1. The chlorophyll meter test procedure is applicable only for what we classify as “High Organic N Input” fields (Table 1).
Table 1
|
High Organic
|
Moderate Organic
|
Low Organic
|
|
Manure since previous crop
and/or
First year after forage legume (alfalfa, alfalfa/grass, clover)
|
Last manure in spring or fall before previous crop
and/or
Second year after alfalfa
and/or
First year after soybeans
|
All other fields:
No manure for at least two last crops
At least one crop since soybeans
At least two crops since alfalfa
|
2. Choose “High Organic N Input” fields that did not receive any blanket preplant or at-plant fertilizer N or N with the herbicide. No more than 15 lbs N/ac in the starter fertilizer is OK.
3. Take chlorophyll meter readings at each field to be tested as close to the six-leaf stage as possible. It is better to do readings a few days later than the six-leaf stage rather than doing readings before the field is at the six-leaf stage. (See Appendix A). Always take readings of the fifth leaf of each plant. Since the meter will hold and calculate an average for up to 30 readings, you should probably try to take close to 30 readings in a field. You may want to do more than one average per field if the field is very large or seems to have distinctly different areas of N fertility. Specific techniques for using the meter and taking leaf readings are explained in Appendix B.
4. Use the Table 2 to determine whether a field needs sidedress N or requires a second meter reading ~4 to 7 days later.
Table 2
High Organic @ LS 6
|
Average meter reading
|
< 42.0
|
42.0 to 45.9
|
= or > 46.0
|
|
N Recommendation
|
Sidedress 80 lb N/ac
|
Test again
or Sidedress 50 lb N/ac
|
No sidedress N needed
|
5. Do meter readings ~4 to 7 days later on those fields that require a second meter reading. Plants should now be at the seven to eight-leaf stage. Depending on weather conditions, fields usually advance one leaf stage in about three to six days. Use the same procedures as for the first reading. Make sure you are reading leaf five. Use Table 3 to predict whether a field needs to be sidedressed.
6. If the first reading is taken at LS 7-8 skip Table 2 and go directly to Table 3 for interpretations and recommendations.
Table 3
High Organic @ LS 7-8
|
Average meter reading
|
< 43.0
|
= or > 43.0
|
|
N Recommendation
|
Sidedress 50 lb N/ac
|
No sidedress N needed
|
