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Irrigation, Nutrition, and Citrus Fruit Quality¹

Mongi Zekri, Thomas A. Obreza and Robert Koo²

Introduction

Florida has the highest citrus fruit quality standards in the world. The most important quality factors for Florida citrus growers, production managers, processors, and packers include fruit juice content, soluble solids and acid concentrations, soluble solids-acid ratio, fruit size, and color. Florida citrus growers discern between quality factors for the fresh and processing markets. For example, fruit size, shape, color, and maturity date are most important for fresh fruit, but high juice content and soluble solids are desired for processing fruit. Fruit quality is affected by several factors including cultivar, rootstock, climate, soil, pests, irrigation, and nutrition.

The effects of irrigation and nutrition on fruit quality are important and should be understood and taken into consideration by citrus growers and production managers to increase profitability and enhance sustainability and worldwide competitiveness. In general, excessive irrigation and fertilization reduce fruit quality. Therefore, supplying sufficient nutrition and using sound irrigation scheduling techniques should be high-priority management practices for every grower. Citrus trees require a properly designed, operated, and maintained water management system and a balanced nutrition program formulated to provide specific needs for maintenance and for expected yield and fruit quality.

Irrigation contributes to the efficiency of fertilizer programs. Citrus trees with sufficient water and nutrients grow stronger, better tolerate pests and stresses, yield more consistently, and produce good quality fruit. On the other hand, excessive or deficient irrigation or fertilization may result in poor fruit quality.

The most important management practices influencing fruit quality are irrigation and nitrogen, phosphorus, potassium, and magnesium nutrition. Some micronutrients like boron and copper can also affect fruit quality, but only if they are deficient in the tree. In general, when any nutrient element is severely deficient, fruit yield and fruit quality will be negatively affected.

Effects of Specific Elements

Trends in fruit quality response to increasing nutrient and water availability are described and summarized below:

Nitrogen (N)

• Increases juice content and color, total soluble solids (TSS), and acid concentration.

• Increases TSS per box and per acre. However, excessive N, particularly with inadequate irrigation, can result in lower yields with lower TSS per acre.

• Decreases fruit size and weight.

• Increases peel thickness and green fruit at harvest.

• Increases incidence of creasing and scab but decreases incidence of peel blemishes like wind scar, mite russeting, and rind plugging.

• Reduces stem-end rot incidence and green mold of fruit in storage.

Phosphorus (P)

• Reduces acid concentration, which increases TSS-acid ratio. Phosphorus rates have no effect on TSS per box but may increase TSS per acre due to increase in fruit production in soils that are low in plant-available P.

• Increases number of green fruit but reduces peel thickness.

• Increases expression of wind scar but reduces that of russeted fruit.

Potassium (K)

• Potassium produces mostly negative effects on juice quality except for TSS per acre. Potassium increases fruit production, therefore producing more TSS per acre.

• Decreases juice content, TSS, TSS-acid ratio, and juice color.

• Increases acid content.

• Increases fruit size, weight, green fruit and peel thickness.

• Reduces incidence of creasing and fruit plugging. In storage, reduces stem-end rot.

Magnesium (Mg)

• Slightly increases TSS per box and per acre, and TSS-acid ratio.

• Slightly increases fruit size and weight, but decreases rind thickness.

Irrigation

• Increases juice content and TSS-acid ratio.

• Reduces TSS and acid concentration. TSS per box decreases, but TSS per acre may increase due to yield increase.

• Increases fruit size and weight, increases green fruit at harvest but decreases rind thickness.

• Increases incidence of blemish from wind scar, scab and Alternaria brown spot, but reduces rind plugging.

• Reduces stem-end rot incidence but increases incidence of green mold in storage.

Summary

Specific effects on juice and external fruit qualities are summarized in Table 1 . This summary is based on numerous field experiments conducted over many years that evaluated the response of oranges to irrigation and fertilization practices. Most of these effects were consistently observed, but some of them appeared to depend on local conditions and growing regions. These observations are useful in developing a strategy to improve fruit quality for a particular variety or location.

For more information on nutrition and irrigation effects on citrus, see http://edis.ifas.ufl.edu/TOPIC_Citrus_Nutrition_and_Fertilization and http://edis.ifas.ufl.edu/TOPIC_Citrus_Irrigation .

Tables

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

Variable	N	P	K	Mg	Irrigation
Juice Quality
Juice Content	+	0	-	0	+
Soluble Solids (SS)	+	0	-	+	-
Acid (A)	+	-	+	0	-
SS/A Ratio	-	+	-	+	+
Juice Color	+	0	-	?	0
Solids/Box	+	0	-	+	-
Solids/Acre	+	+	+	+	+
External Fruit Quality
Size	-	0	+	+	+
Weight	-	0	+	+	+
Green Fruit	+	+	+	0	+
Peel Thickness	+	-	+	-	-
Increase (+), Decrease (-), No change (0), No information (?)

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Footnotes

1. This document is SL 207, a fact sheet of the Soil and Water Science Department, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida. First printed: April 2003. Please visit the EDIS Web site at http://edis.ifas.ufl.edu.

2. Mongi Zekri, Multi-county Citrus Extension Agent, PO Box 68, LaBelle, FL 33975; Thomas A. Obreza, Professor, Soil and Water Science Department, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida, Gainesville, 32611-0290; and Robert Koo, Emeritus Professor, Citrus Research and Education Center, Lake Alfred, FL 33850.

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The Institute of Food and Agricultural Sciences (IFAS) is an Equal Opportunity Institution authorized to provide research, educational information and other services only to individuals and institutions that function with non-discrimination with respect to race, creed, color, religion, age, disability, sex, sexual orientation, marital status, national origin, political opinions or affiliations. For more information on obtaining other extension publications, contact your county Cooperative Extension service.

U.S. Department of Agriculture, Cooperative Extension Service, University of Florida, IFAS, Florida A. & M. University Cooperative Extension Program, and Boards of County Commissioners Cooperating. Larry Arrington, Dean.

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Copyright Information

This document is copyrighted by the University of Florida, Institute of Food and Agricultural Sciences (UF/IFAS) for the people of the State of Florida. UF/IFAS retains all rights under all conventions, but permits free reproduction by all agents and offices of the Cooperative Extension Service and the people of the State of Florida. Permission is granted to others to use these materials in part or in full for educational purposes, provided that full credit is given to the UF/IFAS, citing the publication, its source, and date of publication.