IRRIGATION WATER MANAGEMENT
Training manual no. 3
Part I Principles of irrigation water needs
Part II Determination of irrigation water needs
a manual prepared jointly
by
C. Brouwer
International Institute
for Land Reclamation and Improvement
and
M. Heibloem
FAO Land and Water
Development Division
Drawings by The International Institute for Land Reclamation and Improvement: J. van Dijk
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The designations employed and the presentation of material in this publication do not imply the expression of any opinion whatsoever on the part of the Food and Agriculture Organization of the United Nations concerning the legal status of any country, territory, city or area or of its authorities, or concerning the delimitation of its frontiers or boundaries. |
All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying or otherwise, without the prior permission of the copyright owner. Applications for such permission, with a statement of the purpose and extent of the reproduction, should be addressed to the Director, Publications Division, Food and Agriculture Organization of the United Nations, Via delle Terme di Caracalla, 00100 Rome, Italy.
©FAO 1986
PREFACE
This is one in a series of training manuals on subjects related to Irrigation that will be issued in 1985, 1986 and 1987.
The papers are intended for use by field assistants in agricultural extension services and irrigation technicians at the village and district levels who want to increase their ability to deal with farm-level irrigation issues.
The papers contain material that is intended to provide support for irrigation training courses and to facilitate their conduct. Thus, taken together, they do not present a complete course in themselves, but instructors may find it helpful to use those papers or sections that are relevant to the specific irrigation conditions under discussion. The material may also be useful Co individual students who want to review a particular subject without a teacher.
Following an introductory discussion of various aspects of irrigation in the first paper, subsequent subjects discussed will be:
· topographic surveying
· crop water needs
· irrigation scheduling
· irrigation methods
· irrigation system design
· land grading and levelling
· canals and structures
· drainage
· salinity
· irrigation management
At this stage, all the papers will be marked provisional because experience with the preparation of irrigation training material for use at the village level is limited. After a trial period of a few years, when there has been time to evaluate the information and the use of methods outlined in the draft papers, a definitive version can then be issued.
For further information and any comments you may wish to make please write to:
The International Support Programme for Irrigation Water Management
Land and Water Development Division
FAO
Via delle Terme di Caracalla
00100 Rome
Italy
ABOUT THIS PAPER
Irrigation water needs is the third in a series of training manuals on irrigation. Unlike Volumes 1 and 2, Volume 3 has been divided into two parts.
Part I Principles of Irrigation Water Needs
Part I of this manual describes in general terms the principles to determine the water need of standard grass; how the water need of grass relates to the water needs of the crops actually grown on an irrigation scheme. Lastly it indicates how the irrigation water needs can be estimated for the various crops, taking into account the effective rainfall.Part I is intended for use by village level extension workers who will not be involved - on a project basis - with the determination of the irrigation water needs, but who need to understand the principles behind and the factors involved in their determination.
Part I uses only very elementary arithmetic, provides tables indicating approximate values or orders of magnitude only, but does not elaborate on their more accurate determination.
PART II Determination of Irrigation Water Needs
Part II covers in principle the same topics as Part I: reference crop evapotranspiration, crop evapotranspiration or crop water needs and irrigation water needs. It provides - be it still in a fairly simple manner - methods to calculate these.Part II is intended for use by irrigation technicians at the village and district levels who will be involved in the determination of irrigation water needs for small projects and who are not in a position to obtain these data easily from the Extension Service, Irrigation Department or Ministry of Agriculture.
Although the calculations do not go beyond multiplication and division, the whole calculation procedure to arrive, for the various crops, at irrigation water needs on a monthly basis is rather time-consuming and requires background knowledge. It is advisable that those intending to use Part II first take notice of the content of Part I.
For those technicians who are not involved in the actual determination of irrigation water needs and who can obtain these data locally. Part I may serve as general background to the subject.
This electronic document has been scanned using optical character recognition (OCR) software and careful manual recorrection. Even if the quality of digitalisation is high, the FAO declines all responsibility for any discrepancies that may exist between the present document and its original printed version.
2.1 THE INFLUENCE OF THE CLIMATE ON CROP WATER NEEDS
2.2 INFLUENCE OF THE CROP TYPE ON THE CROP WATER NEEDS
2.2.1 Influence of Crop Type on the Daily Crop Water Needs
2.2.2 Influence of Crop Type on the Seasonal Crop Water Needs2.3 INFLUENCE OF THE GROWTH STAGE OF THE CROP ON CROP WATER NEEDS
2.4 DETERMINATION OF CROP WATER NEEDS
CHAPTER 2: CLIMATE AND CROP GROWTH
3.1 INFLUENCE OF CLIMATE ON CROP WATER NEEDS (ETo)
3.1.1 Introduction
3.1.2 Pan Evaporation Method
3.1.3 Blaney-Criddle Method
3.1.4 Calculation Example Blaney-Criddle
3.1.5 Indicative Values of ETo3.2 INFLUENCE OF CROP TYPE ON CROP WATER NEEDS (Kc)
3.2.1 Introduction
3.2.2 Determination of the Total Growing Period
3.2.3 Determination of the Growth Stages
3.2.4 Determination of Crop Factors3.3 CALCULATION OF THE CROP WATER NEED
3.3.1 Introduction
3.3.2 Crop Water Need Calculation Example
3.3.3 Special Cases
3.3.4 Indicative Values of Crop Water NeedsCHAPTER 4: IRRIGATION WATER NEEDS
4.1 INTRODUCTION
4.2 DETERMINATION OF THE EFFECTIVE RAINFALL*
4.3 CALCULATION OF THE IRRIGATION WATER NEEDS
4.4 IRRIGATION WATER NEED OF RICECHAPTER 5: CALCULATION EXAMPLE
ANNEX I - PAN COEFFICIENTS FOR CLASS A PAN AND SUNKEN COLORADO PAN