Impact of container geometry and hydraulic properties of coir dust, perlite, and their blends used as growing media, on growth, photosynthesis, and yield of Golden Thistle (S. hispanicus L.)

Soilless cultivation is an expanding greenhouse cropping system with the potential to maintain and increase food security in challenging environments and under the eminent climate crisis, and to diversify our diet with crops that could not be sustainably cultivated in open fields. The replacement of soil with blends of organic and inorganic substrates has provided solutions but has also created challenges and opportunities, such as the need to match crop irrigation with their hydraulic properties and the specific requirements of each crop species. In this context, here we investigate the effects of the container type (growbag or pot) and the growing media used to cultivate Golden Thistle (Scolymus hispanicus L.) on crop performance and physiological parameters that may be affected by water and air availability in the root zone. The tested growing media were perlite and coir dust at ratios 4:0, 3:1, 2:2, 1:3, and 0:4, denoted as 4P0C, 3P1C, 2P2C, 1P3C, and 0P4C, respectively. To characterize substrates in terms of their hydraulic properties, the hydraulic conductivity (K), easily available water (EAW), and actual water content (AWC) in the substrate profile at container capacity were determined using HYPROP2. The cultivation of S. hispanicus L. on the blends 4C0P and 3C1Pincreased total plant fresh weight of both leaves and roots (FWL and FWR, respectively) compared to cultivation on sole perlite, while the use of shorter (growbag) container increased FWL:FWR ratio and, concomitantly, decreased in higher container (pot). Results show that the EAW significantly increases when the fraction of coir dust increases in the mixture, while K and AWC decrease considerably when the container height increases from 5 to 25 cm. These results show that in substrategrown crops, both the substrate and the container geometry have a crucial impact on water flux and water availability, and thus their proper manipulation can greatly contribute to maintenance of an optimal water and air status in the root zone of the plants. In conclusion, accurate estimation of the moisture retention curve (MRC) of substrates used in soilless culture is essential to design proper irrigation schedules tailored to crop water and aeration needs. Furthermore, the current study provides valuable information about the agronomic responses of tuberous species such as S. hispanicus L. to the hydraulic characteristics and the container geometry of growing media used in soilless culture systems.