When the spring 2022 rains shut off this year, it really compressed the workload for managing irrigation. Our minds need to shift from “I can’t keep up” to “where does the water I have, need to go.” The next few weeks will be critical for many irrigators as fatigue sets in and many crops are still at high water demand. However, there are things that farmers can do to mitigate both the human and plant stress being experienced.  

The following are recommendations for reducing stress and extending the capacity of irrigation systems.  

Computerized Hole Selection 

Pipe Planner, Rice Irrigation or PHAUCET help plan water distribution across the field. These programs reduce pump time usually between 10% and 50%.  

Plan for it taking longer 

Most crops need between .25 and .35 inches per day to meet peak water demand. As wells are drafted and reservoirs are withdrawn, our pumps reduce capacity because they must lift water further as groundwater declines and reservoirs are drawn down. Thus, irrigation sets we designed with computerized hole selection to irrigate in 24 hours take longer. Some alluvial wells can drop off as much as 50% and it’s not uncommon for relifts to fall off 30% as we get to the bottom. Expect it to take longer to irrigate a set or flood up a field and adjust accordingly.  

Flowmeters aid in predicting how much longer sets will take. For irrigation sets that are planned for 24 hours, that are taking longer because pump capacity is reduced by 30%, those sets may now require 30 hours. Additionally, if the normal application depth of 2 inches was used, but now require 3 inches because the soil is so dry and the furrow flow rates are reduced, the 24-hour set is now a 47-hour set. In addition to heat and drought stress, water stress is now being introduced since water may be standing on some of the field for more than 40 hours.  

Time irrigation for profit  

Deficit irrigation is when irrigation water supply is inadequate to meet full crop demand, and we are using the water to maximize yield. In general, to do this effectively provide just enough water during the vegetative phase of growth and then apply irrigation during the reproductive phase, and if it’s going to be short, do it at the very end. So, for soybeans, provide irrigation sparingly until R3 and use the remaining irrigation supply and capacity until termination. The last irrigation needs to be well before maturity. For example, on soybeans we need 2.9 inches to finish at R6.5 so apply any irrigation before then because any extra may not contribute to yield. In a limited situation, put the last irrigation on by R6 (where 4.7 inches is needed) where the risk of yield penalty is greater than at R6.5. Thus, in water limited situations, refrain from irrigation as much as possible until R3 and apply at R6 to maximize yield if for example only adequate water exists for two irrigations. For corn, once the starch line develops, increase the frequency of irrigation until 50% starch, make last irrigation at this time if water is limited.  

Not too late for soil sensors 

It's not too late to incorporate sensors into irrigation management in 2022 (there are still hundreds in inventory in vendor warehouses). Watermark sensors cost $35 each and 3-4 are needed per location. There is a factsheet series (www.uaex.uada.edu/irrigation) on how to use them or contact county Extension agents or NRCS irrigation water management technicians for help with sensors.  

Using sensors to determine the last irrigation of the season is the largest payback of monitoring soil moisture, it almost always saves at least one irrigation and allows for planning ahead of dwindling irrigation supplies. The last factsheet in the series, “How to Predict the Last Irrigation of the Season Using Watermark Soil Moisture Sensors.” outlines how to do this on www.uada.edu/irrigation. However, the easiest way is to use the mobile app, “Arkansas Watermark Tool.” Just enter the sensor readings, the effective rooting depth, time it takes to irrigate, soil type and crop growth stage and it calculates the amount of water needed to finish out the crop. The app also shows how much water is needed for each growth stage and how much is needed for the rest of the season, a nice piece of information, if you are dry. The fields with the growth stage at the highest water use need attention first.  

Most important, doing this will allow for stopping unnecessary irrigation. It’s now possible to easily plan out if you have enough water for the crop or if measures need to be taken to preserve profitability.  

Even with a handful of sensors, put the sensors in a field, then read two days later, remove and move to the next field. This technique can be used to assess several fields in a week with one set of sensors. Use the sensor readings and the mobile app to predict how much water will be needed to finish out the season. This is a low-cost investment and considerable help is available to aid in doing this through Extension and NRCS irrigation technicians.  

Deep Irrigate 

Instead of flushing water across fields, put a full 2 to 3 ac-in/ac across the field, try to fill the profile when you do irrigate. This will force the roots to go deeper for water and extract the subsoil moisture later. Focus on doing a good irrigation so it will be a while before you need to come back. In sealed up silt loams, where it is not uncommon to only put on 0.5 inches in an irrigation, try irrigating and then irrigating again the next day to get more into the soil. It can have mixed results but can allow more time between irrigations.  

Use the feel method 

NRCS has a published method on how to estimate soil water using the feel method. Download the publication for Estimating Soil Moisture Content by Feel and Appearance on the USDA NRCS website.  

If sensor data is not available, use the feel method and a soil probe to estimate soil water. It will be necessary to probe at least 24 inches down to estimate the moisture in the subsoil.  

Don’t overlook the obvious 

Irrigation pumps in Arkansas operate just under 800 hours per year, but the drought is going to push way past that normal run time. For diesel power units, oil changes, greasing propeller shafts may seem obvious, but changing the oil in the gear head is often overlooked.  

For electric motors, greasing the bearings, often requires grease specific for electric motors, and on vertical hollow shaft motors, there is a dry plug that should be removed then 3-4 pumps max, grease should come out of the dry port. Don’t over lubricate an electric motor, or the grease will fill up the housing and get into the windings. The top bearing in a hollow shaft motor runs on oil and should be changed annually. Obtain the proper lubricants for electric motors from your well driller or pump dealers. If the oil in the sight window is black or white, there is a high risk of bearing failure. Drip oil should be set in the morning, 6-8 drips per minute, when it is cool as the oil expands during the day. Setting the dripper in the heat of the day, could stop the drip when the temperature cools in the morning.  

For poly pipe, there are zipper repair patches and a press-on patch that are good to keep on hand in addition to repair couplers for pipe repairs.  

Heat stress and heat exhaustion awareness are real threats to safely sustaining irrigation, keep ample water to employees and yourself and don’t get in a hurry, it may take more time to do things safely.

Source: University of Arkansas System Division of Agriculture, which is solely responsible for the information provided and is wholly owned by the source. Informa Business Media and all its subsidiaries are not responsible for any of the content contained in this information asset.