Wet Soils and Corn
The 2021 cropping season in Illinois (and the Corn Belt) continues to be a story of haves, have-nots, and have-way-too-much with regard to rainfall. In the first three weeks of June, nearly all of Illinois had below-normal rainfall, and concerns about dryness increased. That ended abruptly: in the three weeks from June 25 through July 14, rainfall totals ranged from below normal in the northwestern counties to 25 to 75% above normal in southern Illinois to 100 to more than 200% above normal in central Illinois, with some parts of western Illinois (and scattered areas elsewhere) getting more than 10 inches of rain during that period.
Crop condition ratings responded accordingly, with good + excellent ratings of 80% for corn and 77% for soybean on May 30 dropping, by July 11, to only 60% for corn and 56% for soybean. Such drops from high to mediocre during the first half of the season are unusual: this happened during the drought of 2012, but it’s more common for ratings to start low and move up than the other way around, and drops in ratings tend to come from dry weather during mid-season. The 2011 season showed a trend like 2021, and for a similar reason—a major rainfall event in the last week of June while the crop was growing rapidly.
The real concern from ponding and saturated soils during mid- to late vegetative development is the health of roots. Root system development was stimulated by dry soil conditions, demonstrated by the fact that corn showed good growth and nutrient uptake despite dry conditions in June. With good conditions for mineralization, good soil aeration, and minimal downward movement of soil N resulting from moderate or low rainfall, plants took up N well: canopy color in most fields was good to excellent by mid-June. In N rate studies, corn in plots without any N fertilizer developed good leaf color as well, and N deficiency appeared in these plots later than it normally does.
The first few inches of rain that fell the last week of June helped replenish soil water supplies, and were welcomed. But when inches kept accumulating, soils became saturated and water began to accumulate in low part of fields. Roots of fast-growing crops quickly use up the oxygen in saturated soils, and oxygen movement into saturated soil is very slow. Carbon dioxide given off by the roots and by soil microbes also accumulates, and is toxic to roots. Roots in saturated soils soon stop taking up nutrients, and plants begin to turn yellow as N deficiency intensifies. Larger plants have more N already in the plants, and this slows the development of deficiency.
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Crop condition ratings responded accordingly, with good + excellent ratings of 80% for corn and 77% for soybean on May 30 dropping, by July 11, to only 60% for corn and 56% for soybean. Such drops from high to mediocre during the first half of the season are unusual: this happened during the drought of 2012, but it’s more common for ratings to start low and move up than the other way around, and drops in ratings tend to come from dry weather during mid-season. The 2011 season showed a trend like 2021, and for a similar reason—a major rainfall event in the last week of June while the crop was growing rapidly.
The real concern from ponding and saturated soils during mid- to late vegetative development is the health of roots. Root system development was stimulated by dry soil conditions, demonstrated by the fact that corn showed good growth and nutrient uptake despite dry conditions in June. With good conditions for mineralization, good soil aeration, and minimal downward movement of soil N resulting from moderate or low rainfall, plants took up N well: canopy color in most fields was good to excellent by mid-June. In N rate studies, corn in plots without any N fertilizer developed good leaf color as well, and N deficiency appeared in these plots later than it normally does.
The first few inches of rain that fell the last week of June helped replenish soil water supplies, and were welcomed. But when inches kept accumulating, soils became saturated and water began to accumulate in low part of fields. Roots of fast-growing crops quickly use up the oxygen in saturated soils, and oxygen movement into saturated soil is very slow. Carbon dioxide given off by the roots and by soil microbes also accumulates, and is toxic to roots. Roots in saturated soils soon stop taking up nutrients, and plants begin to turn yellow as N deficiency intensifies. Larger plants have more N already in the plants, and this slows the development of deficiency.
Click Here to read more.