California Pepper Commission


Weir #27 - Pepper


Bill Weir, Ph.D. - University of California
Zachary Ellis - Score Foliar Nutrients
Bob Giampaoli - Live Oak Farms
Mike Marchini - Live Oak Farms


To verify results of a small replicated test in 2012 in which potassium nitrate (KNO3) was applied as a foliar feed to bell peppers. This test utilized the same concentrations of KNO3 applied in large field size blocks.


A field of healthy, vigorously growing bell peppers on Live Oak Farms was chosen for the experimental site.

On April 29, 2013, prior to any field applications of KNO3, a preliminary test for phytotoxicity was conducted. Six pepper plants at the end of a row were treated with 10 pounds of KNO3 per acre, and another six rows received 5.0 pounds of KNO3 per acre. After one week it was noted that the high rate caused some leaf tip necrosis. Therefore, it was decided to use the 5.0 pound per acre rate for this study.

Twenty four 60 inch beds were treated with KNO3 applied by the grower's equipment. This number of beds was chosen because they resulted in 3.7 acres. Since the packing house handles about 4.0 acres of peppers per day, the 24 beds were a convenient number.

Another 24 beds were treated with Score Foliar Nutrients. Again the plot size was chosen for packing house convenience. Any other 3.7 acre block in the field would serve as the untreated check.

The 3.7 acre block of KNO3 treated peppers was harvested, taken to the packing house, graded and packed, all in the same day. Similarly, the 3.7 acre block of Score treated peppers was harvested, graded and packed in the same day. The untreated check data was collected for all the rest of the field. These peppers were also harvested in approximately 4.0 acre blocks and treated in the same manner as the KNO3 and Score blocks.


1 Potassium Nitrate5.0 lbs/aMay 20, June 3, 2013
2 Score Foliars (12-47-4)
   Albion Micro nutrients (0-0-24)
1.0 qt/a
1.0 qt/a
May 20, June 3, 2013
May 20, June 3, 2013
3 Untreated Check----------

Site Location:Live Oak Farms, Le Grand, California
Host Crop Variety:Classic
Plot Description and Size:3.7 acres per each of three treatments
Experimental Design:Not Replicated
Application Conditions:
Date:May 20, 2013
Time:10:00 a.m.
Wind:8 MPH NW
Temperature:70 F
Date:June 3, 2013
Time:3:00 p.m.
Wind:Light NW
Temperature:77 F


The number of 20 pound cartons of bell peppers obtained from 3.7 acres, after two harvests of green fruits, in KNO3 treated, and Score treated blocks. Number of 20 pound cartons of bell peppers harvested from non-treated acreage of the same field.


Table 1 - Numbers of 20 Pound Cartons of Bell Peppers on Two Harvest Dates for each of Three Treatments.


1 Potassium Nitrate1465.94218.641684.58
2. Score Foliars (12-47-4)
   Albion Micro nutrients (0-0-24)
3. Untreated Check890.60365.001255.60

Table 1 shows numbers of 20 pound cartons of peppers from each of two harvests and their sums. It can be seen that KNO3 treated peppers out yielded the untreated check by 428.98 cartons/acre, and the Score treatment by 219.73 cartons/acre.

Tables 2a, 2b and 2c are actual packout sheets from Live Oak Farms for the blocks utilized in this study. Fruits were graded into four categories (Jumbo, Ex-Large, Large, and Medium). The tables give the number of cartons of each as well as net weights and % of fruit in each category.

In the first harvest, the KNO3 treatment had 164 cartons or 4.8% of the peppers in the Jumbo category. The Score treatment had 116 cartons or 7.3%, while the untreated check had 375 cartons or 13.1% in the Jumbo category.

In the first harvest, the KNO3 treatment had 1765 cartons or 52.3% of the peppers in the extra large category. The Score treatment had 260 cartons or 16.4%, while the untreated check had 1248 cartons or 43.5% in the extra large category.

In the first harvest, the KNO3 treatment had 852 cartons or 25.3% of the peppers in the Large category. The Score treatment had 751 cartons or 47.5%, while the untreated check had 780 cartons or 27.2% in the Large category.

In the first harvest, the KNO3 treatment had 591 cartons or 17.5% of the peppers in the Medium category. The Score treatment had 454 cartons or 28.7%, while the untreated check had 468 cartons or 16.3% in the Medium category.

The test was not replicated and therefore could not be analyzed statistically, but there were very strong trends regarding yields. These data indicate that KNO3 applications might result in more extra large fruits (52.3%) and more total cartons (1465.94) than the other two treatments. The Score treatment had the highest percentages of large and medium fruits.

Tables 2a, 2b and 2c - Packout Sheets for Three Pepper Blocks on Live Oak Farms


This field study which employs the grower's cultural practices, verifies the finding of an earlier, small scale randomized complete block test. Foliar applied KNO3 during fruit formation and development can result in increased yields.

This was a well conducted, closely monitored test with unarguable results. The only issue might come from the untreated check values being form 32.5 acres while the treatments values were from 3.7 acres each. Workers may have begun harvesting the large block when fruits were somewhat less mature in order to harvest most fruits at peak maturity. This is only an assumption, however.

May 20, 2013 - Date of first foliar applications

June 3, 2013 - Date of second applications

June 10, 2013 - Test in progress

July 13, 2013 - Date of first harvest

July 27, 2013 - Date of second harvest

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