Center Pivot Irrigation Short-Course
Crop Update 6-20-13
The sun has been welcomed and crops are rapidly growing in South Central Nebraska! Corn right now is between V6-V8 (6-8 leaf) for the most part. Quite a few farmers were side-dressing and hilling corn the past two weeks. It never fails that corn looks a little stressed after this as moisture is released from the soil and roots aren’t quite down to deeper moisture.
Installing watermark sensors for irrigation scheduling, we’re finding good moisture to 3 feet in all fields in the area. The driest fields are those which were converted from pasture last year and we want to be watching the third foot especially in those fields. Pivots are running in some fields because corn looks stressed, but there’s plenty of moisture in the soil based on the watermark sensor readings I’m receiving for the entire area. So we would recommend to allow your crops to continue to root down to uptake deeper moisture and nitrogen.
The last few weeks we observed many patterns from fertilizer applications in fields but as corn and root systems are developing, they are growing out of it. We’ve also observed some rapid growth syndrome in plants. This can result from the quick transition we had from cooler temperatures to warmer temperatures, which leads to rapid leaf growth faster than they can emerge from the whorl. Plants may have some twisted whorls and/or lighter discoloration of these leaves, but they will green up upon unfurling and receiving sunlight. This shouldn’t affect yield.
Damping off has been a problem in areas where we had water ponded or saturated conditions for periods of time. We’ve also observed some uneven emergence in various fields from potentially a combination of factors including some cold shock to germinating seedlings.
We began applying sugar to our on-farm research sugar vs. check studies in corn. We will continue to monitor disease and insect pressure in these plots and determine percent stalk rot and yield at the end of the season.
Leaf and stripe rust can be observed in wheat fields in the area and wheat is beginning to turn. We had some problems with wheat streak mosaic virus in the area again affecting producers’ neighboring fields when volunteer wheat wasn’t killed last fall. Alfalfa is beginning to regrow after first cutting and we’re encouraging producers to look for alfalfa weevils. All our crops could really use a nice slow rain right now!
Preparing Irrigation Scheduling Equipment
It’s wonderful receiving the rain we did, seeing how quickly planting progress came along, and how quickly corn is popping out of the ground! Being mid-May, it’s time to get our Evapotranspiration (ET) gages out. A reminder to only use distilled water in the gages, make sure to fill up the ceramic top portion of the gage before inserting the stopper, and gently dust off the ceramic top and replace the white membrane and green canvas cover. We recommend replacing those membranes and covers each year so if you need a new one, please let the Natural Resources Districts (NRDs) or me know and we’ll get you a new one! For those of you recording ET information online, please be sure to do so consistently each week to help your neighbors and crop consultants.
Early after crop emergence is the best time to install watermark sensors. For those of you with watermark sensors, read them to ensure they read 199 kpa (dry). Then “prime” them first by soaking them for 24 hours in water to ensure all the air bubbles have been released. The sensors should have a reading of 10 kpa or below to be considered good. If they read higher than that, either continue soaking them another 24 hours and read them again, or plan that they no longer are reading correctly and replace them with others from the NRDs. Remember after soaking sensors that water moves up into the PVC pipe via capillary action, so be sure to dump the water out of the pipe as well.
When installing the sensors, be sure to install them wet, drain excess water, and look for areas that are not compacted, avoid tractor wheel tracks, and look for even spacing of plants. Carefully install without breaking off any plants (thus easier when plants are small!). It’s also important not to install sensors into extremely wet fields. What we have found is that a thin soil layer can cover the sensor when pushing it into the soil of very wet fields. When that soil layer dries, it can provide a reading of 199 saying the sensor is dry when it truly isn’t. If this happens to you, simply remove the sensor, rewet for one minute and re-install. It should be acclimated to field conditions within 48 hours. If you have any questions regarding the installation process, please let the NRDs or your local Extension Educator know. You can also view videos of the installation process and receive additional information to answer your questions.
Wow, I’m sorry I haven’t published much the past two months! Much has happened though as we’re in the middle of winter Extension ag programming season! I love this time of year seeing farmers and ag industry reps-and just chatting about what happened last year and speculating about the upcoming season.
Many of you are also attending numerous meetings. You’re gathering information regarding products and production practices. You may be wondering “Will this work on my farm?” Why not go a step further and see for yourself? On-farm research is a great way to test these questions for yourself using your own equipment in your own fields!
UNL Extension has partnered with the Nebraska Corn Board and Nebraska Corn Growers to form the Nebraska On-farm Research Network. There are three main studies we are conducting state-wide: corn population, corn nutrient, and corn irrigation studies…but we are open to helping you design a valid research experiment for your field to test what you would like-and it can be for a crop other than corn.
We have some upcoming opportunities for you to learn more. On February 11 and February 12 from 9:00 a.m.-3:00 p.m. at UNL’s Ag Research and Development Center near Mead and the York Co. Fairgrounds in York respectively, growers who conducted on-farm research in 2012 will be sharing their results; you can also learn more about conducting on-farm research in your own field. There is no charge for the meetings courtesy of the Farm Credit Services of America but we do need an RSVP for meal count and handouts. Please RSVP by calling (402)624-8030 for ARDC or (402)362-5508 for the program in York. I hope to see you at these meetings as well!
More on Last #Irrigation
It’s been a long irrigation season thus far, but we are so thankful for irrigation in this part of the Country during this drought of 2012! Questions continue to roll in regarding last irrigation for corn and soybeans. Corn at 1/2 starch only needs 2.25″ to finish up so it’s important to know what your soil moisture status is. For most irrigated producers, at 1/2 starch, you should be finished irrigating.
For soybeans at R5 or beginning seed fill, you still need about 6.5″ to finish out the crop. At R6 when the seeds are filling, that drops to 3.5″. At R7 when you begin to see leaves yellowing, that is beginning maturity and you are finished irrigating. They key is we don’t want to fill the profile going into the fall as we’d like to replenish the profile with fall and spring rains and winter snow. However, with soybeans, it’s also critical not to stop irrigating too soon during seed fill.
Gary Zoubek, Extension Educator in York County sheds more light in the following video produced by UNL’s Market Journal.
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 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.|
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.
Crazy? Perhaps! Which according to one of my farmer friends is a little typical of me when I put my mind to figuring out something. So I had been analyzing my crop water use data from my dryland corn, sorghum, soybean crop water use comparison study. It’s the one where we had coon problems this year and ended up trapping a skunk! I noticed how much the soil moisture profile had been depleted and knowing we’ve received minimal precip during fall and winter, I wondered what our soil moisture profile would be for dryland fields by planting. During a meeting yesterday I thought it would be good to install some watermark sensors to determine soil moisture profile recharge with the pending storm. Problem was I was at a meeting over 100 miles from my equipment and the pending storm was starting today. But I was still determined to get them in the ground as early as possible in order to measure the soil moisture status. So I woke up at 4:00 a.m. to heavy rain. Great! It was such a gorgeous day yesterday, and the past week…past month… The first thing my colleagues had asked me when I told them my idea was “Why didn’t you think of this sooner?” Answer: “Guess I needed a precipitation event!”
So I drive to the field in the rain, get the gear together and start installing the sensors. First foot went in easy with the rain that had soaked in. Then it seemed like I tried for 20 minutes (although probably not near that long) putting all my weight on the soil probe to get the 2nd foot in. Wind-driven rain soaked my jeans since I didn’t have rainpants on…fingers were numb from the cold. I kept telling myself this will still hopefully be worth it! On the research data from this field, the second foot was driest of all the crops (was depleted well above plant available water). I got the third foot in and John, the man who farmed the field appeared.
While he thought it was crazy he graciously volunteered to help as he always does. He put in the rest of the sensors while I
hooked everything up.
The last several years we have been blessed to have a fully charged profile going into planting. Even with this rain/snow event, I’m not sure we will have that in dryland fields in this area of Nebraska. So I thought it would be interesting to know where we stood before planting and figured the farmers may want to know that as well. Perhaps a little crazy regarding installing the sensors on such a bad weather day but hoping the data in the end will benefit our farmers and be worth it!