Growth and Physiological Responses of Rangpur Lime Seedlings Irrigated by a Prototype Subirrigation Tray

Abstract

Citrus rootstock production in Brazil commonly uses manual overhead irrigation systems to water plants. Manual irrigation systems present low efficiency, apply more water than needed, and result in release of nutrients and pesticides into the soil with a potential to contaminate groundwater. Closed irrigation systems that avoid the disposal of nutrient solutions like subirrigation can be used to increase production efficiency and reduce the environmental contamination. Our objective was to evaluate the effect of subirrigation applied by a prototype tray on plant growth and morphological and physiological responses of Rangpur lime (Citrus limonia Osbeck ‘Limeira’) seedlings subjected to different water levels in conic containers filled with pine bark substrate. We tested three treatments: T1) subirrigation with water reaching two-thirds of the container height (8 cm); T2) subirrigation with water reaching one-third of the container height (4 cm); and T3) control with manual overhead irrigation. Subirrigation resulted in higher plant growth of Rangpur lime seedlings. At 90 days after sowing (DAS), we observed significant effects of T1 over the other treatments on plant growth, as indicated by higher total dry mass (P = 0.0057), shoot/root ratio (P = 0.0089), shoot height (P = 0.0004), leaf area (P = 0.0005), and root length (P = 0.0333). The number of bifurcations was 400% higher in T3 than at the subirrigated treatments, which can lead to an increase in the labor costs for pruning. Seedlings grown under T1 presented leaf water potential 13% higher compared with T3 at predawn, which was the time of highest stomatal efficiency, presenting the lowest water loss, maximum stomatal closure, and higher transpiration at lower stomatal resistance. T2 plants displayed intermediate water status with a water potential 5% higher than T3. T3 plants showed a higher transpiration rate under maximum stomatal closure, reducing leaf water potential. The subirrigated treatment with water level of two-thirds of container height (8 cm) induced higher plant growth and shortened the crop cycle, anticipating the transplanting to the next phase (grafting) with the possibility of reducing production costs in the nursery.