CFAES Give Today
Agronomic Crops Network

Ohio State University Extension


C.O.R.N. Newsletter 2011-09

Dates Covered: 
April 19, 2011 - April 25, 2011
Steve Prochaska

Three Reasons Why Soybean Planting Date Matters

1. You want your soybean crop to collect as much of the seasonally available solar radiation as possible, simply because plants require the energy of sunlight to convert carbon dioxide into carbohydrates, protein, and lipids (oils).

Clearly, 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. Why waste free sunlight by letting it hit the ground? Indeed, the goal each year for a soybean producer is simple: “Get that soybean canopy green to the eye by the 4th of July.”

Also keep in mind that day length increases from the equal day/equal night cycle of the spring equinox to the longest day/shortest night cycle of the summer solstice.  A soybean crop, when planted in late April or early May, is likely to close its canopy within a week or so after the summer solstice. Later planted soybean crops will be deprived of the opportunity to collect as many hours of sunlight compared to earlier planted crops, and thus will invariably have less yield potential.

2. You want to have your soybean crop transpire a greater fraction of the seasonally available water, simply because 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 order for plants to acquire carbon dioxide to produce plant and seed organic dry matter, the pores in the leaves (known as stomata) must open, allowing water inside the leaf to escape. In effect, plants must exchange water for carbon dioxide. As a general rule, the soybean exchange ratio translates into about one acre-inch of water (27,154 gallons) being required for every three bushels of seed produced per acre.

Crop water use includes water lost via evaporation directly from the soil, as well as water lost as transpiration from the leaves. Crop water use efficiency can be improved by reducing evaporative water loss as this means more water will be available for transpirational water loss. Early planting helps in this regard, because

·       the cooler soil and air temperatures prevailing in late April or early May are much less conducive to soil water evaporation than the temperatures in late May and early June,

·       the canopy closes earlier in the season, which reduces the interception of solar radiation by the soil surface, thereby lessening the heating of soil surface that drives soil water evaporation , and

·       the  higher humidity that often prevails in a closed (versus open) soybean canopy minimizes the degree of evaporative soil water loss.

In addition to allowing plants to collect more seasonal solar energy for use in photosynthesis, early planting also 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.

3. You want to have your soybean crop produce as many plant stem nodes as possible, simply because plant nodes are where the plant produces its flowers, then pods, and ultimately seeds within those pods.

The rates of soybean germination and emergence are temperature sensitive, so these processes are slower in cooler soil temperatures that prevail during early plantings. However, once soybean plants reach the V1 stage,  (temperature sensitivity is much less, given that a new node is produced on the main plant stem about once every 3.7 days (i.e., about two nodes per week), until node accrual ceases at the R5 stage, when seed enlargement begins in the uppermost stem nodes. The node accrual rate between V1 and R5 is not impacted much by the calendar date of planting.

What is impacted by planting date is the calendar date when V1 occurs. This is quite important, given that the V1 date establishes the earliest date that linear node accrual can start. Moving the planting date earlier typically results in an earlier V1 date , even though an earlier planting lengthens the number days from planting to V1 due to the sensitivity of soybean germination and emergence to soil temperatures.

Later planted soybeans simply do not have the opportunity to catch up to the soybean node development of earlier planted soybeans. Thus, earlier soybean planting can increase crop yield potential by allowing plants to generate more stem nodes. It also induces the beginning flower (R1) stage to occur nearer the date of the summer solstice.


So, what kind of yield advantage does a producer gain by planting soybeans early?  In Nebraska,  research reported in the Agronomy Journal demonstrated that for each day that soybean planting was delayed after May 1, the yield penalty per day was as much as 5/8 (0.63) bu/ac in a “great” soybean year (like 2004), and still a substantive ¼ (0.25) bu/ac in a “not so great” soybean year (like 2003). Multiplying these yield penalties by the current soybean price provides a clear indication of the importance of planting date in terms of optimizing the net profit potential in a soybean production system.

The yield penalties accruing from delaying soybean planting beyond early May in Nebraska have also been documented in other states ( Wisconsin, Indiana and Iowa).

The yield reward arising from early planting should not be used as a reason to plant seed into seedbeds that are too wet to plant. Other than trying to plant early, exercise good judgment relative to the other seed planting practices.

Factors to Consider When Planting Soybeans and Corn in 2011

Risks to Early Planted Corn

1.   Uneven or reduced plant emergence due to extended periods of wet, cold weather can significantly reduce corn yields.

2.   If need to replant, there is a loss of growing season and corn yield potential.

3.   Cost of replanting in the event of failure.

4.   Additional weed control costs due to lack of early crop canopy or need to control corn from early failed planting.

5.   In failed plantings where corn is replanted, loss of applied nitrogen may occur via leaching or de-nitrification due extended exposure to weather extremes and the period of heavy nitrogen use by the corn plant (grand growth stage) will likely be delayed if corn is replanted.

6.   Pre-emergence corn herbicides applied may preclude planting soybeans in the event of corn stand failure.

7.   Any nitrogen applied for corn is essentially lost if failed corn is replanted to soybeans.

Risks to Early Planted Soybeans

1.   Poor emergence (due to a variety of possible factors such as extended periods of wet, cold weather, soil pathogen infection, insect attack, etc).

2.   Loss of growing season if stand is lost and replanting is necessary (may be less yield loss to replanting soybeans than penalty to replanting corn).

3.   Cost of replanting in the event of stand failure.

4.   Hard freeze after soybeans are up may kill plants (soybeans will withstand temperatures to about 27 degrees F; however the probability of such an event will be low in 2011 given the weather delays).

5.   Possible added weed control costs due to lack of early crop canopy if soybean growth is delayed to unfavorable weather conditions.

Soybeans – Factors to Consider if Planting Early

1.     More time to evaluate and make a mitigating response in the event of a poor soybean stand while maintaining yield potential (than corn).

2.     May tolerate an imperfect seed bed better than corn and will compensate over reduced plant populations (must still have a relatively uniform stand).

3.     Soybeans have the ability to flex over different final plant stands, weather extremes and planting dates, and still yield well.

4.     Spreading of harvest work load.

5.     Seed treatments such as Apron, Maxim, etc may help protect soybean seeds from various soil pathogens that may be present in the soil environment.

6.     Not any significant loss of primary nutrients (P2O5 and K2O) applied to soybeans in event of crop failures.

7.     Opportunity to plant wheat in a timely manner in late September or early October by the possibility of an earlier soybean harvest.

8.     Extended growing seasons with high quality sunlight (more photosynthesis possible).  The maximum amount of sunlight occurs in the months of May, June and July in Ohio.

9.     Opportunity to grow later maturity soybeans.

10.   Most favorable temperatures and soil moisture levels for crop growth and development may occur from April 25 to July 15, as opposed to July 15 to September 1 (carbohydrate deposition).

11.   Opportunity to grow and harvest high yield soybeans (yields greater than 60 bushels/acre).  Later planting may not allow such an opportunity due to loss of growing season.

Corn - Factors to Consider if Planting Early

1.   Extended growing season with high quality sunlight (more photosynthesis possible) and perhaps maximum yield potential.  The maximum amount of sunlight occurs in the months of May, June and July in Ohio.

2.   Generally, adequate moisture for early season crop development.

3.   Generally more favorable temperatures for crop growth and development and thus carbohydrate deposition.

4.   Pollination may also occur during a period of more favorable temperatures and soil moisture availability.

4.   May offer best seedbed of year and thus reduce yield robbing soil compaction.

5.   Spreading out of the work load (both spring and fall).

6.   Seed treatments such as Apron and Maxim may help to protect corn from various soil pathogens in adverse soil environments.

7.   Can withstand a frost as long as growing points below ground.

8.   Opportunity to grow and harvest highest yielding corn.

9.   Longer growing season and thus the opportunity to have dryer corn at harvest.

10. Opportunity to grow full season corn hybrids and thus reduce production risks associated with growing only a single maturity hybrid or only short season hybrids(s).


One of the major attributes of successful farmers is timeliness.  With our present knowledge and experience of planting corn and soybeans, there are reasons to consider planting soybeans before or at the same time as corn if equipment and labor is available.  

With farm size increasing, and many working off the farm, it is imperative to effectively utilize all available planting days.  Stating it in another way, one of the major impediments to large or small farm operation success is the lack of planting time on dry soils.  Thus, realizing there are later time windows to replant soybeans or repair poor stands and maintain high yields  and one realistically may have but one chance to get a good stand with corn for maximum yield potential in 2011, soybeans might be the better option if planting  under less than ideal soil conditions. 


Getting Reacquainted with Ohio Wheat Diseases

The resistant varieties section has color pictures of common disease we see in Ohio.

wheat disease figure

The disease scouting section list threshold levels of diseases and stage of grow information.

The full publication can be viewed at Bulletin 785, Wheat Disease Management in Ohio or purchased on line.

SmartStax Approved for Refuge-In-Bag

Alfalfa Weevil Update

April Weather Outlook

The outlook for summer is still for at or above normal temperatures and at or below normal rainfall. Usually we get a better handle on summer outlooks in early May and we will update you then
La Nina continues in the Pacific Ocean but should weaken and end by summer. Any threat of an El Nino would likely not occur before autumn. Remember, there is a 3-6 month lag between ocean temperatures and responses in our weather so even if an El Nino formed it would not impact our weather much before next winter. For now, the La Nina wet spring continues as has been widely expected since last summer and autumn. Latest updated information on La Nina can be found here:


Archive Issue Contributors: 
Archive Issue Authors: 

Crop Observation and Recommendation Network

C.O.R.N. Newsletter is a summary of crop observations, related information, and appropriate recommendations for Ohio crop producers and industry. C.O.R.N. Newsletter is produced by the Ohio State University Extension Agronomy Team, state specialists at The Ohio State University and the Ohio Agricultural Research and Development Center (OARDC). C.O.R.N. Newsletter questions are directed to Extension and OARDC state specialists and associates at Ohio State.