Automated ebb-and-flow subirrigation for citrus liners production. II. Pests, diseases and nutrient concentration
2017
Ferrarezi, Rhuanito Soranz | Testezlaf, Roberto
Subirrigation has the potential to reduce water and nutrients losses in citrus seedlings production by recirculating fertilizer solution (FS) and eliminating improper disposal of salts into the environment. The objectives of this study were to evaluate the effect of an automated ebb-and-flow system on pest and disease incidence and nutrient concentration of Rangpur lime (Citrus×limonia) liners. Nutrients were determined on plant tissue (shoot and root), substrate, and recirculated FS collected on 121-L water tanks. The treatments were four volumetric water content (VWC) to trigger subirrigation (0.12, 0.24, 0.36 and 0.48m3m−3), three FS concentrations (25%, 50% and 75% of the fertilizer recommendation) and a control (nursery manual overhead irrigation using breaker nozzles), arranged in a completely randomized 4×3+1 factorial plus design, with three replications. The system was automated by 39 capacitance sensors connected to a data logger, multiplexer and relay drivers, which controlled submersible pumps inside 121-L tanks with different FS. Subirrigation was turned on when VWC dropped below the set thresholds. There was occasional appearance of leaf miners (Phyllocnistis citrella, Lepidoptera: Gracillariidae) and fungus gnats (Bradysia sp. nr. coprophila, Diptera: Sciaridae), and no diseases (especially Xanthomonas axonopodis and Phytophthora nicotianae). Different treatments resulted in changes on macro and micronutrients content in shoots and roots, substrate, and FS at 0, 30, 60 and 90days (p<0.0001). Higher FS concentrations increased the nutrient content over time (p<0.0001). There was a decrease in pH and an increase in electric conductivity on treatments with higher VWC and FS (p<0.0001). The substrate electric conductivity reached 5dSm−1 twice, demanding substrate washing by water application on treatments with VWC of 0.36 and 0.48m3m−3 and FS of 75%. Subirrigation is suitable for liner production in 56-cm3 cone-shaped containers.
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