Winter 2014/15, No. 2
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].