Excessive rainfall over the weekend (5/12 and 5/13) in the North Western river counties has resulted in several calls this week concerning flooding and standing water in corn and to a lesser extent in soybean. Crop response will depend on the length of time the crop remains submerged and varies between corn and soybean. With rain still in the forecast for the next few days, here are a few agronomic considerations to be aware of.
|Tolerance to Submergence: ≤ 24 hours.
When corn remains submerged for longer than 24 hours, damage to the crop or affected area may occur. Where the water recedes quickly there is usually little to no damage. However, floodwaters can transport downy mildew, a pathenogenic ‘water mold’, via silt. When deposited in the whorl it may negatively impact tassel and ear development, but you won’t know if plants have been affected until later in the growing season. This condition in corn is referred to as ‘crazy top’. Additionally, it is unlikely that all plants will be affected even if some are. No treatments exist for crazy top once these plants are infected.
|Tolerance to Submergence: up to 48 hours or more.
Soybean are certainly more tolerant to flooding and being submerged than corn, but only up to a point. Plants that remain submerged for > 4 days may experience stand loss, a reduction in vigor, and eventually a reduction in yield.
In my most recent blog post (Nutrient Deficiency: Nitrogen), I discussed the symptomology of nitrogen deficiency in both corn and soybean. One of the potential sources of nitrogen loss after application is denitrification.
Denitrification occurs when nitrate nitrogen (NO3–) is converted to N2, N20, and NO by denitrifying bacteria that then escape into the atmosphere. This conversion of nitrate and subsequent nitrogen loss primarily occurs under flooded or waterlogged (anaerobic) conditions. Bacteria that normally obtain their oxygen from the air within the soil begin to scavenge it from the nitrate. Gaseous N2, N20, and NO then diffuse through the flooded soil and escape in the atmosphere.
This is mainly a concern in corn closely following fertilizer application, but is worth mentioning with soybean as well. Even if the crop is not damaged by submergence, it is prudent to be on the lookout for nitrogen deficiency symptoms over the next week if excessive soil moisture persists.