14 - 2020 Soybean Management Field Days - Soy Planting Date – Sunlight Capture
Soy Planting Date –Sunlight Capture - Jim Specht, UNL Emeritus Professor of Agronomy and Horticulture covers the following: Crops must capture solar radiation to produce plant and seed dry matter. By planting the crop earlier in the spring, more sunlight can be captured during the growing season. Let’s examine how this happens.
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[00:00:07.730]Okay, my name is Jim Specht,
[00:00:10.060]professor in agronomy now retired
[00:00:12.120]at the university of Nebraska
[00:00:13.620]and my specialty was soybean physiology and production
[00:00:18.150]in addition to genetics genomics,
[00:00:20.090]but today we're gonna focus on physiology
[00:00:22.260]and production of soybeans.
[00:00:24.550]So let's take a look
[00:00:26.263]at why soybean planting date,
[00:00:31.020]an earlier one, increases potential yields.
[00:00:33.680]And since I'm a physiologist
[00:00:36.520]I'm gonna offer you a three reasons.
[00:00:38.010]Here's reason one, a soybean crop can capture
[00:00:41.220]and use daily radiation,
[00:00:42.780]solar radiation that's available
[00:00:44.300]for photosynthesis in early May.
[00:00:48.760]So again, let's go back to that same two picture dates
[00:00:53.040]in 2003 and 2004.
[00:00:54.900]Remember the red, blue, green
[00:00:56.720]and brown lines in there because we're gonna see those
[00:00:59.360]on the slides that are coming up.
[00:01:03.170]So when we talk about the summer solstice
[00:01:06.040]you realize in Nebraska the longest day
[00:01:08.080]of the year is on June 21, and of course the equinox
[00:01:12.250]is in the spring and the fall
[00:01:13.550]is when the day length is equal.
[00:01:16.455]The longest night of the year of course
[00:01:18.240]is December 21, but take a look at those arrows
[00:01:21.300]and you can see that the peaks that differ in there
[00:01:24.490]are different for different latitudes.
[00:01:26.540]Nebraska resides between say 40 degrees,
[00:01:33.030]with its boundary with Kansas, and about 43 degrees north
[00:01:36.730]with its latitude with South Dakota border.
[00:01:41.570]Now that means at the Nebraska Kansas border,
[00:01:44.500]the longest day of the year will be 15 hours
[00:01:47.230]as you can see here, 15 hours of day length.
[00:01:50.700]So if you translate that to where we are
[00:01:52.400]in Lincoln Nebraska,
[00:01:53.480]where we have a latitude here,
[00:01:56.298]that is at 40.82 as you can see there,
[00:02:00.140]the longest day of the year on June 21st
[00:02:02.550]is gonna be about 15 hours and six minutes.
[00:02:06.050]And so I point to that with a red arrow down there
[00:02:08.670]to where that brown line,
[00:02:10.860]or where that orange circle is at the top of the peak.
[00:02:15.180]And of course, if you look left and right
[00:02:16.900]you can see the other ones circles
[00:02:18.640]that give you the spring and fall Equinox
[00:02:20.560]where the day lengths are the same as the night lengths.
[00:02:23.400]So the red, blue, and green and brown lines there
[00:02:26.240]represent those four planting dates
[00:02:27.910]that were in the photos.
[00:02:31.232]So let's go back though.
[00:02:32.150]You can see red, blue, brown and green
[00:02:34.680]and now you can see that we have more green
[00:02:38.480]on the left side
[00:02:39.390]on the late April side,
[00:02:41.740]than you do on the mid June side.
[00:02:43.620]So let's go back to here.
[00:02:45.460]So if you're gonna wait until June 15th to plant,
[00:02:48.490]I put in skin color here,
[00:02:50.020]the amount of daylight that you're gonna capture
[00:02:52.070]for the rest of the year.
[00:02:53.850]And it's about a hundred days,
[00:02:56.380]if you look down below.
[00:02:58.060]I also put a little sorry sign down there too as well
[00:03:02.420]what they call an emoticon,
[00:03:04.310]but you could see if you've only
[00:03:05.400]about a hundred days to use the radiation
[00:03:07.410]that's left after planting on June 25th,
[00:03:10.510]June 21st or June 1st, I should say.
[00:03:15.690]Here again it's the same material,
[00:03:17.590]so if you enhance or advance your slaving planting day
[00:03:20.770]to late April early May,
[00:03:22.620]you're gonna use 144 days.
[00:03:24.750]So comparing those two differences of a hundred,
[00:03:26.637]and 144 days,
[00:03:29.170]you're using 44% more solar radiation.
[00:03:33.960]And it's solar radiation that provides the energy
[00:03:36.260]to derive photosynthesis
[00:03:37.590]to create bio matter and biomass.
[00:03:42.480]So how early can you plant your soybean?
[00:03:44.790]Well, this is way too early obviously.
[00:03:47.730]You can look at some weather data,
[00:03:50.130]it's available from NOAA
[00:03:51.450]at the URL I described down there below,
[00:03:55.020]and remember that soybeans can only freeze
[00:03:57.100]when they get out of the ground.
[00:03:58.770]So if you plan on April 26
[00:04:00.677]and they don't get out of the ground
[00:04:02.480]until May 4th,
[00:04:03.980]you're not risking those soybean seedlings
[00:04:06.280]to any freeze damage.
[00:04:08.450]So here you can see on the 26th of April,
[00:04:11.230]you only have about a 26% of a freezing temperature
[00:04:15.410]on that day, but that is an air temperature
[00:04:18.430]not a soil temperature.
[00:04:19.890]Soils very rarely freeze.
[00:04:23.490]So if you look at the 10% 30F spring date in Nebraska,
[00:04:28.250]you can see that for seedlings out of the ground
[00:04:31.608]on May 3rd,
[00:04:32.530]they might risk some frost potential, but not much.
[00:04:36.960]And of course these dates will change
[00:04:39.290]if you choose a different temperature.
[00:04:41.790]Most seedling material doesn't exactly freeze at 32,
[00:04:45.240]because it has a freezing point depression
[00:04:48.330]because the cells and the seedling leaves contain solutes,
[00:04:52.320]so it's like having an antifreeze.
[00:04:54.930]Here it shows you that you get until October 27th
[00:04:58.680]to get your crop done with a 10% 30F fall date, freeze date.
[00:05:03.720]So the idea here is that
[00:05:06.340]you can capture more of that early spring solar radiation
[00:05:09.120]by planting your soybeans earlier.
[00:05:11.750]And remember, sunlight is free,
[00:05:14.090]let your crop harvest more of it
[00:05:15.900]to create more biomass and yield.
[00:05:18.850]In the Nebraska example we showed that you can capture
[00:05:22.640]by advancing your planting date from 15 June to may 1
[00:05:25.830]by 44 more days, compared to the a hundred days you got,
[00:05:29.210]so that's 144% more.
[00:05:33.330]How does the using an irrigated
[00:05:36.010]versus a rainfed field compare
[00:05:38.240]in terms of going forward with an earlier planning date
[00:05:41.820]is the question.
[00:05:44.950]Obviously that's our good question,
[00:05:46.790]because you can't plant soybeans
[00:05:48.580]until, you know, you have a moist soil to plant them into.
[00:05:52.680]And I'm gonna cover that in the next set of slides
[00:05:56.040]that I talk about here,
[00:05:57.760]mainly because you do have to put soybeans
[00:06:02.020]in a moist ground,
[00:06:02.853]more so than corn,
[00:06:04.560]and so you do need that water there.
[00:06:07.750]As far as delaying the planting date,
[00:06:09.320]you're always gonna be subject
[00:06:10.410]to the rule of not using all the solar radiation.
[00:06:13.050]So, I mean in theory at least
[00:06:15.760]you're behind the eight ball there,
[00:06:17.060]even in the practicality
[00:06:18.960]if the rest of this rainfed season
[00:06:21.340]has plenty of water,
[00:06:23.110]then your yield should be as good as the irrigated
[00:06:25.270]but it usually suffers,
[00:06:27.200]and early planting may suffer in rainfed fields
[00:06:30.870]because drought in August can mitigate the trend
[00:06:33.760]of that line that I showed in this segment.
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