Handbook of Irrigation Technology

Volume 2

herman J. Finkel

• Publisher: CRC Press
• Year: 2019
• Print ISBN: 9781315893556
• eBook ISBN: 9781351089555
• Topic: Sciences biologiques
• Subtopic: Science environnementale

This book was first published in 1983. It provides a comprehensive overview of irrigation technologies, techniques and economics, tailored to a multitude of different crops.

1
Land Grading

Dov Nir

General

Most natural soil surfaces, as well as many cultivated fields, are more or less irregular, consisting of alternating depressions and elevated areas. This results in pondage of water and interrupted surface drainage on one hand, and in accelerated soil erosion on the other; other effects may be nonuniformity of yield and crop quality, difficulties in mechanized field operations, as well as inadequate drainage.

Under irrigated conditions, surface irregularity is even more harmful. Gravity irrigation methods require even and continuous overland flows over nonexcessive slopes, in order to provide uniform wetting of the root zone, decrease deep percolation losses, and prevent soil erosion. Even when sprinkler (or trickle) irrigation is used, irregular soil surfaces may cause nonuniformity of wetting and surface pondage.

Consequently, in most cases it is advisable to re-form the land surface so as to provide continuous, gentle slopes, regulated water flows, and adequate drainage. This is expensive and therefore must be well-designed, carefully executed, and constantly maintained. Design should take into account soil type and depth, natural slopes and drainage system, and the method of irrigation to be employed.

The following three main types of land forming are used:

1. Land leveling is creating an almost horizontal soil surface, sometimes in the form of bordered basins, with not more than 0.5% slope in the direction of cultivation, and at most 1% at right angles to this direction. This conserves water and helps in flood control, and is used both under irrigation and dry farming conditions.
2. Land grading provides a continuous sloping plane surface in the graded plot. Generally the slope would not exceed 5% and will remain roughly parallel to the original general slope of the field; this would help decrease the amount of soil to be moved. A method of land-grading design will be presented here; this includes, as a particular case, the design of land leveling as well.
3. Land smoothing is a means of removing local elevations and filling local depressions, in order to permit continuous surface water flow to the field outlet. This is done with no calculated design — with the implement (generally, bulldozer) operator using his keen eye, good judgment, and past experience to guide him in the efficient execution of his work. This consists of a rough lowering of elevations and filling of depressions, followed by two to four fine smoothings in different directions.

When Not To Grade

Grading should not be done when: (1) soil (infiltration, slopes, depth, etc.) and water (discharge) conditions counterindicate surface irrigation, (2) soil is shallow; and (3) topography is so irregular that grading would require excessive earthmoving and will be too expensive. In general, movement of more than some 1500 m³/ha would be considered too costly.

Principles of Land Grading

1. Minimum of earth moving
2. No cut to exceed a certain maximum (about 15 cm); if in some points this principle is not adhered to, the exposed soil should be fertilized or covered with stripped topsoil
3. Minimum haul distances
4. Cut should exceed fill by 15 to 50%. This is due to compaction during fill, transportation losses, and soil crowning near the stakes. (Generally a 20 to 30% shrinkage factor is indicated)
5. Maximum convenience and efficiency in the operator’s work

Equipment

Grading equipment consists of various types of machines, either self-propelled or hitched to tractors (crawler or wheeled). Heavy work is generally done by scrapers (or bulldozers, for short hauls and stony soils); finer grading and smoothing are best done by graders and land planes, or even by animal-drawn floats. See Figures 1, 2, and 3.

During the 1970s a significant advance in land grading has been achieved by the introduction of laser-operated controls, allowing a higher level of accuracy and efficiency of operation. A rotating laser beam (at 10 to 300 rpm) defines a control reference plane; this is “read” by a 360° sensor on the equipment’s cab which automatically controls its operation by means of a direct link to its hydraulic system. More than one machine (each with its own sensor) can use a single laser source to distances exceeding 0.5 km, even in daytime.

Steps for Land Grading

1. Decide on a suitable irrigation method according to surface conditions, soil type, crops and rotation, manpower, water availability (amounts, discharge, quality), local usage, etc.
2. Divide the field into plots according to size, alignment of farm roads and water-ways, and local slopes. Each plot will be graded as one unit.
3. Determine required or permissible slopes, both in the direction of cultivation and in the cross-direction.
4. Stake the area, preferably at a square grid of 10 to 25 m in each direction. The more irregular the topography, the smaller the squares. Stakes should be 120 cm long, 2.5 × 2.5 cm in section, and should be driven into the ground to a depth of 30 to 40 cm.
5. Survey the plot by means of a surveyor’s level, determining surfa...

Table of contents

• Cover
• Title Page
• Copyright
• Contents
• 1 Land Grading
• 2 Drainage of Irrigated Fields
• 3 Criteria for the Choice of Irrigation Method
• 4 Health Hazards of Irrigation
• 5 Economics and Costing of Irrigation
• 6 Automated Computerized Irrigation
• 7 Irrigation Management and Scheduling
• 8 Irrigation of Cotton
• 9 Irrigation of Sugar Crops
• 10 Irrigation of Oil Crops
• 11 Irrigation of Cereal Crops
• 12 Irrigation of Alfalfa
• 13 Irrigation of Citrus
• Index