18 - 2020 Soybean Management Field Days - Soy Planting Date – Vegetative Growth and Reproductive Duration
Soy Planting Date – Vegetative Growth and Reproductive Duration - Jim Specht, UNL Emeritus Professor of Agronomy and Horticulture covers the following: Soybean vegetative growth and reproductive development follows a predictable pattern in which main stem nodes accrue at a rate of one new node every 3.7 days from V1 to R5, with seed number and size established from R1 to R7. Let’s take a look at how soybean planting date influences the start and duration of these two phases.
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[00:00:07.730]Okay, my name is Jim Specht.
[00:00:09.660]I'm professor in agronomy, now retired,
[00:00:12.140]at the University of Nebraska,
[00:00:13.600]and my specialty was soybean physiology and production,
[00:00:18.160]in addition to genetics, genomics,
[00:00:20.090]but today we're gonna focus on physiology
[00:00:22.260]and production of soybean.
[00:00:24.490]So another reason we want to explore about physical reason
[00:00:28.100]that helps soybeans yield more under earlier planting
[00:00:33.700]is the fact that
[00:00:35.850]earlier planting puts soybean stages V1 and R1,
[00:00:39.440]which are critical phases in soybean,
[00:00:42.860]relative to having an earlier start in the spring.
[00:00:46.500]And what an earlier start to stage V1,
[00:00:49.910]which I'll show here in a minute,
[00:00:51.650]is that you have more days and an earlier start
[00:00:54.550]of the linear V1 to R5 main stem node accrual,
[00:00:58.920]which generates nodes every,
[00:01:01.040]in maturity group 3 varieties, every 3.7 days.
[00:01:05.470]And it will also have an earlier start of R1,
[00:01:08.180]which means you can lengthen the reproductive first flower
[00:01:12.160]to in the physiological maternity stage of R1 to R7.
[00:01:18.520]So take a look at this again.
[00:01:19.800]We're gonna talk about the red, blue,
[00:01:21.150]and green and brown lines again.
[00:01:24.960]So you're familiar with...
[00:01:26.180]Let's see it, and if you look at the bottom row,
[00:01:28.160]you'll see the stages, the V stages,
[00:01:30.700]at which these plants are in 2003 and in 2004.
[00:01:35.607]And in 2004, you're already at V8,
[00:01:38.280]and you're actually well into R1 and almost R2
[00:01:41.640]in that 26 April plant date.
[00:01:47.550]So it may be hard to see these,
[00:01:49.560]but what you can see there, I'll point out,
[00:01:51.400]is that once you start stem node accrual in soybeans,
[00:01:56.900]It's subject to a little bit of temperature,
[00:01:59.010]but at a given location on the same planting date,
[00:02:03.350]a two-week-later-planted soybean
[00:02:05.330]can never catch up very well,
[00:02:07.150]or a four-week one cannot catch up during the season.
[00:02:11.020]And so what you see there, these are from irrigated trials.
[00:02:13.890]So you can see there that V1 starts,
[00:02:17.910]and by the way, the little pink boxes down there indicate
[00:02:21.070]the portions of this graph
[00:02:23.120]that were photographed in the prior slides
[00:02:25.820]a few days after the summer solstice.
[00:02:29.414]And you can note there, in the middle chart,
[00:02:31.670]the V1 stage that are out on each of those dates,
[00:02:34.200]and that corresponds to what we saw in the picture.
[00:02:37.300]And you can also see below that in 2003,
[00:02:41.260]we didn't reach R1 on the 3rd of May planting date.
[00:02:47.177]But in 2004, we did get past R1 and almost to R2
[00:02:51.550]by that few days after the summer solstice there.
[00:02:54.960]So what that amounts to is once you plant soybeans early,
[00:02:58.260]you commence an earlier V1,
[00:03:00.140]and at V1 is where the linear node accrual starts.
[00:03:03.800]And you can see the blue, green,
[00:03:06.690]and brown lines get to R5 without merging.
[00:03:12.600]So that means these soybeans planted later
[00:03:16.070]never catch up in terms of that linear rate.
[00:03:19.110]And so they're behind by R5.
[00:03:22.350]So here's what V1 is for those of you who're interested.
[00:03:25.490]This is the diagram from the Fehr and Caviness.
[00:03:28.570]It shows the unifoliate out there
[00:03:31.340]and a first trifoliate just barely
[00:03:34.520]having its leaf edges untouched.
[00:03:36.620]This is what it looks like in the field.
[00:03:38.230]You can see the unifoliate leaf and the first trifold.
[00:03:41.470]It's just, third leaflet's just unfolding.
[00:03:44.250]And so main stem node accrual becomes linear at that point.
[00:03:49.000]And it goes that way until R5.
[00:03:50.940]And here's a diagram of R5 of having
[00:03:53.550]about an eighth of an inch of a seed within a pod
[00:03:56.840]and the top four nodes of the plant.
[00:03:59.440]Here's what it looks like.
[00:04:00.400]If you go out the field and have a pocket flashlight
[00:04:02.990]and you shine it upward in the deep part of the canopy,
[00:04:06.240]you can see those small seeds there.
[00:04:07.740]It's easier to see this way
[00:04:08.990]than holding up the pod to the sun,
[00:04:11.460]which may blind you if you're not careful.
[00:04:14.420]So here's the change that occurs.
[00:04:16.070]On the left, I show the V1 to R5 phase,
[00:04:19.310]and you can see when you plant early on April 30,
[00:04:22.970]you have 66...
[00:04:25.440]It takes you...
[00:04:26.600]You have 66 days for the V1 to R5 main stem node accrual.
[00:04:32.730]But if you wait until the end of, or until June 15,
[00:04:36.860]you only have 53.
[00:04:38.990]And if you look at the little arrows
[00:04:40.630]on the dots on April 30 and the dots on June 17,
[00:04:46.180]going from R1, which the photos on the right show,
[00:04:49.240]there's R1, and R7 has one brown pod
[00:04:51.760]on every plant in the field.
[00:04:53.630]You can see there's a difference of six days.
[00:04:56.260]So planting early gives you more main stem node accrual
[00:04:59.720]and more seed fill days for accumulating yield.
[00:05:04.800]So this is the third reason why you get more yield.
[00:05:08.230]So the take-home points here is
[00:05:11.400]that earlier planting allows the soybean crop
[00:05:13.700]to attain earlier V1 and R1 stages.
[00:05:17.340]With an earlier and longer V1 to R5 period,
[00:05:20.230]you get more main stem nodes, about two for every two weeks.
[00:05:23.600]You advance the planting, and the same thing for R7.
[00:05:28.750]You'll get a few more days greater
[00:05:30.690]when you advance the planting.
[00:05:33.350]And both contribute to greater yield potential
[00:05:36.260]in early plant dates.
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