thie - Plant PhysiologyJONES and ROSA (2) state that the claim is often madethat potassium, applied in manure, favorablyaffects theflavor, quality, orsugarcontentofwatermelons. They

THE EFFECT OF FERTILIZER ON THE QUALITY ANDKEEPING QUALITY OF WATERMELONS'

W. D. KIMBROUGH

Introduction

There is a belief among many people in the South that the quality ofwatermelons is affected by the fertilizer treatment given the soil on whichthe plants are grown. Many people believe that melons from plants fer-tilized with nitrate of soda are not sweet. Some believe that when melons,which have been fertilized wvith this source of nitrogen, are eaten, the con-sumer is likely to be made ill. The claim is made that melons from plantsfertilized with nitrate of soda can be detected by taste. Buyers oftendiscriminate against melons which have been fertilized with nitrate ofsoda. The reason given is that the melons are likely to have white heart,and be of poor quality.

Manure is generally considered an excellent fertilizer for melons andwas used almost exclusively while it was cheap and easily obtainable. Asmanure becomes scarcer and more expensive, commercial fertilizer is beingused more extensively in the melon fields. This makes it important thatinformation concerning the influence of fertilizers on watermelons be ob-tained. For this reason, an experiment was started at the Alabama Ex-periment Station, in 1926, to determine the effect of fertilizer treatmenton the quality and keeping quality of watermelons.

Review of literatureBEATTIE (1) states that some of the melon growers' associations of Texas

prohibit the use of nitrate of soda as a top dressing, as they consider thatit makes the melons soft and of poor carrying quality. JONES and ROSA(2) state that the claim is often made that potassium, applied in manure,favorably affects the flavor, quality, or sugar content of watermelons. Theyfurther say that the literature does not afford any evidence for such belief;but that potassium is a nutrient no doubt profitably applied in some cases.STUCKEY (3) reports that the results obtained for one year showed thatthe amount or type of white heart could not be attributed to the kind offertilizer used. Unfavorable weather conditions during the fruiting periodseemed to be the chief cause of white heart. Judged by taste, melons fromplots receiving different fertilizer treatments gave no indication that thequality of melons was influenced by fertilizer treatment.

1Work on certain phases of this problem is being continued.373

Copyright (c) 2020 American Society of Plant Biologists. All rights reserved.

PLANT PHYSIOLOGY

Procedure and methodsWatermelons were grown on well drained Norfolk sandy loam. The

location of plots was changed three out of four years to avoid serious in-jury from disease. The first two years the same area was used and theplots were 1/40 acre with plants 6 feet apart each way. The third yearplots were 1/10 acre and the fourth year 1/20 acre with plants 8 feet aparteach way. Plots were separated by 3-foot alley ways. The third year theplots were on new ground, while the other years old land was used that hadnot been fertilized for a number of years. The variety "Wondermelon"was grown the first year and "Tom Watson" was grown the other threeyears. Melons were thinned to two to a vine.

Fertilizer treatments were run in duplicate, while check plots receivedno fertilizer. Fertilizer treatments are indicated by N, P, and K or multi-ples of these. The explanation of the symbols used is: N= 200 pounds ofnitrate of soda, or equivalent per acre; P = 400 pounds of superphosphateper acre; K=50 pounds of muriate of potash or equivalent per acre.Sources of fertilizer named were used unless otherwise stated. All fertili-zer, except the nitrate of soda that was applied as top dressings, was ap-plied broadcast before planting the first three years, and thie fourth yearit was applied along the rows in strips about four feet wide. Nitrate ofsoda was applied at times varying from entire application before plantingto as many as four top dressings during the season. Nitrate of soda wasnot applied in amounts exceeding the rate of 200 pounds per acre or lessthan 100 pounds per acre at one application. Top dressings of nitrate ofsoda were applied to some plots after many melons were approximatelyhalf grown. Fertilizer applications were so varied in rate and sources,and in the time of application of nitrate of soda, that if fertilizer treat-ment affects the quality or keeping quality of melons this should have beentrue of melons produced in this experiment.

Quality was determined by taste and by determining the sugar andmoisture content of the edible portion of melons. Judged by looks, onlymelons that were ripe and in good condition were sampled. In takingsamples for analysis a portion of the melon extending from the rind to thecenter of the heart was freed of seed and ground in a food chopper. Sam-ples for sugar determinations were preserved in alcohol in the usual way.Individual melons from a plot were sampled, rather than taking a samplefrom a group of melons. Only melons weighing 20 pounds or more weresampled for analysis.

Moisture content was determined by drying thoroughly mixed samplesof material to constant weight in a vacuum oven at 800 C. and 26 inchesof mercury. Reducing sugars were determined and expressed as glu-

374


KIMBROUGH: FERTILIZER ON WATERMELONS

cose, and total sugars as invert sugar. Inversion was brought about byacid hydrolysis at room temperature. Reducing sugars were determinedby the Bertrand modification of the Munson and Walker method.2

Keeping quality was determined by storing melons at room tempera-ture and at 35, 40, and 500 F. The storage temperature range was ingeneral 20 F. each way from that given.

Experimental results

EFFECT OF FERTILIZER ON PLANT GROWTH

The plants showed a marked response in growth to the applications offertilizer. Check plots produced plants that grew very slowly, but in somecases very good melons were eventually produced. The addition of bothnitrogen and phosphorus was necessary for good growth, while the addi-tion of potash along with these was necessary for best growth. Plants onplots receiving 2N made better growth than those on plots receiving 1N,but the addition of more than 2N made no apparent difference in plantgrowth. The third year of the experiment heavy rains apparently leachedout nitrate of soda applied before planting to such an extent that plantsgot no benefit from it. Plants on manure plots made good growth but notas good as those on plots receiving 2N. Melons were a little earlier onmanure and cottonseed meal plots than on plots receiving nitrate of sodaas a source of nitrogen.

The response in plant growth to fertilizer treatment of the soil showedthat the materials added were being utilized and indicated that if melonscould be influenced by fertilizer treatment, this influence should have beenobtained in melons produced on these plots.

EFFECT OF FERTILIZER ON QUALITY OF WATERMELONS

No laboratory was available in 1926, so quality of melons was deter-mined by taste only. Three watermelon cuttings were held that were par-ticipated in by many members of the station staff and a few others. Melonsfrom plots receiving different fertilizer treatments were cut and sampled.Those tasting the melons did not know the fertilizer treatment of the plotson which the melons were grown. The results obtained showed that therewas apparently as much difference in melons from the same plot as therewas between melons from plots receiving different fertilizer treatments.There was considerable difference of opinion as to which melons were best

2 Sugar content of the juice from the edible portion of several melons was deter-mined with a Brix hydrometer and compared with the sugar content of the edible portiondetermined by the Bertrand modification of the Munson and Walker method. Theaverage of determinations from nine melons showed that the Brix hydrometer methodwas about 1 per cent. higher than the other method.

375


PLANT PHYSIOLOGY

but there was good agreement as to which melons were good, which weremedium, and which were only fair in quality. Melons of good quality wereproduced from all treatments. The results of the watermelon cuttingsindicated that the source of fertilizer did not materially influence the tasteof the melons. After the tasting was over many ate large quantities ofmelons, including those that had been heavily fertilized with nitrate ofsoda, but no one became ill. During the period of four years, there wasno report of melons from any plot being injurious to the consumer.

TABLE IMOISTURE AND SUGAR CONTENT OF WATERMELONS FROM PLOTS RECEIVING DIFFERENT FERTILIZER

TREATMENTS IN 1927

MOISTURE SUGAR-FRESH WEIGHTFERTILIZER REDUCING TOTAL AS INVERTTREATMENT | MINDIVIDUAL AVERAGE INDIVIDUAL AVERAGE INDIVIDUAL AVERAGE

MELONS ~~MELONS MELONS

Cheek

NP

NPK

NPK (N fromurea)

NPK (K fromK-SO4)

2N2P2K

3N2P2K

2NP2K

per cent.90.2690.5490.71

89.7991.43

90.4490.84

90.44

90.27

90.3390.04

89.9391.20

90.15

per centt.

90.50

90.61

90.64

90.18

90.56

per cent.3.954.904.63

4.474.40

4.985.00

5.104.59

5.184.57

4.533.93

5.454.53

4.315.31

N2P2K

per cent.

4.49

4.58

4.99

4.84

4.87

4.23

4.99

4.81

per cent.8.957.987.73

8.697.30

8.117.89

8.007.90

8.358.21

8.188.10

per cent.

8.05

8.00

8.00

7.95

8.28

8.14

8.407.34

7.87

8.188.17

8.17

8.22

376

90.56 4.88



The last three years of the work a laboratory was available and deter-minations were made to find the effect of fertilizer treatment on themoisture and sugar content of watermelons. At the time samples foranalysis were taken the melons were tasted for quality by the writer and atleast one assistant.3 In general, the quality of melons judged by tastevaried directly with the sugar content.

TABLE IIMOISTURE AND SUGAR CONTENT OF WATERMELONS FROM PLOTS RECEIVING DIFFERENT

FERTILIZER TREATMENTS IN 1928

MOISTURE SUGAR-FRESH WEIGHTFERTILIZER REDUCING TOTAL AS INVERTTREATMENT INDIVIDUAL INDIVIDUAL INDIVIDUAL

MELONS AVERAGEINDvrDA AVERAGEIDVDA VRGMELONS IMELONS

Manure (rate of7.5 tons per acre)

NPK

4N2P2K

3N2P2K

2N2P2K

3 Afterquality.

per cent.89.6890.1090.5690.7491.3991.6392.12

89.7890.2090.4990.5190.5591.7892.44

89.5289.5289.9190.3890.5190.8091.38

89.7189.9290.77

90.2890.6590.4191.92

per cent.

90.89

90.82

90.37

90.13

90.81

per cent.3.683.773.593.774.054.454.35

5.193.904.094.424.364.794.59

4.584.263.944.313.864.454.99

4.364.584.45

4.364.594.454.72

per cent.

3.95

4.48

4.33

4.46

4.70

per cent.8.478.157.807.607.126.996.63

8.277.917.907.907.826.776.17

8.538.378.307.787.617.487.11

8.478.297.57

7.897.777.476.5-5

per cent.

7.52

7.54

7.88

8.11

7.42

tasting a number of melons it was difficult to make fine distinctions in

377


PLANT PHYSIOLOGY

Results of analyses are given on individual melons as well as averages.This is done in order that the actual variation in the melons may be seen.In this way the relation between moisture content and sugar content is

TABLE IIIMOISTURE AND SUGAR CONTENT OF WATERMELONS FROM PLOTS RECEIVING DIFFERENT FERTILIZER

TREATMENT IN 1929

FERTILIZERTREATMENT

Check

Manure (at rate of6 tons per acre)

2N2P4K

2N2P4K (K fromK2S04)

2N2P

2N2P4K (N fromC. S. M.)

MOISTURE

INDIVIDUAL AVERAGEMELONS

per cent.89.3590.1990.0290.4890.6091.13

90.0389.9490.4490.7390.9791.52

89.1289.6989.7090.1491.68

89.4389.4989.8589.4992.05

89.9690.0890.4990.6290.41

89.7790.3091.1491.0290.63

per cent.

90.33

90.60

90.07

90.06

90.31

90.57

SUGAR-FRESH AVEIGHT

REDUCING

INDIVIDUAL AVERAGEiMELONSper cent.

4.053.853.824.343.814.38

3.533.503.863.623.954.43

3.954.003.954.104.17

4.633.644.693.893.69

4.533.734.463.214.39

4.804.114.384.004.63

per cent.

4.04

3.81

4.03

4.13

4.06

4.18

TOTAL AS INVERT

INDIVIDUAL AVERAGEMELONS

per cent.8.317.967.787.727.587.07

7.917.877.537.327.176.65

8.497.877.827.686.56

8.698.278.198.126.26

8.117.927.627.507.48

8.177.927.387.357.26

per cent.

7.74

7.41

7.68

7.91

7.73

7.62

378



also clearly shown. The results secured in the different years are pre-sented separately because of seasonal differences and differences in fertilizertreatments. Results are presented only from those plots that received fer-tilizer treatments most likely to affect the melons. The most importantcomparisons are between melons from the heavily nitrated plots and thosefrom check plots, manure plots, and plots receiving cottonseed meal as asource of nitrogen. Results are given in tables I, II, and III.

The data in tables I, II, and III show that melons having high sugarcontent were obtained regardless of the fertilizer treatment. Melons fromplots receiving heavy application of nitrate of soda had as high sugar con-tent as melons from check, manure, and cottonseed meal plots. The rateor time of application of nitrate had no appreciable effect on sugar con-tent. Potash fertilizers had no apparent influence on the sweetness ofmelons. There was approximately as much variation in moisture andsugar content in melons receiving the same fertilizer treatment as in melonsfrom plots receiving different fertilizer treatment.

The consistency of the inverse relationship of sugar and moisture con-tent is interesting. The sum obtained by adding the percentage ofmoisture and of sugar is almost constant.

EFFECT OF FERTILIZER TREATMENT ON THE KEEPING QUALITY

OF WATERMELONS

The first two years of the experiment melons from plots i'eceiving dif-ferent fertilizer treatments were kept at room temperature. No apparentdifference in keeping quality due to fertilizer treatment was found.Melons were kept as long as six weeks without rotting, but when cut theflavor was such that they were not eatable.

Sugar and moisture content of a few melons that had been stored atroom temperature, were determined. The results obtained from melonsthat had been stored for 14 and 18 days respectively are shown in table IV.

If tables IV and I are compared it will be seen that there was a con-sistent decrease in sugar content and an increase in moisture content in thestored melons. The average moisture and sugar contents of similar melonssampled the days of harvest and after being held at room temperature for14 and 18 days respectively are shown in table V.

Melons cut after being kept from one to three weeks at room tempera-ture seemed redder in color and had thinner rinds than melons cut imme-diately after harvest. This might indicate that melons continue to ripenafter harvest but the quality of the melons cut the day of harvest was betterthan that of melons kept at room temperature for several days after harvest.The sugar content has been shown to be decreased when melons are kept at

379


380 PLANT PHYSIOLOGY

TABLE IVMOISTURE AND SUGAR CONTENT OF MELONS KEPT AT ROOMI TEMPERATURE

SAMPLED 14 DAYS AFTER HARVEST SAMPLED 18 DAYS AFTER HARVEST

FERTILIZER SUGAR SUGARTREATMENT MOISTURE TOTAL AS MOISTURE TOTAL AS

REDUCING INVERT REUIG INVERT

Check

NPK ..

N2P2K

2N2P2K

3NPK ...

3N3P3K

2NP2K

3N2P2K

per cent.90.79

90.85

91.22

91.69

91.81

91.68

91.09

91.35

per cent.3.28

3.36

3.41

2.84

3.80

3.80

2.89

3.80

per centt.7.48

7.15

7.20

6.65

6.52

6.82

7.19

6.82

per cent.91.09

92.13

91.53

91.93

92.00

per cent.3.37

3.21

3.41

3.36

2.71

per cent.7.31

6.39

6.94

6.65

6.60

room temperature, so it is doubtful if melons ever get sweeter after theyare harvested. The increase in moisture content shown in table V is notlarge, but it evidently occurs. The loss of moisture due to transpirationis not enough to balance the loss in sugar content plus the moisture formedin the respiratory process.

TABLE VCOMPARISON OF AVERAGE MOISTURE AND SUGAR CONTENT IN MELONS SAMPLED THE DAY OF

HARVEST AND MELONS KEPT AT ROOM TEMPERATURE

SUGAR DECREASE IN

TIME OF SAMPLING MOISTURE TOTAL AS SUGARREDUCING

INETCONTENT

per cent. per cent. per cent. per cent.Day of harvest ... 90.47 5.09 8.03

14 days after harvest 91.31 3.32 6.95 13.45

Day of harvest.90.69 4.47 8.20

18 days after harvest 91.73 3.21 6.77 17.44



In 1928 and 1929 melons were stored at temperatures of 35, 40, and500 F. There was no apparent difference in keeping quality due to fertil-izer treatment.4 The lower the temperature the better the melons kept.Melons kept for two months at 35° F., however, were in bad condition in-ternally even though they seemed in fair condition externally. It seems

that in order to store melons for long periods a temperature below 350 F.is necessary.

TABLE VIMOISTURE AND SUGAR CONTENT OF MELONS STORED AT 400 F. FOR ONE MONTH

FERTILIZER SUGAR-FRESH WEIGHTTREATMENT MOISTURE

REDUCING TOTAL AS INVERT

per cent. per cent. per cent.Manure 90.09 3.18 8.13

90.60 2.59 7.6991.19 2.87 7.23

2N2P2K 90.22 2.80 7.8990.51 2.97 7.7890.81 3.19 7.48

TABLE VIIMOISTURE AND SUGAR CONTENT OF MELONS STORED AT 350 F. FOR ONE MONTH

FERTILIZER SUGIAR-FRESH WEIGHTTREATMENT MOISTURE

REDUCING TOTAL AS INVERT

per cent. per cent. per cent.Manure ......... 90.61 2.42 7.58

2N2P2K .. 90.06 3.31 8.1391.39 4.37 6.44

3N2P2K 89.80 3.25 8.0991.41 4.25 6.95

PNK ...... 89.93 2.92 8.0890.50 2.33 7.69

Check ... ......... 89.27 3.33 8.6290.58 3.90 7.6490.68 3.11 7.53

4 In 1928, symbols indicating the fertilizer treatment of the plot from which themelon came were scratched on the melons. This proved a means of entrance for decayorganisms.

381


PLANT PHYSIOLOGY

Moisture and sugar contents of some melons stored for a month at 350 F.and 400 F. respectively were determined. Results obtained are showni intables VI and VII. These tables show that there is probably very littledifference in the moisture and sugar content of the stored melons andfreshly harvested melons, except that the reducing sugars are apparentlydecreased slightly. In storage, part of the reducing sugars seem to bechanged to non-reducing sugars. When cut after removal from storage,the melons were lighter red than melons kept at room temperature.

EFFECT OF FERTILIZER ON WHITE HEART IN MELONS

Due to the limited number of melons during the first two years thatthe experiment was conducted there was no special cutting of melons toexamine for white heart. Most of the melons produced were cut for va-rious reasons, however, and no white hearted melons were noted.

TABLE VIIIMELONS EXAMINED FOR WHITE HEART AND PERCENTAGE FOUND IN 1928

FERTILIZER NUMBER OF MELONS NUMBER WITH WHITE HEARTED MELONSTREATMENT EXAMINED WHITE HEART

per cent.Check ...... 35 3 8.62P2K 10 0 0.0N2P2K .5.57 3 4.92N2P2K ............ 99 13 13.13N2P2K ............ 83 8 9.74N2P2K .............. 72 5 7.0Manure 57 7 12.3

TABLE IXMELONS EXAMINED FOR WHITE HEART AND PERCENTAGE FOUND IN 1929

FERTILIZER NUMBER OF MELONS NUMBER WITH WHITE HEARTEDTREATMENT EXAMINED WHITE HEART MELONS

per cent.Check ................... 30 6 20.0NP2K .................... 33 5 15.1N2P2K ....................... 31 2 6.52N2P2K 25 1 4.02N2P4K 54 9 16.72N2P4K (K from

K2S04) 31 3 9.72N2P4K (N from

cottonseed meal 21 2 9.5Manure ... ........... 27 5 14.8

382



The last two years, 1928 and 1929, a number of melons from plots re-ceiving different fertilizer treatments was examined for white heart.Melons having a distinct white streak in the middle and otherwise ripe,were considered to have white heart. The results obtained are shown intables VIII and IX.

There does not seem to be any correlation between fertilizer treatmentand white heart in melons. There was no higher percentage of melons withwhite heart from plots receiving heavy applications of nitrate of soda thanfrom plots receiving manure or from the no fertilizer plots. The fertilizertreatment seems to have little, if any, effect on the production of whiteheart in melons. Most of the white hearted melons were found late in theseason when unfavorable climatic conditions or disease had injured thevines.

DiscussionThe results of four years work on the effect of fertilizer treatment on the

quality and keeping quality of watermelons have been presented. The sea-sons have been variable enough to cover quite a range of climatic condi-tions. Three different plot areas were used and while all were of a lightsandy nature, and well drained, they were somewhat variable. The re-sponse in plant growth to the fertilizer applied was usually striking, andshowed that the plant was making use of the fertilizer. Especial emphasiswas placed on the effect of nitrate of soda on the water-melons and this wasapplied at such varying rates and times that the effect, if any, should havebeen detected. Quality of melons was determined by taste and by analysisfor moisture and sugar contents of the edible portion. Melons from heavilynitrated plots were compared especially with melons from check plots,manure plots, and plots receiving cottonseed meal as a source of nitrogen.The moisture and sugar contents of 175 individual melons were deter-mined over a period of three years. Melons were stored at room tempera-ture and in cold storage rooms at temperatures of 35, 40, and 500 F. todetermine keeping qualities.

The data presented show no apparent difference in the quality of melonsdue to fertilizer treatment. The sugar content of melons varied as muchbetween melons of the same treatment as those of different treatments.Melons from plots receiving heavy applications of nitrate of soda and ap-plications late in the season had as high sugar content as melons frommanure, cottonseed meal, or check plots. Potash fertilizers did not increasethe sugar content. Melons from plots receiving nitrate of soda did notcause sickness when eaten. There was no indication that white heart inwatermelons was correlated with fertilizer treatment. White heart wasnot usually found unless dry weather or disease had injured the vines.

383


PLANT PHYSIOLOGY

There was no indication that fertilizer treatmelnt of plants affected thekeeping of the melons.

In general, quality, determined by taste, agreed very well with thesugar content, the better quality melons having the higher sugar content.Sugar and moisture content varied inversely. The sugar and moisture con-tent relationship was such, in fact, that moisture content will give a fairestimate of sugar content.

Melons kept at room temperature for periods of one to nearly threeweeks showed consistently a slight increase in moisture content and a de-crease in sugar content. The decrease in sugar content is largely in thereducing sugar. The rapid decrease in sugar content in melons at roomtemperature is a partial explanation of the difference between shipped andhome grown melons which are eaten soon after harvest. The rapid de-crease in sugar at room temperature is also further evidence that the sup-posed ripening of melons which are kept for several days in order to im-prove them does not occur. The Tom Watson melon is not generallypraised because of its sweetness, but many melons of this variety werefound to have a high sugar content.

Summary1. On sandy soil no apparent influence of fertilizer treatment on quality

of watermelons was found.(a) Nitrate of soda did not prevent melons froimi having a high sugar

content and being sweet.(b) Potash did not increase the sugar content.2. The edible portion of the watermelon is about 98 per cent. sugar

and water. The moisture and sugar content vary inversely with eachother.

3. After harvest the sugar content of melons kept at room temperaturedecreases rather rapidly.

4. Moisture content may increase slightly in melons kept at room tem-perature.

5. No effect of fertilizer treatment on keepiing quality of watermelonswas found.

6. Temperature as low as 350 F. was not effective for keeping melonsin good condition for much over a month.

7. No correlation between fertilizer treatment and white heart in melonswas found.

8. White heart seems to be caused by unfavorable climatic conditions ordisease injury to the vines.

DEPARTMENT OF HORTICULTURE,ALABAMA EXPERIMENT STATION.

384


KIMBROUGII: FERTILIZER ON WATERMELONS 385

LITERATURE CITED1. BEATTIE, W. R. Watermelons. Farmer's Bull. 1394. 1927.2. JONES, H. A., and RoSA, J. T. Truck crop plants. McGraw-Hill.

New York. 1928.3. STUCKEY, H. P. Watermelons. Georgia .Agr. Exp. Sta. Bull. 143.

1924.


Documents

thie - Plant PhysiologyJONES and ROSA (2) state that the claim is often madethat potassium, applied in manure, favorablyaffects theflavor, quality, orsugarcontentofwatermelons. They