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Challenging Yields for Corn on Corn in 2020

By Jim Torkelson • December 7, 2020

2020 has been quite a challenge on multiple levels. Not only has the pandemic been an issue along with all of its nasty implications, but our weather through much of the corn belt left a lot of farmers curious about their yields. The hotter than usual weather had some positive implications such as better than expected test weight for our corn, as well as muted foliar diseases for both corn and beans but some areas were not as lucky, especially those hit by the August 10th Derecho.

During much of July and August in Iowa, the pollination and grain fill period, 98 of 99 counties experienced some level of drought and corn on corn was especially hard hit. Typical observations of aborted kernels ranging from a few per row up to 15 kernels missing were very common along with shallow kernels to boot. It truly wasn’t until harvest, however, that we saw the drastic differences between corn following beans and corn following corn. Below I will discuss some of the reasons beyond just water limitations for some of the highly variable and in some cases disappointing yields.

I received a call from a Renk customer in late October expressing concerns about his yields. His continuous corn field had a fairly high yield history but this year it seemed further behind on yield relative to his corn following beans. Upon arrival at the field, and doing a few quick stand counts, I quickly recognized what the problem may be but used a spade to confirm the issue. The pictures below are from the field and hopefully a couple of points are somewhat obvious.

First, there is a noticeable stalk diameter difference between the stalks side by side in each of the pictures on page 4 – also take note of first above ground internode which is circled in red. In photo A you can see one stalk is smaller in diameter but also notice the first internode for both stalks is relatively similar in length. In photo B, we again have a diameter difference, as well as a difference in internode length. In both cases we found smallish size ears – about half size – on the smaller diameter stalks which is hardly shocking but what is the cause of the smaller stalks and subsequent ears?

A typical conclusion is that we had late emergence which resulted in smaller stalk diameter and in fact that is the case with photo B. How do we know this was a late emerging plant? That longer internode tells us that plant came up later and “stretched” to try to catch up with the surrounding plants but that does not appear to be the case with photo A.

Upon retrieving my spade, I checked for compaction which was not an issue as we had good root development for all stalks and no apparent compaction layer. Once compaction was ruled out, I started to examine the roots for rootworm feeding and found none despite this being corn on corn for many years. Seed placement appeared to be pretty uniform in both spacing and depth but, while examining the roots, I found the problem which is illustrated in the pictures below.

In photos C and D, you can see in the circled areas of poorly decomposed residue from the previous year. This by itself is not typically a problem but the proximity of this residue to the seed at planting is a BIG problem, especially in drier years.

Simply put, to get good decomposition, we need several main factors: heat, water, a nitrogen source, other fertilizer elements, microbes and time. There are others but, in this case, the late harvest of 2019 set the table for almost no decomposition to occur in the fall, so that work had to begin in the spring, representing lost time. Secondly, a very cold May, along with our drier than normal growing season, slowed this process with the result of those two elements leading to the third. A tug of war ensued for our applied nitrogen between our corn plant and the microbes trying to decay the previous year’s residue, and as we can see, the corn plants and the farmer typically lose.

Also of note, you can see that the deposition of the residue is quite close to where the seed was placed at planting and in the past I have described this as residue encroachment syndrome, or for short what I call RES. So what can be done to prevent this in the future? My first recommendation is to try to develop a tillage management plan whereby the residue is adequately buried, or left on top of the ground, as in the case of no till. Secondly, when doing spring tillage, check to see if your tillage is depositing the residue in the 2-4 inch depth and if so, try adjusting depth to move it from that range. Also, additions of fall nitrogen can aid in speeding up decomposition in the spring but I would advise nitrogen stabilizers where appropriate. Finally, and maybe most importantly, make sure trash whippers on the planter are deep enough to move any surface debris away from the row at planting.

As a result of an early end to harvest, the opportunity to do a large amount of fall tillage combined with an uptick in grain prices, we are off to a great start heading into 2021. Let’s stay positive as we look toward a better 2021. Never underestimate the importance you play in feeding the world. Thank you for
all you do.