Fertilizers

Fertilizer recommendations for vegetable crops should be made in conjunction with a soil test report. Repeated use of the same analysis fertilizer without regard to soil test level will likely lead to excess levels of certain elements, nutrient imbalances, poor return on fertilizer investment, and increased risk of nutrient losses to the environment. For example, yearly applications of 10-10-10 can lead to excess levels of P2O5. (See nutrient recommendation tables for each crop and Table 6).

Fertilizer grades refer to the guaranteed percentages of plant nutrients. The ratio refers to the proportion of nitrogen (N), phosphate (P2O5) and potash (K2O) in the fertilizer. For example, the grade is 5-10-5, and the ratio is 1-2-1. High analysis fertilizers are those with grades such as 20-20-20, 35-0-0 or 0-46-0, and are more economical to use on the basis of price per pound of nutrient.

Liquid starter fertilizers are materials that are completely water soluble and are high in phosphorus content such as 16-32-16, 10-52-17 or 9-45-15. These materials are used at the time of transplanting. Dry starter fertilizer can be banded at the time of seeding. The band is normally placed 2" below and 2" to the side of the seed. When using either dry or liquid starter fertilizer, follow label directions because an excess of starter could burn seeds and young seedlings. Starter fertilizer promotes early and rapid growth that leads to greater yields with certain crops such as tomato, pepper, and melon. See individual crops for rates.

The table "Plant Nutrient Content of Various Fertilizer Sources" lists many fertilizers commonly used for vegetable cropping systems. Similar information for fertilizers and amendments commonly used in certified organic cropping systems are provided in the section entitled Guidlines for Organic Fertility Management


Table 6: Plant Nutrient Content of Various Fertilizer Sources (% by weight)

Fertilizer Source Material

Total Nitrogen
N%

Available Phosphoric Acid
P2O5 %

Water Soluble Potash K2O %

Combined Calcium Ca %

Combined Magnesium Mg %

Combined Sulfur S %

Ammonium sulfate

21

 0

0

 0

0

23

Ammonium nitrate

34

 0

0

0

0

0

Anhydrous ammonia

82

 

 

 

 

 

Calcium nitrate

15

 

 

19

 

 

Calcium ammonium nitrate

27

 

 

 

 

 

Diammonium phosphate

18

46

 

 

 

 

Monoammonium phosphate

11

48

 

 

 

 

Epsom salts

 

 

 

 

10

13

Granulated Sulfur

 

 

 

 

 

90 to 92

Gypsum

 

 

 

19 to 23

 

15 to 18

Muriate of potash

 

 

60

 

 

 

Nitrate of potash

13

 

44

 

 

 

Nitrate of soda-potash

15

 

14

 

 

 

Nitrate of soda

16

 

 

 

 

 

Superphosphate

 

20

 

18 to 21

 

11

Sul-po-mag

 

 

22

 

11

23

Sulfate of potash

 

 

50

 

 

17

Triple superphosphate

 

44 to 46

 

13

 

 

Urea

45 to 46

 

 

 

 

 

 

 

Table 6a: Conversion Factors for Boron Nutrient Sources

Fertilizer Source Material

Boron content, %

Pounds of Material Required to Supply One Pound of Boron

Fertilizer Borate Granular1

14.30 (B)

7.0

Fertilizer Borate-48

14.91 (B)

6.7

Solubor

20.50 (B)

4.9

Fertilizer Borate-68

21.13 (B)

4.7

1 Best for fertilizer blends.