Citrus industry is a prominent agribusiness in Brazil, generating thousands of direct and indirect jobs and a substantial income to all in the production chain. Citrus represents almost 50% of the country’s fruit production (Brazilian Ministry of Planning, Budget and Management, 2012). Brazil is the world’s largest orange producer with a cultivated area of 580,770 ha and a production of 15,384,048 t in 2011. In addition, Brazil is the largest exporter of frozen concentrated orange juice with a revenue of U.S. $3.2 billion in 2012 (Brazilian Ministry of Development, Industry and Foreign Trade, 2012).
The success of the Brazilian citrus industry can be attributed to the use of high-quality seedlings, critical for maximum yield and health of orchards. The State of São Paulo banned the commerce and transportation of citrus rootstocks and citrus plants produced in field nurseries (Gonçalves et al., 2011), establishing a seedlings production system based on certified nurseries using screen houses that follows strict sanitary regulations. The mandatory use of antiaphid screens for protection against pests and disease vectors allows the production of healthy seedlings, permits traceability, and guarantees genetic quality, reducing disease spread in the field and increasing both tree longevity and productivity (Carvalho et al., 2005).
Manual overhead irrigation is used in 92% of the nurseries (Almeida, 2003; Salvador, 2010). This irrigation system involves overestimated irrigation volumes and high frequency to guarantee adequate substrate moisture (Ferrarezi et al., 2014). Mismanaged irrigation can increase plant losses and lead to uneven growth as a result of poor uniformity in substrate water content (Augusto et al., 2007; Landis et al., 2006). Manual irrigation systems also promote excessive water loss resulting from runoff and salt accumulation with potential to contaminate surface and groundwater (Soares, 2003).
As an alternative, subirrigation applies water to the bottom of pots using the substrate capillary action to wet the roots. The system has zero runoff (Uva et al., 2001), provides higher substrate soil moisture (Geneve et al., 2004), improves root water distribution, and induces greater root development (Augusto et al., 2007). One of many advantages of subirrigation is the maintenance of uniform substrate moisture. Excessive or deficient substrate water content levels negatively influence plant growth (Fachini et al., 2004; García-Sánchez et al., 2007). Subirrigation also has the potential to improve vegetative growth of citrus rootstocks (Teixeira et al., 2009) and shorten the crop cycle with minimal water wastage (Landis, 2005; Verdial et al., 1998). Moreover, this system eliminates the disposal of water with nutrients and pesticides into the environment because it is a closed system that recycles nutrient solution (Million et al., 1999).
Although subirrigation has a number of advantages over manual methods, improper use can result in increased salt concentration in the substrate surface (Richards and Reed, 2004) and changes in the root/shoot ratio of citrus rootstock seedlings in cases of prolonged saturation (Hartmond et al., 1987). This can result in lower specific root area and inhibition of seedlings canopy development, delaying the plant development (Ranney et al., 1991).
Roots under water saturation or drought stress for prolonged periods promote alterations in leaf gas exchange, resulting in morphological changes and hormonal imbalance in plants (Sojka, 1992). Irrigation management of nursery crops must address plant water requirements, which vary throughout different growth stages (Fachini et al., 2004). These changes occur as a result of a microclimate generated in a controlled environment (Machado et al., 2005; Pimentel et al., 2007) and the nutritional management used by the growers (Bañuls and Primo-Millo, 1995). These factors influence the plant physiology and, therefore, their growth, specifically shoot height and stem diameter, which are useful characteristics for transplanting citrus rootstock seedlings for grafting.
The School of Agricultural Engineering (FEAGRI) from the University of Campinas (UNICAMP), in Campinas, São Paulo, Brazil, has been performing studies since 2006 that aim to develop subirrigation equipment that can be used for citrus seedling growers to improve the efficiency of rootstock production in conic containers during sowing and to reduce the environmental impact. We developed a prototype tray, the “capillary irrigation equipment,” to apply subirrigation on citrus rootstock seedlings production. This tray consisted of a closed reservoir in the bottom connected to polyvinyl chloride (PVC) pipes where the containers were inserted. The equipment was tested regarding to its application on Rangpur lime seedling production.
Our objective was to evaluate the effect of subirrigation applied by a prototype tray on growth, 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.
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