With the profit outlook for Delta crops less than bright going into the planting season, the best way corn growers can increase profitability, says Erick Larson, is to increase yield potential.
“Corn yield has increased substantially in recent years, perhaps more than any other crop we work with in our state,” he said at the annual meeting of the Mississippi Agricultural Consultants Association.
Several factors can have a significant influence on yield, says Larson, Mississippi State University Extension grains specialist. They include:
Nighttime temperature during grain fill period: “Nighttime temperatures are very important to the corn plant’s respiration rate. Higher temperatures increase respiration rate, and the plant burns energy that could otherwise be used to produce yield.
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“Normally, in years with lower nighttime temperatures during grain fill, our yields are much higher, as we’ve seen in 2013 and 2014. In the worst years for nighttime temperatures, 2010 and 2011, yields were way down, as was the case in 1998, when we had aflatoxin. Last year’s nighttime temperatures were the fourth highest in the past 20 years, which limited Mississippi corn yield in 2015, particularly for corn grown with irrigation.”
Planting date: “About the only management practice that can affect how the crop deals with nighttime temperatures is planting date,” Larson says. “We know that early planting is extremely important to corn yields. However, Mother Nature often limits our ability to successfully plant as early as possible, and strongly affects corn productivity by influencing other factors, including stand uniformity, irrigation, and nitrogen management.
“Over the last several years, Mississippi growers have faced a lot of challenges during the planting season, particularly from delays due to excessive rainfall and issues related to stand uniformity. If we have problems with stand uniformity, it doesn’t really matter when we plant — yield potential is going to be considerably reduced.”
When planting early, Larson says, “One of the things that plays an extremely important role in seed germination, emergence, and uniformity is soil temperature at planting. We’ve experienced times in the last three years when the soil temperature was far less than 50 degrees during the earliest opportunity for planting.
“The baseline temperature for corn germination is 50 degrees. As temperature increases from that level, the germination rate will increase substantially, and success in getting a uniform stand is a lot higher.”
Wet soils during the planting period can also result in compaction, which can reduce yield potential, Larson says. “One of the things we saw in last year’s wet spring was a lot of tire traffic patterns through fields. This was particularly apparent during the mid-vegetative stages.”
Compaction limits root functions
“I think the primary cause of the compaction was either the planter or side-dress rig, or a combination, going across wet fields. This compaction can limit the ability of roots to feed the plant and perform other physiological functions. We saw significant stunting during the entire season as a result of tire compaction. When you limit root development, it’s going to have a tremendous detrimental effect on growth of the crop and, ultimately, its productivity.”
Compaction may further limit nutrient and water uptake, which is an annual spring challenge for corn with shallow roots. “As soon as it turns hot and dry, we can see a lot of crop wilting,” Larson says. “There may actually be plenty of moisture present in the soil, but shallow roots limit uptake by the plants.
“Corn in rapid vegetative growth stages will show wilting more readily than at any other physiological stage, particularly after tasseling. Also, wide temperature swings — in the low 60s/70s, then suddenly switching to 80s/90s — will cause wilting.”
But, the bottom line Larson says, “Wilting is not a foolproof indicator of soil moisture stress, and choosing the proper time to initiate irrigation can be an emotional issue. Corn is most sensitive to stress at tassel and during early reproductive stages, but the key thing we need to realize is that during mid- to late vegetative growth stages, not only does corn not utilize nearly as much water as later in the year, the consequences from excessive water at this stage are more harmful than too little.
“Jason Krutz [Extension irrigation specialist at the Delta Research and Extension Center, Stoneville, Miss.] and I generally recommend being very judicious with irrigation in the early part of the season. Use soil moisture sensors and soil probes to determine what the moisture level is in the rooting zone, and make sure the crop actually needs water, rather than just basing irrigation on leaf wilting.”
In the last couple of years, Larson says, there have been situations when excessive soil moisture, rather than too little, was the primary yield limitation. “Keep in mind that 75 percent of root development occurs from the time corn is about thigh high until tassel. If we irrigate during the early season, it will temporarily retard root development, and we likely won’t see as much root depth over the course of the season. Saturation early in the season could also have an impact on nitrogen availability late in the season, especially if rainfall occurs after irrigation.”
"A lot more leeway than you think"
Growers often say they begin irrigating early season because they don’t want to fall behind and then not be able to catch up, he says. “But if there’s plentiful soil moisture a foot deep, there’s little reason you’re going to fall behind. There’s a lot more leeway than you think. By knowing the soil moisture level you have and what the crop needs, you can be more judicious with irrigation and avoid some of the negative impacts associated with soil saturation. You not only save water by not applying an unneeded irrigation, you also enhance yield potential by not oversaturating the soil.”
Soil moisture sensors “can tell a lot about the crop, resources in the field for the crop, soil moisture levels at different depths through the soil profile, and rooting depth,” Larson says. “In fields where you don’t have soil compaction issues, you can get effective rooting depth by the end of the season of as much as 36 inches.”
In the MSU corn hybrid demonstration program, he says, “We put crews in the field to count number of kernel rows around the ear, number of kernels, and seed weights at the end of the year. We compared the 10 top hybrids in dryland and irrigated plots and, lo and behold, there were more kernel rows in our dryland plots than the irrigated plots. If water deficit had been a significant limiting factor during those growth stages, there should be no way the corn grown in dryland plots would have a higher number of kernel rows than the irrigated.
“Not only was there not a significant difference, but the irrigated hybrids actually had lower kernel numbers than the dryland. There are data to back up the contention that using irrigation more judiciously in the early part of the season may actually enhance yield potential, because the yield component that’s determined during that period is actually higher in dryland fields than in irrigated fields.”
Another opportunity to scale back irrigation is in late season, Larson says. “I don’t think it will hurt yield potential if you make an extra irrigation late season. But if you’re on a weekly schedule throughout the season, there is opportunity early season and late season to significantly reduce the number of irrigations per season.
“Research shows very little yield reduction during late reproductive stages, right before reaching physiological maturity, so I see no reason not to deplete stored moisture as the crop approaches maturity. Soil moisture sensors can help to make a more informed decision on whether or not to apply another irrigation.”