Soybean Growth - Nutrient Management

Soybean plants (as well as the symbiotic bacteria) require some of each of the essential nutrients. Of the three primary nutrients - N, P, and K - nitrogen is supplied by the symbiotic bacteria in the nodules. The other nutrients come from the soil and will be taken into the plant as it takes up water.

Table 20 shows nutrient uptake requirements for soybeans under maximum economic yield conditions at various stages of growth, based on research by - Dr. Ray Flannery, who raised 101 bu/A soybeans in 1986. The research was performed on a Freehold sandy loam soil, testing very high in P and K, with a pH of 6.0 to 6.5. Total nutrient applications were 150 lbs/A N, 200 lbs/A P2O5, and 300 lbs/A K2O applied preplant, and two fertigations. Figure 13 shows nutrient storage in plant parts at the green stage of development.

Figure 13. Illustrates the plant parts in which the nutrients are stored at the green stage of development. (See Table 20)

Table 20: Dry Matter Accumulation and Nutrients Absorbed Per Acre by Soybeans at Various Growth Stages

Growth Stage

(2) Three Tri-leaf

(3) Six Tri-leaf

(5) Full Bloom

(7) Pod Dev.

(9) Soft Green

(10) Mature

Days

40

51

67

82

103

119

Lbs/Acre

Dry Matter

784

1585

4757

9495

16,900

16,594

N

30

46

171

308

548

494

P2O5

6

12

40

74

132

112

K2O

27

57

149

293

433

397

Ca

11

20

49

101

152

165

Mg

4

8

20

34

55

56

S

2

3

11

20

32

28

Micronutrient uptake (lbs/Acre)

Mn

Fe

Cu

B

Zn

Near Maturity

1.03

6.32

0.12

0.08

0.74

Source: Dr Roy Flannery

Phosphorus accumulates in the seed and pods while potassium is important to the stems and leaves as well as the pods.

As a consequence, the potassium needs are about twice as great as the phosphorus needs. However, only about half of the phosphorus and potassium needs are for the vegetative growth, whereas the balance is for seed development. Soybeans remove about 0.80 pounds of P2O5 and about 1.40 pounds K2O per bushel of yield harvested.

Early Soybean Growth and Development

Growth Stage

Time (Days) (Ideal Growing Conditions)

First trifoliolate leaf emerges with leaflets on trifoliate above not touching (V1 stage)

10 to 12

Photosynthesis by the developed leaves is adequate for the plant to sustain itself

12 to 14

The first (V1) through the fifth (V5) trifoliolate leaves emerge

5-day intervals

V2 Stage

• 6 to 8 inches (15.2 to 20.3 cm)

• Active nitrogen fixation begins

• Lateral roots are proliferating rapidly into the top 6 inches (15.2 cm) of soil

V3 Stage

• 7 to 9 inches (17.9 to 22.9 cm)

V5 Stage

• 10 to 12 inches (25.4 to 30.5 cm)

The sixth (V6) to the last trifoliolate leaf [V(n)] develop (about the beginning of seed development in the pod

3-day intervals

At V6, lateral roots grow completely across a row spacing of 30 inches (76) cm) or less: 50% leaf loss at V6 reduces yield approximately 3%