The drought of 2000-01 continues. Parts of central Florida have had a rainfall deficit of 18 to 24 inches over the past 18 months. The Climate Prediction Center in Maryland has predicted that rainfall through March, 2001 will be below normal. This could mean that our normally dry season could be drier than usual. It is ironic that as recently as February, 1998, parts of Florida had extensive flooding because of El Nino rains.

Because of the drought of 2000, much of the fruit is smaller in size and the crop estimate for oranges was lowered in December by 11 million boxes, or 4.6%. This demonstrates that, in spite of all the irrigation that was done, yield and fruit size are strongly influenced by the rainfall Florida receives. As Florida continues its rapid growth, competition for water between urban areas and agriculture will become more intense. Additional water restrictions are likely with more pressure on agriculture to further conserve water.

What can you, the grower, do when water supplies are tight? How can you take best advantage of what little rainfall there might be during a drought? Below are listed some things for you to consider that can help stretch your water supplies:

-- Do not overirrigate in the winter or spring. Earlier work showed that irrigation doesn't need to commence in the fall or winter until available water is 50 to 66% depleted. In the spring, irrigate at 25 to 33% depletion.

-- Know the general irrigation requirements for your grove and soil. Table 1 shows that trees use relatively little water during the winter months. Because of shorter days and cooler weather, average daily evapotranspiration (ET) for December and January is 0.07 inch/day. If the grove has 140 trees/acre (e.g. 25 x 12.5 foot spacing), trees use about 14 gallons per tree per day during those months. If the tree density is 200 trees/acre (e.g. a spacing of approximately 20 x 11 feet), those trees would use about 9.5 gallons per tree per day in those months.

-- Use tensiometers or some device that gives an indication of soil or plant water status. Tensiometers measure in units of tension (centibars or kilopascals) that indicate how tightly water is held in the soil. From August through January, you don't need to irrigate with microsprinklers until 50% depletion, which corresponds to a tension of about 15 cbar on the ridge and 30 cbar on the flatwoods. In the spring when irrigation is more critical, irrigation should start at 25 to 33% depletion which corresponds to a tension of around 10 cbar on the ridge and 15 cbar on the flatwoods. Tensiometers should be placed at depths of 6 and 12 inches on the ridge and flatwoods. On the ridge, an occasional tensiometer can be placed at 18 or 24 inches to see if water is getting to roots at that depth. Other devices estimate soil water content instead of tension, and water content levels can be calculated to fit the depletion points indicated above.

-- Have adequate irrigation coverage underneath the tree canopy. If a microsprinkler system has one jet per tree and 140 trees/acre, a system with 10-foot diameter emitters covers only about 25% of the total land area. Since roots spread throughout much of the entire grove floor in a mature grove, this spray pattern would irrigate only a fraction of the total roots. The majority of the roots are in the top 3 feet of soil on the ridge. In a drought when there is very little contribution of water from the non-irrigated zone, it is tempting to run the system for a long time to make up for the lack of rainfall. This would drive the water deeper into the soil. It may make you feel better, but irrigating for long durations wastes water by moving it below the root zone.

-- Consider partial deficit irrigation in the winter. Mild water stress in the fall and winter can help improve flower induction. Temporary leaf wilt for a short time at midday is acceptable, but irrigate periodically to avoid severe wilt. Do not stress the trees too much because excessive stress can weaken the tree and reduce cold hardiness. If you provide for daily water needs, but do not fill up the entire soil profile, rainfall can be more effective. If irrigation is done just before a rain, that rain can essentially waste the irrigation water by driving some of it below the root zone.

-- Inspect the irrigation system. After harvesting and ground spray operations, emitters can be damaged or lines can be broken. All emitters need to be operating whether they will be used for frost protection or regular irrigation. In freeze-prone areas, elevated microsprinklers are a good idea; but in drought times, it is best to have the microsprinkler near ground level to maximize coverage. In the spring, low hanging branches that distort the spray pattern reduce coverage and cause uneven soil wetting.

For reasonable growth and performance, trees need a certain amount of water. Following at least some of these practices can make for more effective use of the limited water you have. And let's hope that the drought ends soon.

This website is designed and maintained by Mark Ritenour, Ph.D.

Design contributions also provided by: Mike Burton, Jim Ferguson, Ph.D, Kenny Osteen, David Coleman, and Buddy Tignor, Ph.D.  This site was supported through FCPRAC grant #999-210 & #7276182-12.  For questions or comments, contact Mark Ritenour.