EFFECT OF NITROGEN SOURCE AND CONCENTRATION IN RECIRCULATED SOLUTION ON INCIDENCE OF CUCUMBER MORTALITY BY PYTHIUM AND FUSARIUM CROWN ROT

Crop N nutrition has a major impact on plant susceptibility to various root path-ogens.
The objective of this work was to investigate the effect of N concentration and NH₄:NO₃ ratio in a closed-loop irrigation system, on cucumber (Cucumis sativus L.) mortality caused by pythium and fusarium crown rot. Pythium aphanidermatum-inoculated cucumber was used as a test crop.
Treatments included four NH₄:NO₃:urea ratios with the same total N concentration (9 ± 1 mM), and four N concentrations at constant NH₄:NO₃ ratio (30:70) in the fill solution.
The threshold EC for solution discharge was 3.5 dS/m.
Three days after planting the recycled solution in all treatments was inoculated with Pythium aphanidermatum. After 40 days of growth the mortality increased from 70 to 94% as the NH₄:NO₃ ratio was raised from 20:80 to 80:20. Repl-acing NH₄ with urea reduced mortality to 22%. At NH₄:NO₃ ratio of 30:70, increasing the total N concentration from 2 to 4-8, to 16 mM elevated the mortality after 40 days from 0 to 18-30, to 74%, respectively, and at 2 mM N no plant died until the end of the experiment.
During the first 20-25 days after transplanting, the NH₄ facilitated nitrite accumulation in the solution, which may have elevated the incidence of plants’ infection.
Later, increased NH₄ concentration in the solution reduced the solution pH and the plant Ca concentration, two factors that were associated with enhanced mortality.

International Symposium on High Technology for Greenhouse System Management: Greensys2007

B. Bar-Yosef, G. Kritzman, I. Levkovich, P. Klaering

pH, ammonium, calcium, nitrite, closed loop irrigation, perlite

https://doi.org/10.17660/ActaHortic.2008.801.185