Petiole sap nitrate guidelines

Editor’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

Related Events

Related Articles

Related Resources