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JenREES 8/28/22

Last Irrigation: This really is dependent upon everyone’s individual soil moisture situation by field, crop development stage and crop rooting depth for that field. I have a fairly proven method I’ve used for watermark sensors, but being there’s so many different irrigation scheduling tools used, it won’t be applicable to everyone. We’re most likely done irrigating most ‘normal season’ corn in the area at this point. Corn at ½ milk needs approximately 13 days and 2.25” to finish. Corn at ¾ milk needs about 7 days and 1” till black layer. At this point, we’d say you can draw soil moisture down to 60% of field capacity. If you have the top foot at field capacity for a silt loam soil, there would be at least an inch available in the top foot alone, not accounting for soil moisture in the next several feet. So, you could wait a week and see where soil moisture is and adjust from there.

Photo via Dr. Jim Specht. Soybean pods collected from stage R7 plants (one mature pod per plant) that were opened to determine if the pod wall interior membrane was still clinging tightly to the seeds (leftmost pod), or if it was beginning to detach from the seeds (second pod), or if the membrane was now permanently attached to the pod wall (third pod). After attaining physiological maturity, seeds undergo a dry-down period from about 60% moisture to about 13% moisture. Note that the Rx.x numbers used here are pod-based stages, not plant-based stages.

What I said for corn above can also be applied for soybean. I think what’s trickier for soybean is determining the end reproductive stages, especially as we have been conditioned to look at ‘leaf yellowing’ as the beginning of physiological maturity, yet many factors can cause leaf changes. So I feel perhaps a better indicator of maturity is to look at the pods. For soybean development stages from R2 (full flower) to R6 (end of seed enlargement), we are looking at pods at the top 4 nodes of the plant. For R7 (full maturity), we are looking for at least 50% of the plants having one mature pod anywhere on the main stem.

So how do we know a pod is mature? Inside of each soybean pod, there is a whitish membrane around each seed that provides water and nutrients to the seed. A mature pod is considered when the pod membrane no longer clings tightly to seeds in that pod (this is like black layer on corn where the nutrient/water supply is cut off from the kernel forming the black layer). So essentially, if you pull off a pod on the main stem, carefully open it up and look at the white membrane surrounding the seed. If it’s still clinging tightly to it, it’s not quite mature. If you see separation of the membrane and seed, it’s considered mature and will no longer use water.

Soybeans at full seed (R6 end of seed enlargement) need approximately 18 days to maturity or 3.5” of water. At R6.5 (leaves yellowing/pod membranes still clinging to seed) the soybean needs 10 days or 1.9” yet until R7 (physiological maturity), in which the pod membrane has separated from the seed and requires no more water.

Soybean stems typically turn brown shortly after R7 begins, though the stem can remain green longer due to a number of reasons, including fungicide use. The final soybean stage is R8, which occurs when 95% of pods have attained maturity and have a variety-dependent color of brown or tan. Seed moisture in a soybean pod dries down from 70% at R7 to about 13% at R8. This has shown to be around 12 days based on research, but can be faster or slower depending on solar radiation, humidity, temperature, wind speed and soil surface moisture.

Eastern Nebraska Wheat and Alfalfa Expo will be held Sept. 1 at the Tuxedo Park Exhibition Building in Crete. The expo will begin at 8 a.m. with a light breakfast and exhibitor booths. The educational program starts at 9 a.m. and ends at 3 p.m. Wheat topics in the morning include: wheat variety recommendations, underseeding red clover, hail damage and wheat streak mosaic virus, cost-share programs for growing wheat, and feeding wheat grain to cattle. Topics on alfalfa in the afternoon include: benefits of diverse crop rotations for wildlife, managing potato leaf hoppers, irrigating alfalfa, and herbicide management. There’s no charge but please RSVP to 402-821-2151. More info. at: https://croptechcafe.org/alfalfawheatexpo/.



For Fun: Something that brings me great joy is the opportunity to teach youth who love to learn. I’m so blessed to have a wonderful group of families with youth interested in plants and science in my Crop Science Investigation (CSI) group! The youth pictured above were interested and old enough to compete at State Fair for the 4-H Weed and Grass ID (left) and 4-H Horticulture (right) judging contests. They invested a lot of time into studying and what makes my heart so happy is to see them so greatly enjoy learning and having fun while we identify plants! The York teams received 1st and 3rd place teams in Weed and Grass ID with 6 of the 7 youth placing in the top 10. We also had an individual place in the top 10 in Horticulture ID. So cool to see these youth learning these identification skills they will use for life!

JenREES 8-30-20

Grateful Nebraska held our State Fair this year! Seeing the youth competing, showcasing 4-H projects, and the excitement, smiles, and friends reconnecting from across the State this past weekend was heartwarming!

Received many calls about end of season irrigation this past week. Would encourage our farmers to finish the season well! You’ve been through much in another trying year and the past few weeks have been extra hard keeping up with irrigation, cleaning out bins, and getting combines ready in the heat. It can be tempting to just stop but would encourage you not to quit irrigating too soon, particularly on soybeans. Soybean maturity (R7) is defined when 50% (or all) of the field plants possess one mature pod (when the interior white membrane no longer clings to the seed). In most years, most leaves and pods will have changed color (from green to yellow-green or yellow) by this plant-based R7 date.

The heat has pushed crops along, but we’ve also had a great deal of humidity. Corn is moving the starch line slower in irrigated fields. That’s a good thing for fill and a harder thing regarding labor, time, and money. A lot of corn in this area is 1/3 milk and I just saw a few fields at ½ milk over the weekend. 

  • Corn at ¼ milk needs 3.75” (approximately 19 days to maturity)
  • Corn at ½ milk needs 2.25” (approximately 13 days to maturity)
  • Corn at ¾ milk needs 1” (approximately 7 days to maturity)
  • Soybean at full seed (R6) needs 3.5” (approx. 18 days to maturity)
  • Soybean with leaves beginning to yellow and pod membrane still attached to seeds (R6.5) needs 1.9” (approx. 10 days to maturity)

So, we’re potentially looking at one to two more irrigations yet for some of this corn and soybeans depending on the current status of your soil moisture profile, development of the crops in your particular fields, and any rain. It is recommended to allow that soil moisture profile to dry out to 50-60% depletion towards the end of the season to capture moisture in the off-season. So one way to consider this is a step-wise approach. If you typically irrigate at 35% soil moisture depletion and have around 2” left, the next week you could wait till a trigger of 40% depletion with the following week’s trigger around 50%. Again, this depends on your individual field’s soil moisture status and crop development after a taxing August.

Upon physiological maturity, corn ears begin drooping down. However throughout the area, corn ears are doing this that aren’t at ½ starch yet. These ears will black layer prematurely at the cost of yield. Dr. Bob Nielsen from Purdue shares that yield penalty can be as much as 40% at denting when there’s essentially no milk line visible and around 12% at half milk. So what causes this? The ear shank can collapse when there’s a lack of turgor pressure due to stress from the inability to keep up with crop water demand. August has been abnormally dry with warmer than average temperatures the past few weeks. Sometimes the ear shank also cannibalizes itself, similar to what can happen in stalks. Perhaps part of this can be from poor root development or lack of root development into deeper layers? In areas that have received less rain, perhaps deeper soil layers are drier in spite of having moisture in the top soil layer from irrigation? For those with conventional hybrids, European corn borer tunneling can also cause this type of collapse. There’s also some hybrids that I notice this happening more than others; perhaps genetics also plays a roll? That shank is the source for feeding the ear, so when it collapses, it weakens it. Keep an eye on ears in these fields as we approach harvest and consider getting at them sooner if possible.

Drooping corn ears in this irrigated field with green plant tissue above ears. This corn was getting close to 1/2 milk.
Photo by Dr. Jim Specht showing end of season soybean development stages. Notice the white membrane still attached to the seed in R6 stage and how it disconnects at R7 (maturity). Not all pods on the plant may be at R7 at the same time. R7 for all the plants in the field is considered when 50% (or all) of the field plants possess one mature pod (when the interior white membrane no longer clings to the seed). In most years, most leaves and pods will have changed color (from green to yellow-green or yellow) by this plant-based R7 date.
Sudden Death Syndrome (SDS) has been observed for the past several weeks in fields. Thankfully it’s been minor this year compared to last year. It’s wise to take a soil sample for soybean cyst nematode (SCN) in these areas of the field to determine if you also have a nematode problem. The combination of the diseases has a synergistic impact on yield.
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