FERTILIZATION AND IRRIGATION EFFECTS ON FRUIT QUALITY

ROBERT C. J. KOOIP'AS, CREC-Lake Alfred

Both fertilization and irrigation play iaportant roles in fruit production andfruit quality. Nitrogen and potassium are the two principal nutrient elements usedin citrus fertilization. Nitrogen affects both fruit production and fruit quality&Ore than other nutrient elements. The influence of potassium on fruit productionand fruit.quality is not as apparent as that of nitrogen but it plays an importantrole. More investigations have been reported on these two elements than othernutrient elements in citrus literature. Other macronutrient and most micronutrientelements do not playa significant role in fruit quality except when the element in

question is severely deficient.

Irrigation is practiced to promote tree growth and increase fruit productionIts effect on fruit quality is .ostly negative. Irrigation contributes to theefficiency of the fertility prograa.

Trends in fruit quality response to fertilization and irrigation aresummarized in Table 1. Tables 2 to 5 are data to illustrate how differentfertilizer elements and irrigation affect fruit quality measurements.

FERTILIZER ELEMENTS ON FRUIT QUALITY

Increasing rates of nitrogen application will result in:Nitrogen:

Juice Quality:A.

increase in juice, soluble solids, acid contents and juice color

in'tensity1.

increase soluble solids per box2.increase soluble'solids per acre up to a certain point. Excessivenitrogen will lower the fruit production and lower the yields ofsoluble solids per acre.

3.

External Fruit Quality:B.

decrease in fruit size and weight1.

increase in percent of green fruit at harvest2.3. increase peel thickness

decrease the incidence of wind scar, russet and plugging in peel

blemishes4.

increase the incidence of creasing and scab5.Storage Decay: a reduction in the incidence of stem-end rot and greenmold. Nitrogen has no effects on sour rot.

c.

35

Effects of mineral nutrition and irrigation on fruit quality.Table 1.

Irriga-tion

Kacronutrient element Micronutrient elementN p K -ca- -:;;;;g Mn Zn Cu Fe BMeasurements

0

0

0

0

0

0

0

+

0

0

0

0,

0

0

0

0

0

0

'0

0

0

0

+'

0

0

Q

0

0

0

+

+

+ +

Juice Quali ty

juice content

soluble solids

acid

SS/A ratio

juice color

red

yellow

solids/box

solids/acre

'+ + +

1

1

0

0

?

?

0

0

f

f

0

0

?

?

?

?

0

0

0

..

0

0

0

1

1

0,

0

~.(,,t

+

+ -+ +

0+ + + ++

0

0

+

0

0

0

0

0,

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

.0

+ +..

+

0

+

+ +

External Fruit Quality

size -

weight -

green fruit +

peel thickness j.':+

peel blemisheswindscar -

russet -

creasing +plugging -

scab +

+ + , +

0 0+

?

0

?

?

?

?

0

?

?

?

?

0

?

.,

?

0

?

'1

'l

0

?

,

?

0

?

?

0

0

?

?

?

?

?

+

0

0

+

Q...

0

0 ? t ? ?0 -+

Storage Decay

stem-end rot

green mold

sour rot

0

0

0

?

?

?

?

?

?

?

?

?

?

'1

'1,?

.,

0

0

? ? +

1. ?.1. 00 ?

1)Increase (+) Decrease (-) No change (0) No information

36

High rates of phosphorus application will result in:Pho8phorus:

A. Juice Quality: lower the acid content which will give higher solublesolids-acid ratio. Phosphorus rates have no effect on soluble solids perbox but may increase the soluble solids per acre due to increase in fruitproduction in soils that are low in phosphorus.

External Fruit Quality: increase the percent of green fruit and decreasein pe~l thickness. Phosphorus will increase the incidence of wind scarbut reduce the incidence of russet fruit.

B.

storage decay is not affected by phosphorus appl1cat1~.c. Storage Decay:

Potassium: High rates of potash application will result in:

Juice Quality: lower juice quality. Potas8ium applications producemostly negative effects on juice quality except soluble solids per acre.Potash fertilization will increase fruit production and thus produce moresoluble solids per acre.

A.

Ex:ternal Fruit Quality:B.

increase fruit size and weight1.

2. .ore green fruit at harvest

3. increase in peel thickness

Potash fertilization hasreduced incidence of creasing and plugging.no effect on wind scar, russet or scab.

4.

c. reduced incidence of stem-end rotStorage Decay:

Calciua: Calcium has little or no effects on juice quality and most of theeXternal fruit quality characteristics. No information is available on peelbleaish or storage decay.

Magnesium: The effects of magnesium on fruit quality is negligible except insevere deficiency. High rates of magnesium application will result in:

Juice Quality: slight increase in soluble solids, soluble solids-acidratio, soluble solids per box and soluble solids per acre.

A.

External Fruit Quality and Storage Decay: slight increase in fruit si;e.fruit weight and a decrease in peel thickness. NO information isavailable on other fruit quality characteristics.

B.

Micronutrient Elements: There is ~ot much information in the literature on theeffects of micronutrient elements on fruit quality. Data that are availableindicate most micronutrient elements do not affect fruit quality. Iron willincrease the soluble solids content of juice and result in higher solublesolids per box. However. no difference in soluble solids per acre was foundwhen fruit production was taken into consideration.

37

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IRRIGATION ON FRUIT QUALITY

Overly frequent irrigation will adversely affect most fruit qualitycharacteristics. Adequate irrigation will result in:

Juice Quality:A.

higher juice content, soluble solids-acid ratio1.lower soluble solids and acid contents. Soluble solids per box willdecrease but soluble solids per acre will increase because ofincreased fruit production fro. irrigation.

2.

External Fruit Quality: irrigation will increase fruit size, weight andproduce more green fruit. It will decrease the rind thickness. Among thepeel ble.ishes, irrigation increases the incidence of windscar and scab,but reduces plugging. It has no effect on russet and creasing.

B.

Storage Decay: irrigation will reduce the incidence of ste~end rot butit will increase the incidence of green mold. It has no effect on sourrot.

c.

SUlDmary

Nitrogen is the dominant nutrient element that affects fruit quality. Other.nutrients and irrigation have lesser effects except under certain conditions.Increased nitrogen rates will result in saaller fruit size, lower incidence of windscar, russet, plugging and stem-end rot. High nitrogen rates will produce moregreen fruit, more creasing and more intense juice color. High nitrogen rates willalso produce fr~it of higher soluble solids per box and per acre but the increasein soluble solids per acre is not proportional to the increase in soluble solidsper box because excessive nitrogen will cause a decrease in fruit production. Itseems a range of 150 to 250 pounds of nitrogen per acre per year would be desirablefor most citrus varieties with fruit produced for fresh market using the lower endand processed fruit using the high end of the range.

Increased potassium rates will produce larger sized fruit and more greenfruit at harvest. Higher potassium rates will reduce the incidence of creasing,plugging, ste~end rot and juice color intensity. A potash rate of 150 to 250pounds per acre per year is sufficient for most citrus varieties. A balancedprograa of nitrogen and potassium rates is iaportant to aaintain good fruitproduction of high quality fruit. This is especially true for groves under highfertility prograa. A number of fruit disorders can be attributed to the imbalanceof nitrogen and potassiua progra8s.

Effects of irrigation on fruit quality is mostly negative. Therefore,increased fruit production and yield of soluble solids should be primeconsiderations in determining the frequency of irrigation. Irrigation will lowerthe soluble solids and acid contents of juice and increase the soluble solids acidratio. The increased ratio obtained by irrigation can be used to hasten thematurity of oranges, mandarins, lemons and limes for fresh fruit market early inthe season which will command a premium price.

Most successful groves in Florida are under a program of good fertilization

and sound water management.

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Effects of micronutrients on juice quality and solids (Pineapple)Table 4.

ss/ A.

ratioSoluble solidsSoluble

solidsJuice

content Acid Box AcreElement

% % Ib Ib.%

5.575.78

13261214

10.911.1

0.74Q..71

14.715.0

56.857.9

+ Manganese- Managaese

14.314.4

5.635.77

11031559

57.457.8

10.911.1

0.760.77

+ Zinc- Zinc

5.635.70

1~O31117

10.911.1

0.760.77

14.314.4

57.457.4

+ Copper- Copper

11031058

0.760.77

14.314.3

5.635.60

57.456.6

10.911.0

+ Boron- Boron

6.075.61

807825

11.811.1

0.780.76

15.114.6

57.256.2

+ Iron- Iron

Effects of micronutrients on external fruit

quality (Pineapple).Table 5.

Peelthickness

Fruitweight

Fruitsize

GreenfruitElement

% lamg ca

3.83.7

188190

7.37.3

26.723.7

+ Manganese- Manganese

3.73.9

185194

7.37.3

25.422.7

+ Zinc.- Zinc.

7.37.2

25.416.2

3.74.0

+ Copper- Copper

185194

25.419.8

3.73.9

185195

7.37.2

+ Boron- Boron

178180

7.27.2

13.121.3

3.83.9

+ Iron- Iron

41

References

1. H. C. 1968. The aineral nutrition of citrust p. 127-289. In: W. Reuther etale (ed.). The Citrus InduatrYt Vol. lIt Rev. ed. University of Californiapresst Berkeley.

Embleton, T. W., W. W. Jones, C. K. Labanauskas and W. Reuther. 1973. Leafanalysis as a diagnostic tool and guide to fertilization, p. 183-210. In:W. Reuther (ed.). The Citrus Industry, Vol. III, Rev. ed. University ofCalifornia Press, Berkeley.

2.

3. Koo, R. C. J. 1971. The effects of omitting single nutrient elements fromfertilizer on growth and performance of 'Pineapple' orange. Proc. Fla. StateBort. Soc. 84:11-16.

4. 100, R. C. J. 1979. Nutr1cao E. Abubacao Dos Citro, p. 99-122. In: T.Yaaada (ed.). Nutricao Mineral E. Aducacao Citro., Bol. Tec. 5. Instituto daPotassa & Fosfato (EUA); Inst1tuto International da Potassa (Suica).13.400-P1rac1caba-SP-Bra81l.

5. Koo, R. C. J.Agriculture.Madison, WI

1985. Potassium Nutrition of Citrus. In: Potassium inChap. 46:1077-1086. ASA-CSSA-SSSA, 677 South Segoe Road,

53711.

6. 100, R. C. J., C. A. Anderson, I. Stewart, D. P. H. TUcker, D. V. Calvert andH.'K. Wutscher. 1984. Recommended fertilizer and nutritional sprays forcitrus. Fla. Agric. Exp. Stu. Bull. 536D.

7. loot R. C. J. and R. L. Reese. 1977.irrigation on citrus fruit quality.

Influence of nitrogen, potassium andProc. Int. Soc. Citric. 1:34-38.

42