It's time to re-think corn irrigation

Recently, a corn farmer asked me if he needed to irrigate his corn now. It was stressing but the old-time farmers told him it was good for corn to stress early since it made the roots grow deeper.

I jokingly asked him if he was talking about the old-time farmers in the 1950s when Georgia farmers averaged 25 bushels per acre or the old-time farmers in the 1960s when Georgia averaged 40 bushels per acre or the old-time farmers in the 1970s when Georgia averaged 50 bushels per acre. I wouldn't go to the 1980s since I wouldn’t want to be classified as an old-timer.

With a little bit of humor, I said if he is happy making 25, 40 or 50 bushels per acre, then by all means, let your corn stress early. But if he was interested in making optimum yields with record-high corn prices, then I would be irrigating.

I have a great deal of respect for what our forefathers did with the resources they had. But the times and technology have changed. Georgia averaged 130 bushels per acre in 2007, and I realize there are other reasons, including improved hybrids, better fertilization, improved weed control, and other factors for Georgia’s better corn yields.

But a major reason for our higher yields is that a greater percentage of our corn crop is being irrigated and more research is being conducted on irrigation timing.

Even with $4 per gallon fuel, it will still pay to irrigate corn with the current prices. Irrigation requires a relatively high investment in equipment, fuel, maintenance and labor, but it offers a significant potential for increasing net farm income. Frequency and timing of water application have a major impact on yields and operating costs.

To schedule irrigation for the most efficient use of water and to optimize production, it is desirable to frequently determine the soil water conditions throughout the root zone of the crop being grown. A number of methods for doing this have been developed and used with varying degrees of success.

In comparison to the investment in irrigation equipment, these scheduling methods are relatively inexpensive. When properly used and coupled with grower experience, a scheduling method can improve a grower’s chances of success.

Any plan typically is better than no plan or method at all, particularly with corn. A good plan pays dividends in terms of yield, water-use efficiency, and net returns. Growers who take a “wait for the crop to tell me” approach never get the greatest benefits for their irrigation.

In corn, irrigating too late causes yield loss while irrigating too much wastes energy, water, money and can leach nutrients beyond the root zone.

The most simple and practical way of scheduling corn irrigation is to use the moisture balance or check-book method. This helps a grower keep up with an estimated amount of available water in the field as the crop grows. The objective is to maintain a record of incoming and outgoing water so that an adequate balance amount is maintained for crop growth.

Growers will need certain basic information to use a check-book method. The soil type of the field, expected daily water use of corn, water-holding capacity of the soil, and a rain gauge or access to nearby rainfall information are the basic starting point items.

Check-book type methods can be enhanced with other different tools or methods such as the EASY pan method. The UGA EASY (Evaporation based Accumulator for Sprinkler enhanced Yield) Pan is designed to be easy to operate, economical and representative of the water used by the crop in humid areas.

A couple of the unique operating characteristics include the ability to read the unit from a distance and the fact that no record-keeping is required. This makes the Easy Pan a simple tool for scheduling irrigation.

The float-based mechanism is designed to represent both the effective root depth of a crop and the soil water holding capacity. The covering screen on the pan unit is designed to limit evaporation to a level similar to the evapotranspiration rate (water use) of a crop.

Also, expert systems such as Irrigator Pro (software by USDA), or other scheduling software is available to help you make decisions regarding when to irrigate.

Soil moisture measuring devices such as Echo and Watermark can be used in conjunction with corn growth curves to enhance irrigation scheduling as well. These devices provide instant readings of either soil moisture content or tension in the root zone and can identify exactly when water is needed to replenish the root zone.

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