By Tom Yeager
Water and fertilizers are controllable costs, but until you examine some of the factors that affect the efficiency of applying them, you might not be controlling those costs to your maximum benefit.

Here are some important management strategies regarding container plant nutrition and irrigation. Implementing any one of these management strategies could reduce your production costs or result in other benefits, such as a reduction in water and nutrient loss from containers. Nutritional management considerations

Understand substrate physical properties. A container substrate will hold or retain a given quantity of water based on its composition. The water-holding capacity of the substrate, or the amount of water held in the container after irrigation and drainage, is important to know. You don't want to apply more water to a container than it can absorb or hold. This leads to loss of nutrients along with water.

Reduce the leaching fraction. Leaching fraction is the amount of water leached from the container compared to amount of water entering the container. As the leaching fraction decreases, nutrient leaching decreases.

Consider the irrigation method. Cyclic irrigation applications, or dividing the total amount of water applied into small multiple applications, will reduce nutrient leaching.

Test fertilization methods. Plant growth response and container nutritional levels may vary depending on whether fertilizer was incorporated in the substrate or surface applied. Test representative plants to determine their response.

Consider container temperatures. The release of nutrients from some fertilizers is affected by temperature with more release of nutrients at high temperatures. Check the product label.

Monitor nutrients. Longevity of nutrients in the substrate will vary with cultural practices and environmental conditions. Consequently, monitoring the nutritional status of the substrate is the best way to determine when fertilizer is needed.

Use collection basins. Runoff water should be contained or collected in basins to prevent nutrient discharge into natural waters and to conserve water.

Irrigation management considerations

Check uniformity of irrigation water delivery. Several articles listed at http://edis.ifas.ufl.edu explain in detail how to measure uniformity of overhead and microirrigation systems. On a frequent basis, such as weekly, observe sprinkler rotation speeds, water angles, water drop sizes or measure water discharge pressure from sprinklers. This will determine if the irrigation system is working properly. Recording the time to fill the same sized bottle at different locations within an irrigated zone is a convenient way to check microirrigation system uniformity.

Check the amount of water applied. Cups or rain gauges can be placed in the nursery to record the amount of water applied. Jugs or bottles that receive water from microirrigation emitters are an effective means of monitoring microirrigated volumes.

Consider the plant's water requirement. Plants in the nursery should be grouped according to their irrigation requirements. At the Web site listed above you will find survey results from questions asked to nursery producers about irrigation requirements of many container-grown plants.

Consider effective water delivery. Plants grown in spaced (not pot-to-pot) 7-gallon containers or larger containers should be irrigated with microirrigation. This is necessary because under common production situations with overhead irrigation only about 20 percent of the applied water enters spaced 7-gallon containers.

Consider container temperatures. Spaced black containers can have the potential to evaporate about twice as much water as pot-to-pot containers. Therefore, plants of the same size in spaced containers will need more water than those in jammed containers.

Look at container designs. Squat containers hold more water than taller conventional containers of the same volume, so squat containers may require a longer duration between irrigations. Other container designs may function similarly.

© 2001 Branch-Smith Publishing