Watering fruit and vegetables — How much do they really need?

“How much water should I apply to my plants?” is an often-asked question. The simple answer is – just enough.

Drip irrigation system in cucumber.
Drip irrigation system in cucumber.

“How much water should I apply to my plants?” is an often-asked question. The simple answer is – just enough (the Goldilocks Principle). Too much and too little both lead to problems. The difficulty comes in defining “just enough”. Growers often want a single figure they can use all season and it just does not work that way given all the factors that come into play.

Soil Type plays a major role in irrigation amount and strategy. Course textured, sandy soils don’t hold as much water as fine textured, silt or clay soils. Therefore, sand-based soil need watering more often, faster and for shorter periods. Long events on sandy soil lead to leaching nutrients beyond the root zone, and faster time in a drip irrigation situation allows water to spread out and wet a larger area. Conversely, silt and clay soils need slow watering to prevent run-off and longer watering times, but less often since their greater surface area in a similar soil volume allows for increased water retention.

General climate is also a consideration. Factors such as temperature, humidity, light intensity, wind and day length figure in. In a consistent climate like California, daily or weekly needs are easier to predict, but in a climate like Michigan, these factors vary widely from week to week and even day to day during the growing season. High temperature, light, wind and low humidity all increase plant water needs. Evapotranspiration values in Michigan can change greatly from one day to the next.

Plant density and plant stage are significant in water use requirements. It makes sense that the more plants per acre, the greater the water demand. Smaller plants have less demand than larger plants. To obtain maximum economic quality and yield, fruiting plants during fruit sizing will require more water since fruit is 90 percent+ water.

The best way to determine plant water needs in any growing situation is not to guess but to actually measure how plants draw water from the soil. Estimates can be obtained from daily evapotranspiration tables but actual readings are best obtained through installation of soil moisture monitoring sensors. There are several types on the market ranging from relatively inexpensive tensiometers to more expensive computer automated capacitance systems. Attendees at Michigan State University’s Agriculture Innovation Day will have a chance to view various types of soil moisture sensors installed in vegetable production systems. They will be able to make comparisons between the systems and hear a discussion on how soil texture affects sensor readings.

MSU Agriculture Innovation Day: Focus on Fruit and Vegetable Technologies, 8:30 a.m.-5 p.m. June 28 at the MSU Southwest Research and Extension Center in Benton Harbor, Michigan, offers a variety of fruit, vegetable and grape growing technologies, including the latest information on pollinators and equipment. The event has been approved for Restricted Use Pesticide Credits (6 credits) and Certified Crop Advisor CEUs in Integrated Pest Management, Crop Management, Soil and Water Management and Sustainability. For detailed session descriptions, visit http://www.canr.msu.edu/msu_agriculture_innovation_day/  or contact Ron Bates at batesr@msu.edu.

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