- Early-season water-logging reduced yields by as much as 24%.
- Applying nitrogen (N) following saturated conditions recovered 55% of lost yield potential.
- Hybrids varied greatly in their tolerance to waterlogged soils and sidedress N applications.
Saturated Soils
Excessive rainfall and soil types that are poorly drained can cause saturated or “waterlogged” soil within fields. At times of heavy precipitation, there can be ponding water in certain areas of a field. Prolonged wet soils will negatively affect crop growth and yield. Saturated soils reduce oxygen availability to the roots and increase risk of nitrogen loss through leaching and denitrification. The level of standing water, crop growth stage, air temperature and days of soil saturation all play a role in the degree of impact on yield.
Artificial Soil Saturation Trial
In 2023, Golden Harvest Agronomy in Action Research expanded on a trial first conducted in 2022, designed to address three questions:
- What impact does saturated soil have on crop growth and yield?
- If early-season ponding water creates N deficiency, how much yield can be “rescued” with a sidedress application of N?
- Do hybrids differ in how they tolerate low soil oxygen levels and N loss from saturated soils?
Surface drip irrigation at Slater, IA or sprinkler tape irrigation at Clinton, IL and Waterloo, NE was used to create zones of artificially saturated soil conditions (Figure 1).
Treatments included two water regimes, two nitrogen programs and 10 Golden Harvest® corn hybrids. The water regimes were either blocks watered repeatedly for 6-10 days to create artificial soil saturation or blocks that were rainfed. When the ground was dry enough to drive across after irrigation, half of both water regime blocks received 50 lbs/A of N sidedressed as 32% UAN dribbled on the soil surface along both sides of the crop row using a hand applicator. Irrigation treatment schedule and quantities are outlined in Graph 1.
Weather Patterns
All three locations experienced between 3.5-inches to 5.5-inches less precipitation during April and May than the 30-year average. In addition, all locations received little rainfall during the two weeks prior to irrigation. Due to the dry conditions, filling the soil profile with water and maintaining saturation was challenging. Only at Slater, IA, using surface drip irrigation, was the desired effect of creating conditions conducive to denitrification along with yellow and stunted plants achieved (Figure 2). The surface drip irrigation applied a constant low volume supply of water (0.5-inch/hour) keeping the soil waterlogged. In contrast, at Clinton, IL and Waterloo, NE, the sprinkler tape output was (1.5-2-inches/hour), and the system had to be ran in intervals to avoid surface water runoff. The hot and dry conditions during irrigation made it difficult to maintain soil saturation using this irrigation method.
Soil Test Results
Soil samples were taken from the rainfed and excessive irrigation blocks when ground was fit to walk on after irrigation. Although no yellowing or stunted plants were observed in the irrigated blocks at Clinton or Waterloo, the excessive irrigation did result in a reduction in soil nitrate levels (54-83%) likely from nitrate leaching (Table 1). Lower soil nitrate levels in the excessive irrigation blocks at Slater were likely from N loss through a combination of leaching and denitrification.Soil sulfur (S) and sodium (Na) levels increased in the irrigated blocks from 10 to 32 S ppm and 11 to 65 Na ppm, indicating the irrigation water contained both elements (Table 1).
Effect of Excessive Irrigation and Sidedress Nitrogen
On average, excessive irrigation tended to increase yield by 6 bu/A at Clinton, IL and significantly increased yield by 35 bu/A at Waterloo, NE (Graph 2). The combination of starting the irrigation schedule with a dry soil profile, sprinkler tape application system, and extended dry weather after irrigation, all contributed to why the blocks receiving excessive irrigation yielded more than rainfed blocks. Filling the soil profile with extra water provided more value than the detrimental effects excessive moisture such as N loss and/or temporary low soil oxygen levels. At Slater, IA, utilizing surface drip tape to maintain soil saturation reduced yields by 88 bu/A (Graph 2). N loss through denitrification and leaching along with low soil oxygen levels stunting root and plant growth all were contributing factors in reducing yield.
Like results from the study conducted in 2022, the 50 lbs/A of N sidedressed post-irrigation provided a greater yield response in the excessive irrigation blocks compared to the rainfed blocks at all three locations. Sidedress N significantly increased yield by 7 bu/A at Waterloo, NE and 10 bu/A at Slater, IA within the rainfed blocks. In comparison, in the excessive irrigation blocks, sidedress N significantly increased yield by 9 and 49 bu/A at Waterloo and Slater, respectively. Sidedress N at Slater mimicked a rescue N application after a week of heavy rain events which was successful at mitigating a portion of the lost yield potential. However, sidedressing N was not enough to fully recover all yield lost due to the excessive moisture. It is suspected that the N response at Clinton was lower because of a lack of measurable precipitation until 10 days after surface application resulting in N volatilization.
Hybrid Response to Nitrogen Sidedress
When averaged across water regime and all three locations, there was a significant difference on how hybrids responded to the additional 50 lbs of N/A sidedress. All hybrids had a positive yield response range from 9 to 21 bu/A (Table 2). G12S75, G14B32, and G15J91 brands were the three most responsive hybrids to sidedress N while G13B17 brand was the least responsive hybrid.
Hybrid Response to Saturated Soils
Like many other management and environmental factors, hybrids varied in their tolerance to an extended period of saturated soils at Slater, IA. The yield potential was statistically decreased for all hybrids in the excessive irrigated block ranging from -48 to -85 bu/A (Table 3). G08B38, G12S75, G06A27, and G06B57 brands were statistically more yield tolerant to waterlogged soils than G09B15, G10B61, and G15J91 brands. Responsiveness of G06A27, G12S75, and G15J91 brands was similar to their response in 2022.
There can be many genotypic and phenotypic hybrid characteristics influencing why some hybrids tolerate saturated soils better than others. Compared to all the other hybrids, G13B17 brand experienced the smallest yield increase with the sidedress N application, however, it was one of the more negatively affected hybrids from the excessive irrigation. This is an indication that N stress was not the main factor for the yield reduction with excessive irrigation but rather related to another factor such as reduced root growth from low soil oxygen levels or potentially elevated disease pressure. In comparison, G12S75 brand was one of the more tolerant hybrids to waterlogged soils but had the highest yield response to additional N sidedressed. It is speculated that G12S75 brand is genetically more tolerant to saturated soils and can maintain root growth under low soil oxygen levels increasing the ability to utilize the sidedress N.
Summary
Results from this study demonstrate that yield decreases from waterlogged soils can be mitigated but not eliminated with rescue N applications. With heavy rain and/or irrigation events, N loss through leaching and/or denitrification is a concern and nitrogen management becomes even more important under these conditions.
Although all hybrids were negatively affected by growing in waterlogged soils, the degree of impact was different between hybrids. Similarly, all hybrids showed a different level of response to sidedress N. This information can be used to place specific hybrids on fields known to have drainage issues or areas of a field with a history of ponding. In addition, after a heavy rain event, rescue N applications should be targeted to hybrids that are less tolerant to N stress.
At locations where maintaining complete soil saturation and creating an environment conducive to denitrification was not achieved, the importance of soil water profile was demonstrated. Filling the soil water profile was more advantageous than the detrimental effects of over-watering.
Understanding the dynamic between environment and hybrid selection can help mitigate yield losses from potential weather risks.
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