Recent rains have caused periods of flooding in many cornfields. Growers are asking questions 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:

timing of flooding (plant stage of development when flooding occurs), frequency and duration of flooding, and air-soil temperatures during flooding.

Flooding restricts root growth in the upper 18 inches of soil, but root elongation continues in deeper horizons. Almost immediately leaf elongation ceases and N, P and K concentration in the leaves decrease, whereas in roots N, P and K concentrations increase (Ashraf and Rehman, 1999). Measurable short term reductions for root and leaf growth rates begin immediately within 1-12 h, but tend to recover quickly within 2-3 d (Wenkert et al., 1981).

Prior to V6 (6 visible leaf collars) the growing point is near or below the soil surface. The oxygen supply in the soil is depleted after about 48 hours in a flooded soil (Purvis and Williamson, 1972; Fausey and McDonald, 1985). Without oxygen, the plant cannot perform critical life sustaining functions; e.g. nutrient and water uptake is impaired, root growth is inhibited, etc. 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.

Even if flooding doesn't kill plants outright, 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 during a dry summer because root systems are not sufficiently developed to access available subsoil water. Flooding can also result in losses of nitrogen through denitrification and leaching.

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.

Disease problems that may become greater risks due to flooding and cool temperatures are corn smut and crazy top. There is limited hybrid resistance to these diseases and predicting damage is difficult until later in the growing season.

Literature Cited

Ashraf, M. and H. Rehman. 1999. Mineral nutrient status of corn in relation to nitrate and long-term waterlogging. Journal of Plant Nutrition 22:1253-1268.

Fausey, N. R. and M. B. McDonald. 1985. Emergence of inbred and hybrid corn following flooding. Agronomy Journal 77:51-56.

Kanwar, R. S., J. L. Baker, and S. Mukhtar. 1988. Excessive soil water effects at various stages of development on the growth and yield of corn. Transactions of the American Society of Agricultural Engineers 31:133-141.

Lizaso, J. I. and J. T. Ritchie. 1997. Maize shoot and root response to root zone saturation during vegetative growth. Agronomy Journal 89:125-134.

Meyer, W. S., H. D. Barrs, A. R. Mosier, and N. L. Schaefer. 1987. Response of maize to three short-term periods of waterlogging at high and low nitrogen levels on undisturbed and repacked soil. Irrigation Science 8:257-272.

Mukhtar, S., J. L. Baker, and R. S. Kanwar. 1990. Corn growth as affected by excess soil water. Transactions of the American Society of Agricultural Engineers 33:437-442.

Purvis, A. C. and R. E. Williamson. 1972. Effects of flooding and gaseous composition of the root environment on growth of corn. Agronomy Journal 64:674-678.

Ritter, W. F. and C. E. Beer. 1969. Yield reduction by controlled flooding of corn. Transactions of the American Society of Agricultural Engineers 12:46-50.

Wenkert, W., N. R. Fausey, and H. D. Watters. 1981. Flooding responses in Zea mays L. Plant Soil 62:351-366.