Improving Drought Tolerance of Bedding Plants with Controlled P Fertilization progress Report — june 1997
Date 5/28/97
Title of Project: IMPROVING DROUGHT TOLERANCE OF BEDDING PLANTS WITH
CONTROLLED P FERTILIZATION
Institute where work is being conducted: Pennsylvania State University
Amount of Endowment Grant: $10,000
Covering Period: 9/1/96 - 8/31/97
Anticipated Date of Project Completion/Final Report: 8/31/97
Individual Conducting Project:
(List Project Leader First)
Jonathan P. Lynch - Assoc Professor
fertilizer at adequate P (30 uM, 50 x lower than conventional) flowered
at the same time and had similar shoot size and weight to conventionally
fertilized plants. However, the roots of buffered P elongated to nearly
double the length of conventional P roots, distributing the roots more
uniformly through the available media. When plants were subjected to water
stress, the buffered P plants were better able to extract moisture from
the media. In addition, buffered P plants lost water more slowly as a result
of reduced leaf area. This change in leaf area did not detract from the
appearance of the plant. On the contrary, buffered P plants appeared more
compact. The use of buffered-P fertilizer shows promise as a technology
for improving bedding plant quality while providing a convenient method
of fertilization.
Objective: To evaluate the ability of solid-phase-buffered P
fertilizer to improve crop tolerance to postproduction drought stress by
improving water use efficiency.
Results
Experiments in Seramis: Seramis, a granular clay product with
high porosity and high water- holding capacity, was used in some experiments
because it allowed us to easily remove the media from the roots and investigate
root length and branching. Marigold seedlings were grown in high (1.5 mM,
medium (30 uM) and low (10 uM) phosphorus in 4″ pots. High P was provided
by ammonium phosphate at 100 ppm. Medium and low P were supplied by our
alumina-buffered fertilizer at I% by volume of media. Plants were grown
in a greenhouse until maturity, defined as a few days before anticipated
flowering. There were no significant differences in flowering date among
treatments. Plants grown under adequate P had lower lateral root density
and greater root elongation than the control or deficient P plants. Enhanced
root elongation had the effect of distributing the root system through
a greater soil volume. Leaf area was significantly lower and plants appeared
somewhat more compact. The root-to-shoot ratio was higher in adequate and
deficient P plants than in controls, but deficient P plants were severely
stunted. Deficient-P roots had lower lateral root density than controls
and maintained root elongation equal to that of control plants. The drastic
reduction in leaf area and shoot dry weight, as well as the lack of enhancement
of root elongation as observed in adequate P plants, suggests that the
deficiency of P throughout the plant had become severely limiting to the
plant’s capability to undertake adaptive responses. Adequate P plants had
a higher photosynthetic rate per leaf area than either deficient or control
P plants, both before drought and after drought stress and rewatering.
This indicates that adequate P plants, but not deficient P plants, can
compensate for their reduced leaf area with higher photosynthetic rate,
resulting in adequate photosynthate for growth and development.
Experiments in peat: By growing marigold plants in peat and measuring
water loss gravimetrically during drought, we showed that plants with reduced
phosphorus availability transpire less than plants with control P nutrition.
This could be explained by their smaller leaf area, which is a common response
to reduced P. Deficient P plants lost more water to evaporation, probably
because the soil surface was more exposed due to the very reduced leaf
area in these Plants. In a long term drought experiment, plants were supplied
with half their normal water requirement At the end of 3 weeks, when plants
were beginning to look stressed but were not visibly wilted, variables
related to water status were measured. Adequate and control P plants had
extracted about the same amount of water from the media, and deficient
P plants had extracted less, probably because their growth was severely
inhibited. Leaf osmotic potential, which indicates solute accumulation
in leaves, increased as P decreased in well-irrigated plants. After three
weeks of drought, control P plants had accumulated more solutes whereas
no changes were found in adequate P plants and deficient P plants, which
may suggest a greater degree of water stress in this treatment.
Future plans: Our experimental work on this project is complete
and we are currently preparing manuscripts for publication. We will also
write an article for a trade publication to disseminate this work to growers.
We now would like to extend this technology to N and K, in order to generate
a complete buffered fertilization regime for container production (not
part of this project).
Benefits for industry: We had previously shown that the use of
an alumina-buffered phosphorus fertilizer provides adequate phosphorus
for plant growth while reducing P leaching by about 97%. After a chance
observation that low (but adequate) P fertilized plants wilted more slowly
than conventionally fertilized controls, we have undertaken research demonstrating
improved drought tolerance when P fertilization is reduced from conventional
levels (1000 - 1500 PAW to a much lower but steady supply of 15-50 uM P
released by the alumina-buffering system. We have investigated this response
in detail in marigold (this project) and have shown that it also occurs
in impatiens and poinsettia. Penn State has patented this technology and
is seeking an industry partner for commercialization. If a commercial product
can be developed and marketed, the industry will have a convenient and
environmentally friendly means for providing optimal P for plant growth
while improving quality and drought resistance.
