Automated ebb-and-flow subirrigation accelerates citrus liner production in treepots

Abstract

Over the past decade, citrus production has sharply decreased in Florida because of citrus greening or Huanglongbing (HLB), a disease that reduces fruit yield and quality and eventually kills the citrus trees. With the increased mortality and need to resetting trees, the demand for healthy trees from citrus nurseries has risen drastically in the last few years. To meet the demand and accelerate tree growth, the citrus nursery industry should use modern horticultural practices such as more efficient irrigation methods, fertigation, and more vigorous rootstocks. This study evaluated the effect of subirrigation systems in tree production time, water and fertilizer inputs, and plant growth of commercial citrus rootstocks cultivated in treepots. We tested five irrigation methods [three ebb-and-flow subirrigation systems triggered at specific volumetric water contents (θ, 0.24, 0.36, and 0.48 m3 m−3), capillary mats, and a conventional drip irrigation system], and six commercial rootstocks (Kuharske, UFR-2, UFR-16, US-802, US-812, and X-639). The experiment was arranged in a split-plot design, with the main plot consisting of the five irrigation methods and sub-plots the different rootstocks. Ebb-and-flow subirrigation benches conserved 98% more water than conventional drip irrigation. Rootstocks grown under ebb-and-flow systems reached adequate stem diameter for grafting four weeks before the drip irrigation. Pummelo hybrids used in this study (UFR-16, UFR-2, and US-802) were 55% taller, 24% thicker, and 150% heavier on biomass production than the other varieties tested, irrespective of the irrigation method utilized. Although the substrate electrical conductivity was higher in all subirrigation methods, the values were below 1 dS cm−1, not causing symptoms of osmotic stress in plants. Our results show that the ebb-and-flow subirrigation system at θ of 0.24 m3 m−3 is the best option for accelerating citrus growth in treepots with peat: perlite substrate and to conserve water in Florida nurseries in comparison to capillary mats and drip irrigation.