Agronomy Talk

Agronomy Update

E. Indiana and Ohio: Anhydrous Ammonia Application, Seed Spacing, and Terminating Cover Crops

Published on Wednesday, April 16, 2014

How long do I wait between applying anhydrous ammonia and planting?
Based on how the 2014 season is shaping up so far, we will be doing many field activities all at once. One question on many farmers mind is “How long do I need to wait between applying anhydrous (NH3) and planting?” There are stories of growers who have applied NH3 and planted the same day. Although I don’t recommend this, it is important to understand what is happening when you apply anhydrous.

Anhydrous ammonia has a high affinity for water. As soon as the anhydrous is injected into the ground it is looking for water molecules to attach to. If the soils are dry (which they are not this year), then the NH3 will move further away from the injection point looking for water. If the soils are too wet, the knife will create sidewall compaction which will channel the NH3 up closer to the surface. If the NH3 moves too close to the seed zone it can cause “burning” (in reality it dehydrates the seed) and the seed may never germinate or the roots may look burned.

If conditions are ideal to apply NH3, then I would suggest injecting the ammonia about 8 inches deep. As a general rule, if there is moisture in the ground the ammonia will move about 3-4 inches away from the injection point allowing the NH3 to be absorbed by the soil particles and keeping it safely away from the seed. If conditions are too wet, too dry, or injected too shallow, then it would be best to wait 5-7 days prior to planting.

Uniform Seed Spacing for Maximum Yield How important is uniform seed spacing?
According to research from Purdue University-very important! Purdue looked at plant to plant spacing over a 6 year period and measured yield loss. They measured the plant to plant distance over a 30 foot area in 2-3 areas of a field. They measured both the average distance between plants and the standard deviation. The standard deviation is the difference between the actual plant spacing and the average. For example, if you have an average plant spacing of 7.5”, but one plant is spaced 5” from another and 10” away from another, then the standard deviation is 2.5”. An ideal standard deviation to shoot for is <3”. Over 80% of the fields tested had standard deviations more than 4” and more than 20% of the fields had standard deviations greater than 6”.

According to their research, for every one inch increase in standard deviation there is, on average, a 2.5 bu. yield loss. Over 80% of the fields tested had standard deviations more than 4” and more than 20% of the fields had standard deviations greater than 6”. This means over 80% of the fields lost between 10-15 bu. just by unequal seed spacing. Be sure to adjust your planter according to the manufacturer’s recommendations. For vacuum planters you may need to adjust the air pressure or use discs that contain larger or smaller seed holes. Finger pickup planters are less flexible to different seed sizes, but be sure to adjust the finger tension. Seed size is only one consideration when planting. The right genetics on the right field is still the most important determination for yield you can make.

Terminating Cover Crops
We had another extraordinary year in cover crops, and with the number of acres that were covered I wanted to remind everyone of the importance of getting your cover crop, that did not winter kill, terminated in timely fashion. For tips on this, please refer to Trek Murray’s article from the February issue of CropTalk.

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Mark Apelt
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