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The most important point to take home from this event is that your Virginia Soybean Association's hard work over the years was not in vain. Virginia is one of the leaders in biodiesel use and availability. The Virignia Soybean Association was very instrumental in getting the refinery (the first in the Mid-Atlantic region) up and running. And many thanks go out to all of you that are currently using this alternative fuel and reducing the country's dependence on foreign oil.
If you have not joined the Virginia Soybean Association, I ask that you do so. The payoff is great, as stated very clearly by our President this week
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First, Dr. Dunphy's research (24 locations) does in fact indicate that seeding rates can be lowered well below recommendations without substantial yield loss. In full-season plantings, he showed no yield loss down to about 50,000 plants per acre! In plants per feet, this is less than 1 plant/foot in 7 1/2- inch rows and less than 2 plants/foot in 15-inch rows! This is half of our (Jim's and my) recommendations. I don't doubt the data and I'm sure that under many circumstances, 50,000 plants per acre are all you need to maximize yield. So, why do I (& Jim) still recommend seeding rates to give 100,000 or more plants in full-season systems?
The main reason is risk. There are three major risks as I see them: 1) a poor stand; 2) poor weed control; and 3) a dry year. The first just may be the greatest. While 50 thousand plants per acre may be sufficient in some instances, once you drop below this level, yield drastically drops. I'm talking about several bushels here with every 5-10,000 plant per acre reduction. There is no margin for error. Yes, the extra seed is insurance; but, in my opinion, it may be the best insurance ever spent.
Another risk is poor weed control with low populations. I'm not saying that excellent weed control cannot be achieved with low populations; I'm just saying that it'll be more difficult. The Roundup-Ready system, like all total postemergence systems, is heavily dependent on rapid canopy closure. I've conducted research in Virginia that shows about a 10-day delay in complete canopy closure when populations are reduced in half. Although I did not evaluated weed control (we kept all plots weed-free), I would assume that new weeds would emerge much faster with half a stand. This scenario would then require an additional herbicide application. Or worse yet, the uncontrolled weeds will reduce yield.
Some might suggest that an extra application is much less expensive than twice the seed. I cannot argue. But, when combined with the yield risk from low populations with poor stands, then the extra seed can easily justify higher seeding rates.
Finally, I'll there is weather risk, particularly a dry year. The average yield in Dr. Dunphy's May-planted experiments was over 45 bushel per acre. I suspect that with such a yield, canopy development was not hindered. When we can completely close the canopy by flowering (LAI = 3.5 to 4.0), further plant population increases will not usually increase yield. I've shown this many times. But, what about dry years, when we can't close the canopy? What would have happened if yield potential was only 35 bushels? What about 30 bushels?
I've found that soybean yield response to plant population is highly dependent on available soil moisture. So, if early-season, intermittent drought causes lack of leaf area development, then one would expect significantly lower yields with half a stand.
Drought risk is directly related to soil type. On a very productive soil with high plant-available water-holding capacity, there is less risk of adequate leaf area development because there is less risk to drought. In such circumstances, fewer plants per acre are required to close the canopy and maximize yield. On the other hand, deep sands with low plant-available water-holding capacity have a greater risk of not accumulating adequate leaf area because of greater risk of drought stress. Therefore, the risk of yield loss from less than recommended plant populations on such soils is much greater.
In addition to soil type/soil moisture issues, we must also consider planting date and maturity group when selecting our seeding rate. As one delays planting, there is less time to produce adequate leaf area. The same reasoning holds true as one move to earlier-maturing varieties. I think that you see that the risk of lowering seeding rates is even greater when planting is delayed or an earlier variety is used. Therefore seeding rates should be increased as planting date is delayed and as one plants earlier-maturing varieties.
Because of this leaf area development theory (built upon several years of Virginia experimentation), I do not make an across the board plant population recommendation for all soils, planting dates, and yield potentials. Furthermore, I do not recommend reducing seeding rates below those that I have traditionally suggested. Below are my suggestions for final soybean plant population in plants per acre. For those of you that would rather talk in terms of seeds/foot, I'm including a chart converts plants per acre to seeds per foot, assuming an 85% emergence rate.
In conclusion, can you lower your seeding rate? Yes, if you've been using higher rates than those suggested below. No, if you've been following these guidelines.
Final Plant Population Suggestions (no. per acre x 1,000) for Virginia Soybeans
| Avg. Yield Potential* (bu/acre) | Maturity Group | May 1-31 | June 1-15 | June 16-30 | July 1-15 |
|---|---|---|---|---|---|
| 20-30 | III | 140 | 160 | ---- . | ---- |
| IV | 130 | 150 | 200 | 220 | |
| V | 120 | 140 | 180 | 200 | |
| 30-40 | III | 120 | 140 | 200 | ----- |
| IV | 110 | 130 | 180 | 200 | |
| V | 100 | 120 | 160 | 180 | |
| >40 | III | 120 | 120 | 180 | ----- |
| IV | 100 | 110 | 160 | 180 | |
| V | 100 | 100 | 140 | 180 |
Seeding Rate = Desired plant population ÷ (43,560 sq. ft./acre ÷ row width in ft.) ÷ % emergence
Example (15" rows):
= 120,000 ÷ (43,560 ÷ 1.25 ft.) ÷ 0.85
= 120,000 ÷ 34,848 ÷ 0.85
= 4.1 seeds per foot on 15" rows
| Desired Plant Population Per Acre | |||||||
|---|---|---|---|---|---|---|---|
| Full-Season | Double-Crop | ||||||
| Row Width | 100,000 | 120,000 | 140,000 | 160,000* | 180,000 | 200,000 | 220,000 |
| Seed/ft. (assuming 85% emergence) | Seed/ft. (assuming 85% emergence) | ||||||
| 36" | 8.1 | 9.7 | 11.3 | ---** | ---** | ---** | ---** |
| 30" | 6.8 | 8.1 | 9.5 | ---** | ---** | ---** | ---** |
| 24" | 5.4 | 6.5 | 7.6 | 8.6 | 9.7 | 10.8 | --- |
| 20" | 4.5 | 5.4 | 6.3 | 7.2 | 8.1 | 9.0 | 9.9 |
| 18" | 4.1 | 4.9 | 5.7 | 6.5 | 7.3 | 8.1 | 8.9 |
| 15" | 3.4 | 4.1 | 4.7 | 5.4 | 6.1 | 6.8 | 7.4 |
| 7.5" | 1.7 | 2.0 | 2.4 | 2.7 | 3.0 | 3.4 | 3.7 |
Seeding Rate = Desired plant population ÷ (43,560 sq. ft./acre ÷ row width in ft.) ÷ % emergence
Example:
= 140,000 ÷ (43,560 ÷ 1.25 ft.) ÷ 0.85
= 140,000 ÷ 34,848 ÷ 0.85
= 4.7 seeds per foot on 15" rows
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First, let's look at this independent of soybean rust. In general, there is a 10-day delay in maturity as you move from a group 3 to a group 4 or a group 4 to a group 5. So if you would plant a MG 4.4, a MG 4.8, a MG 5.2, and a MG 5.6; the later three varieties would flower, set pods and seed, and mature about 4, 8, and 12 days later than the earliest MG planted (if these varieties were planted on same day).
Here's another rule of thumb. For every 3-day delay in planting, you'll delay maturity by 1 day. By mid-June, this changes to for every 5-day delay; you delay maturity by 1 day. But, let's focus on our full-season crop now. This means that a month delay in planting will result in a 10 day delay in maturity. With this information, you quickly realize that if a group 5 is planted one month earlier than the group 4, then both varieties will basically develop and mature at the same time. If you were to schedule your planting in this way, I see no real benefit to planting a range of maturity groups.
On the other hand, if you begin with the earliest MG, you will not only spread out the maturity date (and potential harvest dates), you also spread out the flowering, pod development, and seed fill date. When you do this, you spread risk. If a drought occurs early, the later MG will be able to better utilize later-season rains. If a late-season drought occurs, the earlier MG's will perform relatively better. So, you spread your risk to drought.
There is another reason that I suggest planting your earlier-maturing varieties first. This relates to the earlier discussion on seeding rates. Earlier varieties need more time to develop adequate leaf area. If you planted your group 5's in May and wait until June to plant the 4's, you are giving less time to the group 4's and more time to the group 5's; just opposite of what is logical. This is also a risk management strategy.
Now, let's address the rust issue. If you were to follow my suggestion of planting your group 4's first and group 5's last, then the 4's would be at much less risk to losing yield to rust than the group 5's. So, you may be able to treat the group 4's with less fungicide or possibly not at all. On the other hand, if you were to do the opposite, there is no risk avoidance. So, my suggestion does not change just because of rust.
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Let's first review some basics about controlling soybean rust. There is little to no benefit of spraying soybean before flowering (R1-R2 stage) or after physiological maturity (R7). But, the soybean crop must be protected from flowering through full-seed (R6). From R1 (one flower anywhere on the main stem) to R6.5 (All normal pods on the top four nodes of the main stem have pod cavities completely filled; ~80% of dry matter accumulated) requires about 50 to 55 days (7-8 weeks).
The number of fungicide applications will depend on three main factors: 1) the stage of crop development; 2) the incidence and severity of infection as determined by crop scouting; and 3) current and forecasted weather conditions. The last point is very important. Rust requires free moisture, high humidity, and/or moderate temperatures (68-77o is optimal). Our relative humidity is usually high, and 6-8 hours of leaf wetness occurs on most summer nights. But, too dry or too hot can be very detrimental to the fungus. We have both of these conditions quite often in Virginia.
The following would be a worse-case scenario. Rust arrives at or before flowering. The first "curative" or premix ("curative" + "preventative") fungicide spray would have to go on at R1-R2, the second application 3 weeks later (R4; full pod), and a third application might be needed 3 weeks after the second (R6; full seed). Applications after R6.5 would violate many preharvest intervals and would not result in much benefit. Again, this is a worse case scenario.
A better scenario would be that rust arrives at R5 (beginning seed); one application would suffice. If rust were to arrive after R3 (beginning pod), then 2 applications would be enough to protect the crop. Of course the best scenario would be that rust does not come in until after R6.
Now with that information, we'll return to the question, which maturity group should I spray first? I'll assume that two varieties with a maturity range of 0.7 are planted over a period of 2 weeks and the average difference in crop development is 10 days. It will take you a week to 10 days to spray your entire acreage.
Let's also assume that conditions are favorable and both varieties have adequate leaf area, therefore rust will sporulate and develop. Lack of canopy, relative humidity, or temperature is not a limiting factor. Yield potential for the two varieties is equal. Rust is not yet in the local area, but the risk is high; therefore a preventative or premix fungicide spray is recommended. If fungicides cannot be applied until 10 days later, a curative product will be needed.
Scenario 1: MG 4.6 is just beginning to form pods (R3 stage); MG 5.2 is flowering (R2 stage). Protect the earlier maturity group first with either a preventative or premix fungicide. It is likely that the group 4 variety will need two sprays regardless of whether you spray it before or after the group 5. Then, you would spray a curative (or premix) fungicide on the R3-stage group 5 variety. Both varieties would need 2 sprays. On the other hand, if you sprayed the group 5 first (R2), you may need to spray this variety two more times (3 times total). The group 4 would then be sprayed with a curative (or premix) fungicide at R4. This would still require another spray to protect the crop through R6.5 (2 sprays total for the group 4 variety).
Scenario 2: MG 4.6 is beginning to form seed (R5 stage); MG 5.2 is in the full-pod stage (R4). Protect the later maturity group first with a preventative or premix fungicide. It is likely that the group 5 variety will need two sprays regardless of whether you spray it before or after the group 4. Then, spray a curative or premix fungicide on the late-R5 stage group 4 variety. If you wait until this stage with a curative product, you may get by with one spray. The group 5 variety will need two sprays; the group 4 variety will need one. On the other hand, if you sprayed the group 4 first at the beginning R5 stage, it would need 2 sprays to protect the crop through R6.5, just like the maturity group 5 variety.
Scenario 3: MG 4.6 is in the late R5 to early R6 (full seed) stage; the MG 5.2 is in the R5 stage. This is the hardest scenario. You could potentially not spray the group 4 variety. Remember my original assumption: rust is not yet here, but the risk of infection is high. Assuming that the crop will not be infected for 3-5 days and assuming that it will take 10 days for the infection to produce pustules, then that maturity group could potentially avoid a yield loss. But there's some risk here. If would be safest to just put on a preventative or premix fungicide to the group 4 at this time. Then, by the time you got around to spraying the group 5 variety, it would be in a later stage and not require but one spray. If you sprayed the group 5 variety immediately, it may need another spray later. So, a risk-averse reaction is to spray the group 4 first, then the group 5 (both varieties would need two sprays). A risk -taking, but potentially more profitable option would be not to spray the group 4 variety, then wait about 7-10 days and spray the group 5 variety with a curative or premix fungicide.
So, I imagine that you're totally confused. These are issues that we will work out and make specific recommendations when the time comes. But, this just gives you a preview.
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Dear Biodiesel Alliance-Backers Supporters:
In an effort to offer you timely information about the benefits of biodiesel, we are providing a fact sheet on Biodiesel and Energy Security. With sky-high fuel prices, continued turmoil in the Middle East and rising oil imports, biodiesel has an important role to play in increasing domestic energy security. National opinion surveys tell us that energy security is the leading reason for the general public's support of biodiesel.
U.S. oil consumption and imports continue to rise, and by 2025 imports are expected to account for 68 percent of consumption. The transportation sector ranks first in consumption. About 38 billion gallons of on-road diesel are used each year in the U.S. (about 55 billion gallons total). Annual biodiesel production has increased from 500,000 gallons in 1999 to 30 million gallons in 2004, making it the fastest growing alternative fuel in America. The biodiesel tax incentive that went into effect January 1, 2005 is causing biodiesel demand to climb even more.
As we search for ways to free our nation from the hold of imported oil and stretch existing petroleum supplies, biodiesel must be part of the solution. It is an immediately available fuel to put us on the road to energy security.
Thanks for your continued support of biodiesel.
Sincerely,
Joe Jobe,
Executive Director
National Biodiesel Board
The National Biodiesel Board is funded in part by the United Soybean Board and state soybean board checkoff programs
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Sincerely,
David L. Holshouser
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