Fertilizers

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.

Table 6, "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 Guidelines for Organic Fertility Management (Table 10).


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

0

0

0

0

0

Calcium nitrate

15

0

0

19

0

0

Calcium ammonium nitrate

27

0

0

0

0

0

Diammonium phosphate

18

46

0

0

0

0

Monoammonium phosphate

11

48

0

0

0

0

Epsom salts

0

0

0

0

10

13

Granulated Sulfur

0

0

0

0

0

90-92

Gypsum

0

0

0

19-23

0

15-18

Muriate of potash

0

0

60

0

0

0

Nitrate of potash

13

0

44

0

0

0

Nitrate of soda-potash

15

0

14

0

0

0

Nitrate of soda

16

0

0

0

0

0

Superphosphate

0

20

0

18-21

0

11

Sul-po-mag

0

0

22

0

11

23

Sulfate of potash

0

0

50

0

0

17

Triple superphosphate

0

44-46

0

13

0

0

Urea

45-46

0

0

0

0

0

 

 

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.