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Now is the Time to Gather Soybean Leaves for Plant Tissue Testing

Posted: June 30, 2015

Since we cannot test the soil with accurate assessment of micronutrients, the best way to determine hidden hunger is with a simple $24.00 plant tissue test.

Several growers are considering more high yield management for their soybean crop. There are numerous foliar fertilizer products with ideal nutrient levels for numerous micronutrients. Our research indicates tremendous variation in the response to these products. Yield enhancement is tied to whether the plant is deficient in micronutrients or not. Since we cannot test the soil with accurate assessments of micronutrients, the best way to determine hidden hunger is with a simple $24.00 plant tissue test. A few growers last season enjoyed 90 bu/acre plus while managing for high yield soybean crops, and many utilized tissue testing to determine foliar fertilizer applications. The first step is to gain an accurate soil test and maintain optimum levels of P at 150 ppm and K at 300 ppm. The second step is to collect a sample at the R1 to R2 stage (full flower) for plant analysis. The Ag Analytical Lab at Penn State and numerous other labs provide the lab testing for the results.

Here are the specifics to gather the samples. Once the plant begins to flower (R1), which is occurring at the time of this writing in early planted fields, in the following two weeks gather the samples and send them off via overnight mail to gain quick results. This will allow for adequate time to determine a nutrient strategy before peak growth at R3 when pods are being filled.

Soybean Specifics

Growth Stage

Plant Part to Sample

Number of Plants to Sample

Seedling stage (less than 12") or

All the above ground portion.

20-30

Prior to or during initial flowering

Two or three fully developed leaves at the top of the plant.

20-30

Note: Sampling after pods begin to set is not recommended.

Interpretive Nutrient Levels for Plant Analysis

Nutrient Low Normal High Excessive
Nitrogen (% DW)
3.10  4.01  5.51  7.01
Phosphorus (% DW) 0.16  0.26  0.51  0.81
Potassium (% DW) 1.26  1.71  2.51  2.76
Calcium (% DW)   0.21  0.36  2.01  3.01
Magnesium (% DW) 0.11  0.26  1.01  1.51
Sulfur (% DW) 0.16  0.21  0.41  2.00
Manganese (ppm DW)  15  21  101  251
Iron (ppm DW)  31  51  351  501
Copper (ppm DW)   5
 10  31  51
Boron (ppm DW)  10  21  56  81
Zinc (ppm DW)  10  21  51  76

DW = Dry Weight

Contact Information

Del G. Voight, M.S
  • Senior Extension Educator - Agronomy
Email:
Phone: 717-270-4391