Petiole sap nitrate guidelines
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EmailEditor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included.
The total nitrogen or nitrate nitrogen concentration in plant leaf or petiole tissue provides an indication of the nitrogen status of the plant. Many testing labs do tissue analyses for total nitrogen and nitrate nitrogen content of dry plant tissue. Time is required for sending, drying, grinding and analysis of the plant tissue. A quicker diagnostic test is the petiole sap nitrate test. Sap is squeezed from petiole tissue, and the nitrate content is determined with a handheld nitrate meter or with nitrate test strips. Tests can be done frequently to monitor changes in the nitrate status of a crop. Guidelines are available getting an indication of the relative nitrogen status and the potential needing to apply nitrogen. The nitrate concentration in petiole tissue does gradually decline as the plant goes through various maturation stages. Some decrease in nitrate content is normal.
To do the test, collect 15 to 20 petioles from the area of interest. Chop the petioles into quarter-inch pieces, mix well and squeeze the juice from a subsample. A garlic press works well for expressing the juice.
Table 1 provides some general guidelines for various crops at various stages of growth. The actual adequate levels will vary with variety and growing conditions. These guidelines are a compilation of information from California, Florida and Michigan. Use the first time a petiole sap nitrate test is done on a crop as a benchmark to compare future test results.
Table 1. General Petiole Sap Nitrate Guidelines. (ppm Nitrate x 0.23 = ppm Nitrate N)
|
Crop |
Stage of Growth |
Acceptable Sap Nitrate Conc. (ppm) |
|
Cantaloupe |
Early Flower |
4300-5150 |
|
Muskmelon |
Fruit Bulking |
3400-4300 |
|
First Harvest |
3000-3400 |
|
|
Watermelon |
Early Flower |
3900-4700 |
|
Fruit Bulking |
3000-3900 |
|
|
First Harvest |
2150-3000 |
|
|
Cucumber |
First Bloom |
3400-4300 |
|
Fruit 3 inches |
2600-3400 |
|
|
Harvest |
1700-2600 |
|
|
Carrot |
Prior to sizing |
3000-3900 |
|
Up to 0.25 in. |
2150-3000 |
|
|
0.25 – 0.5 in. |
1700-2600 |
|
|
0.5 – 1.5 in. |
1100-1700 |
|
|
. 1.5 in root |
850-1300 |
|
|
Celery |
Transpl. + 4 wks |
3400-4300 |
|
5 to 7 wks. |
2600-3400 |
|
|
8 to 9 wks. |
1700-2600 |
|
|
1 wk prior harvest |
1100-1700 |
|
|
Squash |
First Bloom |
3900-4300 |
|
First Harvest |
3400-3900 |
|
|
Pepper |
Vegetative |
3900-5150 |
|
Early Flower |
3000-4300 |
|
|
Fruit Bulking |
3000-3900 |
|
|
Harvest |
2500-3300 |
|
|
Fruits half size |
5150-6000 |
|
|
First Harvest |
3400-4300 |
|
|
Second Harvest |
2150-3400 |
|
|
Tomato |
First Buds |
4300-5150 |
|
First open flowers |
2600-3400 |
|
|
Fruit 1-2 in. |
1700-2600 |
|
|
First Harvest |
1300-1700 |
|
|
Second Harvest |
850-1700 |
|
|
Lettuce |
Mid-growth |
1700-2600 |
|
Preharvest |
1300-2150 |
|
|
Onion (roots) |
Up to 5 leaves |
3400-4300 |
|
5 to 7 leaves |
2600-3400 |
|
|
Bulb Initiation |
1300-2150 |
|
|
Bulb Bulking |
850-1700 |
