Controlled deficit irrigation – effects on growth and water relations of Daucus carota L. roots

Regulated deficit irrigation (RDI) comprises controlled reduction of irrigation during certain phases of plant development, accepting minor yield reduction but maximising net returns. To optimise RDI, plant response-based irrigation scheduling may be essential. For this, the knowledge of plant reactions to soil water regimes is indispensable. In field trials (randomized block design, 3 repetitions), ‘Nanthya’ carrots (F1-hybrid) were grown at 20, 40, 60 and 80% field capacity (determined by TDR sensors), yielding soil water contents of 5.1±0.2, 6.2±0.8, 10.1±0.5 and 11.2±0.2% (controls). To guarantee constant controlled soil water contents, plastic rain shelter (76% transparency) were applied. Plots were irrigated if necessary. Treatments started 23 d after sowing (DAS), first sampling was 91 DAS, while final harvest was 106 DAS. On each date, fresh and dry mass, water content, water potential, osmotic potential, turgor and stiffness of carrot tubers were analyzed. Root fresh mass (n=20 carrots per treatment) was higher at high water availability only at the 1st sampling but not at the final harvest. Here, water regime did not affect yield. At this time, root tuber water potential was lower than at the 1st sampling and it was also lower at low soil water availability (20%, 40%). Similar results were obtained for the mean osmotic potential. These variations partially resulted from osmotic adjustment (at 1st harvest) and from a lower root tuber water content at the final sampling. The generally higher modulus of elasticity at this date indicated water volume-independent cell wall-stiffening, i.e. elastic adjustment. The presented results point out that moderately reduced (by 20%) irrigation of carrots does not affect their yield, while pronounced water shortage may induce physiological adjustment.