Publication #SL 278

# Crop Water Use and Irrigation Scheduling Guide for North Florida1

Thomas Obreza2

## Introduction

This guide presents average daily water use for 13 north Florida crops that can be used to help schedule irrigation. Knowledge of crop water use and field soil water-holding capacity allows a grower to develop a realistic irrigation schedule that minimizes plant water stress, saves water, and reduces nutrient leaching.

Crop water use as defined in this guide is a combination of evaporation and plant transpiration. Evapotranspiration, abbreviated ET, is the term used to describe these two processes acting together.

Major factors that affect daily crop water use include:

• Crop type.

• Crop age.

• Plant spacing and/or percent ground coverage.

• Weather or climatic conditions, such as:

• Amount of sunshine—ET is much greater on a sunny day compared with a cloudy day.

• Air temperature—ET increases from winter to spring to summer.

• Amount of wind—ET is greater on a windy day compared with a calm day.

• Humidity—ET is greater on a dry day compared with a humid day.

The average daily crop water use estimates in this guide were determined by multiplying reference ET by a factor that takes crop type and age into account. Reference ET is the ET rate of a short, healthy, well-watered grass. Depending on crop type, crop factors ranged between 0.2 for emerging plants to 1.2 for actively growing plants with a large canopy volume.

## How to Use This Guide

Caution: Actual ET on a given day can differ substantially from the average daily ET values shown in this guide, depending on weather conditions. For example, crop water demand will be higher than average on days that are warmer and/or windier than normal, and demand will be lower on days that are cooler and/or cloudier than normal. However, when estimating crop water demand for a period of several days, the values shown in this guide are of sufficient accuracy to help guide irrigation scheduling.

1. Locate the table for the crop of interest.

2. Find the current month along the left side of the table.

3. Determine the point of interest in the growing season using plant growth stage, key points in the growing season, or week after planting. (Note: Week after planting is the least accurate method to estimate plant growth stage due to effects of planting date and weather. Use weeks after planting with caution.)

4. Estimated crop water demand in inches per day is shown at the intersection of month (horizontal row) and plant growth stage (vertical column).

5. Determine the crop rooting depth, then find a base irrigation schedule from the tables at the back of this guide. Suggested irrigation schedules apply for these conditions:

• Overhead irrigation systems with an application efficiency of 75%.

• Soil water-holding capacity of 0.7 inches per foot or 1.0 inches per foot.

• Available soil moisture depletion of 50%.

If irrigation system, soil, or allowable depletion differs from above, the irrigation schedule should be adjusted accordingly.

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### Footnotes

1.

This document is SL 278, one of a series of the Department of Soil and Water Sciences, UF/IFAS Extension. Original publication date December 2008. Reviewed June 2016. Visit the EDIS website at http://edis.ifas.ufl.edu.

2.

Thomas Obreza, professor, Soil and Water Sciences Department; UF/IFAS Extension, Gainesville, FL 32611.

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 UF/IFAS Extension publications, contact your county's UF/IFAS Extension office.

U.S. Department of Agriculture, UF/IFAS Extension Service, University of Florida, IFAS, Florida A & M University Cooperative Extension Program, and Boards of County Commissioners Cooperating. Nick T. Place, dean for UF/IFAS Extension.