When does soil get too dry for young corn?

Chad Lee and John Grove, Extension Agronomist and Agronomic Soil Scientist, University of Kentucky

Young corn seedlings require very little water. 

When does soil get too dry for young corn? Or, when will you know that the young corn seedlings will not make it? Variations of these questions have been coming in as the lack of rain continues and the temperatures rise on young corn plants. The quickest, and perhaps most practical answer, is to scout fields regularly and identify areas where plants are not recovering from drought stress. In other words, the best indicator of when the plants will not make it is when they have died.


A more technical answer is that a soil gets too dry when the ‘permanent wilting point’ is reached - the level of soil moisture at which plants will fail to recover(Taylor and Ashcroft, 1972, Physical Edaphology: Physics of Irrigated and Non-Irrigated Soils, Freeman and Co., San Francisco).
Most plants will display drought symptoms long before the permanent wilting point is reached. Most silt loam soils will reach the permanent wilting point around 8% moisture content (weight/weight), while a clay loam will reach the permanent wilting point around 10% moisture content (weight/weight).The permanent wilting point varies with temperature, compaction/structure/pore arrangement, and the resulting ability of the soil to conduct water.

Dry Weather and Young Corn

Chad Lee and Jim Herbek, Extension Agronomists, University of Kentucky

A lot of corn is germinating and emerging across the state and these young seedlings find themselves in dry soil conditions. The Weekly Crop and Weather Report, released on April 30, 2012 documented that 56% of the corn crop had emerged. In addition, about 40% of the topsoil was short to very short on moisture.

Corn at the seedling stage does not require much water. Nebraska's Irrigation Management for Corn states that emerged seedlings (VE growth stage) use about 0.08 inches of water per day. Corn at the 4-leaf stage uses about 0.10 inches per day.

The upper six inches or so of the soil is where the critical water is being held for these young seedlings. Fields that received tillage (even the minimal "vertical till" systems) are drying out faster in the seeding depth area than fields that are in no-tillage. If we do not receive rain for an extended period, then the tilled fields are most likely to see water stress problems first.

Even if conditions get dry enough to hinder seedling growth, yield losses typically will not be more than 20% on water stress before tasseling, according to Arkansas' Corn Production Handbook.