10 Tips for Good Water Management By Charles L. Bethke

As many growers are facing water restrictions, now is the time to practice efficient water management.

Today, fresh water supplies for agriculture/horticulture are a serious matter. For some, future supplies are questionable. Many growers are faced with water use restrictions. It’s not a surprise that officials often feel that water is needed more for residents than for your crops. So what should a grower do? Learn, plan, conserve and optimize!

Here are 10 things to consider when striving to become water wise and efficient in growing crops.

Some growers collect the deflected rainwater in high-capacity tanks.

1. Know Where It Comes From — Secure Your Source

Understand your water source and know the vulnerabilities. Catastrophic events can disrupt water supplies for weeks or months. Surprising events (restrictions, breakdowns and disruptions to the flow) may limit the availability of water from normal sources.

In many areas, weather cycles have caused droughts, and sources have dried up or all water is diverted to “essential” uses. Be sure you learn all there is to know about your main water supply and the vulnerabilities. Establish a plan for an alternate source. Collected rainwater, ponds, creeks, wells, municipal supplies, recycling and reclaiming should be considered to ensure a constant supply. Know where your main and alternate sources are and what the quality of each is.

2. Know What Your Plants Are Drinking — Water Quality

Whether your water source is well or municipal, collected or reclaimed, know its properties. Testing frequently for irrigation suitability applies doubly when minimizing water use. Always opt to use water free of toxic materials like boron and sodium and low in total soluble salts. Very low alkalinity is a plus.

Remember that growing substrates tend to act like a filter absorbing, concentrating and holding minerals from applied water. Avoid interference from extra minerals and pollutants. They increase the possibility of salt build up and pH shifts. Bad water increases the need for flushing the substrate to leach away excessive undesirable salts. Remember nutrients can always be added to desired levels but take lots of water to remove. Be careful about what you give your plants to drink.

3. Keep It Sweet Not Salty — Proper pH and Fertilizer Rates

Start with a substrate that has the proper pH and good nutrient balance. Initially, a sufficient but low and optimally balanced nutrient charge avoids the need to use irrigation water to correct a problem. Keep injected fertilizer rates at the lowest optimal level. Use slow release and coated fertilizers sparingly.

Always remember that the release of soluble nutrients is greatest under warm conditions. When crops use water for cooling, soluble salt levels
concentrate and increase in the substrate.

Always avoid practices that assume water applications will correct a problem. Keep a close watch on pH and EC levels to keep the substrate sweet and not salty.

This calibrachoa has been exposed to water containing high alkalinity and salts, increasing the pH to undesirable levels. Excessive quantities of properly adjusted water can correct the problem.

4. What Is At The Root — A Good Substrate

A good substrate will act like a sponge, readily absorbing and releasing the most available water. Select materials that readily absorb and deliver water thus maximizing the use of applied water.

Many factors influence the selection of a substrate. Water use efficiency is rapidly becoming the most important factor. A good substrate must not shrink when dry. It must easily absorb water. Water-loving or hydrophilic materials that absorb applied water quickly, even when dry, are best. Surfactants can be used (see No. 6).

Blends that have high water holding capacity, while still providing sufficient air porosity, will be the best tool for efficiently delivering water to the plant. Finer textured materials usually have more plant-available water per unit volume than coarser and chunkier materials. Coarse materials typically have a poor ability, called hydraulic conductivity, to translocate water throughout the container. Materials that have good hydraulic conductivity when saturated (saturated hydraulic conductivity) or nearly dry
(unsaturated hydraulic conductivity) are best. They allow water to easily move through the substrate to the roots.

Some newly developed manufactured fibers, made from recycled materials, have exceptional ability to hold and deliver water while maintaining sufficient air porosity. They may help greatly in optimizing the available water at the roots.

5. Hold On To What You’ve Got — Optimize Container Capacity

How you handle a substrate and the containers you use will influence the water holding properties. The total amount of water held in the container after fully saturated is called the container capacity. The quantity of
plant-available water in a container is dependent on the size, depth and substrate conditions.

To make the most water available, the container should be the largest appropriate size holding the most possible substrate. To optimize both air and water holding porosity, the substrate should be pre-moistened before filling and slightly compacted.

Avoid nesting filled containers in a stack as that can reduce both air and water holding porosity. Deep containers lend themselves a greater gravitational pull to drain water. Handle your substrate properly and it will hold on to more of the water you apply.

6. Make The Water Wetter — Use Surfactant

The unique properties of water make it possible for life on earth. The molecular bonding angle of 108° provides many special properties. Among them is what is called hydrogen bonding, which contributes to producing surface tension. Without that special angle, water would not stick together at normal temperatures and it would evaporate instantly.

However, this surface tension can make water management difficult. As a result many dry substrates components do not readily absorb applied water. They are called hydrophobic (water fearing).

Other materials absorb water much more readily and are called hydrophilic. Using wetting agents or surfactants makes your water wetter by interference in the surface tension. It will move more freely in and out of the fine substrate matrix. Apply surfactants to your substrate and inject them into your water especially when using a hydrophobic blend.

Hand watering often wastes the majority of water applied.

7. Hit Your Target — Don’t Water The Sidewalk

The greatest amount of water is wasted when applied to surfaces other than crops. Flood or sub-irrigation with collection and re-circulating systems are among the most efficient.

Direct container watering through drip and mist emitters also is very efficient. Pot-to-pot hand watering can waste up to half the water applied.

Sprinkler systems can be inefficient. Benches and sidewalks often get more than half the water applied. Boom systems work best when good zone management is practiced. However, often much of the area covered by a boom has had the crops removed. Always remember that only the water that hits the target can be absorbed for use by the crop.

8. Stay in The Zone — Group Crops

Crops vary greatly in water demands. Some nurseries specialize in only growing crops for arid landscapes. Most growers have a variety of crops.

By grouping varieties into management zones; first by temperature requirements, then subdividing by light requirements, and further segregating by water requirements, one can apply only the minimum water needed.

The shaded zones help cool crops reducing water requirements and saving water. Buy grouping crops into management zones optimal water levels can be more easily maintained.

9. Keep Them Thirsting For More — Grow Dry

Occasionally, lush growth is desired but most often we want firm solid plants. Long before growth-regulating chemicals were used extensively, growers kept their plants thirsty to control growth. By keeping them on the dry side plants became firm and increasing in toughness. I know a grower that once instructed, “Geraniums love dust.”

Unfortunately with excessive drying peat-based substrates typically shrink, pulling away from the sides of a container. Rewetting is difficult and large volumes of water pore down the edges of the pot.

Monitor moisture levels closely and water before plants get too thirsty, but carefully avoid excess watering and leaching. Remember large containers will hold more water and dry more slowly requiring less frequent watering.

10. Not Just Blowing in the Wind — Minimize Evapotranspiration

Bright sunlight, high temperatures, rapid air-flow and low relative humidity all increase the need for water. The majority of water is used in transpiration for plant growth and leaf cooling. Some is lost by evaporation from substrate surfaces.

Together these water uses are termed evapotranspiration. It increases when the air humidity is low and sunlight is intense. Some growers monitor the water vapor pressure deficit in the air to predict transpiration rates. With high vapor pressure deficits plants use much more water to remain turgid and to cool its tissues.

During high light periods shading reduces the crop cooling requirements and also reduces the greenhouse ventilation requirements all while increasing the relative humidity and decreasing the vapor pressure deficit. Shading can greatly minimizes evapotranspiration and cuts down on ventilation requirements so the water isn’t just blowing away in the wind.

In Summary

In today’s world it is the growers responsibility to learn all that can be done to conserve fresh water resources. Plans to optimize water use will not only save water and possible related expenses but will demonstrate environmental responsibility.

Charles L. Bethke

Charles L. Bethke is a horticultural soils and nutrition consultant based in Williamston, Michigan. He can be reached at 517.655.3236.



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