Harvest Watchouts after too Much Early Season Rain & Management

A challenging spring can often lead to lurking issues through the summer and into the fall. Going into harvest, watchouts resulting from these challenges may include compaction, loss of nitrogen, lodging, and disease development favored by a wet spring.

Compaction. Plentiful and continuous early season rain can result in a struggle to get crops planted timely and into good soil conditions. When planting gets pushed into unfit soil conditions, compaction can occur. The main issue for plants with compaction is poor root growth and development which can lead to a multitude of potential issues for the plant (Figure 1). Tillage, cover crops, and freeze/thaw cycles can help mitigate soil compaction.

Nitrogen Loss. Nitrogen is lost in three ways - volatilization, denitrification, and leaching. Excessive spring rainfall can be a glaring concern for nitrogen. Volatilization is the loss of organic nitrogen (urea) on the surface to the atmosphere as ammonia gas (NH3). Nitrogen in manure can also be volatilized when it remains on the soil surface as well as residue as it decomposes^.1,2

Denitrification is a process in the soil by which bacteria converts nitrite (NO2ˉ) and nitrate nitrogen (NO3ˉ) forms into plant unusable nitrogen (N2) and nitrous oxide (N2O) gases and are lost to the atmosphere.³ Denitrification happens in anaerobic conditions such as fully saturated soils where the bacteria responsible for denitrification can thrive.

Leaching is the other main form of nitrogen loss caused by excessive rainfall. Again, this only affects the nitrate form of nitrogen.^4,5 Nitrate can move up to 6 inches in the soil for every one inch of water moving through the soil profile.⁵ With heavy rain nitrate can be pushed deeper into the soil profile where it is harder or impossible for the plant to reach.

Nitrogen deficiency symptoms appear as a yellow to brown inverted “V” from the leaf tip down the midrib to the stalk of the oldest leaves (Figure 2). The two main concerns from lack of adequate nitrogen are overall yield loss and cannibalization of stalks. Cannibalization happens when the plant remobilizes nutrients from the stalk to complete ear development. This leads to weak stalks and a higher potential for stalk lodging.

Late season scouting should include a “push test” where 4 or 5 plants are pushed just above the ear into the next row. The plants should spring back to their original position. If stalk quality is a concern, they often kink over below the ear. A “pinch test” can also be used to help determine stalk integrity. When the lower stalk is pinched, it should be firm and hard to pinch together. If it is soft and easy to pinch, the field should be prioritized for early harvest to help avoid potential yield loss due to lodging.

Early season wet weather can create an environment that favors increased disease development throughout the growing season. Overall disease pressure on the plant can weaken the stalk as leaf area conducting photosynthesis decreases and the plant pulls from the stalk to fill out the ear. These challenging weather conditions can also favor stalk rot development. Stalk rots often manifest later in the season as plant defenses break down and plants reach maturity.

Scouting is a key to identifying potential problems and prioritizing harvest. For fungal diseases, a fungicide application should be considered as they can improve crop health and standability. Fungicide should be applied at V5 and/or VT/R1 growth stages for the best results.

All or a combination of these issues can lead to poorer test weight and grain quality. Harvest timely and dry quickly. Monitor the grain very closely when facing these concerns as storage is more problematic with these types of issues.

Channel Agronomist
Kelly Siverhus

Sources

¹Killpack, S.C. and Buchholz, D. (Reviewed by Brune, D.) 2022. Nitrogen in the environment: ammonia volatilization. University of Missouri Extension. https://extension.missouri.edu/publications/wq257.

²Jones, C., Brown, B.D., Engel, R., Horneck, D., and Olson-Rutz, K. 2020. Management to minimize nitrogen fertilizer volatilization. Montana State University Extension. https://landresources.montana.edu/soilfertility/documents/PDF/pub/UvolBMPEB0209.pdf

³Killpack, S.C. and Buchholz, D. (Reviewed by Brune, D.) 2022. Nitrogen in the environment: denitrification. University of Missouri Extension. https://extension.missouri.edu/publications/wq255.

⁴Killpack, S.C. and Buchholz, D. (Reviewed by Brune, D.) 2022. Nitrogen in the environment: leaching. University of Missouri Extension. https://extension.missouri.edu/publications/wq262

⁵Peltier, A. 2023. Climate factors and nitrogen fertilizer management: what should Minnesota growers know. Minnesota Crop News. University of Minnesota Extension. https://blog-crop-news.extension.umn.edu/2023/01/climate-factors-and-nitrogen-fertilizer.html.

Web sources verified 7/24/24. 1110_434701