Plant soybeans early to pump up yields
Early-planted soybeans can provide profitable yield advantages in most cases. “Plant soybeans early, but do it right,” recommends University of Nebraska-Lincoln soybean expert James E. Specht.
His research has shown that for each day soybean planting was delayed after May 1, the yield penalty per day was as much as 0.63 bushel per acre in a “great” soybean year, such as the 2004 season, and 0.25 bushel per acre in a “not so great” soybean year, such as the 2003 season.
At a glance
• Research from UNL, other universities verifies advantages of early planting.
• More sunlight and more nodes are among the reasons researchers cite.
• But there are risks to understand when going too early.
Specht, a professor of agronomy and horticulture at UNL, says researchers in Iowa, Indiana and Wisconsin have documented similar yield penalties from delaying planting beyond early May.
He cites these three primary reasons why the yield potential of any soybean crop can be greatly enhanced by planting as early as reasonably possible:
• More sunlight. Early planting helps to ensure soybeans collect as much of the seasonally available solar radiation as possible because plants require the sunlight’s energy to convert carbon dioxide into carbohydrates, protein and oils.
With earlier planting, a soybean crop canopy will cover the ground sooner in the growing season, collecting nearly all of the incoming sunlight from that day forward, Specht explains.
Also, remember that day length increases from the spring equinox to the summer solstice. Later-planted soybeans won’t be able to collect as many hours of sunlight compared to earlier-planted soybeans.
• More available water. Early planting helps soybeans yield more because they transpire a greater fraction of the seasonally available water. There is a linear relationship between the amount of total water transpired by the crop and final crop yield.
The seasonally available water includes off-season rainfall that was stored as soil water prior to planting, plus all of the in-season rainfall. In addition to allowing plants to collect more seasonal solar energy for use in photosynthesis, early planting increases the yield potential by allowing the crop to use more of the seasonally available water for transpiration because less soil water is lost to evaporation.
Crop water use includes water lost via evaporation directly from the soil, as well as water lost as transpiration from leaves. Crop water-use efficiency can be improved by reducing evaporative water loss.
This means more water will be available for transpirational water loss. Early planting helps in this regard because cooler soil and air temperatures prevailing in late April or early May are much less conducive to soil water evaporation than temperatures in late May and early June.
• More plant stem nodes. Earlier planting helps soybeans produce as many plant stem nodes as possible. This is important because nodes are where the plant produces its flowers, then pods and ultimately seeds within those pods.
The rates of soybean germination and emergence are slower in the cooler soil temperatures that prevail during earlier plantings. Once soybean plants reach the V1 stage, temperature sensitivity of node accrual is much less. In general, earlier soybean planting can increase crop yield potential by allowing plants to generate more stem nodes and induce the beginning flower (R1) stage to occur nearer to the date of the summer solstice, Specht says.
The yield reward from early planting should not be used as a reason to plant seed into seedbeds that are too wet, Specht emphasizes. He also cautions to exercise good judgment relative to other seed planting practices.
Carlton writes from Lincoln.
This article published in the March, 2011 edition of NEBRASKA FARMER.