cabbage | 75 | 2.5 | 0.5 | 3 |
| Cabbage (Spring) | 80 | 3 | 0.8 | 4 |
| Cabbage (Summer) | 60 | 3 | 0.56 | 2 |
| Carrots | 40 | 2.5 | 0.5 | 3 |
| Cauliflower (Long season) | 30 | 2.5 | 0.5 | 3 |
| Cauliflower (Mid season) | 30 | 2.5 | 0.5 | 3 |
| Cauliflower (Short season) | 30 | 2.5 | 0.5 | 3 |
| Celery | 30 | 2.5 | 0.5 | 3 |
| Chinese cabbage | 22 | 2.5 | 0.5 | 3 |
| Chives | 25 | 2.5 | 0.5 | 3 |
| Chayote | 12 | 2.5 | 0.5 | 3 |
| Cucumber | 22 | 2.5 | 0.5 | 3 |
| Endive | 11 | 2.5 | 0.5 | 3 |
| Garlic | 12 | 2.5 | 0.5 | 3 |
| Gem squash | 20 | 2.5 | 0.5 | 3 |
| Green beans (bush) | 15 | 2.5 | 0.5 | 3 |
| Green beans (Climing) | 14 | 2.5 | 0.5 | 3 |
| Horse radish | 12 | 2.5 | 0.5 | 3 |
| Hot chillies | 4.5 | 2.5 | 0.5 | 3 |
| Kale (fodder kale) | 30 | 2.5 | 0.5 | 3 |
| Kohlrabi | 22 | 2.5 | 0.5 | 3 |
| Leek | 30 | 2.5 | 0.5 | 3 |
| Lettuce (Butter) | 22 | 2.5 | 0.5 | 3 |
| Lettuce (Head) | 22 | 2.5 | 0.5 | 3 |
| Lettuce (Speciality) | 22 | 2.5 | 0.5 | 3 |
| Marrows | 22 | 2.5 | 0.5 | 3 |
| Melons | 25 | 2.5 | 0.5 | 3 |
| Okra | 7.5 | 2.5 | 0.5 | 3 |
| Onions (Medium day) | 50 | 2.5 | 0.8 | 3 |
| Onions (Pickled) | 50 | 2.5 | 0.8 | 3 |
| Onions (Sets) | 50 | 2.5 | 0.8 | 3 |
| Onions (Short day) | 50 | 2.5 | 0.8 | 2 |
| Parsley | 2.5 | 2.5 | 0.5 | 3 |
| Parsnip | 25 | 2.5 | 0.5 | 3 |
| Peas (Dry) | 2.5 | 2.5 | 0.5 | 3 |
| Peas (green: pods) | 12 | 2.5 | 0.5 | 3 |
| Peas (green: shelled) | 5 | 2.5 | 0.5 | 3 |
| Potatoes | 40 | 2.5 | 0.5 | 3 |
| Pumpkin (Boer) | 20 | 2.5 | 0.5 | 3 |
| Pumpkin (Ceylons) | 50 | 2.5 | 0.5 | 3 |
| Pumpkin (Hubbard) | 20 | 2.5 | 0.5 | 3 |
| Rabarber | 0 | 2.5 | 0.5 | 3 |
| Radish | 20 | 2.5 | 0.5 | 3 |
| Salsify | 25 | 2.5 | 0.5 | 3 |
| Shallot | 12 | 2.5 | 0.5 | 3 |
| Spinach | 12 | 2.5 | 0.5 | 3 |
| Spring onions | 25 | 2.5 | 0.5 | 3 |
| Strawberries | 3 | 25 | 0.5 | 3 |
| Sweet potatoes | 50 | 2.3 | 0.2 | 1.5 |
| Swiss chard | 50 | 2.5 | 0.5 | 3 |
| Tomatoes (Determinate; field) | 100 | 2.5 | 0.75 | 3 |
| Tomatoes (Indeterminate; field) | 120 | 2.5 | 0.75 | 3 |
| Tomatoes (Processing) | 60 | 2.5 | 0.75 | 3 |
| Turnip | 25 | 2.5 | 0.5 | 3 |
| Water melons | 50 | 2.5 | 0.5 | 3 |
If you have some knowledge of your soil you can compensate for the type of soil as well by using soil factors (see table below).
For instance if you have a silt loam soil the following N, P, K values will be adjusted accordingly;
N: 250 kg N/ha × 0.8 = 200 kg N/ha
P: 75 kg N/ha × 0.8 = 60 kg P/ha
K: 300 kg K/ha × 0.8 = 240 kg K/ha
Fertilizer recommendation soil factors| Soil type | Soil Factor |
|---|---|
| Clay | 0.9 |
| Clay loam | 1 |
| Loam | 1 |
| Loamy sand | 0.8 |
| Sand | 0.9 |
| Sandy clay | 1 |
| Sandy clay loam | 1 |
| Sandy loam | 1 |
| Silt | 0.8 |
| Silt loam | 0.8 |
| Silty clay | 0.9 |
| Silty clay loam | 0.95 |
The final adjustment to be made is top dressings. In most cases phosphorus can be applied in the beginning of the season but there are exceptions to the rule. I will write about it in a separate article.
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