guidelines for predicting crop water requirements

 

 

Summary iii

 

Table of Contents v

 

List of Tables vii

 

List of Figures ix

 

Conversion Factors xi

 

Climatological Nomenclature xii

 

PART I - CALCULATION OF CROP WATER REQUIREMENTS 1

1. CALCULATION OF REFERENCE CROP EVAPOTRANSPIRATION 3

 

1.1 Blaney-Criddle Method 3

 

1.2 Radiation Method 8

 

1.3 Penman Method 15

 

1.4- Pan Evaporation Method 30

 

2. SELECTION OF CROP COEFFICIENT 35

 

3. FACTORS AFFECTING CROP EVAPOTRANSPIRATION 55

 

3. 1 Climate: variation with time, distance, size of irrigation

 

development, advection, altitude 55

 

3.2 Soil Water: level of available soil water, groundwater, salinity,

 

water and crop yields 59

 

3.3 Method of irrigation: surface, sprinkler, drip or trickle, subsurface irrigation 62

 

3.4- Cultural Practices : fertilizers, plant population, tillage, mulching,

 

windbreaks, anti-transplants 65

 

PART II - APPLICATION OF CROP WATER REQUIREMENT DATA IN IDENTIFICATION , DESIGN AND OPERATION OF IRRIGATION PROTECTS 67

1. PROJECT IDENTIFICATION AND PRELIMINARY PLANNING 68

 

1. 1 Introduction 68

 

1.2 Seasonal and Peak Project Supply Requirements 69

 

1.2.1 Crop water requirements 71

 

1.2.2 Net irrigation requirements : effective rainfall, groundwater

 

contribution, stored soil water 72

 

1.2.3 Irrigation requirements : leaching requirements , irrigation

 

efficiency 76

 

1.2.4 Summary of calculation of seasonal and peak project supply

 

requirements 81

 

2. PROJECT DESIGN 83

 

2.1 Introduction 83

 

2.2 Field and Project Supply Schedules 83

 

2.2.1 Field irrigation schedules: depth of irrigation application, irrigation application interval, calculation of field irrigation

 

schedules 86

 

2.2.2 Field irrigation supply schedules: surface, sprinkler drip 90

 

2.2.3 Design and operation of supply system: continuous, rotational,

 

supply on demand 96

 

2.2.4 Summary calculation of project design and operation 100

 

3. PROJECT OPERATION 102

 

3.1 Refinement of Field Supply Schedules: adaptive research, data

 

collection, project monitoring 102

 

3.2 Application of Field Irrigation Data 104

 

Appendix I Persons and Institutes Consulted 107

 

Appendix II Background and Development of Methods to Predict Reference Crop

 

Evapotranspiration 108

 

Appendix III Computer Programme for Estimation of Reference Crop Evapotranspiration 120

 

Appendix IV Glossary 133

 

Appendix V References 137

 

Appendix VI Constants for the Radiation Equation Rs = (a + b n/N)Ra 144