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2012 Last Irrigation Scheduling

While farmers may be tired of irrigating right now, I think all who have irrigation are thankful for it in such a dry year.  Honestly, thankfully with our irrigation we have some of the best looking crops in the Corn Belt right now.  Even so, with corn that hasn’t been replanted nearing dent or stages of starch fill, you may be wondering how to schedule for your last irrigation.

For those of you in our Nebraska Ag Water Management Network using watermark sensors, the goal is to use them to determine when the soil profile reaches 60% depletion (for silty-clay soils in our area aim for an average of 160 kpa of all your sensors).  You may be thinking, “An average of 90kpa was hard enough!” but as Daryl Andersen from the Little Blue Natural Resources District points out, you’re only taking an additional 0.30 inches out of each foot.  So if you’re averaging 90kpa on your three sensors, you have depleted 2.34 inches in the top three feet so you still have 0.96 inches left (see the Soil Moisture Depletion Chart).  If you add the fourth foot (using a similar number from the third foot), it would bring the water available to the plant up to 1.28”. 

At beginning dent corn you need 24 days or 5 inches of water to finish the crop to maturity.  If you subtract 1.28 from 5 you will need 3.72” to finish out the crop.  Corn at ½ milk line needs 13 days or 2.25” to finish the crop to maturity-so subtracting it from 1.28 would be only 0.97”.  

Soybeans at the beginning of seed enlargement (R5) need 6.5”.  Soybeans in R6 or full seed which needs 3.5 inches yet for maturity.  Subtracting off the 1.28” in the four foot profile would lead to 2.22”.  The UNL NebGuide Predicting the Last Irrigation of the Season provides good information on how determine your last irrigation in addition to showing charts on how much water the crop still needs at various growth stages.  

Several people I’ve talked to who have been irrigating using watermark sensors aren’t replenishing the second foot, so you may have a few rounds yet to go  on corn and beans.  For a quick way to know where you’re at, think about irrigating this way as explained by Daryl Andersen at the Little Blue Natural Resources District:

One way to look at this is by the numbers of days left.  At 1/4 starch, there are about 19 days before maturity so you can let your sensors average 130kpa on the first week and 150kpa on the next week.  If these targets are met during the week, you would put on about 1 inch of water.  By going to these numbers, it might give you a higher probability for rain in the next couple of weeks.  I’m hoping for many answered prayers that we will see rain in August!

High Heat & #Corn Pollination

With the high heat, lack of rainfall, and pollination occurring in many fields or just around the corner, questions have been rolling in regarding how high heat affects corn pollination.  Dr. Tom Hoegemeyer, UNL Agronomy Professor of Practice wrote the following article and I’m sharing it for the excellent info. Hybrid Maize simulations will be shared in this week’s CropWatch and in next week’s news article.

“Corn was originally a tropical grass from the high elevation areas of central Mexico about 7,400 feet above sea level, 2,000 feet higher than Denver. Today, corn still prefers conditions typical of that area — warm daytime temperatures and cool nights. Areas that consistently produce high corn yields share some significant characteristics. These areas — central Chile, the west slope of Colorado, etc. — are usually very bright, clear, high light intensity areas with cool nights.
     This year, in the prairie states and in the Cornbelt, conditions have been dramatically less than optimal.  Corn maximizes its growth rate at 86°F. Days with temperatures hotter than that cause stress. In the high yield areas, cool night temperatures — at or below 50°F — reduce respiration rates and preserve plant sugars, which can be used for growth or reproduction, or stored for yield. These are optimum conditions for corn, and interestingly, are fairly typical for areas around central Mexico where corn is native.
     In years when we get high day and nighttime temperatures coinciding with the peak pollination period, we can expect problems. Continual heat exposure before and during pollination worsens the response. Daytime temperatures have consistently stayed in the upper 90s to low 100s.The high humidity, which helps reduce crop water demand, also increases the thermal mass of the air—and provides extra stored heat and insulation at night.
     Corn pollen is produced within anther sacs in the anther. The plant releases new, fresh anthers each morning, starting from near the top of the tassel, on the first day of shed, and proceeding downward over several days. The process of releasing the pollen from the anthers is called “dehiscence.” Dehiscence is triggered by the drop in humidity, as the temperature rises. However, when it is extremely humid and the humidity falls very little, dehiscence may not occur at all, or it may be delayed until late in the day. If one has breezes, while the humidity is still very high, the anthers may fall to the ground before pollen is released. If the temperature rises too high before pollen dehiscence occurs, the pollen may have reduced viability when it is shed.  A person experienced at hand pollination in corn will often see this happen. There will be anthers in a “tassel bag,” but little pollen. The usual solution to this is to wait a couple hours until the temperature rise reduces the humidity. However, last year we had some conditions where pollen was never released from the anthers. This can impact silk fertilization, particularly in open-pollinated situations.
     Corn is a “C4 Photosynthesis” plant, making it extremely efficient at capturing light and fixing CO2 into sugars. One drawback of this system is that with high daytime temperatures, the efficiency of photosynthesis decreases, so the plant makes less sugar to use or store. High nighttime temperatures increase the respiration rate of the plant, causing it to use up or waste sugars for growth and development. This results in the plant making less sugar but using up more than it would during cooler temperatures.  Heat, especially combined with lack of water, has devastating effects on silking. If plants are slow to silk, the bulk of the pollen may already be shed and gone. Modern hybrids have vastly improved “ASI” or anthesis-silk interval (the time between mid-pollen shed and mid silk). Regardless, in some dryland fields we see seed set problems because of “nick” problems between pollen and silking.
     Even in some stressed areas within irrigated fields (extreme sandy spots, hard pans or compaction areas where water isn’t absorbed and held, and some “wet spots”) we can see stress-induced slow silking and resulting seed set issues. Historically, this has been the most important problem leading to yield reduction, particularly in stressful years. Once silks begin to desiccate, they lose their capacity for pollen tube growth and fertilization.
     Even with adequate moisture and timely silking, heat alone can desiccate silks so that they become non-receptive to pollen. This is a bigger problem when humidity is low and on hybrids that silk quite early relative to pollen shed. Even with dew points in the 70s, when temperatures reach the high 90s to the100s, the heat can still desiccate silks and reduce silk fertility.
     Heat also affects pollen production and viability. First, heat over 95°F depresses pollen production. Continuous heat, over several days before and during pollen-shed, results in only a fraction of normal pollen being formed, probably because of the reduced sugar available. In addition, heat reduces the period of pollen viability to a couple hours (or even less). While there is normally a surplus of pollen, heat can reduce the fertility and amount available for fertilization of silks. Research has shown that prolonged exposure to temperatures reduced the volume of pollen shed and dramatically reduced its viability.  For each kernel of grain to be produced, one silk needs to be fertilized by one pollen grain.”

#Crop Update

While every growing season is unique and there’s an element of risk involved, this year seems to take the cake.  

Drought conditions have affected much of Nebraska.  In our area in south-central Nebraska particularly in our southern tier of counties, we’re seeing brown pastures and alfalfa that stopped growing.  Wheat was harvested nearly a month early and yields range from 0-50 bu/acre depending on if it was hit by the hail storm Memorial Day weekend which totaled it out.

I’m unsure how many planting dates we currently have in Clay County!  The spring planting season went so well with corn and many beans being planted in April.  Soybeans planted in April that haven’t received hail are forming a nice canopy.  Corn that hasn’t received  hail should be tasseling by beginning of July.  One Clay Co. field planted in March was only 3 leaves from tasseling when I took this picture this week and looks great (it’s probably 2 leaves by now!).  Adding another picture from a farmer friend Bob Huttes near Sprague, NE showing his field currently tasseled out and love the smiley face barn 🙂

But then there’s the hail damaged fields.  The hail pattern has been fairly similar all year for this area of the State with some producers receiving four consecutive hail events on their fields.  Every week of May was spent helping our producers determine replant decisions, particularly for soybeans…leaving irrigated stands of 85K and dryland stands of 60-65K when beans were smaller before stem bruising was so severe later.  We would leave a stand one week and end up needed to replant after the hail hit again the following week.  Some farmers got through the first two hail storms but the Memorial Day weekend storm did them in.  I never saw hail like where ground zero of this storm occurred.  After replanting after that weekend, they received yet another hail storm last week with the wonderful, much needed deluge of rain we received in the county.  My heart hurts for these farmers yet for the most part they have good attitudes and are making the most of it.  That’s the way farming is…lots of risk, thus an abundance of faith and prayer is necessary too.  One farmer I talked to has had hail on his house seven times this year (including prior to planting).

Pivots have also been running like crazy prior to the rain last Thursday night where we received 3.30-4.40 inches in the county.  Installing watermark sensors for irrigation scheduling, we were able to show the farmers that there was truly moisture deeper in the soil profile and attempted to convince them to hold off.  It’s a hard thing to hold off on water when the neighbors are irrigating, but several farmers who didn’t irrigate told me they were able to let the rain soak in and their plants weren’t leaning after that rain because the ground wasn’t saturated prior to the rain event.  

Crop Water Use Comparison Study

Water use efficiency (or crop water productivity) is important in crop production. The seed Industry has invested scientific efforts and financial resources into developing hybrids and varieties that can better tolerate environmental stresses such as water stress.

Rainfed corn has increased in acres, replacing sorghum year after year.  This trend may be partly due to the basis price, herbicide options, and newer corn hybrids bred with root systems to better withstand water stress.  In 2009 the question was posed, “Is sorghum still the most crop-water-use-efficient crop, given newer corn hybrids in rainfed fields are providing decent yields and more herbicide options?” To answer the question the Nebraska Grain Sorghum Board funded a project in south-central Nebraska.

On-farm research was conducted for three years in rainfed production fields near Lawrence with the most adapted and high-yielding corn, sorghum, and soybean hybrids and varieties for that area. The research was conducted in no-till fields where the previous crop had been sorghum. A randomized complete block design with three replications was used.

Corn and soybean were planted between May 5 and May 7; sorghum planting ranged from May 19 to May 28. Corn was planted at 20,000 seeds/acre, soybean at 135,000, and sorghum at 65,000.  Rainfall in this area varied greatly from 2009 to 2011: 2009 was dry with only 10 inches of rain during the growing season; 2010 had 16 inches, and 2011 had 20.5 inches from May 1 to October 15.

To monitor soil moisture, Watermark sensors were placed at 1-, 2-, 3-, and 4-foot depths in each plot and the readings were recorded hourly throughout the growing season via Watermark dataloggers. Data were compiled and analyzed to determine crop water use efficiency (CWUE) values. The CWUE values were determined from the Watermark soil moisture data, actual crop water use (evapotranspiration), and grain yield for each crop.

Results:  Table 1 shows actual crop evapotranspiration (ET) in inches, grain yield, and crop water use efficiency for each crop in each year. Corn was the most water use efficient of the three in 2009. Sorghum results in 2009 might have been different if rainfall had occurred to activate the sorghum herbicide as grass pressure was heavy in the sorghum plots that dry year. In 2010-2011, sorghum yielded the most, had good weed control, and had the best crop water use efficiency value.

Table 1.  Crop water use efficiencies in on-farm field trials conducted near Lawrence, Nebraska, 2009-2011.
2011
ET (in)
2011
Yield
(bu/ac)
2011
CWUE
(bu/in)
 2010
ET (in)
2010
Yield
(bu/ac)
 2010
CWUE
(bu/in)
2009
ET (in)
2009
Yield
(bu/ac)
2009
CWUE
(bu/in)
 Corn  22.0  127.2  5.8  23.3  101.2 4.3  14.5  97.5  6.7
 Soybean  21.3  61.3  2.9  22.0  44.0  2.0  14  33.4  2.4
 Sorghum  17.3  138.9  8.0  21.3  118.0  5.5  13.7  77.4  5.6

Overall in this study, sorghum had a crop water use efficiency of at least 5.5 bu/inch; corn, at least 4.3 bu/inch, and soybean, at least 2.0 bu/inch. These results show sorghum’s continued value as a crop that efficiently uses water. Sorghum produced more grain per unit of water used than corn or soybean, an important benefit in water-limited environments. On a three-year average, sorghum resulted in 1.2 bu/inch and 3.5 bu/inch more grain production per inch of water used than corn and soybean, respectively. This study did not compare sorghum or soybean with new “drought-tolerant” corn hybrids.  Graphs, charts, and production information can be found here.

Acknowledgements:  Special thanks to John Dolnicek of Lawrence, Nebraska for allowing this research to be conducted on his farm and for all his help and efforts to make it a successful study and to the Nebraska Grain Sorghum Board for funding this study.

Water Jamboree & Removing Irrigation Scheduling Equipment

Last week was fun and somewhat exhausting teaching with my colleagues in Extension and several area Agencies at the Water Jamboree at Liberty Cove in Lawrence.  Water Jamboree started over 15 years ago to teach 5th and 6th graders about the importance of water and water-related subjects.  Nearly 800 youth learned about where water goes when it goes down the storm drain, about irrigation and siphon tubes, the aquifer, life inside and outside of the lake, mosquitoes, water movement, and much more.  Holli Weber and I utilized the nature trails through the tallgrass prairie to teach a session on life outside the lake focusing on the importance of plants as buffers to filter chemicals and allowing youth to run through the trails doing a photo ID scavenger hunt of the area plants (also to burn off energy!).  While I’ve done this session the past 5 years, this year I took time to show the youth specific characteristics to ID grasses.  God created each plant unique and I was showing them how Indiangrass has rabbit ears when you pull the leaves back from the stem…or the M/W on the smooth brome leaves.  It was fun watching the youths’ faces light up and then try to find these and other characteristics for themselves while on the trails.  It was a great day, although I really don’t know how teachers do it day in and out!  I wish I could’ve attended something like this when I was young!  A special thanks goes to Marlene Faimon at the Little Blue NRD for coordinating this each year.

After Water Jamboree, I headed to my research plot at Lawrence.  It’s been a trying year of coon damage and most recently a skunk inside our traps instead of the coons (and it still smelled like skunk out there!).  Anyway, I was pulling watermark sensors and the 1st and 2nd foot ones were really rough but the 3rd and 4th feet came out easily.  So just a reminder, when pulling watermark sensors, clamp a vice grip below the cap, twist and pull up.  I’ve taken out hundreds of these and have only pulled apart four.  If your sensor won’t pull up, simply take a spade and dig around the sensor and also bring a jug of water with you.  This is the first time I’ve had to dig sensors out but the water really helped as I got it to run down the tube, it eventually loosened at the base to pull out easily without removing the sensor from the pvc pipe.  Sensors can be gently washed with a hose or in a bucket of water using your fingers to gently clean them-don’t use a brush.  Allow to dry and store in your shed, garage, basement, etc.  Also a reminder (although I should’ve done this during the cold of Husker Harvest Days), to get your ET gages inside.  Pour out the water and empty the ceramic top by pulling out the tube and then store that inside where it won’t freeze during the winter.  

Last Irrigation Scheduling

With corn in various stages of dent and starch fill, you may be wondering how to schedule for last irrigation.  For those of you in our Nebraska Ag Water Management Network using watermark sensors, the goal is to use them to determine when the soil profile reaches 60% depletion (for silty-clay soils in our area aim for an average of 160 kpa of all your sensors).  You may be thinking, “An average of 90kpa was hard enough!” but as Daryl Andersen from the Little Blue Natural Resources District points out, you’re only taking an additional 0.30 inches out of each foot.  So if you’re averaging 90kpa on your three sensors, you have depleted 2.34 inches in the top three feet so you still have 0.96 inches left (see the Soil Moisture Depletion Chart).  If you add the fourth foot (using a similar number from the third foot), it would bring the water available to the plant up to 1.28”. 

At beginning dent corn you need 24 days or 5 inches of water to finish the crop to maturity.  If you subtract 1.28 from 5 you will need 3.72” to finish out the crop.  Corn at ½ milk line needs 13 days or 2.25” to finish the crop to maturity-so subtracting it from 1.28 would be only 0.97”.  Taking into account the good potential for rainfall and what moisture is in the profile, you should be done irrigating corn.  Soybeans at the beginning of seed enlargement (R5) need 6.5”.  Most soybean fields that I’ve looked at are in R6 or full seed which needs 3.5 inches yet for maturity.  Subtracting off the 1.28” in the four foot profile would lead to 2.22”.  If we don’t get a few more rains then beans may need one more round.  The UNL NebGuide Predicting the Last Irrigation of the Season provides good information on how determine your last irrigation in addition to showing charts on how much water the crop still needs at various growth stages. 

Daryl Andersen explains how to use this information in a simplified way.  One way to look at this is by the numbers of days left.  At 1/4 starch, there are about 19 days before maturity so you can let your sensors average 130kpa on the first week and 150kpa on the next week.  If these targets are met during the week, you would put on about 1 inch of water.  By going to these numbers, it might give you a higher probability for rain in the next couple of weeks.  ET rates this summer have been running less than 0.25” per day for the most part, so with the humidity we’ve had, the crops have not been using much water, which has really helped our dryland corn again in areas where we aren’t receiving rain events.    

CropUpdate 7-18-11

While it may be strange, I love the smell of corn pollinating and don’t mind walking fields this time of year!  Summer is flying by but it seems like it’s taken a long time to get to tasseling in our fields this year.  Now that corn is tasseling, we can take into account the third foot root zone for irrigation scheduling.  There still is moisture to consider in the third foot so continue to check your readings on your irrigation scheduling tools and now take averages for all three feet.  You may be surprised as some of you won’t need to water till end of July/beginning of August!  If you have any questions about your irrigation scheduling tools, please continue to call any of us Extension educators or the NRD personnel as we want to help you and work with you now to answer them.

Disease just isn’t an issue so far in fields, so for those of you who purchased fungicide, wait till disease is present when you may need it.  UNL research by Dr. Tamra Jackson has proven yields are just as good with delayed fungicide applications as they are at tassel.  The longer you wait to use it for gray leaf spot, the more chances you will have residual for southern rust when it comes in.  While corn prices are high, you want to keep as much of that money as you can!  I don’t recommend fungicides on soybeans as we don’t have the disease to warrant it.  If you did pre-pay fungicide for soybeans as well, the timing of that application should be R3 (beginning pod).

Soybeans are approaching beginning pod for many of you.  For soybeans, this is a critical time for moisture in addition to seed fill at R5.  Many irrigation systems were running on beans last week and I just cringed because the time we don’t want to water soybeans is full flower or (R2).  The reason for that is because it can create disease issues.  We’ve seen a large increase of sudden death syndrome (SDS) the past few years in our county.  Part of that is due to early planting in cold soils, but irrigation during flowering can also play a role.  The major disease that occurs when irrigating during flowering is sclerotinia stem rot (also known as white mold).  While we have very few cases of this in the area, this disease is one that you don’t want to get started in your fields.  Like the fungal pathogen causing SDS, the fungal pathogen causing white mold is soil borne.  Thus, once you have it, you can never get rid of it.  White mold gets started during R2 when flower petals begin to die and the fungus develops on those dead petals. Wet, humid conditions during flowering are key to fungal development, so in the future, avoid irrigating beans during the flowering stages to avoid problems with these two diseases.

CropUpdate: 7-5-11

Last week was a blur of phone calls but it’s great to receive them and know so many of you are doing your best to wait for your soil to be depleted before scheduling your first irrigation!  There are some of you in the Little Blue NRD who haven’t received the rains the past few weeks and have hit the 90-100 trigger on your watermark sensors to schedule your first irrigation.  Most of you reading this won’t have to irrigate till after tassel (and then you can take into account the 3rd foot in your average)!  The 90-100 trigger relates to 35-40% soil moisture depletion and is proven by research via Dr. Suat Irmak at South Central Ag Lab for our silty clay soils.  Waiting for the trigger, regardless if you’re on load control or not, will still allow you at least a week to 10 days before you have to worry about getting behind.  Please continue to call with questions.  There’s also a discussion topic on my blog for your comments/questions.  

Corn and beans are looking good overall, are closing canopies, and corn is rapidly growing.  Wheat is being combined in the southern tier of counties and there has been quite a range of yields due to the dry weather producing small heads and disease issues such as scab, smut, and ergot.  Scab (Fusarium Head Blight) is a concern when we receive rain and high humidity during and around flowering.  We were recommending fungicides at that time.  Some people escaped it, some put the fungicide on, and others didn’t-so there’s a range of yields out there from that.  Common bunt (stinking smut) is the smut that creates clouds of black spores when you’re combining and the grain smells like fish.  Loose smut is loose in the head and doesn’t form a kernel shape like common bunt does.  Both can be prevented by not saving contaminated seed and using fungicide seed treatments at planting.

Ergot is one I hadn’t seen in wheat since I’ve been here but have in roadside grasses.  Ergot is caused by a fungus that infects the wheat head during cool, wet conditions during flowering.  Like the fungus that causes scab, it simply replaces the normal pollination process and instead, a black/purple hard fruiting body (sclerotia) is eventually formed.  Before this is formed, a sugary drop called honeydew is formed which then turns into the sclerotia.  It’s a problem for our producers because I don’t know that you can set your fans to blow it out like you can for light, scabby kernels since ergot sclerotia are denser.  The problem with ergot is that it contains toxic alkaloids (one is like LSD)…in fact, it’s blamed that ergot-contaminated grain is what caused the Salem Witch Trials.  These alkaloids are also toxic to livestock so contaminated grain should not be fed or even blended off for livestock.  Federal grain standards classify wheat as ergot infested when it contains more than 0.3% sclerotia.  If you are finding ergot-contaminated grain in your fields, do not save seed back next year; start over with disease free certified seed.  The sclerotia will live on top of the soil for a year (they will produce spores next growing season so don’t plant contaminated wheat fields back into wheat, barley, oats, or triticale).  Mowing roadside ditches and keeping wheat fields free of other grasses can help prevent ergot infested grasses from spreading the ergot fungus to wheat via blowing spores and rain splash.  More information can be found by checking out the UNL Extension publications Head, Grain, and Seed quality on the http://cropwatch.unl.edu/web/wheat/disease Web site.

Discussion: Irrigation Scheduling

I’m adding this post as a discussion topic as we get into the growing season for producers to post their irrigation scheduling questions or to share what their sensors and ET gages are reading.  With the Nebraska Ag Management Network, we’ve learned that producers often need other producers to check their readings with-kind of like a support group for producers involved with this effort.  That’s because it’s hard to not irrigate when neighbors are irrigating and your irrigation scheduling tools are telling you that you don’t need to irrigate!  We’ve had some good discussions in the past so I look forward to the discussions this coming year!

Irrigation Scheduling Equipment

It’s nearing mid-May and crops should hopefully be emerging soon! For those of you utilizing watermark sensors for irrigation scheduling, it’s important to install those shortly after emergence so you can monitor soil moisture fluctuations long before you ever need to think about irrigating.  I’ve found that our cooperators who install these early after emergence are far more confident in the readings than those who install them closer to irrigation time.  That’s why we no longer install these for anyone past June 15.  

In case you’re wondering what is a watermark sensor, it’s a 3″ sensor filled with fine sand with a fiber glass mesh around it that measures how much energy it takes for the plant roots to extract moisture from the soil.  The sensor measures this in a unit of energy called kilopascals or centabars…units that don’t mean much to you or I.  That’s why we’ve created charts that convert these units to inches of depletion/foot-terms with which we are more familiar!  We recommend farmers install one set at 1′, 2′, and 3′ depths in their fields to monitor when their soil reaches at least 35% depletion.  The basic rule of thumb based on research by Dr. Suat Irmak at UNL is to take the average of the top two sensors prior to the reproductive stages of the crop and the average of all three sensors once the crop has reached the reproductive stages (tasseling or flowering).  When the average of these sensors reaches 35%, we suggest you consider scheduling an irrigation.  

The other tool we use are Evapotranspiration (ET) Gages.  The green canvas cover mimics the leaf surface and essentially as the cover is exposed to different environmental conditions such as wind and low humidity, water is moved out of the tube through the canvas cover and the depletion is noted on a site gage on the front.  This tool has helped farmers visually better understand why their crop did or didn’t use water for any given week as they can look at the ET gage and consider the weather conditions and the influence they had on what the crop used.

On average, our farmers have saved 2.0-2.5″ of water in corn and soybeans since participating in this program.  This program called the Nebraska Ag Water Management Network began in 2005 and now has over 500 cooperators State-wide in Nebraska.  More information about the Network, the tools and charts I described above, and videos demonstrating the equipment can be found at: http://water.unl.edu/nawmdn

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