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Controlled release phosphate fertilizer shows promise

Applying phosphorus (P) fertilizer with seed is important for improving fertilizer efficiency and promoting early crop growth.


November 19, 2007
By Donna Fleury

Topics

12aApplying phosphorus (P) fertilizer with seed is important for improving fertilizer
efficiency and promoting early crop growth. However, the amount of P that can
be safely placed in the seedrow is limited and can be an issue with more sensitive
crops such as forages. As a result, producers often struggle with how to optimize
phosphate nutrition without compromising germination and emergence.

Researchers at the University of Saskatchewan are comparing a polymer coated,
controlled release P fertilizer (CRP) with conventional mono-ammonium phosphate
(MAP) fertilizer. The CRP is a concept product from Agrium. The research is
comparing the fertilizers placed in a seedrow at different rates, and their
effects on emergence, yield and P uptake.

"In our research, we're comparing different rates of seed-placed CRP in
comparison to conventional P fertilizer with a variety of crops," explains
Dr. Jeff Schoenau. "This is an extension of some work we were doing the
year prior, looking at rates of regular P fertilizer that can be safely placed
with the seed of various crops. With the trend towards low disturbance seeding
systems and low seedbed utilization configuration, the increased risk of injury
from seed-placed fertilizer is of particular concern."

The research is also trying to develop maximum safe rates for crops such as
mustard, alfalfa brome grass and canaryseed, for which there is little current
information available.

CRP, like ESN – a slow release nitrogen – uses a polymer coating
applied to the phosphate granule. The polymer coating controls the release of
the P into the soil and soil solution. The controlled release brings other benefits,
outside of the potential for improved seedling safety.

"Controlling the release of P, for example, can improve P use efficiency
because soil reactions with applied fertilizer P are reduced, thus improving
the potential for plant P uptake," explains Ray Dowbenko, an agronomist
with Agrium. "In western Canada, our soils have a great deal of calcium
and magnesium within them. Fertilizer applied P reacts with calcium and magnesium,
forming less soluble P compounds, making the applied fertilizer P less usable
plant P forms." The CRP has the ability to overcome that problem.

The University of Saskatchewan project, which began in 2005, is being conducted
in the laboratory and in growth chambers, under conditions that would be found
in field situations. There are 11 different crops being compared in the project:
wheat, oats, canola, yellow peas, chick peas, pinto bean, flax, oriental mustard,
alfalfa, canaryseed and brome grass. The final results of the second year of
study are not yet available.

"One of the biggest differences we're finding so far between conventional
MAP and CRP fertilizer, is that you can put on significantly more seed-placed
P using CRP without any crop injury," explains Schoenau.

For example, with conventional MAP some injury was observed in canola at rates
of 30kg/ha of P2O5 and higher,
but with CRP rates, more than double that could be safely applied. "With
CRP we didn't see any significant negative impact even at rates up to 100kg/ha
of P2O5, or with crops such as
canola, flax, alfalfa, mustard and yellow pea, which are reported to be relatively
sensitive to seed-placed P." The preliminary results from 2005 and 2006
are similar.

In the past, P application rates for canola were usually around 20lb/ac. With
the move to higher yielding varieties, higher rates on P deficient soils may
be recommended, sometimes along with other starter nutrients like potassium.
CRP is showing promise that these higher rates could all be seed-placed safely.
"One of the places CRP has a lot of potential is for crops that are inherently
sensitive to high rates of P with the seed, and where seed placement may be
the only option," says Schoenau. "Another good example is forage crops,
such as brome grass and alfalfa, where you might want to put down enough P at
the time of seeding to supply that stand with enough P for a significant time
to ensure its longevity. For forages, the better safety this product seems to
afford would be advantageous if your fertilizer placement is in the seedrow."

In terms of P availability, there does not seem to be any significant differences
of P uptake at the lower application rates between conventional MAP as compared
to CRP. "However, the benefit of using CRP fertilizer due to its less harmful
effect on seed germination and emergence is evident at higher rates," says
Schoenau. So far, only wheat and canola results have been analyzed for the P
availability and yield response, the other crops are in the process of being
analyzed.

Researchers are waiting for final results, but so far it seems that CRP offers
a lot of promise. "Overall, we're finding that using CRP has the ability
to substantially increase the rate of P that can be safely placed with the seed
for a wide range of crops," says Schoenau. "However the use will depend
on each situation, the practicality of the application and an assessment of
the requirements, economics and other aspects."

Although CRP is showing positive results at the research stage, commercial
availability is still in the future for growers. "CRP is an extension of
the technology we use for ESN Smart Nitrogen," explains Dowbenko. "We're
currently focusing our limited resources on the successful introduction of ESN,
so the introduction of CRP is quite a ways in the future." Further research
on CRP is expected to continue over the next few years.

"CRP does provide increased seed safety for higher rates of P placed with
the seed and provides the potential for P reductions if we continue to see increased
P use efficiency from the CRP product research." This project is sponsored
by Saskatchewan Agriculture Development Fund, Potash and Phosphate Institute
and Agrium. -30-