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Corn Hybrids’ Yield Response to Limited Well Capacities in the Central High Plains
Macie McPeak: M.S in Irrigation and Water Management
Sumit Sharma : Extension Specialist for High Plains Irrigation and Water Management
Background
The Central High Plains, which include the Oklahoma Panhandle, Southwest Kansas, Southeast Colorado, and Northern Texas Panhandle, is a heavily farmed semi-arid region that depends on the Ogallala Aquifer for irrigation to ensure stable crop yields. However, the continuous decline of the Ogallala Aquifer has resulted in increased need for irrigation strategies that conserve water while maintaining crop profitability. Corn remains the most water consuming crop with highest productivity per unit of irrigation applied, and strong economic returns in the Central High Plains region. However, corn is also the most sensitive to water stress among all the existing cropping systems (including sorghum, cotton, and sunflower, soybeans and wheat). Declining water table has reduced the well capacities in many areas in the region, which cannot meet crop water demand, making it a growing challenge for corn production. Therefore, there is a need for research in irrigation strategies and agronomic choices such as drought tolerant hybrids, seeding rate, planting date, and hybrid maturity for sustainable and profitable corn production with reduced well capacities in the region. This blog discusses the yield response of different corn hybrids to limited well capacities in the Oklahoma Panhandle area of the Central High Plains.
Limited well capacities only meet partial crop water demand, which in general leads to yield declines especially in high water demanding crops such as corn. Several previous studies suggest that crop productivity does not significantly decrease as long as irrigation is maintained at approximately 75–80% of full evapotranspiration (ET) replacement (Su et al., 2022; Klocke et al., 2007; Zhao et al., 2019). However, when irrigation levels are more restricted, such as under reduced well capacities, there can be substantial yield losses and diminished economic returns. The magnitude of yield reduction varies with region, hybrids, and growth stage at which water stress occurred. For example, in the Central High Plains the corn ET demand is highest in Texas Panhandle and decreases as we move north towards Nebraska. Zhao et al. (2019) found that applying 75% ET in the Texas Panhandle produced corn yields equivalent to full irrigation, whereas reducing irrigation to 50% caused significant yield reductions. Similarly, Klocke et al. (2007) reported that limited irrigation at roughly 50% of full ET replacement in Nebraska achieved 80–90% of fully irrigated yields across multiple crop rotations. Therefore, the irrigation strategies which work in one region may not work the same way in other regions with different crop water demand and must be tested for the region-specific climatic conditions.
The current study was conducted in 2025 at the Oklahoma Panhandle Research and Extension Center in Goodwell, OK. Four Pioneer brand corn hybrids including P13777 (113 day maturity), P10625 (110 day maturity), P05810 (105 day maturity), and P14346 (114 days maturity) were planted at 22,000 and 28,000 seeds per acre. The hybrids were irrigated with a center pivot fitted with variable rate irrigation system at 200, 300, 400, and 500 GPM well capacities. The well capacities were simulated by adjusting the frequency of irrigation events.
Results & Discussion
The crop received 12.1 inches of rain from planting until physiological maturity, while total rainfall from April till September was over 15 inches. Manual probing of the field showed near 4 feet soil profile at the time of planting which can hold up to 2 inches of plant available water per foot. The well capacities 200, 300, 400, and 500 GPM treatments received 7.4, 8.9, 10.8, and 12.0 inches of irrigation, respectively. The data showed no significant effect of population on corn yield across hybrids for any well capacity. However, the hybrids showed significant interaction with well capacities, which indicated that hybrid yield response varied at different capacities (Figure 1). In general, the average yield declined from longest maturity to shortest maturity hybrids irrespective of the well capacity, but was only statistically significant at for 200 GPM (Figure1). At this irrigation level, the shortest maturity hybrid P05081 yielded significantly lower yield than longest maturity hybrid P14364, while P13777 and P10625 were not different from either of these two hybrids.
Although there was no statistical difference among the hybrids at 500, 400, and 300 GPM, when compared across well capacities, yield reductions were most pronounced at the 200 and 300 GPM irrigation levels for each individual hybrid, indicating that irrigation capacity was the primary yield limiting factor under restricted water availability (Figure 2). While the exact causes of this abrupt decline are not yet understood, as mentioned in the beginning of this blog, previous literature has suggested that severe yield decline in corn can be expected when irrigation is reduced to 60% ET replacement in the study region. Both 300 and 200 GPM well capacities met 60 and 65% crop ET demand, while 400 and 500 GPM met 71 and75% crop ET demand, respectively. More data will be needed to ascertain these threshold levels of well capacities for corn production in this region.
All the hybrids showed a positive yield response to Irrigation+Rain with different yield gains per inch of water applied (Figure 3). Hybrid P10625 registered highest yield gain of 14.1 bushel per inch of water applied, followed by P13777 (12.0 bu), P05081 (11.9 bu), and P14364 (11.6 bu). The stronger coefficient of regression (>80%) for two short maturity varieties indicated that irrigation was stronger yield limitation factor for these hybrids, in comparison to 114 and 113-day maturity hybrids for irrigation explained on 67 and 69% variability, respectively. This suggests that besides irrigation there might be other factors which could contribute to filling the yield gaps for given irrigation levels in longer maturity hybrids.
Planting population did not significantly affect grain yield across irrigation capacities. When pooled across the hybrids for individual planting populations, 28,000 seeding rates resulted in gain of 0.1, 2.6, 5, and 12 bushels per acre for 200, 300, 400, and 500 GPM, respectively. This indicates that higher planting populations at well capacities of 400 or above should be considered, while reducing population at 300 GPM or lower might be more cost-effective option.
Take Home
- Irrigation capacity remains the primary determinant of yield potential under limited well capacities in the Central High Plains.
- Pre-irrigation and recharging the soil profiles will be critical to support crop water demand for limited well capacities.
- Short maturity hybrids appeared to have consistently lower average yield and more vulnerable for yield losses at limited irrigation. However, one must consider that the growing conditions were more conducive for corn production in 2025 which generally favor long maturity hybrids. Therefore, long-term data will be required to assess the performance of short maturity hybrids during inclement growing seasons.
- Even though population didn’t significantly influence the grain yield. The 28,000 seeding rates overall had higher average yield at 400 and 500 GPM. Therefore, producers should consider the higher population at these well capacities or more.
- Overall, irrigation is the most important factor for yields, but there is a need for long-term agronomic data on hybrid maturity and population along with economic analysis to ascertain these findings.
Using soil moisture trend values from moisture sensors for irrigation decisions
Sumit Sharma, Extension Specialist for High Plains Irrigation and Water Management
Kevin Wagner, Director, Oklahoma Water Resources Center
Sumon Datta, Irrigation Engineer, BAE.
Sensor based and data driven irrigation scheduling has gained interest in irrigated agriculture around the world, especially in semi-arid areas because of the easy availability of commercial irrigation scheduler technology such as soil moisture sensors and crop models. Moisture sensing has particularly gained interest among the agriculture community due to ease of availability of the sensors to the producers, affordable costs, and easy to use graphical user interface. Economic potential of sensors in saving irrigation costs, data interpretation training through extension education programs, and policy initiatives have also helped with adoption of the sensors, especially in the United States. However, sensor adoption and efficient use can still be challenging due to poor data interpretation, steep learning curves, overly high expectations and subscription costs. This blog briefly discusses scenarios where sensors can be helpful in irrigated agriculture. For moisture sensor types, functioning and installation, readers are referred to BAE-1543 OSU extension factsheet.
Irrigation Scheduling
Irrigation scheduling with soil moisture sensors follows traditional principles of field capacity (FC), plant available water, maximum allowable depletion (MAD), and permanent wilting point (PWP). Figure 1 shows the transition of soil moisture level from field capacity to MAD, and to permanent wilting point in a typical soil. The maximum amount of water that a soil can hold after draining the excess moisture is called field capacity. At this point, all the water in soil is available to the plants. As the moisture content in the soil declines, it becomes more difficult for the plants to extract moisture from the soil. The soil moisture level below which the available moisture in soil cannot meet the plant’s water requirement is called the MAD. The water stress that occurs once moisture level goes below this moisture level can cause yield reductions in crops. Therefore, irrigation should be triggered as soon as the soil moisture level approaches this point (MAD) to avoid any yield losses (for detailed information on MAD, its value for different soils and crops, and irrigation scheduling, readers are referred to BAE-1537). Modern soil moisture sensors can come self-calibrated and are equipped with water stress threshold levels for different crops to avoid water stress or overwatering (Figure 2). These decisions are useful in furrow and drip irrigation systems where irrigation triggers can be synchronized with MAD values.
Figure 2: Screenshots of graphic user interface of three sensors a) GroGuru b) Sentek c) Aquaspy (Top to bottom) with threshold levels for soil moisture conditions. Aquspy and Sentek credits: Sumit Sharma. GroGuru image credits: groguru.com
Soil Moisture Trends and Irrigation Depths
Soil moisture sensors can help make data-informed decisions about scheduling irrigation. Previous studies have shown that the moisture values may vary from one sensor to the other and may not represent the exact moisture levels in soil. However, all soil moisture sensors exhibit trends in recharge and decline in soil moisture conditions. These real time soil moisture trends can be used to make informed decisions to adjust irrigation and improve water use efficiency. In high ET demand environments of Oklahoma, pivots are usually not turned off during the peak growing season, yet sensors can help in making decisions for early as well as late growing periods.
One of the easiest adjustments that could be made using soil moisture sensor data is the adjustment of irrigation depth. In an ideal situation, every irrigation event should recharge the soil profile to field capacity; however, this is often limited by the crops’ water demand and the well/irrigation capacity to replenish soil moisture levels. Each peak in soil moisture detected by sensors shows irrigation or rain, which ideally should be bringing moisture to same level after irrigation. However, reduction in moisture peaks in the soil moisture profile with every irrigation often indicates greater crop water demand than what is replenished with irrigation. In such scenarios, as allowed by capacity and infiltration rates, the irrigation depth can be increased. These trend values are particularly useful for center pivot irrigation systems, where triggering irrigation based on MAD might lag due to time and space bound rotations of the pivots in Oklahoma weather conditions.
Figure 3: A screenshot from Aquaspy agspy moisture sensor showing moisture at 8” (blue) and 28” (red) with each irrigation event. Data and image credit: Sumit Sharma
Last irrigation can be a tricky decision to end the cropping season. For summer crops, this is the time when crop ET demand is declining due to decline in green biomass and cooler weather patterns. Similar moisture trends can be used to make decisions for the last irrigation events, which can be skipped or reduced if the profile moisture is good, or can be provided if profile moisture is low. This is important because in an ideal situation, one would want to end the season with a relatively drier profile to capture and store off-season rains. Additionally, saving water on last irrigation can save operational cost and potentially cover the cost of moisture sensor subscriptions.
These decisions can be illustrated with Figure 3, which shows the trends of declining and recharging in a soil profile under corn at 8- and 28-inch depth. This field was irrigated with a center pivot irrigation system which was putting 1-1.25 inches of water with each irrigation event; however, the peak water recharge rate at both depths was declining with each irrigation. This coincided with peak growth period indicating rising ET demand of the crop than what was replenished by the irrigation. Later, two rain events, in addition to irrigation, replenished soil moisture in both layers. As the pivot was already running at a slow speed, slowing it further was not an option without triggering runoff for this soil type and this well capacity. Further in the season, when the crop started to senesce and ET demand declined, each irrigation event added to the moisture level of the soil. This allowed the producer to shut down the pivot between 70% starch line and physiological maturity for the crop to sustain at a relatively wet soil profile and leave the soil in relatively drier profile for the off-season.
In high ET demanding conditions of Western Oklahoma, crops often rely on moisture stored in deep soil profiles during the peak ET period when well capacities can’t keep up with crop water demand. In the high ET demanding environments of Oklahoma, irrigated agriculture depends heavily on profile moisture storage. Declining soil profile moisture is common during peak ET periods in high water demanding crops such as corn. These observations are useful if one starts the season with considerable moisture in the soil profile, however such trends may be absent if the season is started with a dry soil profile. Dry soil profiles can be recharged early in the season with pre-irrigation or deeper early irrigations (if allowed by the infiltration rate of the soil), when crop ET demand is low, to build the soil moisture profile. As such, sensors can be used in reducing the irrigation depth or skipping irrigation in early cropping systems if one starts with a full profile. This usually allows root growth through the profile to chase the moisture in deeper layers. It should be noted that the roots will grow and chase moisture only if there is a wet profile, and not through a dry soil profile.
Sensor installation and calibration are important for efficient use of these devices in irrigation decision making. Poor installation can often lead to poor data and wrong decision making. Although modern sensors are self/factory calibrated, some do provide the option to adjust threshold levels manually based on field observations. Early installation of sensors can be useful in making informed decisions as soon as the season starts. For a more detailed analysis of proper sensor installation, refer to BAE-1543. Producers are encouraged to integrate other means of irrigation planning with soil moisture sensing, such as a push rob to probe the soil profile or OSU Mesonet’s irrigation planner to further validate the sensor data. Further, the cliente should consider their irrigation capacities before investing in soil moisture sensors, as sensors may always show a deficit in low well capacities which cannot meet crop’s water demand.
References:
Taghvaeian, S., D. Porter, J. Aguilar. 20221. Soil moisture-sensing systems for improving irrigation scheduling. BAE-1543. Oklahoma State Cooperative Extension. Available at: https://extension.okstate.edu/fact-sheets/soil-moisture-sensing-systems-for-improving-irrigation-scheduling.html
Datta, S., S. Taghvaeian, J. Stivers. Understanding soil water content and thresholds for irrigation management. BAE-1537. Oklahoma State Cooperative Extension. Available at: https://extension.okstate.edu/fact-sheets/understanding-soil-water-content-and-thresholds-for-irrigation-management.html
For more information please contact Sumit Sharma sumit.sharma@okstate.edu
Pre-plant Irrigation
Sumit Sharma, Irrigation Management Extension Specialist.
Jason Warren, Soil and Water Conservation Extension Specialist.
Pre plant-irrigation is a common practice in Western Oklahoma to recharge soil profile before growing season starts. Pre-plant irrigation is useful when the irrigation capacity is not enough to meet peak ET demand. It can also be important to germinate and provide for optimum emergence of the crop. As such, pre-plant irrigation is not useful when the soil profile is already wet, or soil profile is not deep enough to store moisture, or if planting dates are flexible and can wait until rains can recharge soil profile. Pre-plant irrigation becomes an important consideration if the previous crop had extensive rooting systems, which depleted moisture from deep in the profile. The crops in western Oklahoma especially in the Oklahoma Panhandle depend on stored water in the profile to meet ET demand during peak growth period, especially when well capacities are limited. Deep profiles and excellent water holding capacities of soil found in the region make the storage of a considerable amount of moisture possible. While pre-plant irrigation to recharge the whole profile (which can be 6 feet deep) may not be possible or advised, producers can still use certain tools to assess the stored water in the profile and make decisions on pre-plant irrigation.
A soil push probe (Figure 1) can provide a crude estimate of the moisture in a soil profile. For example, if an average person can push the probe to 2 feet, this means that the first 2 feet of the profile has moisture stored in it. The profile beyond 2 feet is considered too dry to push the probe through. This method does not provide the amount of water stored in the profile. For accurate measurements of soil moisture, soil samples could be collected, weighed, dried and weighed again to determine the water content in the soil. An alternative is to install moisture sensors, however this is usually not practical due to potential damage during planting, although some probes that can be permanently buried are becoming available. On average a clay loam soil in western Oklahoma can hold up to 2 inches of plant available water per foot. The approximate water holding capacity of your soil can be found on the websoilsurvey. Your county extension or NRCS personnel should be able to help you navigate this website if necessary. When the water holding capacity of your soil is known, the use of a push probe can provide a preliminary estimate of soil water content. Probing should be done at multiple locations in the field on both bare and covered (with crop residue) spots. The presence of crop residue reduces evaporation and increases infiltration so the first thing you will notice is that it is generally easier to push the probe into the surface where the ground is covered by residue. If the soil water content is near full the probe will be easy to push into the soil and it may even have mud on its tip when you pull it out. In this case you can estimate that the water content to the depth of penetration is near field capacity and that the current water content is equal to the water holding capacity. For example, if you can push the probe 2 ft into a soil with a water holding capacity of 2 inches/ft then we expect to have 4 inches of plant available water. In contrast if it takes some effort to push the rod 2 ft the estimated water content may be reduced.
When pre-irrigation is applied it can be useful to assess the increase in the depth to which the probe can be pushed into the soil after the irrigation event. For example, if 1 inch of irrigation is applied to the soil in the example above, we may expect that after this irrigation event we can push the rode 2.5 ft. However, in some case we may be able to push the rod 3 ft. The reason being that although we could not push the rod beyond 2 ft before the irrigation event, the soil below this depth was not completely dry. Therefore, the 1 inch of water was able to move to a depth of 3 ft. This is useful information, telling us that the soil below the depth we can push the rod contains some water and that each inch we apply may drain a foot into the profile. Generally, we expect the rooting depth of most crops to be able to extract water from at least 4 ft. Although it is certainly possible to extract water from below this depth, we generally don’t want to pre water our soils to full beyond 4 ft. When we fill the profile with pre water, we are increasing success of the following crop by providing the stored moisture that can offset deficits that may occur in the growing season. However, we are reducing our opportunity to capture and utilize spring rainfall. We must consider this when applying pre-irrigation, because if it is followed by rainfall in excess of ET our irrigation efficiency is greatly reduced by the drainage or runoff that can occur.
Down and Dirty with NPK 