Washing and/or Cutting Petioles Reduces Nitrate Nitrogen and Potassium Sap Concentrations in Vegetables

ABSTRACT

Petiole sap testing using ion-specific electrodes is a simple method that can be used to guide in-season applications of nitrogen (N) and potassium (K) to vegetable crops. This method requires petiole sampling and sap extraction using a sap press. Because some vegetables are grown with foliar applications of N and/or K and because some crops have large petioles, petioles may need to be washed and/or cut before being pressed. Limited information is currently available on the effect of washing/cutting on sap-testing results. Hence, muskmelon (Cucumis melo L.), bell pepper (Capsicum annum L.) and tomato (Lycopersicon esculentum Mill) petioles were used to test whether washing/cutting reduced NO₃ (nitrate)-N and K concentrations and changed the subsequent interpretation of plant nutritional status. Washing for 30, 60, or 120 sec in distilled water and cutting petioles before or after washing significantly reduced sap concentrations (p = 0.01 and p = 0.04 for NO₃-N and K, respectively) in seven of 12 tests when compared with the control method (petioles cut and not washed). The average concentration reductions between the control and the lowest value among all the washing/cutting treatments were 30% for NO₃-N and 19% for K. These losses due to washing/cutting are likely often to change the diagnosis of nutritional status from “sufficient” to “less than sufficient” and, therefore, may suggest the need for unnecessary fertilizer applications.

Keywords:

• foliar fertilizer
• crop nutritional status
• tomato
• pepper
• muskmelon
• BMP

Notes

^z Means followed by different letters within each column are significantly different at the 0.05, level, according to Duncan's multiple range test.

^y Number of petioles in each sample was 10 and 20 in experiments 1 and 2, respectively.

^x Reduction calculated only when treatment effect was significant.

^v The contrast was calculated as “control vs. cut then washed.”

^z Means followed by the same letters within each column are significantly different at the 0.05, level according to Duncan's multiple range test.

^y Number of petioles in each sample was 10 and 20 in experiments 1 and 2, respectively.

^x Reduction calculated only when treatment effect was significant. n/c = not calculated.

^v The contrast was calculated as “control vs. cut then washed.”

^z Means followed by the same letters within each column are significantly different at the 0.05, level, according to Duncan's multiple range test.

^y Number of petioles in each sample was 10 and 20 in experiment 1 and 2, respectively.

^x Reduction calculated only when treatment effect was significant. n/c = not calculated.

^v The contrast was calculated as “control vs. cut then washed.”