Fertilizers

Nutrient uptake of vegetable crops and calculating fertilizer requirements

fertilizer recommendation calculation bags vegetables

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
Nutrient removal of crops from soil
CropYield
(t/ha)
N Uptake
(kg/ton yield)
P Uptake
(kg/ton yield)
K Uptake
(kg/ton yield)
Artichoke (Jerusalum)272.50.53
Artichoke globe6.52.50.53
Asparagus02.50.53
Baby carrots402.50.53
Baby marrows102.50.53
Beetroot2550.77
Brinjal2020.252.4
Broad beans1225.52.615.3
Broccoli152.50.53
Brussels sprouts1810911.2111.8
Butternut222.50.53
Cabbage752.50.53
Cabbage (Spring)8030.84
Cabbage (Summer)6030.562
Carrots402.50.53
Cauliflower (Long season)302.50.53
Cauliflower (Mid season)302.50.53
Cauliflower (Short season)302.50.53
Celery302.50.53
Chinese cabbage222.50.53
Chives252.50.53
Chayote122.50.53
Cucumber222.50.53
Endive112.50.53
Garlic122.50.53
Gem squash202.50.53
Green beans (bush)152.50.53
Green beans (Climing)142.50.53
Horse radish122.50.53
Hot chillies4.52.50.53
Kale (fodder kale)302.50.53
Kohlrabi222.50.53
Leek302.50.53
Lettuce (Butter)222.50.53
Lettuce (Head)222.50.53
Lettuce (Speciality)222.50.53
Marrows222.50.53
Melons252.50.53
Okra7.52.50.53
Onions (Medium day)502.50.83
Onions (Pickled)502.50.83
Onions (Sets)502.50.83
Onions (Short day)502.50.82
Parsley2.52.50.53
Parsnip252.50.53
Peas (Dry)2.52.50.53
Peas (green: pods)122.50.53
Peas (green: shelled)52.50.53
Potatoes402.50.53
Pumpkin (Boer)202.50.53
Pumpkin (Ceylons)502.50.53
Pumpkin (Hubbard)202.50.53
Rabarber02.50.53
Radish202.50.53
Salsify252.50.53
Shallot122.50.53
Spinach122.50.53
Spring onions252.50.53
Strawberries3250.53
Sweet potatoes502.30.21.5
Swiss chard502.50.53
Tomatoes (Determinate; field)1002.50.753
Tomatoes (Indeterminate; field)1202.50.753
Tomatoes (Processing)602.50.753
Turnip252.50.53
Water melons502.50.53

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 typeSoil Factor
Clay0.9
Clay loam1
Loam1
Loamy sand0.8
Sand0.9
Sandy clay1
Sandy clay loam1
Sandy loam1
Silt0.8
Silt loam0.8
Silty clay0.9
Silty clay loam0.95

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.

NOTE; Use this table as a guideline. After calculating the fertilizer requirements stand back and THINK, does the numbers make sense. Does it compare with other recommendations and what other growers use.

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