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Water Conservation Methods for the Greenhouse

Steps

 

Commercial Greenhouses The following steps are provided to help greenhouse growers utilize water properly with the minimum amount of waste, while maintaining quality crops. The guidelines below are divided into three steps for ease of implementation. Step 1 should be implemented wherever feasible by all greenhouses. Step 2 is strongly recommended for implementation whenever physically and financially possible. Step 3 illustrates the ideal.

Irrigation of greenhouse crops is a critical, yet often overlooked practice. Waste or overuse of water is common, particularly when watering is mistakenly treated as the least precise of all cultural inputs. When relying on the "eyeball" or the clock when timing irrigation, crops often receive excessive amounts of water, creating runoff.

Step 1 - Reduce Wasted Water/Runoff

A. Group plants with similar water needs together to improve irrigation efficiency. Adjust individual sections of the irrigation system to avoid excess watering in some sections.

B. How Much to Water? The general rule of thumb is to apply 10 - 15% more water than the container will hold. This will help leach salts at each irrigation. Don't allow water to flow over the top of the container. The rate of irrigation must be low enough to allow the water to percolate through the growing media.

Make sure media has adequate porosity (well drained) as well as good water holding capacity. This will help minimize irrigation frequency.

 

Step 2 - Examine Efficiency of Irrigation System. Work towards adapting new irrigation technologies to production systems to help lower costs and reduce water waste or runoff. A well designed, efficient irrigation system is a large part of the water use reduction equation.

There are several means by which to supply a crop with irrigation water: overhead sprinkler, hand watering, drip or trickle irrigation systems, and subirrigation. Overhead irrigation and hand watering are typically more wasteful delivery systems. These systems also wet the foliage, increasing the potential for disease. Drip or trickle systems are more efficient and provide the greatest control over the amount of water applied.

Subirrigation (ebb and flow, flood floors, troughs or capillary mats) systems are extremely effective at reducing water waste. These systems also require half the fertilizer of overhead irrigation and lead to less disease as the foliage remains dry. However, they are expensive to install and water may need to be treated before reuse can occur.

When to water? There are several methods that can be used to measure media moisture levels.

Appearance or feel - many growers usually water when the media will crumble easily when compressed in the hand. Examine the media at several depths.

Tensiometers - these devices are made of porous cups attached to a vacuum gauge. The cup is inserted in the soil and filled with water. As the rooting media dries, water leaves the cup and the resulting tension is recorded.

Weight of media moisture - one pot plant on a bench is used as a control. It rests on a scale that is adjusted to trip a switch when the moisture level drops below a certain level. As the plant grows the setting must be adjusted to account for added plant weight.

Light Accumulators - these systems are based on the idea that increased light causes increased evaporation. A photoelectric cell and counter activate a solenoid valve when a predetermined level of light is received.

Soil Moisture Conductivity - several devices relate soil moisture to electrical conductivity. When the soil dries to a preset level, the electronic circuit activates the solenoid valve.

Step 3 - Collect and Reuse/Recycle Irrigation Water. Why capture runoff and recycle irrigation water: The benefits.

Many greenhouse operations across the country have already adopted capture and recycling systems. Whether voluntary or mandated these capture systems have environmental and monetary benefits. Many greenhouse and other horticulture production facilities that have adopted these practices state the most important benefit realized is savings on the cost of water. For others the most compelling reason for adoption has been to assure that an adequate supply of sufficiently high quality water would be available when needed during production.

Implementation of a new system means there will be an inevitable learning curve. Potential problems that may occur with recycled water systems can be easily avoided with careful planning and some monetary investment.

A common method of collection and reuse of water is the installation of retention basins, storage ponds, storage tanks and additional pumping capacity. Concerns, or potential disadvantages of these systems include build up of salts, chemicals, nutrients, and pH. These may then be recycled back onto crops, ultimately decreasing crop quality. Studies have also shown that water-borne pathogens such as Pythium sp. may be present in runoff water at relatively high concentrations. Sometimes these pathogens can be detected in recycled irrigation water at the point of delivery to crops. Unfortunately, there are no scientifically derived thresholds for levels of pathogens in irrigation water. Because of the potential that these water "impurities" may build up in recycled water over time, many growers err on the side of caution by decontaminating recycled water before reuse.

These potential disadvantages of using recycled water can be overcome by:

1. Monitoring salts, chemicals, nutrients and pH. Test irrigation water three times a year for salt levels, bicarbonates, and pH. Review the results before any fertilizer is applied.

a. If buildup of salts in recycled water becomes a problem dilute with fresh water.

b. Many growers use water treated through a process known as reverse osmosis (RO) to remove potentially harmful salts. The systems are relatively expensive but work well as a source of water for back blending. RO water has almost no nutrient value and if used over an extended period of time, growers may experience micronutrient deficiencies

2. Becoming proactive when dealing with water-borne pathogens such as Pythium, which ultimately cause root rot:

a. Increase the frequency of scouting of problem crops.

b. Remove diseased plants from the system quickly.

c. Monitor pathogen levels of irrigation water. Water can be sampled at different points to determine pathogen presence and levels. Tests to determine which pathogens are present can be conducted at some plant disease testing laboratories.

d. Water can be treated for disease organisms by retention and dilution, filtration, chlorination, ozonation, and/or UV light.

Costs associated with installation of holding ponds, tanks, pumps, and possible treatment systems eventually pay for themselves. However, the phasing in of these capture systems, will help spread out capital outlay over a number of years.

Obviously there is no single water collection process that will work for all greenhouse operations. Different greenhouses will have different water quality problems, different irrigation demands, and different abilities to deal with each situation. For some systems, complete decontamination may not be economically feasible. Each system will have to accommodate the unique requirements and conditions of the operation for which it is designed.

References:

Aldrich, Robert A. and John W. Bartok, Jr. Greenhouse Engineering. NRAES-33 Natural Resource, Agriculture, and Engineering Service. 1994.

Panter, Karen L., Steven E. Newman and Reagon M. Waskom. Pollution Prevention for Colorado Commercial Greenhouses. XCM -206 Colorado State University Extension

vonBroembsen, Sharon L. and Mike Schnelle. Best Management Practices (BMPs) for Nurseries to Protect Water Quality. In E-951, Water Quality Handbook for Nurseries, Oklahoma State University Extension Service.

vonBroembsen, Sharon L. Disease Management for Nurseries Using Recycling Irrigation Systems. Department of Entomology and Plant Pathology, Oklahoma State University Http://zoospore.okstate.edu/nursery/recycling/why.html

Waskom, Reagon M. Best Mangement Practices for Irrigation Practices. Colorado State University Extension, XCM 173 August 1994

Wilkerson, Don. Irrigating Greenhouse Crops. From, Texas Greenhouse Management Handbook. Texas Agriculture Extension Service.

Wilkerson, Don. Treating and Recycling Irrigation Runoff. From, Texas Greenhouse Management Handbook. Texas Agriculture Extension Service.


 

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