Removal of Nutrients from the Soil

Fertilizer is applied to vegetable fields to supply the nutrient needs of the crop. Normally it is not necessary to supply all these needs from fertilizer alone because the soil already contains some nutrient elements that are available for crop growth. It is necessary to test the soil to determine its nutrient status. Only then can you determine the additional amounts of appropriate fertilizer materials to apply. Frequently growers apply more fertilizer than the crop can use and the excess, especially nitrogen, is often leached from the root zone into the groundwater. There are also situations where increased application of a certain nutrient element can increase yield or improve quality.

Table 5 lists amounts of certain nutrient elements that are removed by vegetable crops. It includes the amounts removed by harvest and the amount that remains in crop residue and is returned to the soil. This information is taken from several sources that sometimes vary considerably. These figures for crop removal are not accurate for all crops and fields, but can be used to estimate the amount of nutrients to return to the soil. They can be used as a basis for adjusting your own application rates up or down on a trial basis initially. Keep in mind that nutrient removal varies with factors such as soil moisture, temperature and pH. Plants can absorb large amounts of a nutrient if it is in abundance; but this may not increase yield. Excess levels of some nutrients can reduce the yield and/or quality of some crops.

Nutrients that are relatively immobile in the soil, such as phosphorus, calcium, magnesium and the micronutrients, are not all extracted by plants because the roots do not come in contact with all of the nutrients. This is especially true of certain vegetables that have small or sparse root systems. Most of the phosphorous applied to the soil becomes fixed in a form unavailable to plants. For these reasons, it is necessary to provide some excess amounts of nutrients, especially phosphorus, when soil test levels are below the optimum range, and why rates sufficient to replace the amount removed by crops are recommended for soils that test in the optimum range.

 

Table 5: Approximate Nutrient Removal by Selected Vegetable Crops. 

Vegetable

 

Yield per acre1

Nutrient removal, lbs/acre

N

P2O5

K2O

Ca

Mg

Snap beans

Total

250 bu

30

20

35

7

3

Broccoli

heads

5 tons

20

2

45

 

 

 

other

 

145

8

165

 

 

 

Total

 

 

 

 

 

 

Cabbage

Total

20 tons

125

30

130

28

10

Carrots

roots

25 tons

80

20

200

 

 

 

tops

 

65

5

145

 

 

 

Total

 

145

25

345

 

 

Cauliflower

 

6 tons

45

18

43

4

3

Celery

tops

50 tons

170

 

380

 

 

 

roots

 

25

 

55

 

 

 

Total

 

195

80

435

110

27

Cucumbers

 

24 tons

100-200

33-72

100-400

 

 

Eggplant

 

16 tons

207

46

34

 

 

Kale

 

10 tons

125

30

110

50

10

Lettuce

 

15 tons

75

35

150

13

5

Muskmelons

fruit

11 tons

95

17

120

 

 

 

vines

 

60

8

30

 

 

 

Total

 

155

25

150

 

 

Onions

bulbs

20 tons

110

20

110

12

14

 

tops

 

35

5

45

 

 

 

Total

 

145

25

155

 

 

Peppers

fruits

12 tons

137

52

217

 

 

Potatoes, White

tubers

300 cwt

90

45

160

 

 

 

vines

 

60

20

60

 

 

 

Total

 

150

65

220

 

 

Potatoes, Sweet

roots

15 tons

75

55

160

 

 

 

vines

 

35

5

280

 

 

 

Total

 

110

60

440

10

15

Spinach

 

10 tons

100

25

100

24

10

Squash, Summer

 

10 tons

32

12

56

 

 

Squash, Winter

 

6 tons

12

10

58

 

 

Sweet Corn

ears

250 cr.

55

8

30

 

 

 

stalks

 

100

12

75

 

 

 

Total

 

155

20

105

 

 

Tomatoes

  fruit

30 tons

110

48

180

15

15

 

  vines

 

90

30

100

24

21

 

Total

 

200

78

280

39

1 These are assumed yields. Your expected yield may vary depending on weather and cultural practices. Adjust nutrient removal rates accordingly. To convert to volume or count yield units see Vegetable and Berry Crop Yield Estimates for New England. Vern Grubinger, UVM Extension. (http://www.uvm.edu/vtvegandberry/factsheets/vegetableberryyields.pdf).