The most important thing a farmer can apply to his crops is his shadow,” said Charles Stichler at the Sixth Annual Irrigation Conference and Trade Show held recently in McAllen, Texas.

A farmer has to watch over his crops from the day he plants. Yield potential in most crops is set in the first half of the growth cycle. The second half of the plant's growth cycle is meant to attain that potential. By the time the plants start to bloom, the die has been cast. “In cotton, at least 90 percent of the crop harvested is already on the plant at that point,” said Stichler, Extension Agronomist from Uvalde.

He reminded farmers that management intensifies under irrigation. “You must be sure your plants are receiving the right amount of water.” But does more water mean more yield? “No” said Stichler.

The key is in proper irrigation timing with the correct amount of water.

Many Texas farmers are relying on evapotranspiration, or ET rates, to determine when to irrigate. ET is a measure of how much water is used by plants. Since the ET rate depends on climate, it varies from location to location. Weather stations around the state collect climatic data, including temperatures, relative humidity, wind speed, solar radiation and sunlight intensity to determine the ET rate. By using the Internet and going to, a farmer can create a custom profile and access weather data from a weather station in his area, look up an ET figure for the plants he wants to water, and then quickly calculate when to start the pumps and when to turn them off.

Many factors determine crop water use, including heat and sunlight, humidity, wind, available soil moisture, soil texture, and leaf size and shape. Leaves play an important part in plant growth. They are the solar collectors: the more leaves, the more solar rays collected, and the more yield potential. Leaves are particularly sensitive to water deficits, which result in smaller cells and less leaf area.

Leaves not only collect sunlight but also act like wicks for the movement of water through the plant. When the water infiltrates the roots, they absorb the nutrients dissolved in the water and cool the plant.

Water and fertility management are inter-related.

“You can't replace water with fertilizer, but you can make it go farther,” said Stichler.

Adequate fertilization increases drought tolerance and allows for deeper root systems and earlier plant development. The plant cannot pick up nutrients unless the nutrients are dissolved in water.

The placement of fertilizer is important said Stichler. “You don't put feed in the wrong pasture. It doesn't do any good to feed the cows if they can't get to it.” For maximum uptake, fertilizer must be put where the roots will be.

An important consideration in irrigation is the soil infiltration rates. For instance, clay soil absorbs water slowly. A farmer should be sure water gets deep enough, down to the roots, and then he should water infrequently.

Stichler is a firm believer in minimum till. “The more residue, the better infiltration.”

Since sunshine is an important growth factor, Stichler advises narrow row spacing. “Don't waste your sunshine on bare ground.”

Crop stage is critical to irrigation timing, so a farmer must monitor his plants' development. Stichler warned against five irrigation mistakes a farmer could make:

  1. Failure to build deep soil moisture.

  2. Failure to use residue to increase infiltration.

  3. Irrigating too late in the reproductive stage of the plant.

  4. Failure to recognize physiological maturity.

  5. Failure to use narrow row spacing.