Right Rate, Essential in 4R Nutrient Stewardship

Winter 2014/15, No. 2

RIGHT RATE, ESSENTIAL IN 4R NUTRIENT STEWARDSHIP

 

The 4R Nutrient Stewardship
principles are defined as using the right source of fertilizer at the right
rate, time, and place. All four of the Rs are combined, and important, when nutrients
are applied as fertilizer on a farm field. However, Right Rate, is especially
critical for the full benefit of a fertilizer application. Rate is a threshold
requirement, where if the threshold rate is not reached, other 4R factors of
source, time and place will not be able to compensate.

 

Most crops have a
concentration range for each required nutrient, and if a specific nutrient
concentration within the plant is within that range there shouldn’t be any
growth or yield limitation observed. However if the nutrient concentration is
too low in the crop plant tissues, nutrient deficiency symptoms and decreased
yields can result. For example the chart below shows the nutrient sufficiency
range for seedling corn.

 

Plant Tissue
Nutrient Sufficiency Ranges (%) for Seedling Corn, 2 to 12 inches tall.

Nutrient	Nitrogen (N)	Phosphorus (P)	Potassium (K)	Sulfur (S)
Sufficiency Range	3.5 – 5.0	0.35 – 0.80	3.3 – 5.0	0.2 – 0.5

Source:
http://www.agvise.com/wp-content/uploads/2012/09/Interpreting-Plant-Analysis-Reports.pdf

 

Too low of a rate is often
the cause of a specific fertilizer application combination being less
effective. A useful example is a field research project I was involved in on a
ranch near Invermere, BC.

 

The ranch owner mentioned to
his local fertilizer retail dealer that he thought from visual observation the
annual fertilizer applied on a mixed alfalfa-grass hay field (25% alfalfa and
75% forage grass) wasn’t very effective. The regular early spring broadcast
application was a 40 lb N, 30 lb P₂O₅, 40 lb K₂O,
and 15 lb S/A. After conducting a small plot research experiment it was determined
that the rate of nitrogen was too low to maximize forage growth and yield, and effectively
utilize the other nutrients being added. It was recommended to increase
nitrogen applications up to 70 lb N/A and keep the other nutrient application
rates the same. Too low of a nitrogen rate was limiting crop response, even
though the forms, timing and placement of fertilizer was appropriate.

 

The effect of using too low
of a rate on crop yields can be delayed, and by the time it is observed there
may have already been considerable economic loss. This is especially true for
phosphorus and potassium fertilization, as both of these nutrients are best
managed in the longer-term by maintaining plant available levels where crop
yield is optimized. In contrast, reducing nitrogen rates excessively on a
cereal crop will usually result in severe yield loss within one year.
Suboptimal rates of phosphorus and potassium, less than crop removal, result in
a gradual draw down of plant available soil levels. Reducing nutrient
application rates below crop needs will eventually cause crop yields to
decline.

 

Determining the Right Rate of
various nutrients to be applied is vitally important to the success of a nutrient
management program. I’m not suggesting that you can forget about applying an
effective form of fertilizer, or not applying the fertilizer at the appropriate
time or placement to get the needed nutrients to a crop. But too low of a rate
can result in a low yielding crop even if all other crop fertilizer and
agronomic practices are properly conducted.

 

– TLJ –

 

For more information, contact Dr. Thomas Jensen, IPNI
Director, North American Program, Ph: 306-652-3535; E-mail: [email protected].