Sunday, June 1, 2014

Soybean Emerging in Crusted Soils Need Evaluated

A soybean, not yet emerged, showing signs of swollen hypocotyl due to soil crusting.

Soil crusting has been an issue for many emerging soybeans.  Many have contemplated the use of a rotary hoe or even a running a planter between the rows in hopes of breaking the soil crust.  Some were lucky enough to receive a rain to soften the crusted soil to aid soybean emergence.  If a thick soil crust remains, the “necks” of some soybeans could “snap off” due to these unfavorable conditions at emergence.  To learn more about crusting, you can refer to the blog:  Corn Stand Counts and Avoiding Compaction, Crusting and Poor Seed to Soil Contact

The soybean growing point is located between the 2 cotyledon leaves (when the soybean first emerges at the VE or VC growth stage).  If the growing point becomes injured, the axillary buds will come out of dormancy and develop near the stem, above the leaf petioles (where the leaf meets the stem).  If the soybean plant gets cut or snapped off below the cotyledons, the plant will die. If one of the cotyledons is lost, early in the growth of the soybean, the growth rate will be reduced.  If there is more than one cotyledon or leaf tissue present, there is hope, because soybeans will be able to regrow.

To evaluate your soybean stand, you will need to take at least 5 stand counts (1/1000th of an acre) throughout the field, and then average these counts to get an approximate number of plants per acre.  Do not count soybeans that are missing leaf tissue, have brown leaf tissue, or are cut below the cotyledons.  The hula hoop method can be used to approximate a soybean population at any row spacing.  If you are lucky enough to find or make a hoop that is 28 ¼” in diameter; all you need to do is count the plants within the hoop, and then multiply that number by 10,000 to arrive at that stand count or approximate number of plants per acre.  

You can also use a measuring tape or wheel to measure 17.5 feet of a 30 inch row or if you have 15 inch rows, you can still measure off 17.5 feet, but be sure to count the plants within 2 rows.  Count the number of plants within the 17.5 feet, then multiply that number by 10,000 for the approximate number of plants per acre.  

Remember that soybeans can tolerate low populations and may only have a small amount of yield loss, with a wide amount of plant loss. Populations of 100,000 (narrow rows) have the potential to produce maximum yields and populations around 80,000 (30 inch rows) could potentially produce 90 percent of the maximum yields.  However, the maximum yield potential may be reduced if there are gaps or gaping holes within your field.  You quickly start to lose your maximum yield potential as the plant population average across the field is below 50,000.

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