The "Pot-in-Pot" System Enhances the Water Stress Tolerance Compared with Above-Ground Pot

Abstract

In the nursery, plant cultivation in pots or containers is a very common practice. On the one hand, this is to satisfy market demands for herbal plants and shrubs, and on the other because of its many advantages compared with ground cultivation. These advantages include lower stress for plants during transport and manipulation, space reduction in the nursery, the increased possibility of mechanization, a longer supply period, and greater transplantation success (Davidson et al., 1988). However, container cultivation is more affected by environmental conditions in the substrate-root complex, where extreme temperatures can negatively influence root development. The climatic season (winter or summer) will determine thermal stress through cold or heat. Container characteristics (material, color, form, drainage holes, etc.) also influence temperature in the root system, and many studies have looked at the use of different container types (Franco et al., 2006). In contrast to traditional cultivation in above-ground pots (AGP), pot-in-pot (PIP) production, introduced around 1990 in the USA (Parkerson, 1990), is a nursery production method that combines some of the benefits of both field and container production. In a PIP system, a holder or socket pot is permanently placed in the ground with the top rim remaining above. The container-grown plant is then placed within the holder pot for the production cycle (Ruter, 1998a). Previous research into PIP compared with above ground potting (AGP) determined that PIP improves biomass production (Ruter, 1998b), reduces root zone temperature stress (Young and Bachman, 1996) and enhances efficient water use by decreasing container evapotranspiration (Martin et al., 1999). An additional advantage over AGP is the elimination of extensive staking and blowover and a more easy mechanization. Recent studies by Neal (2010) reported that crabapple and lilac root or shoot mass were greater in PIP compared with another four production systems: field-grown, plastic container, bag-in-pot and above ground system. The disadvantages of the PIP system include high initial cost of pots and installation, potential drainage problems of socket pots in poorly drained soils, and the possibility of root elongation into the socket pot and surrounding soil. In PIP production, containers may stick together; the bottom of the insert pot may sag, causing an uneven base; and there is little or no spacing flexibility once the socket pots are established (Adrian et al., 1998). So, careful