Nursery irrigation regimes and establishment irrigation affect the postplanting growth of Limonium cossonianum in semiarid conditions

The influence of nursery irrigation regimes on the development of both the aerial part and the root after transplantation to the field in minimum management conditions was investigated in Limonium cossonianum, a Mediterranean ornamental plant. In the nursery period (57 days), plants were pot-grown in a greenhouse located near the southeastern coast of Spain. Drip irrigation and three irrigation treatments were used: T6, plants watered 6 days a week to reach the water-holding capacity; T3, plants watered 3 days a week; and T2, plants watered twice a week. The total amount of water applied per plant during the whole nursery period was 5.1 L (T6), 2.6 L (T3), and 1.8 L (T2). After the nursery period, T2 and T6 plants were transplanted to the field, and the development of the aerial part and the root system dynamics, the latter using minirhizotrons, were studied for 435 days. The regime involving the least amount of water in the nursery period produced the plants best adapted to stress after transplantation, as manifested in their greater root length to leaf area ratio and a higher percentage of brown roots. After transplanting to field, T2 and T6 plants showed similar root length density (RLD) in the upper (0-46 cm) and in the deepest (115-160 cm) layers of soil, but RLD was greater for T2 plants in the intermediate levels of the soil profile (46-115 cm deep), where the moisture content was low but sufficient for root development. The aerial part of T2 plants developed more and had a more compact appearance; they also had longer flowering stems than T6 plants. Root development was substantially lower when there was no establishment irrigation than when one establishment irrigation of 50 L·m-2 was applied. In a recovery experiment 415 days post-transplanting and after 76 days without rain, root growth was reactivated by re-irrigation more rapidly in T2 than in T6 plants, confirming the positive effect of hardening in the nursery.