Tag Archives: soybean

Soybean Seed Quality Continues to Deteriorate

Posted on October 16, 2015 by David Holshouser

The warm and wet September combined with early planting of early-maturing varieties have led to some rather severe seed quality problems in soybean this year. Our harvest to date indicates that seed quality in our Northern Piedmont is pretty good, but declines as one moves south. There also seems to be a good correlation with lack of rotation, earlier maturity groups, and earlier planting showing most of the problems. The issues can usually be attributed to the diseases phomopsis seed decay and purple seed stain, which I’ll describe in more detail below. Other diseases such as Alternaria, anthracnose, and frogeye leaf spot can also cause seed discoloration and quality issues, but are less common. The bottom of the plant usually has more seed decay than the top. But if harvest is delayed, the entire plant will be infected.

Phomopsis Seed Decay. When soybeans mature during warm and wet conditions, we can expect seed quality to deteriorate. Because this disease develops more rapidly on plants that are maturing under warm and wet conditions, we usually have more problems with early-maturing varieties. We can however have seed decay on our later- maturing varieties if October is warm. Although pods can be infected earlier, seed decay does not usually begin until after physiological maturity (R7).

Infected seed are shriveled, elongated, and cracked. Severely infected seed may appear white and chalky. The fungus secretes enzymes that degrade the seed coat proteins. Test weight can be lower. High occurrence of these seed can lead to discounts or rejection.

There are a few things that can be done to reduce the disease incidence. It resides in the soil and on infected residue. So, rotation is very important. More decay will occur in a crop deficient in potassium, infected with viruses, and heavily attacked by insects. Later-maturing varieties and later planting dates that delay maturity into the cooler parts of the year will reduce the incidence. Still, timely harvest is the best management strategy. The longer you leave the soybeans in the field, the worse the disease. So, only plant as many early varieties as you can harvest in a timely manner. Foliar fungicides will decrease the incidence of seed decay if applied from pod development (R3-R4) to early seed filling stages (R5). My experience is that a single R3 will do little to prevent seed decay; it will usually take a second application at R5.

Purple Seed Stain. Purple seed stain is caused by the organism Cercospora kikuchii, the same organism that causes Cercospora blight. Before maturity, fields with Cercospora blight can be recognized by reddish leaves and reddish purple blotches on the stem and leaf petioles. When severe, defoliation of the upper leaves of the plant will take place. In many cases, the blotching progressed up the stem and to the pods. Dark, nearly black pods may appear on some varieties. Once it progresses to the pods, there is a higher likelihood that the seed will be stained.

Purple seed stain is very noticeable. The seed will contain pink to pale purple to dark purple splotches, which can cover the entire seed coat. The purple stain itself does not reduce yield, but seed with nearly 100% discoloration may be lower in oil and higher in protein. A lot of staining can result in discounts. Germination of seed with 50% or more staining will likely be delayed.

Usually, the disease first appears on the plant during early seed development. If conditions are right (average temperatures over 80^o for several days), then the disease will build up rapidly. Other weather factors do not generally affect seed infection. Severity of the infection is largely related to amount of infected leaf debris and residue. Therefore, rotation with a non-legume crop is critical for control.

Other control measures include variety selection, planting high quality seed free of visual staining, and fungicides. Varieties differ in their susceptibility of Cercospora kikuchii, but that information is rarely available in seed catalogs. We routinely evaluate purple seed stain in our variety tests. Fungicides will give some control if applied during pod or seed formation.

Wet Conditions May Lead to Soybean Seed Sprouting

Posted on October 7, 2015 by David Holshouser

One of the most disturbing late-season issues can be pod splitting and/or seed sprouting in the pod. Pod splitting is most common when pods develop and seed begin to grown (R4 to R6 stages) during dry conditions and seed finish filling under wet conditions. Sound familiar. This is more-or-less what we experienced this year. Seed sprouting is usually caused by extremely wet conditions after the crop is mature and seed moisture has dropped below 50%.

What causes pod splitting? The reason is not clear, but here are my observations. Generally pod splitting happens when the crop is under severe stress, usually drought conditions up until the full-seed stage (R6). Pods are generally small due to the drought. Then rains set in between R6 (full seed) and R7 (physiological maturity). The seed grow and grow, and seem to outgrow the pods, causing them to split. Obviously, this splitting can then lead to seed quality issues. It can also open the plant up to seed sprouting,

Even if the crop does not experience the above conditions and pods do not split due to rapid seed enlargement, wet conditions after the crop is mature can lead to sprouting seed. Sprouting seed is not always directly related to the pod splitting; pods may not split until seed sprout. I’ve seen up to 30% of pods with sprouted seed when conditions are perfect for this. Although an unusual occurrence, seed sprouting can occur if soybean seed drop below 50% moisture, then increase to 50% or more moisture.

In addition, I have seen more sprouting in pods showing Cercospora blight (very dark pods). I do not understand why and could not definitively relate the sprouting to this disease. But, there appeared to be a relationship. Sprouting occurred primarily at the top of the plant where the dark pods were located. In contrast when pods were not dark, I have observed most sprouting at the bottom of the plant where the relative humidity is greater.

Usually, the number of split pods and sprouting seed is low and yield and seed quality effects are minimal. After a week of drying conditions, the sprouted seed will dry up and may fall out of the pods. At the worst, there could be some lower test weight and seed could contain more foreign material (from the dried up sprouts). However, the light seed will likely be blown out the back of the combine. If you do observe the problem and it is severe, I suggest that the air on the combine be adjusted to remove those light, sprouted seed at harvest. Too many sprouted seed in the bin could lead to rejection by the buyer.

Lodging and It’s Effect on Soybean Yield

Posted on October 1, 2015 by David Holshouser

As I’ve driving throughout Virginia these past few weeks, one thing that is evident is the large amount of vegetative growth on our full-season soybean. While adequate vegetative growth is necessary for maximum yield, it can work against the crop in seasons that experience August/September droughts. In much of Virginia, soil moisture was depleted rapidly due to this large amount of growth and the lack of rain in August and September resulted in pod and seed abortion. I’ve seen many fields that look relatively good from the windshield, especially after some rains perked up the plants. But, closer examination revealed few pods or few seed in the pods. In general, I think that farmers will be disappointed in their full-season yields.

On the other hand, timely rains during August and/or September in some parts of Virginia allowed these full-season soybean to match this seemingly excessive growth with lots of pods and seed. In such scenarios, 60 to 80 bushels per acre are possible. The only thing that may work against such a crop is, ironically, excessive vegetative growth that is causing or might lead to lodging. I always remind those that complain about lodging that 20 bushel soybean do not usually lodge.

Now we have Hurricane Joaquin bearing down on us. This could greatly change our yield potential, especially in our large full-season soybean with a good pod and seed set that is not yet fully mature. With this in mind, I thought that I would review lodging’s effects on soybean yield.

How much will the lodging cost us in yield? This will depend on the degree of lodging and the stage that the soybeans were in. In general, I’d say that our full-season crop is rapidly approaching maturity. Fields planted to earlier maturity groups are physiologically mature (R7, 98-100% of the final yield has accumulated), some are ready for harvest. Many fields are still in the R6 (full seed) stage. Most double-crop soybeans are in the R5 (beginning seed, seed are not yet touching in the pod) and R6. Yield is most severely affected by lodging when the lodging occurs at the R5 stage. Although yield is still affected at R6, yield losses are only half as severe at this stage. Although at a more susceptible stage, double-crop soybeans are much shorter and will not likely have as severe lodging as more full-canopied full-season soybean.

So, what’s my estimate on the amount of yield loss? First, we have to distinguish harvest or traffic loss from physiological yield loss. Harvest losses can vary anywhere from 3-10% depending on many factors. In some cases, we may have to run the combine of the most severely lodged soybeans in one direction.

There is little data on physiological yield loss, but what’s out there seems to be pretty consistent. What do I mean by physiological yield loss? That’s the loss in yield from lodging if all of the soybeans that are now on the plant can be harvested. In controlled studies where researchers simulated lodging and compared it to a crop that was artificially supported, losses have ranged from 0% to over 30%. Why such a range in yield loss? It depends on the severity of lodging and the stage of development in which the lodging occurred.

Let’s first address the severity of lodging. Soybean researchers have traditionally rated lodging on a scale of 1 to 5 as follows:

1.0 = almost all plants erect

2.0 = either all plants leaning slightly, or a few plants down

3.0 = either all plants leaning moderately (45^O angle), or 25-50% down

4.0 = either all plants leaning considerably, or 50-80% down

5.0 = all plants down

Yield loss will be minimal unless most plants are leaning at a 45^O angle or more. Otherwise, yield losses can range from 10-35%, depending on the stage in which the lodging occurred.

Why does lodging cause yield loss? It’s not completely clear, but the generally accepted reason is a reduction in net photosynthesis. With less photosynthesis, there is less energy going to the developing pods and seeds. When plants are lodged, relatively less of the upper leaves and more of the lower leaves are exposed to sunlight. The upper leaves are more photosynthetically active and the lower leaves are less active. When lodging occurs, the entire energy-producing mechanism is disturbed. In other words, we are now exposing less of the most productive leaves and more of the least productive leaves to the sun. So, yield will decline.

Let’s assume that lodging rated above 3.0 will cause a 10-30% loss. Now the severity of the yield loss will depend on the development stage that the soybean plant was in. As I said earlier, there’s little hard data on this subject, but a few older experiments give us some information. In a study conducted in 1972-73, S.J. Woods and M.L. Swearingin of Purdue University indicated that the R5 stage was the most critical time for lodging to occur. At this stage, yield was reduced by 18-32%. At stages R3 and R6, yield was reduced by 12-18% and 13-15%, respectively. Details of that experiment are shown to the right.

In that study, the plots were manually lodged with a long aluminum bar at the indicated soybean stage. Although lodging ratings were not given, I would consider it to be in the 3.5 to 4.0 range from the description given. Two varieties were tested. ‘Corsoy’ was more susceptible to lodging, but was able to branch more; therefore, it yielded higher when lodged. ‘Wells’ is more resistant to lodging, but did not branch as much; therefore, was unable to compensate as much for the lodging. In the natural lodged plots, only slight (2.0 or less) lodging occurred.

From the above data and a few other studies, I’d estimate that where lodging is moderate to severe and the soybean are in the early R6 stage, we could lower our yield potential by 10-15%. If the plants are still in the R5 stage and lodging is severe, losses could be 15-25%. If soybeans are in even later stages (mid-R6), yield loss will be less. If physiologically mature (R7, one pod on the plant has reached is final mature color), 98 to 100% of the dry matter has accumulated and losses will be nearly zero (assuming no harvest losses). Most of our full-season soybeans are close to physiological maturity (R7). Plus, plants with fewer leaves lodge less.

In summary, there may be some yield loss due to Hurricane Joaquin. Yield losses will be greater with later maturity groups or in double-crop acres that have good growth. But, hopefully, the hurricane will move off the coast and the only soybean we need to worry about lodging are those with very high yield potential.

Late-Season Drought Hurting Soybean in Virginia

Posted on September 10, 2015 by David Holshouser

I had never seen fields as wet as they were back in the second week of July. But, things change very rapidly.

In August, it appeared that full-season yield potential was 60 to 80 bushels per acre. Growth was excellent and the crop was loaded with pods and seed. Likewise, corn yield potential was excellent. Double-crop soybean did not look nearly as good, struggling with general poor growth due late planting, wet feet early, and dry soils later.

Now the situation is just the opposite. Well almost – corn yields are coming in very good. But, pods and seed on our full-season soybean crop are rapidly aborting due to the dry weather. Leaves are falling. It appears that the crop is maturing more rapidly. This is not a good thing as yield strongly depends on the length of seed filling. I’ve even seen some soybean dying in the corners of center pivots on the Eastern Shore. Irrigation will definitely pay off this year. As shown in the precipitation deficit map, we are below our seasonal average rainfall over the past 60 days.

This photo was taken this past Tuesday 8:30 am in the Official Variety Test at our Eastern Shore AREC. It looks like maturity group 3 varieties will out-yield group 4s, which will yield better than group 5s. However, a timely rain this week may salvage the late 5s. I don’t expect yields to top 40 bushels and they could possibly be less than 20 bushels if the drought persists.

On the other hand, I feel much better about double-crop soybean. Although there is little growth, these soybean are not showing signs of drought, at least not to the extent of the full-season crop. This photo is from the field adjacent to the full-season soybean shown above.

The main reason for this lack of visual stress is less vegetative growth (usually not an advantage) pulling less moisture from the soil. We also started the season with a soil profile full of water, but not excessive moisture (probably because the wheat had more-or-less depleted the soil moisture by May). Furthermore, these double-crop soybean are just now entering the pod and seed development stages. The seed is not yet requiring great amounts of water. These soybean can also “wait” for a rain as, at this time, there are still excess pods on the plant.

Below are a few more images that show flower, pod, and seed abortion.

The number of seed per acre controls yield most – the number of seed is mainly controlled by the the number of pods at harvest; seed per pod has less effect. Seed size can also greatly affect yield, but not to the extent of seed number. With late-season rains, we can still increase seed size substantially, especially where there has been lots of seed and pod abortion.

Is there anything to be done about this? No, not really – short of irrigation. There’s nothing that you can apply to relieve the stress. But, we can learn from such devastating experience and apply these learnings to the future.

First and foremost, diversify. Although early-maturing varieties don’t usually do as well in full-season systems as those best adapted to a given area, it may be worth it to devote some acreage to such varieties. It may also help to plant a few varieties that mature a little later than the ones you normally plant.
Keep double-crop small grain-soybean systems in your cropping mix. Not only will it increase total income and improve your soils without a cover crop, it will reduce risks by diversifying your crop mix.
Review university, on-farm, and company variety test results to help select drought-tolerant varieties. Not since 2010 have we seen drought to this extent in our variety tests; therefore, we have little information on how current varieties perform under drought stress conditions.
Other stresses such as vascular disease and nematodes will greatly enhance the effects of drought. Identify those poor-yielding fields or parts of fields and take corrective actions next year.
Improve your soils with no-till and cover crops. Better soil structure, more organic matter, and better chemical and biological activity will minimize drought stress.

The Virginia Soybean Field Day is this Thursday

Posted on August 17, 2015 by David Holshouser

VIRGINIA SOYBEAN FIELD DAY
Thursday August 20, 2015

Eastern Virginia Agricultural Research & Extension Center
2229 Menokin Road
Warsaw, VA 22572
(804) 333-3485

Sponsored by
Virginia Soybean Association
Virginia Agricultural Experiment Station
Virginia Cooperative Extension

Join us to see the latest research on soybean varieties, disease and weed management, IPM and sorghum varieties. Experts will also demonstrate no-till drill maintenance and update you on the mid-Atlantic double crop initiative. Registration begins at 8:00 am and field tours begin at 8:50 am. The program will end at noon with a delicious meal by Nixon Catering.

Topics include:
– Soybean Disease Management – Dr. Hillary Mehl
– Soybean Weed Management – Dr. Mike Flessner
– Soybean Insect IPM – Mr. Mike Parish and Drs. Sean Malone and Ames Herbert
– No-Till Drill Maintenance – Mr. Keith Burgess
– Grain Sorghum Management – Dr. Joseph Oakes
– Roundup-Ready Public Soybean Varieties – Dr. Bo Zhang
– Mid-Atlantic Double-Crop Soybean Initiative – Dr. David Holshouser

We hope to see you there!

Should I Apply a Foliar Feed to My Soybeans?

Posted on July 16, 2015 by David Holshouser

The high prices over the last few years have allowed many of us to experiment with certain practices that, at best, might occasionally increase yields. The return of investment usually only required one bushel (or less), depending on the input. But that was when soybeans were $13, $15, and even $17 per bushel. But now, you may be able to sell your crop for $10-11 (if you still have any in storage) and the future prices are reflecting record acreages.

So, it seems that I’ve been asked, “Should I apply a foliar feed to my soybeans?” more this year than in the past few years.

First, I still stand by what I’ve said in the past and still say today: “Feed the roots and not the foliage.” Soybean will remove 3 to 4 lbs of nitrogen, 0.8 lbs of phosphorus, and 1.4 lbs of potassium per bushel of seed produced. These large amounts will need to come via root uptake; it is not economically possible to apply these amounts through the foliage.

But, once the soil needs are met, will additional fertilization help?

First, an application of Manganese may be needed if your soil pH inches much above 6.5. I’ve even seen Mn deficiencies when the pH is as low as 6.2 (using fall/winter soil test levels) and the soil is “wet natured” or if lime was recently applied. There are also certain varieties that tend to show Mn deficiency sooner than others. So, if you see the characteristic interveinal chlorosis of Mn deficiency or if soybean are growing in a field that typically exhibits such a deficiency, then spray Mn.

Another issue that I’m seeing this year is a general yellowing of plants, usually just in seemingly random spots in the field. Upon closer inspection, these are usually very wet areas (there are plenty of those this year) or sandy knolls. In the saturated soils, the yellowing is likely due to lack of oxygen and/or poor nodule development. The only cure for lack of oxygen is for the soil to dry out. Poor nodulation is indirectly a response to lack of oxygen – the nitrogen-fixing bacteria have temporarily stopped functioning. But they will recover and provide the nitrogen when the plant needs it the most, when the pods are forming and seed are filling. Will a shot of foliar nitrogen help? Yes, it will green up the plant if lack of nitrogen is the problem. Will this shot of nitrogen (assuming that nitrogen is the problem) increase yield? Maybe. Maybe not. If lack of oxygen is the problem, then probably not. Even if lack of nitrogen is the problem, probably not.

I want to caution everyone to not make assumptions that lack of nitrogen is the problem.

Is this N or S deficiency?

The only way to know for sure is to take a tissue sample. A deficiency that closely resembles nitrogen deficiency is sulfur. On those sandy knolls, I’ve seen sulfur deficiencies. Sulfur will leach just like nitrogen. But, soybean will not produce its own sulfur. A shot of nitrogen would do nothing to help in this case. The take home message is to determine the cause, then act on that information.

But what about other nutrients? What if there is no visual symptoms of nutrient stress? What if my yield potential is very good? My attitude towards this is that it usually won’t hurt (but be careful mixing with other chemicals), so do what makes you sleep better at night. If you think it is helping your crop, then make the application. It’s your money. You know your fields better than anyone. But, I have rarely seen a response to foliar feeds if you have maintained adequate soil fertility levels and have managed the crop for maximum economic yields. Again, yield response to foliar fertilizers is, at best, inconsistent.

Manganese Deficiencies in Soybean

Posted on June 25, 2015 by David Holshouser

Manganese (Mn) deficiencies are starting to appear. Such a deficiency is common in Virginia soybean, but these deficiencies are not necessarily due to low Mn levels in the soil. Instead, like many micronutrients (nutrients that are needed by the plant in small amounts), Mn availability to the soybean crop is directly related to soil pH.

When pH levels reach 6.5 or above, Mn deficiencies will likely appear, especially on sandy soils. However, some soils with a pH of 6.2 and lower can show deficiencies if soil Mn is low. Generally, Mn deficiencies are more common on our sandier soils as pH changes more rapidly and sandy soils typically have a lower Mn concentration.

The deficiency will appear interveinal clorosis, usually on the younger leaves first since Mn is not a mobile nutrient. This may distinguish Mn deficiency from magnesium (Mg) deficiency. Magnesium deficiency symptoms will usually appear on the lower leaves while the upper leaves remain green. Still, I’ve seen Mn deficiency on the lower to middle leaves. This usually happens when the field has not been checked in a while and the observer missed the symptoms when they were on the younger leaves.

Other problems can cause look-alike symptoms similar to Mn deficiencies. In particular, inter-veinal yellowing is a common symptom of soybean cyst or other nematode damage. Therefore, it may be prudent to further investigate the problem, especially the root system.

Use the following guidelines for Mn applications:

Scout your fields. Mn deficiencies may or may not materialize. The only sure way to determine a deficiency is to observe the deficiency symptoms through visual observation or tissue tests. The characteristic visual symptom is yellowing between the veins on the new leaves. Mn is an immobile nutrient. Therefore, it will not move out of older leaves to the new leaves. Symptoms will appear when the plant can no longer extract sufficient amounts of the nutrient from the soil.

Take a tissue sample. If Mn deficiencies are suspected due to high pH and/or a field history of Mn deficiencies, but no symptoms have yet appeared, you should consider taking a tissue sample. Tissue samples can reveal deficiencies before symptoms appear (hidden hunger). We suggest a tissue test if lime, lime stabilized biosolids, or an ash product was recently applied.

Manganese application. To overcome a deficiency, apply ¾ lb. chelated Mn (elemental basis) or 1 lb. inorganic Mn (elemental basis) per acre to foliage upon appearance of symptoms and prior to flowering. More than one application may be required to correct a severe deficiency.

Don’t use low rates to correct a deficiency. Note that many Mn products recommend applying lower rates of Mn. However, the label usually states that these are maintenance rates. Once a deficiency occurs, these lower rates will not correct the deficiency and the rates stated above will be needed.

Split Mn application on deficiency-prone soils. An alternate method of application can be used before a deficiency is evident on soils that commonly show a deficiency, especially on soils that have a high pH (above 6.8 or so). A lower rate (~ ½ of that listed above) can be combined with another scheduled application, such as a postemergence herbicide or insecticide. This may be a sufficient rate to prevent a deficiency from occurring. But, continue to scout the field and take future corrective measures if visual deficiencies appear. If a visual symptom appears, you need to use the full rate. I will remind you that this is a preventative treatment. A deficiency may not occur. Furthermore, these are only maintenance rates and another application will likely be needed if the field is truly deficient.

Use EDTA chelated Mn formulations when mixing with glyphosate. Be reminded that some Mn formulations in combination with glyphosate herbicide (Roundup, Touchdown, many generics, etc.) will result in reduced weed control of certain weeds. Other herbicides have not shown to interact. If including Mn with glyphosate, use the EDTA chelated formulation as it has shown not to interact.

Don’t spray if you don’t need it. Mn can be toxic to soybean. Spraying greater than recommended rates or spraying as a preventative spray when soil pH is relatively low (5.7-5.9) could lead to toxicity problems

Soybean Replant Decisions

Posted on June 9, 2015 by David Holshouser

Deciding whether or not to replant can be a gut-retching decision. I readily admit that the choice to leave the present stand or replant is not a simple one. With the cost of seed and diesel fuel, the profitability of replanting may not seem a good idea. Low prices make this no more appealing. In the end, your decision should be one based on the estimated dollar gain from replanting. This will require a careful evaluation of the soybean stand and an analysis of yield potential of the present and replanted crop.

In general, there is less benefit of replanting if stands are reduced uniformly across the field. Usually replanting can only be justified where stands have been reduced by half. However, poor stands usually include gaps in addition to merely a lower plant population. These gaps must be accounted for. In addition, one may have a 75-80% stand in parts of the field, while other parts of the field may only have 20-25% of the intended plant population; the decision may be to only replant part of the field.

Remember to take into account the yield loss from delayed planting. Up until mid-June, there is very little yield loss from delayed planting. After this, for every day delay in planting yield declines about half a bushel per day. For instance, if replanting in late-June/early-July (about 2 weeks late), your potential yield will have declined by 7 bushels per acre.

A few more questions must be asked before we can proceed with a step-by-step procedure for estimating the profit of replanting. When considering a replant, do you leave plants in the field and plant through them? In many cases, planting through the poor stand is a possibility. If you’re using rows wide enough to fit a tractor tire comfortably between them, then you can split the rows and plant enough new plants to get the final plant population up to 100 to 120 thousand plants for full-season systems (if re-planting before mid-June) or 180 to 200 thousand plants per acre for double-cropped systems (this may require equipment or tractor tire modifications).

On the other hand, a drill will cut up many healthy plants and make them less productive than the ones that you just replanted. Also, if the drill has wide gauge wheels, then you can severely damage a significant number of plants (there’s a significant amount of down pressure on those wheels – enough to crush a plant on hard soil). And a damaged plant can sometimes act more like a weed than a crop. Recognize that the plants growing in the field are going to be higher yielding that any that emerges after replanting. If you destroy or injure those plants, you’ve just writing off some profit. Therefore, I do not suggest planting through the old stand with a drill.

Another issue is that if you decide to replant, do you switch to an earlier maturity group? There is little need to plant an earlier-maturing variety. Here are two general rules of thumbs:

April/May Plantings: A 3-day delay in planting will result in a 1-day delay in planting. Therefore, if planting 30 days later, the crop will mature 10 days later.

June/July Plantings: A 5-day delay in planting will result in a 1-day delay in maturity. Therefore, if planting 15 days later, the crop will mature only about 3 days later.

Most important is to plant a maturity group that would grow as long as possible (therefore producing an adequate canopy for maximum yield) and still mature before the average frost date. If you’re destroying the old crop and starting over, just make sure that the variety you chose will mature before a frost. Alternatively, if you are planting into the old crop, you may want to choose a variety about one-third to half a maturity group earlier (depending on planting date differences) so that harvest maturity of both plantings will be more in sync. For example, if you planted a relative maturity group 5.6 on June 10, then you could choose a relative maturity of 5.2 to 5.4 if replanting on June 25.

Finally, realize that you’ll need a higher plant population when planting late. Final stand with a double-crop planting should be at least 180 thousand plants per acre. If replanting in July, increase the seeding rate to insure at least 220 thousand plants per acre.

To estimate the profitability of replanting, follow the guidelines listed below. Be sure to incorporate plant population and gaps in your calculations. We’ve found that 2- to 3-foot gaps cause as much or more yield loss that from low plant populations.

Determine the cause of the poor stand. Was the poor stand the result of poor seed quality, cold wet soils, hot dry soils, planting too deep or shallow, soil crusting, herbicide injury, insect or slug feeding, poor soil to seed contact, or disease infection? Determine if the cause can be corrected to avoid a similar situation. If slug or insect feeding or disease is the cause, then you might expect poor stands again.
Estimate the stand and percent stand loss due to gaps. Pace off the sections of row 20 paces long in at least 6 areas of the field. Determine (in number of paces) the total length of row lost to 2- to 3-foot gaps. For drilled soybean, this can be interpreted at 2- to 3-foot diameter gaps. Then determine the percent of row lost to gaps. In addition, count and determine average number of plants per foot in sections of row not reduced by gaps. The simplest method is to count the number of healthy plants (capable of recovery) in a length of row equaling 1/1000 of an acre. For instance:

36-inch rows = 14.5 feet
30-inch rows = 17.5 feet
20-inch rows = 26 feet
15-inch rows = 35 feet
7.5-inch rows = 70 feet

Then, just multiply your counts by 1,000 to get plants per acre.

Or, use the Tables 1 or 2 to determine remaining plant population. The “hula hoop” method (Table 2) is valuable with drilled soybean or when rows cannot be distinguished. This involves placing a circular measuring device such as a hula-hoop on the ground and counting the plants contained within.

Table 1. Plant populations of different row spacing with different plant counts per foot.
Plants/ foot	Row Spacing
Plants/ foot	36	30	24	20	15	7.5
	Plant Population (1,000’s/acre)
1	15	17	22	26	35	70
2	29	35	44	52	70	140
3	44	52	65	78	105	210
4	58	70	87	105	139	278
5	73	87	109	131	174	—
6	87	105	131	157	209	—
7	102	122	152	183	244	—

Table 2. Hula-hoop method for determining drilled soybean populations.
No. ofPlants	Inside Diameter of Hula Hoop
No. ofPlants	30”	32”	34”	36”	38”
	Plant Population (1,000’s/acre)^a
6	53	47	41	37	33
10	89	78	69	62	55
14	124	109	97	86	77
18	160	140	124	111	100
22	196	172	152	136	122
26	231	203	179	160	144
^aPlants/acre = no. plants ¸ (3.14 x r2 ¸ 43,560 ft2) where r = radius of hula hoop in feet.

Estimate the yield of the poor stand. Use Tables 3 and 4 to determine percent of yield potential for full-season and double-crop plantings, respectively. Multiply this percentage by the expected yield. This is the yield to expect from the deficient stand.

Table 3. Yield response (% of maximum) of full-season soybeans to deficit stands^a.
% Stand lost to gaps^b	Remaining Plant Pop (1,000’s/A)
% Stand lost to gaps^b	70	105	140
0	95	97	100
10	93	96	98
20	91	93	96
30	88	90	93
40	83	86	89
50	78	81	84
60	73	75	78
^aSource: Pepper and Wilmot. Managing Deficit Stands. 1991. Illinois Cooperative Extension Cir. 1317.^bGaps of 12 inches or more; 30-inch rows

Table 13.4. Yield response (% of maximum) of double-crop soybeans to deficit stands^a.
% Standlost to gaps^b	Remaining Plant Pop (1,000’s/A)
% Standlost to gaps^b	100	140	180	220
0	80	88	95	100
20	71	79	86	91
40	61	69	76	81
60	48	57	64	69
^aSource: 2001-2004 experiments, Suffolk, VA.^bGaps of 3 feet; 15-inch rows; MG 4 variety

Estimate the yield from replanting. After mid-June, decrease the expected yields an additional half of a bushel per acre per day delay in planting. This is the yield to expect from delayed planting.
Determine the gain or loss from replanting. Subtract the expected yield of the poor stand (step 3) from the yield expected from delayed planting. This is the gain or loss in bu/A from replanting. Multiply this number by the expected price ($/bu), using future prices, to obtain gain or loss in $/A.
Estimate the cost of replanting. Include per acre cost of tillage, herbicide, fuel, seed, and labor.
Determine profitability of replanting. Subtract your cost of replanting from your estimated gain from replanting.

It’s Time to Start Increasing Soybean Seeding Rates

Posted on June 4, 2015 by David Holshouser

Mature wheat Small grains are maturing rapidly and soybean planting will soon follow. While there is little benefit to having more than 70 to 80 thousand uniformly-spaced soybean plants per acre when planted in May, more plants will be needed to maximize yield potential as planting date is delayed later into June. My general seeding rate recommendations (seed per foot, depending on row spacing) are listed in the table below. Note that I give a range for full-season, double-crop after barley, and double-crop after wheat. The range represents how the optimal seeding rate will vary depending on yield potential (determined largely by soil type and weather), planting date, and uniform spacing. With soybean, greater yield potential usually means that lower seeding rates can be used (opposite from corn). This basically reflects the capacity of the soil to produce more-than-adequate leaf area to fill in relatively wide spacing and/or gaps between plants within a row. If it’s a productive soil (good plant-available water-holding capacity and good fertility), early plant growth will generally be greater due to lack of stress. In contrast, if the soil is not as productive, stress may prevent soybean from filling in gaps within and between rows as quickly; therefore, more plants per acre are needed.

Secondly, as planting is delayed, greater seeding rates are needed to make up for the lost time. Although this is not a big factor until the second or third week of June, yield falls rapidly afterwards, on average about 1/2 bushel per acre per day delay in planting. More seed per acre will make up for much of this yield loss.

Finally, note that I stated “uniformly-spaced” plants. Many drills are just pushing seed out a small opening and this seed then bounces to and fro within a long tube (this is sometimes referred to as a “controlled spill”). Without a metering system near the disk opener, this will result in a stand that is far from being uniform – it’s over-planted in some areas, it’s under-planted in others). Therefore, I lean towards the higher seeding rates with planted with a drill that does not meter the seed.

So, where are we today? I lean towards planting around 150 to 180 thousand seed per acre (to give 120 to 140 thousand plants per acre). You should begin to slowly bump up that seeding rate as we near the end of June. We have conducted numerous double-crop soybean experiments over the years. Our data indicate that, in most cases, we need 180,000 plants per acre by the end of June in order to maximize our yield.

Although these seeding rate recommendations are based on lots of data, only the growing season will determine if we chose the correct rate. If we have plenty of sun and rain, little to no plant stress, and excellent early-season vegetative growth, these seeding rates will be too high. But if the opposite occurs, we’ll need all the plants that we can fit into a field.

2014 Virginia Soybean Yield Contest

Posted on October 1, 2014 by David Holshouser

The Virginia Soybean Association in cooperation with Virginia Cooperative Extension would like to announce the 2014 Virginia Soybean Yield Contest. The purpose of the Virginia Soybean Yield Contest is to emphasize and demonstrate the practices necessary to produce maximum economic yields, to recognize those producers who grow high-yielding soybeans, and to gather data on the practices utilized by these outstanding producers. With the help of various seed companies, we reward and promote the achievements of Virginia’s most productive soybean farmers.

There are four Soybean Yield Contest categories: 1) Full-Season, Non-irrigated; 2) Double-Crop, Non-irrigated; and 3) Irrigated (Full-Season or Double-Crop; and 4) Most Efficient Yield (MEY). First, second, and third place winners of the full-season, double-crop, and irrigated contest will be recognized with appropriate trophies or plaques. In addition, cash awards of $200, $100, and $50 will be presented to the first, second, and third place winners in each of these categories. The winner of the MEY contest will receive a plaque declaring him or her the most efficient soybean producer in Virginia for that year.

Printable entry forms and contest details can be obtained from your County Agent or on my website: (http://www.arec.vaes.vt.edu/tidewater/soybean/). I look forward to seeing your entries.