Sometimes a picture tells a story better than words like the 30 day precipitations map of the Mid-South shown below from March 16-April 16, 2019. As you might expect many producers are struggling with getting corn planted while others are struggling to get a stand after heavy rains and cool saturated soils.
Many will be facing replant decisions as soon as soil conditions dry enough for evaluation and field work. Below are some questions that I have been receiving this week and thoughts on each.
Why did I not get a better stand ?
This seems to be a common question and “I should have gotten a better stand” seems to be a common sentiment, even on some of my own plots. When I planted corn in late March to early April, soil temps were marginal (~50 degrees) this combined with heavy rains (8-10 inches in some instances) soon after planting led to multiple issues including saturated soils as the seed was beginning the germination process.
The saturated soil conditions most likely led to a situation where the soil became anaerobic and oxygen was limited, thus damaging the seed that was beginning the germination/emergence process. This has led to seeds that appear to have not germinated, even though they may have been planted for 14-21 days, but in reality these seeds are likely dead or a few may emerge considerably later.
I have also observed soil type making a difference on emergence with sandy loam/silt loam soils typically having a lower emergence rate versus clay soil. This would be a good indication that the lighter soils were cooler and or had a greater temperature fluctuation during the early germination process which would have likely slowed development prior to the soil becoming saturated from rainfall.
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An example I saw yesterday was that the high sandy loam side of the field had a near zero stand, while the bottom of the field which had a clay soil, had a decent stand.
Planting date (even just a couple days) is also having a large impact on stand establishment. The two photo’s below I took yesterday were from the same farm, with the corn on the left planted March 19 that resulted in a very good stand given the conditions (31,000 plants/acre), but the corn on the right was planted March 27 and resulted in a very poor stand (~12,000 plants emerged or just spiking) and likely not many more plants are to emerge.
I am also observing differences in emergence between rows, indicating planting depth differences between rows, bed height differences that resulted in more or less saturated soil conditions, or varying levels of crop residue in the bed.
From the March 27 planted field, there were scattered plants that had fully emerged and many that were just spiking, however a large percentage of the seeds were most likely dead as no developing roots were observed and some of the seed was rotten (see below).
What is an acceptable plant population?
From fields that have or will likely have questionable stands, many are asking at what population would you consider replanting? From plant population work we have done in previous years we know that irrigated corn can be very responsive to plant populations. In many situations we would say that 32,000-34,000 plants/acre would be an optimum plant population for irrigated fields. But an optimum plant population and what I can live with are likely different numbers.
Plant populations less than approximately 25,000 plants/acre that are not uniform would likely be candidates for replanting as this population will not be great enough to come close to maximizing yields on irrigated fields. If plant stands of 26,000 to 28,000 plants/acre are achieved, that may be great enough to consider keeping the original stand, as the cost of replanting may be greater than what you would gain from having a better stand.
Many will be dealing with areas within a field that will have a poor stand, which makes replanting or spot planting a difficult decision. We also need to consider the planting date when a replant could occur. Provided replanting can take place in late April to early May (depending on your location in the state), yields should be similar to that of an earlier planting.
Keep in mind, destroying the old stand is absolutely necessary (no matter how thin it looks) as those surviving plants will be very competitive with younger replanted corn. Tillage, paraquat +(metribuzin, direx, or atrazine), clethodim (6 oz/acre, need to wait 6 days to plant), or glufosinate (non-liberty corn) would all be potential ways to remove the existing first planting.
Consult the MP44 for more details.
How late can I plant or replant and still obtain maximum yields?
Data from irrigated planting date studies conducted from 2008-2013 in Southeast (Rohwer), East-Central (Marianna), and Northeast Arkansas (Keiser) showed that on average 100% of maximum yield could be maintained with planting dates as late as April 25th in Southeast Arkansas and approximately April 30thin areas further north.
A six-year summary of % relative yield potential by planting date and location in the state (NE, EC, SE) is shown below.
Once corn yields started to decline, they slowly declined until Mid-May and then started to more rapidly decline through mid-late May at all locations.
This data is in agreement with multi-year data generated from Dr. Erick Larson at Mississippi State University (here) where he found that irrigated corn still produced optimum yields when planted as late as May 1 at Stoneville and Mississippi State University Campus locations.