In some of the soybean fields in North Dakota, soybean plants are emerged or just emerging. This is the opportunity to evaluate soybean stands and make management decisions.
Replant decisions should only be made after taking stand counts to determine plant populations, as visual observations tend to underestimate the plant population. Narrow row width may exaggerate the impression of low plant stand because there are larger spaces between plants within rows. Replanting is not recommended unless the cause of the previous poor stand can be corrected. Factors to consider when evaluating a stand include: why was the stand reduced (water saturated areas, shallow seeding, planter plugged); how uniform is the remaining stand; what is it’s yield potential; what is the weather forecast for the coming period; is there still enough time to replant (consider maturity of the soybean); and what is the cost of replanting (machinery, seed and labor).
Usually the stand reduction is not uniform throughout the field. Loss of stand is frequently irregular. Gaps may occur in rows, but if the gap is less than 2 feet in diameter, the adjacent soybean plants are capable of developing branches to occupy the space. Plants can adjust to low populations by producing more branches per plant, increasing the number of pods both on the main stem and branches, increasing the number of seeds per pod, and/or increasing seed size. Open spaces more than 2 feet in diameter may lead to reduction in yield.
To determine plant stand, select the area of the field with lowest plant stand and compare with the normal plant stand in other parts of the field. Make at least 10 random stand counts in an area where the stand is reasonably uniform. Use a tape measure and mark off 1/1,000 of an acre for each count. The lengths of rows equal to 1/1,000 of an acre with different row widths is indicated in Table 1. Multiply stand count per length of row by 1,000 to obtain stand per acre. NDSU’s recommendation is 150,000 established plants per acre.
Soybean populations can vary perhaps as much as 50 percent from recommended levels without affecting yields, as long as missing gaps are not too large and weeds are controlled. In summary: before even considering re-seeding count the stand and calculate the cost.