Water Requirements for Irrigation and the Environment

Irrigated agriculture produces about 40% of all food and fibre on about 16% of all cropped land. As such, irrigated agriculture is a productive user of resources; both in terms of yield per cropped area and in yield per volume of water consumed. Many irrigation projects, however, use (divert or withdraw) much more water than consumed by the crop. The non-consumed fraction of the water may cause a variety of undesirable effects ranging from water-logging and salinity within the irrigated area to downstram water pollution.

This book discusses all components of the water balance of an irrigated area; evapotranspiration (Ch.2), effective precipitation (Ch.3) and capillary rise from the groundwater table (Ch.4). Chapter 5 then combines all components into a water management strategy that balances actual evapotranspiration (and thus crop yield) with the groundwater balance of the irrigated area (for a substainable environment). Chapter 6 presents CRIWAR 3.0, a simulation program that combines all water balance components into a single simulation procedure. The chapter describes the use of the CRIWAR software for developing water requirement tables and other useful information based on the selected water management strategy. This version greatly expands upon the capabilities of previously published programs.

1 Introduction: 1.1 Growth of vegetation; 1.2 Crop growth and evapotranspiration; 1.3 Irrigation water requirements; 1.4 The water balance of an irrigated field; 1.5 What does CRIWAR calculate? 1.6 ETp - Pe in the field water balance; 1.7 The irrigation ratios; 1.8 Structure of the Handbook. 2 Evapotranspiration: 2.1 Introduction; 2.2 Developments in Theory; 2.3 The Penman-Monteith Approach; 2.4 The Hargreaves-Samani Method; 2.5 Discussion; 2.6 The potential ET; 2.7 The Dual Kc Method: Incorporating Specific Wet Soil Effects; 2.8 ET during the Non-growing Season; 2.9 Evapotranspiration from Landscapes; 2.10 Estimating Kc from the fraction of Ground Cover; 2.11 Effects of Surface Mulching on Kc . 3 Effective Precipitation: 3.1 Introducton; 3.2 Major factors affecting effective precipitation; 3.3 The USDA Method. 4 Capillary Rise: 4.1 Introduction; 4.2 The driving force of capillary water; 4.3 Steady-state capillary rise; 4.4 Fluctutation of groundwater depth and soil moisture; 4.5 Rooting depth; 4.6 How to correct for capillary rise? 5 Irrigation Water Requirements: 5.1 Concept; 5.2 The Field; 5.3 The Distribution System; 5.4 The Conveyance System; 5.5 Calculating Irrigation Water Requirements. 6 Using the CRIWAR Software: 6.1 Introduction; 6.2 Computer System Requirements; 6.3 Obtaining the Software; 6.4 Software Overview; 6.5 Input Data Requirements; 6.7 Developikng a water management strategy; 6.8 Producing Output; 6.9 Program Options; 6.10 Warning and Error Messages.