TITLE:
The Effect of Nitrogen and Phosphorus Ratios and Electrical Conductivity on Plant Growth
AUTHORS:
Laura Wiser, Theo J. Blom
KEYWORDS:
Tagetes erecta, Helianthus annuus, Lycopersicon esculentum, Solanum lycopersicum, Plant Growth Retardants, PGR
JOURNAL NAME:
American Journal of Plant Sciences,
Vol.7 No.12,
August
19,
2016
ABSTRACT: Environmental concerns surround the use of plant growth retardants (PGRs)
for plant height control, and non-chemical alternatives to PGRs can be labor
intensive and expensive. Macronutrient modification is a little-studied, yet
potentially effective method of controlling plant height. A number of studies
have suggested that phosphorus (P) limitation may restrict plant height. Anecdotal
evidence also suggests that using nitrate (NO3-), rather than ammonium (NH4+), as the principal
nitrogen (N) source may help control plant height. The primary objective of
this study was to evaluate different ratios of NO3-/ NH4+, NO3-/P and NH4+/P as well as electrical
conductivity (EC) on plant height and growth. This was tested in a hydroponic
system using marigolds, sunflowers and tomatoes. Initially, different ratios
were tested at an EC of 1.2 dS·m-1, followed by using the
same ratios at four ECs (0.6, 1.2, 2.2 and 4.0 dS·m-1) as a second objective. Although
ratios did, at times, limit plant height, responses were season and species
dependent, suggesting that modifications in plant nutrition, at the ratios used
in this study, may not effectively control plant height in hydroponic systems.
More consistent, yet species specific, height control was achieved by increasing
EC level.