Flooding Impacts on Corn Growth and Yield
May 27, 2004 11(12):63-64
Joe Lauer, Corn Agronomist
Recent rains have caused flooding and ponding in many cornfields. Growers are concerned
about corn growth and development and any yield effects that might occur from short
periods of flooding. The extent to which flooding injures corn is determined by
several factors including: 1) timing of flooding during the life cycle of corn,
2) frequency and duration of flooding, and 3) air-soil temperatures during flooding
(Belford et al., 1985).
Respiration is the plant physiological process most sensitive to flooding. Flooding
reduces the exchange of air (oxygen) between soil and atmosphere eventually leading
to decreased total root volume, less transport of water and nutrients through the
roots to the shoot, and formation of sulfides and butyric acid by microorganisms
that are toxic compounds to plants (Wesseling, 1974).
Soils contain pores filled with gas and/or water. The two main gases important for
respiration are oxygen and carbon dioxide. The pathway for oxygen into the plant
is from the atmosphere through soil pores to a thin water film surrounding plant
root hairs. It is relatively easy for oxygen to diffuse into soil when pores are
filled by air, but oxygen does not easily diffuse in water so the main constraint
to oxygen movement is the thin water film surrounding root hairs. This boundary
is magnified in flood/pond conditions. Carbon dioxide rarely accumulates to toxic
levels in soil (Wesseling, 1974).
Roots are injured if the soil remains waterlogged. Continued poor aeration causes
cell death and even death of roots. Measurable short term reductions for root and
leaf growth rates begin immediately within 1-12 hours, but tend to recover quickly
within 2-3 days (Wenkert et al., 1981). Almost immediately leaf elongation ceases
and N, P, and K concentration in leaves decrease, but in roots N, P and K concentrations
increase (Ashraf and Rehman, 1999). Flooding restricts root growth in the upper
18 inches of soil, but root elongation continues in deeper horizons. Soil compaction
and flooding will restrict root growth more severely than either factor separately
All biological processes are influenced by temperature (Wesseling, 1974). Wet soils
have a large heat capacity and considerable amounts of heat are required to raise
their temperature. Thus, usually wet soils are cold and corn growth is slower. Drainage
lowers the moisture content of the upper soil layers so air can penetrate more easily
to roots, and transport carbon dioxide produced by roots, microbes and chemical
reactions to the atmosphere. Lowering soil moisture content also leads to higher
soil temperatures and faster growth.
Evaluating damage from flooding
The growing point of corn is metabolically active and is near or below the soil
surface prior to V6 (6 visible leaf collars). Within about 48 hours the oxygen supply
in a flooded soil is depleted (Purvis and Williamson, 1972; Fausey and McDonald,
1985). Without oxygen, the growing point cannot respire and critical functions are
impaired. If temperatures are warm during flooding (greater than 77 degrees F) plants
may not survive 24-hours. Cooler temperatures prolong survival. If flooding
in corn is less than 48 hours, crop injury should be limited.
To confirm plant survival, check the color of the growing point. It should be white
to cream colored, while a darkening and/or softening usually precedes plant death.
Also look for new leaf growth 3 to 5 days after water drains from the field. Once
the growing point is above the water level, the chances of survival improve greatly.
Things to look for later during the growing season
Even if flooding doesn't kill plants, it may have a long-term negative impact
on crop performance. Excess moisture during the early vegetative stages retards
root development (Wenkert et al., 1981). As a result, plants may be subject to greater
injury later during a dry summer because root systems are not sufficiently developed
to contact available subsoil water.
A considerable amount of oxygen is required in the soil for mineralization of nutrient
elements from organic matter by microbes. Oxygen deficiencies reduce microbe activity,
decreasing the rate at which ammonium and nitrate are supplied to plants resulting
in nitrogen deficiency in waterlogged soils (Wesseling, 1974). Additionally, flooding
can reduce the activity of mycorrhizae essential for symbiotic phosphorus uptake
(Ellis, 1998). Flooding can also result in losses of nitrogen through denitrification
and leaching. Where estimated nitrogen loss is significant in fields not yet tasseling
and yield potential is reasonable, corn may respond to additional applied fertilizer.
Flooding causes greater crop yield losses when it occurs early in the season (Meyer
et al., 1987; Kanwar et al., 1988; Mukhtar et al., 1990; Lizaso and Ritchie, 1997).
When six-inch corn was flooded for 24, 48 and 72 h corn yields were reduced 18,
22, and 32% at a low N fertilizer level. At a high N level, these reductions ranged
from 19 to 14% one year and <5% in another year (Ritter and Beer, 1969). When
corn at a height of 30 inches was flooded for 24 and 96 h, yields were reduced 14
to 30%. With a high level of N in the soil, very little yield reduction occurred
even with 96 h of flooding. When flooded near silking, no reduction in yield occurred
at a high N level, but yield reductions up to 16% occurred with 96 h of flooding
at the low level of N.
Mud and sediment caking leaves and stalks could damage plant tissue and allow development
of fungal and bacterial diseases not typically seen. Due to early season stress
the plant may be predisposed to root and stalk rots later and harvest timing of
fields may need to be adjusted accordingly. A disease problem that may become greater
due to flooding and cool temperatures is crazy top, a fungus that depends upon saturated
soil conditions to infect corn seedlings. With warmer, wet or humid conditions Pythium
can reduce stands despite fungicide seed treatments. There is limited hybrid resistance
to these diseases and predicting damage is difficult until later in the growing
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