CORN Newsletter: 2009-22, July 14, 2009

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C.O.R.N Newsletter 2009-22
July 14, 2009 - July 21, 2009

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Understanding Corn Crop Water Needs: Available Soil Moisture
by Peter Thomison, Robert Mullen


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Significant rainfall (0.5 to one inch or more) over the past weekend should ease concerns of growers regarding potential water stress in corn fields that are just starting to pollinate However, the rainfall was not uniform across the state and some areas, especially parts of NE Ohio, received only trace amounts of rain. Given the likelihood that rain for the next week is not great, how much can we rely on soil moisture to meet crop needs. Average water use by a corn crop during pollination and early grain fill is about 1/3 inch per day. Evapotranspiration rates in corn depend on temperature, humidity, wind, solar radiation and total leaf area of the crop. (Evaporation from the soil surface combined with transpiration from plants is evapotranspiration). When temperature is relatively low and humidity is high as on a calm, cloudy day, the evapotranspiration rate will be low. If temperature is high and humidity low as on a sunny, windy day, the rate will be high.

In areas that have received negligible rainfall during the past 3 to 4 weeks, how much of the corn crop’s water needs can be met by subsoil moisture?

The following is information from the National Corn Handbook - Chapter NCH-20 “Irrigation Scheduling for Corn-Why and How” https://engineering.purdue.edu/~abe325/RESOURCES/Irrigation%20Scheduling%20for%20Corn%20Why%20and%20How.pdf to help address these questions.

Soil textural characteristics dictate the water holding capacity, intake rate and drainage rate. Soils may have available water capacity of as little as 4 inches or may exceed 8 inches in 4 feet of soil. Table 1 gives the available-water holding capacities of ten different soil types. Soils also differ as to depth adequate for active root development; some have underlying layers of gravel or hard pan that would restrict root growth.

Information in this table might be used to estimate the number of days that moisture stored in the soil could “carry” a corn crop. For example, with a storage capacity of 1.8 in./ft, a fully charged silty clay loam soil might carry corn with a 3 foot rooting depth up to 18 days during silking and early grain fill stages (1.8 in/ft times 3 foot depth= 5.4 inches available water; 5.4 in. divided by 0.3 inch/A/day water requirement = 18 days). Although corn roots can grow as deep as 8 feet, when actively growing, corn obtains 90% of its water requirements from the top 3 feet of the soil profile.

A major factor determining the ability of corn to extract available soil water is soil compaction. In some Ohio corn fields, surface compaction, combined with excessive soil moisture early in the season, late plantings, etc. have resulted in corn root systems restricted to the top few inches of the soil profile. Shallow root systems make the crop especially vulnerable to drought. In addition to soil compaction, when relating the information from Table 1 to various Ohio soil types, keep in mind that other factors may influence water availability. Differences in soil organic matter and texture often occur at different rooting depths, for example the top foot of soil may be a silty clay loam but underlying layers may be clay, sand, or gravel.

Table 1. Available-Water Holding Capacity of Ten Soil Types.*


Soil type	Textural characteristics	Storage capacity
		in./ft.
0	Sandy clay corn	2.0
1	Silty clay loam	1.8
2	Clay loam	1.8
3	Loam
Low (2%)	Very fine sandy loam	2.0
O.M.	Silt loam
4	Loam
High (3%)	Very fine sandy loams	2.5
O.M.	Silt loam
5	Fine sandy loam	1.8
6	Sandy loam	1.4
7	Loamy sand	1.1
8	Fine sands	1.0
9	Silty clay
	Clay	1.6

*Source: Chapter NCH-20 “Irrigation Scheduling for Corn - Why and How”

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C.O.R.N. is a summary of crop observations, related information, and appropriate recommendations for Ohio Crop Producers and Industry. C.O.R.N. is produced by the Ohio State University Extension Agronomy Team, State Specialists at The Ohio State University and Ohio Agricultural Research and Development Center. C.O.R.N. Questions are directed to State Specialists, Extension Associates, and Agents associated with Ohio State University Extension and the Ohio Agricultural Research and Development Center at The Ohio State University.

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Issued in furtherance of Cooperative Extension work, Acts of May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture, Keith L. Smith, Director, Ohio State University Extension.

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