During the past two years, the open hydroponics (OH) method of crop production has been intensively studied for proof of concept and adaptation as a new advanced production system (APS) for Florida citrus. The foundation of a successful OH system is based on early, high yields, made possible through 1) intensive fertigation, 2) balanced complete nutrition, and 3) high-density planting. The accelerated growth from optimal balanced nutrition and water relations achieved with precise computerized fertigation is a key component of the APS. When combined with high-density planting, the accelerated growth can potentially cut the time in half to economic production and the return on a new grove investment.
Results from replicated treatments obtained in a replanted 15-acre Hamlin orange block in a commercial grove setting demonstrated during the first year a 60% reduction in irrigation water requirement and an 83% reduction in fertilizer application was possible by using carefully regulated drip fertigation. Despite these input savings, canopy growth of the trees during the same period was 65% greater, resulting in a 9.9-fold increase in efficiency. In the APS treatments, significant reductions in nitrate-nitrogen concentrations were recorded in soil water leachates collected below the root zones of the trees. At no time in the first year did nitrate concentrations exceed the 10 mg/L maximum contaminant level in APS plots, while they frequently exceeded the limit in the conventional control plots. At the end of two years in the field, the APS trees produced their first small fruit crop in December 2010, which was 4.75 times greater than yields from the conventionally grown trees. Fruit quality was already good and passed all the required tests for juice processing (ratios of 16 to 19).
One Drop At A Time
• Keep the soil near field capacity (~zero water tension) with short duration frequent (drip) irrigations to wet the top 18 inches of soil.
• Inject fertilizer with most irrigations (100 to 150 parts per million N) to maintain a solution of readily available balanced nutrition in the root zone.
• If possible, apply the main fertilizer after sunrise and before noon, when photosynthesis and transpiration are at their peak.
• Use a complete, balanced nutrient formula (N, P, K, Ca, Mg, S, Mn, Zn, Fe, Cu, B, Mo, Cl) to maximize growth rates and improve plant fitness/disease resistance.
• Skip fertigation on rainy days, while soil is already near field capacity.
• Flush excess salts from the root zone during the dry season with plain irrigation water (three to four times normal irrigation amount every two weeks).
• Monitor nutrient concentrations in the leaf tissue and make corrections to the nutrient formula and fertilizing intensity as needed.
• Monitor and control insect pests frequently since they are attracted to the rapidly growing new leaf flushes.
For more information and frequent updates on this research, visit www.crec.ifas.ufl.edu.