Efficient seed use critical in double-crop beans

Soybean seed in some of the most popular varieties is in short supply in the upper Southeast. Efficiently utilizing these valuable seed will be a critical factor in the profitability of double-crop beans.

While the drought reduced the number of seed available, low soybean stocks and continued good prices have driven demand for seed beyond supply. Most full season growers were able to get seed — though often not their preferred variety. That may not be the case for growers making late decisions to plant double-crop beans.

Every indication is that soybean acreage will be up across the Southeast and Mid-South. Small grain plantings, especially wheat, are usually a good indicator of double-crop soybean acres. In a year where soybean prices are good, past ratios of beans to wheat may be higher as farmers try to take advantage of good soybean prices.

Nationally, soybean acreage is expected to jump by 18 percent. In states that grow the same soybean maturity groups as the Carolinas and Virginia, acreage is expected to jump by two million acres. In these states, including Arkansas, Maryland, Missouri and Tennessee, analysts admit the number of double-crop beans that will be planted is an educated guess at best.

Virginia Soybean Specialist David Holshouser says, “regardless of how you crunch the numbers, it looks like a greater demand for a seed that was already in short supply.”

Holshouser says he is not so concerned about full-season beans. Research has shown we can cut seeding rates on conventional beans and still do well. The rule of thumb we tell our growers is to plant enough seed to get 80,000 plants per acre when using a planter and 100,000 plants per acre when using a drill, Holshouser notes.

In Virginia, Holshouser calculates that double-crop beans alone will require 500,000 units of seed for more than 350,000 acres of double-cropped soybeans.

There may be some potential relief for seed supplies in North Carolina. It was determined that a limited amount of seed of lesser quality are held "on reserve" in the state for use if needed. However, supplies of lower quality seed are limited and would likely be utilized only in extreme emergencies.

It is expected the price for these seed would likely be reduced. Some companies have already lowered their germinations for certain varieties to 75 percent. Lower germination levels are legally acceptable, down to 70 percent for soybeans, sold in North Carolina. Many producers may not be able to plant their preferred soybean varieties and/or maturity groups.

Jim Dunphy, longtime North Carolina State University soybean specialist, says soybean seed labeled at 80 percent germination or higher, need no adjustments from normal seeding rate. If soybean seed is labeled at 70 percent to 79 percent germination, seeding rates should be increased by 10 percent for full season May plantings, or by 5 percent for double-crop plantings in June and early July.

Dunphy cautions growers to be sure to account for seed size, as reflected in the number of seeds per pound, since this may be variable for the 2008 season. There is also concern that the lower germinating seed may well be accompanied by lower vigor, which would be more serious with the cooler May planting dates than with the warmer June plantings.

Holshouser says factoring germination and seed vigor data into double-crop soybean plantings can be a big yield saver for growers. “A germination test is the best way to know for sure what you have.”

“To conduct a simple germination test, wet two towers thoroughly, place in a tray and tilt the tray to remove excess water. Place 100 seed between the towels and cover the entire tray with plastic. Place the tray in direct light and in an environment that is in the 75-85 degree F temperature range. Take out moldy and diseased seed in 5-7 days. Then, count the remaining seed that have the tap root intact and that gives you the percentage germination,” Holshouser says.

The Virginia Tech soybean specialist says seed vigor is usually not on the bag, but should be available from the seed dealer.

Some rules of thumb about planting soybean seed using germination and vigor percentages are:

• High germination (90 percent) and high vigor (70 percent) should be planted first and under the most adverse soil and climatic condition. If soil temperatures are at least 65 degrees F no fungicide should be needed and seeding rates should not exceed recommended amounts.

• High germination and medium vigor (60 percent to 69 percent) may need extra seed at planting, if planting under adverse conditions. Seed in this category should be treated with a fungicide.

• Medium germination (80 percent to 89 percent) and medium vigor seed should not be planted under adverse soil conditions. If the soil is less than 65 degrees F at planting, seed rates will need to be increased and for certain seed rates will need to be increased to compensate for low seed vigor.

Price of other commodities may influence the level of increase in double-crop beans in the Southeast. Both cotton and peanuts have performed well in limited use behind wheat, and both are viable economic alternatives for soybeans to plant behind wheat.

Peanuts at $600 per ton and cotton at 85 cents per pound are attractive alternatives to any of the grain crops grown in the Southeast. Reaching yield potential of either crop is much more common than for soybeans to average the 42-43 bushel per acre national average.

If soybean acreage in the Southeast reaches projected levels, late planted, double-crop beans will be at the biggest disadvantage for seed. With good weather and careful management of seed at planting, profitability looks good for double-crop beans in the Southeast.

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