Re: How does density and nitrogen availability affect plants?
Date: Fri Apr 17 11:42:13 1998
Posted By: Eric Biddinger, Grad Student, Horticulture, Penn State University
Area of science: Agricultural Sciences
Your timing with this question is perfect!! We just finished
up a nitrogen experiment in a Horticulture lab I teach here at
First off, I have to ask a question. What exactly do you mean
by density? For the time being, I am going to assume you mean
number of plants in a given area.
The number of plants in a given area will determine amount of
competition for the available resources. Obviously, there is
only so much nitrogen, potassium, phosphorus, and other
essential elements in the soil. The more plants that share
that given block of soil, the less nutrients each plant will be
able to pick up. In addition, competition for water and light
(shading) should also be considered.
From an agricultural perspective, the objective with planting
densities is to maximize the yield. More plants will produce
more crop only up to a certain point. Above that, the plants
compete for resources causing a reduction in plant size and
health, thus reducing yield.
Nitrogen is a very important element to the survival of the
plant. It is a major component of, among other things, amino
acids, numerous proteins, and chlorophyll. Without nitrogen,
plants are unable to carry out some of the most basic functions
they need to survive.
A plant that does not have enough nitrogen exhibits the
- Restricted growth
- Generally yellow in color (chlorotic) due to a lack of
chlorophyll, especially in lower leaves.
- Stems, petioles, and lower leaf surfaces can be purple in
- Increased root mass in comparison to shoot mass (high root to
Misapplying fertilizer can lead to too much nitrogen, which
- Dark green color
- Abundant foliage and a restricted root system (low root to
- Flowering and seed production can be retarded, delayed, or
prevented all together.
Plants have mechanisms to help them survive when they encounter
the rather common condition of nitrogen deficiency. The plant
allocates its energy to making roots so that it can search more
soil at the cost of reducing foliage growth. On the other
hand, plants have no way to stop taking up nitrogen and no
place to store it. The response is the produce less roots so
it takes up less nitrogen and produce more leaves so it has
some place to use the excess nitrogen.
Like planting density, more nitrogen can only increase the
yield up to a certain point. There is a point called the
"economic threshold". What this means is that applying more
nitrogen will increase the yield, but will not produce enough
crop to offset the cost of more nitrogen. Due to the various
fertilizer needs of different crops, different soils, and
economic situations of farmers, this threshold is varies
Texas A&M has put together a good sight for identifying nutrient
problems and diseases on cucurbits (squash,
cucumbers, pumpkins, and the like).
Thanks for the question!
Eric J. Biddinger
Grad Student - Department of Horticulture
Penn State University
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