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/Ac 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/Ac N, 200 lbs/Ac P2O5, and 300 lbs/Ac K2O applied preplant, and two fertigations. Figure 13 shows nutrient storage in plant parts at the green stage of development.
|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|
|Micronutrient uptake (lbs/Acre)|
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|
• 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
• 7 to 9 inches (17.9 to 22.9 cm)
• 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%|