 |
Agri-Gro and Plant Nutrient Interactions
David N. Sasseville, Ph.D.
207 Foster Hall
Lincoln University
Jefferson City, Missouri 65101
Introduction
Plants require sixteen essential nutrients. Thirteen of these are
provided by the soil or growing media. Agri-Gro is a product sold to
reduce fertilizer usage by increasing nutrient availability in the soil
by microbial and enzymatic activity and as a supplemental micronutrient
fertilizer. This study is an initial step in understanding the mechanism
whereby Agri-Gro is able to increase yields with crops.
Procedures
In 1999, a greenhouse study was conducted at Lincoln University in
Jefferson City, Missouri using tomato plants grown in pot culture.
Growing media was a clay loam soil taken from a Central Missouri site
and mixed with washed pure quartz sand. The treatments included Agri-Gro
applied according to manufacture recommendations for tomato plants, and
fertilizer treatments of complete Hoagland fertilizer solution,
macronutrients alone, and micronutrients alone. The plants were
harvested on three separate dates with soil and tissue analyzed for
nutrient composition and dry weights of tissues determined. The first
harvest was during vegetative stage, the second during flower initiation
and the last harvest was conducted shortly after initial fruit
maturation. A randomized complete block design was used with 10
replications.
Results and Discussion
The key findings of this study include:
- Agri-Gro significantly increased the availability of boron, iron and
zinc in the growing media (soil mixture), the concentration of boron and
iron in the vegetative tissues was increased by Agri-Gro, but the total
quantity of these nutrients taken up by the plant on a whole plant basis
was not affected. The soil used for this study already had adequate
levels of these nutrients for the plants’ needs and thus the additional
amounts were not used by the plant, but primarily accumulated in the
soil. Consequently, the other observed effects of Agri-Gro cannot be
attributed to the application of these fertilizer nutrients, but to
other active components of Agri-Gro.
- The vegetative component of the plants (as measured by dry weights)
was slightly smaller with Agri-Gro than to the control. Possible
explanations include:
a) Reduced nutrient availability at the very early growth stages of
plant growth when Agri-Gro was applied. Since Agri-Gro stimulates
microbial populations, these organisms tie up plant nutrients causing
reduced nutrient availability. The greatest effect occur upon initial
application and stimulation of microbial growth. As the microbes die,
these nutrients again become available to the plant at a later stage of
development.
b) Growth regulating compounds within Agri-Gro itself or by the
stimulation of production of these compounds by soil microbes by
Agri-Gro.
- The smaller size of the plant was not reflected in the fruit yield
with Agri-Gro; in fact, yield was significantly increased with Agri-Gro
on the initial harvest. The concentration of nutrients in the fruit was
significantly higher with Agri-Gro, but Na was significantly reduced.
The quantity of several nutrients which had moved into the fruit was
significantly higher with Agri-Gro treatment. These included N, S, B,
Ca, Cu, K, Mg, P and Zn. The soil concentration of nutrients with
Agri-Gro greatly dropped during the third harvest, but the quantity of
nutrients in the vegetative tissues were not greatly increased
indicating that the nutrients taken up from the growing media were translocated to the growing fruit. The limitation in this data is that
the plants did not complete their normal productive life cycle to be
able to compare the total yield production from the crop.
- In addition to boron, iron and zinc, Agri-Gro resulted in
significantly higher soil concentrations of N, Ca, Cu, K, Mg, Mn and P
in the growing media than untreated plants and soil. And with the
exception of Mn, these same nutrients had similar or significantly
greater concentrations of nutrients in the vegetative tissues with the
use of Agri-Gro. Possible explanations for these results are:
a) Agri-Gro enzymes or microbes stimulated by Agri-Gro are "mining" the
soil by making more nutrients available from the exchange sites on the
soil, especially calcium, potassium and magnesium. This is supported by
the nutrient treatment that received no macronutrients (N, P, K, Ca, Mg
and S). Agri-Gro resulted in an increase in available macronutrients in
the soil indicating a "mining" effect of Agri-Gro for the cations NH, K,
Ca and Mg. The presumed effect here is to stimulate cation exchange or
release off the soil particles. Additionally, the concentration of
available P increased with Agri-Gro treatment over the three harvest
dates, but decreased over the same harvest periods without Agri-Gro. It
would be expected that the P levels would decrease over the harvest
dates as the plants grew, but the increase in P levels indicate that
Agri-Gro is making P more available possibly by enzymatic action or
promotion of microbes with enzymatic activity for P.
b) Agri-Gro is interacting with the applied fertilizers to retain them
in the soil in a more available form. Similar processes as above may be
able to keep applied nutrients more available to plants, e.g. keep from
being bound to soil particles or converted to unavailable chemical
compounds.
c) The nutrients tied up by the increased number of soil microbes are
released by the dying microbes causing more available nutrients over
time.
- Another interesting observation was that while Agri-Gro promotes
increases in cations, Na was consistently lower in Agri-Gro treated
soils and plants. This may be worthy of further investigation with
saline soils since high Na competes with K for uptake by plants.
Conclusions This study indicates that Agri-Gro has potential to reduce fertilizer
application to crops, and that the effects of Agri-Gro go far beyond its
micronutrient content. With soils having adequate or near adequate
micronutrient content, the greatest benefit is the increased
availability of both macronutrients and micronutrients. Maintaining high
levels of micronutrients and macronutrients, especially K, in the
growing media until the plant needs them for fruit and seed development
may play a critical role in the value of Agri-Gro to these crops.
Agri-Gro also has potential to reduce environmental pollution by more
efficient utilization of fertilizer nutrients and thus the potential
reduction of applied fertilizers. Traditionally, fertilizers have been
applied in large quantities early in the season (e.g. preplant), only to
have a high percentage of the fertilizers lost to leaching, volitization,
and being tied up by biotic and chemical reactions. The use of
micronutrients, enzymes and microbes such as provided by Agri-Gro may
offer a real opportunity to reduce the environmental impact of crop
production while at the same time increasing the efficiency and
profitability of crop production. Further research is needed to better
understand the mechanism whereby Agri-Gro is able to accomplish this, as
well as how to maximize the benefit of Agri-Gro to get the most
efficient use of all fertilizer nutrients.
Research conducted by Dr. David Sasseville, Lincoln University |
|
