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Small Grain and Corn Development Ahead of Normal this Season (06/23/16)

During my recent travels and based on reports from Area Specialists and County Agents, field conditions vary considerably across the state this season.

Small Grain and Corn Development Ahead of Normal this Season

During my recent travels and based on reports from Area Specialists and County Agents, field conditions vary considerably across the state this season. In the northeast, excessive moisture has delayed or precluded planting and delayed getting into to the field for timely chemical applications. In other parts of the state, plants are starting to show signs of stress due to the lack of moisture. In the southeast, this has been one of the few seasons in recent memory when there have not been huge losses of nitrogen due to denitrification and leaching associated with excessive rainfall. In some fields, rainfall is sorely needed.

One feature of this season that has impacted the crops throughout the state uniformly is that of warmer than normal temperatures. Growing degree day accumulations for both wheat and corn are running well ahead of normal (about 8% for wheat and 20% for corn), last year and the average of the last five years (see attached table). This means that crop development is substantially ahead of normal (this is borne out in the most recent USDA-NASS Crop Progress Reports). Additionally, since the yield potential development of small grains is favored by cooler weather, this also means at this point, our yield potential may not be as high as in recent years. Hot temperatures accelerate development usually at the expense of yield potential (smaller spikes and fewer tillers). Given the tremendous adaptive capacity of small grains, however, there is still opportunity for high yields if conditions are favorable during grain filling (i.e. larger kernels and/or more fertile kernels per spikelet). Reduced growth during hot temperature can partially be explained by reduced net photosynthesis; the optimum temperature for net photosynthesis in wheat is about 77 degrees. Cool night temperatures reduce losses from dark respiration, which may be a positive for us this season as night temperatures have generally not been excessive.

Corn’s growth is less affected by hot temperatures, at least within the range we have been experiencing. But even corn yields best when temperature do not exceed 90 degrees. Having full canopy closure in corn during the long days of early summer allows for greater utilization of the sunlight. Some of the better looking early-planted corn fields have already canopied, which bodes well for high yield potential – as long as they don’t get constrained by lack of moisture later in the season. Drought stress during vegetative stages of corn is well tolerated. Nevertheless, the effect of drought stress tends to accumulate and depletes reserves of moisture in the soil so that yield losses will be even more pronounced if drought persists through the more sensitive stages of flowering and early grain fill.

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Joel Ransom

Extension Agronomist for Cereal Crops

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