Tag Archives: seeding rate

Soybean Planting Dates, Seeding Rates, Re-planting, Weeds, etc.

June is usually the time of the year when full season soybean is kicking into high gear and we begin planting double-crop soybean.  And like always, various issues are beginning to arise, whether its the weather or finding out mistakes made a few weeks earlier.

Unbelievably, double-crop soybean is wrapping up in many areas due to small grain maturing earlier than normal.  Out of necessity, we were forced to harvest wheat and plant soybean at the same time we were trying to make timely postemergence herbicide applications and generally trying to pay attention to the rapidly growing soybean that we planted in April and May.  But, issues such as these are not unusual.

This week, I thought I’d mention a few things that we are facing and continue to remind you of the need to plant as soon as possible and adjust seeding rates accordingly.

Planting Date.  We are now losing about 1/2 bushel per acre per day with each delay in soybean planting.  Plant as soon as possible, but don’t cause more serious problems by planting into too wet or dry soils.

Seeding Rate.  My data indicates that seeding rates now need to be at least 180,000 seed per acre, even on the best of soils.  I would bump those up about 20,000 seed for each week’s delay in planting.  See Soybean Seeding Rates for June and Later for more information.

Replanting.  Generally, replanting does not pay this time of the year (due to the planting date penalty) unless the stand is horrible.  For more information, see Soybean Replant Decisions or contact me.

Seed Treatments.  I’ve seen few benefits of fungicide or insecticide seed treatments this time of year.  Plants usually emerge and grow quickly.  The exception is wet soils – soybean will emerge very slow when soils are saturated.  With that in mind, you may consider a fungicide on the seed if you have poorly-drained soils, your soils are already wet, and rain is predicted.

Seeding Depth.  Those of you know that I usually don’t like to plant soybean greater than 1 inch.  But, I’ve found that planting soybean at 1.5 inch (and occasionally 2 inches) works just fine when soils are warm.  Sometimes, it’s better to plant deeper to hit moisture than to plant into dry soils.

Weeds.  First, Drs. Charlie Cahoon and Mike Flessner is who you need to consult regarding weeds, but here are a few of my observations.  We may have let a few weeds get too big for adequate control – this is especially a problem with glyphosate-resistant weeds.  Marestail continues to be a problem.  When this weed is glyphosate resistant and you’re not growing Liberty-Link soybean, about the only somewhat effective herbicide that we have left in our arsenal for Roundup Ready soybean is FirstRate, although a few other herbicides may burn the weed – just don’t expect very much from anything.  I’ll let you mull over your other options if you have planted Xtend soybean.  Finally, don’t depend on glyphosate alone – even if you weeds are not yet resistant, its a good practice to diversify to insure that they do not become so.

Greater Yields are Possible for Double-Crop Soybean in 2017!

It appears that wheat harvest will be 1 to 2 weeks ahead of schedule this year.  We actually harvested some high-moisture wheat and planted soybean plots behind it today (May 31) in northeast N.C.  This is good news for soybean.  Earlier planting means greater yields!  This is clearly shown by the recent data obtained from our multi-state, multi-year double-crop project.

With earlier planting, have my recommendations for double-crop soybean changed?  In general no.  But below are a few things to consider.

Seeding Rate:  In general, you can probably back off on your seeding rates from what you were planning if you get your double-crop soybean in by mid-June.  I’d suggest that you start out with 120-160,000 seed/acre (depending on when you start planting) and gradually ramp that up by 20-30,000 for each week delay in planting.  For more information, see my recent blog, Soybean Seeding Rates for June and Later.

Relative Maturity:  Actually, my standard recommendation still stands, more or less.  Plant as late of a relative maturity (RM) as possible that will mature before the frost.  However, there are now some caveats.   By planting a week earlier, you’ll gain about 3 days in maturity.  Although a slightly later RM may work, I wouldn’t count on it – frost date will affect this more than planting date.  So, don’t plant a later RM.

But, can you plant an earlier RM, say go from an early-5 to a late-4?  Possibly.  Why do I say this?  Two things.  First, by planting a week or two earlier you have greater yield potential (see the above graph), which is due to the ability to grow more leaves.  So your yields are not necessarily so dependent on leaf area as they are with a late-June to early-July planting.  A slightly earlier RM planting in early- to mid-June will only have slightly less leaf area than a later RM.  And, we have generally found that under greater yield potentials, early RM will yield more than later ones.  Still, these are not great reasons to change your RM.  Generally, stick with what you planned.

Soybean Seeding rates for June and Later

Due to the rainy weather over the past two weeks, we are still planting full-season soybean in some areas.  In addition, it appears that wheat harvest is not far off (some wheat at the Tidewater AREC was at 23% moisture today!).  So, should we be increasing our seeding rates?

In general, yes.  But, big increases probably will not be needed until late-June.  Below are some seeding rate data that we collected from soybean planted in early-June after barley.  First, we don’t have a lot of data of soybean grown after barley, so I don’t have as much confidence in the exact seeding rate needed.  Note that there is a wide range in the optimal seeding rates, illustrated by the area between the dotted lines in the graph.  Although, these data may not directly apply to full-season soybean (no small grain), it should be close.

I think that we should now be using 120,000 to 160,000 seed/acre.  The range will depend on the planting date.  In general, I’d suggest bumping up your seeding by 20-30,000 seed/acre per week through June.

If you remember the seeding rate data that I shared in this blog last month for May-planted soybean (see Soybean Seeding Rates – How Low Can We Go?), I stated that maximum yields could be obtained with only 95,000 to 110,000 seed/acre when the yield potential is greater than 40 bushels/acre.  That’s pretty low, but was adequate for maximum yield under good growth conditions.  For less than 40 bushel potential, seeding rates needed to be a little higher.   In the above graph, it appears that more seed is needed to obtain 55 to 70 bushels/acre after barley, I cannot fully explain why; therefore, I would assume that this response is primarily due to the location that we obtained the data (again, we don’t have a lot of data).

Once we get into mid- to late-June, I’d rather see a seeding rate of 180,000 to 220,000 seed/acre, depending on planting date.  This is based on the data to the right.    You’ll notice that, like full-season soybean, the optimal seeding rate falls with greater yields.  This is most likely due to greater leaf area with those high-yielding locations.  As I’ve stated often, the seeding rate response can usually be traced back to whether or not the crop developed enough leaf area to capture 90-95% of the light by early pod development.  Unfortunately, I don’t have any double-crop data planted following wheat with yields greater than 55 bushels/acre.  I hope to solve that problem this year with new experiments.

Soybean Seeding Rates – How Low Can We Go?

It seems that everything that you read about soybean seeding rates is that we are planting too many seed.  In general, I agree – at least for full-season soybean.  We still seem to have that mindset that it takes 1 bag of seed per acre.  But many of you have been listening and are taking the seeding rate down to 100,000 to 120,000 seed per acre, with no noticeable difference in yield.   But, can you go lower?  And how low can you go?

To help answer this question, we have re-analyzed about 10 years of data that we collected from dozens of experiments conducted from 2003 through 2011.  But instead of just looking at average yield response, we separated these responses into soybean yield potentials.

Why did we do this?  I’ve always thought that more seed is needed to maximize yield on low-yielding fields (or portions of fields) and less seed are needed or high-yielding fields or portions of fields.  Yes, this means that I’m asking you to spend more money on the least profitable fields and less money on the most profitable fields.  Still, this strategy will likely be more profitable over all acres.

There are a few things worth noting about the graphs to the left.  First, I’ve separated the data into low (20-40 Bu/A), medium (40-55 Bu/A), and high (55-70 Bu/A) groupings.  We decided on these levels by analyzing the data over and over at many different yield levels.  The resulting three levels were most stable and predictive.

Second, we used two statistical methods to fit a curve to the data to intentionally give us a range of seeding rates needed to maximize yield.  This allow us to recognize the variability in the data and reflects our confidence in the response.  Pay particular attention to the wide range of seeding rates necessary to maximize yield at the 20 to 35 bushel yield potential.  This reflects the yield variability and the variability in the response of yield to seeding rates that are common in low-yielding years or fields.  We just are not as confident in this set of data.  Some years or locations, we could get by with 100,000 seed/acre; in others, it took more than 140,000.  With the other yield potentials, the range is pretty tight.  In other words, I have more confidence in recommending 110,000 or even less than 100,000 seed/acre in these instances.

Finally, we see that it takes, in general, less seed at high yields – which verifies my earlier statement that less seed are needed for higher yield potentials.

So what have I settled on?  Below are my suggestions.

But, you may ask, “What about yields greater than 70 bushels per acre?  That’s a good question.  But, I cannot answer it confidently since we have little data in that range.  We are however conducting new experiments this summer to update our data.

But until that data is available, here are my thoughts.  I think that lower seeding rates will work until you get to the 100+ bushel yield range.  After that, I suspect that we are running low on reproductive nodes (node on the plant where pods can form).  For instance, if we only have 80,000 plants/acre, we would need 15 reproductive nodes containing 4 pods on every one of these nodes!  While this is possible, I’m assuming in this calculation that we will grow 2,500 seed/pound and 3.0 seed/pod. Taking that down to a more normal 2800 seed/pound and 2.5 seed/pod, that means we need 6 pods per node!  I think that we are starting the expect a little much from single plant in this case.

So, for 100+ bushel yield environments, I’d suggest to gradually increase your seeding rate from the ones suggested above.  I do understand that we have very few 100+ bushels fields, but I have seen parts of the field exceeding this when I’m watching a yield monitor.   An we commonly have plots within our small-plot tests exceeding 90 and 100 bushels.

Finally, am I suggesting that we may be able to vary our soybean seeding rate as we do corn?  Yes, I’m suggesting that.  We will be validating some variable-rate-seeding (VRS) on two farmer’s fields this year.  If you know of anyone who has VRS planters and who would like to participate in an on-farm test, let me know.

Do we need to bump up our soybean seeding rates?

It’s hard to believe, but June is here and we need to start thinking about increasing our soybean seeding rates.  I’ve been recommending only 100 to 115 thousand seeds per acre for full-season production, enough to give you 70 to 80 thousand plants – yes, that’s all you need to maximize yield.

But as the season gets shorter, yields will start falling with delays in planting date.  On average, we lose about 1/2 bushel/acre per every day we delay planting after the middle of June.  The graph below shows the results of last year’s 4-state early wheat harvest/soybean planting double-crop study.  Note that yield does not decline very much during the first week or two of June, but rapidly drops off afterwards.

2015 DC Soy Yield across Plant DateThe main reason for this yield decline is that the crop struggles to develop enough leaf area to capture 90-95% of the sunlight by early pod development, due to the shorter growing season.  We can alleviate some of this by narrowing rows and increasing seeding rate.

I usually suggest that farmers plant enough seed to result in a final plant population of 180,000 plants/acre for double-crop soybean.  That means planting 200,000 to 220,000 seed/acre.  Yes that is a lot of seed, but my research shows that yields (and profit) continue to increase up to this seeding rate, especially when planting is delayed until late-June and early-July.

There are stipulations.  More productive soils and irrigated soybean usually require less seed.  Good years that allow lots of quick growth require less seed (but who can predict a good year?).  Later maturity groups may require slightly less seed.  Less seed are needed as you move south (growing season is longer and you can plant a later relative maturity).  I think that a soil profile that is full of water at soybean planting (this year) might allow less seed to be planted – but I have not documented that – It just makes sense to me that plants will grow better when the small grain has not depleted most of the subsoil moisture.

What about now?  How many seed/acre do we need to plant in the first week of June?  Here are my suggestions.  Keep in mind that these are general guidelines; you need a gradual increase in seed/acre.  I’m assuming 80 to 85% emergence for June/July plantings.  To easily determine how many seed you need per row foot, see VCE pub 3006-1447, Suggested Soybean Seeding Rates for Virginia

May: 100 to 115K

June 1-7:  120-140K

June 8-14: 140-180K

June 15-21: 180-200K

June 22-30: 200-220K

July: 220-250K

It’s Time to Start Increasing Soybean Seeding Rates

Mature wheatSmall 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.  Suggested Soybean Seeding Rate TableNote 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 GP1200 Drill Seed Feed Back View Closeand 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.