With a little effort, producers can ground truth their fertilize or manure application rates to determine if they are applying at rates for maximum yields, Montana State University researchers say.
A ramp calibration strip method to assess a range of nutrient application rates on annual or perennial crops was developed by Oklahoma State University, and has been adopted by personnel from Manitoba Agriculture, Food and Rural Initiatives.
For a ramp calibration strip, an area 10-feet wide by 80- to 120-feet long is marked in a representative area of the field. The strip is segmented into 10-feet long sections, or 100 square feet cells, with each cell receiving a different rate of fertilizer or manure.
Ideally, the rate would range from zero (untreated checks) to a high of fertilizer or manure. The rates are increased, or ramped up, at increments of 10-30 pounds of N or phosphorus (or any other nutrient of interest) per acre.
For example, in 100 square feel cells, each 10 pounds of nitrogen per acre increase requires an additional .8 ounces of urea (46-0-0). Each 10 pounds of P205 per acre increase requires .7 ounce of monoammonium phosphate (11-52-0). The quantity by which to increase manure is more difficult to calculate because manures are highly variable in their nutrient concentrations. Labs can provide nutrient analyses of manure.
It is best if the product is applied by small hand-held equipment in these relatively small cells, the researchers report.
The crop grown in the ramp calibration strip is then visually inspected or evaluated with a chlorophyll meter mid-season to determine the effectiveness of the different rates."Plant height and leaf color are good indicators of plant health and are useful to help calibrate in-season adjustments of plant-available nutrients, such as nitrogen or sulfate," says Clain Jones, MSU Extension soil fertility specialist in the Department of Land Resources and Environmental Sciences.