In this article we will discuss about:- 1. Introduction to Land Grading 2. Factors Affecting Land Grading 3. Planning and Survey 4. Construction Procedure 5. Paddy Field Layout 6. Equipments.
Contents:
- Introduction to Land Grading
- Factors Affecting Land Grading
- Planning and Survey for Land Grading
- Construction Procedure for Land Grading
- Paddy Field Layout
- Equipment’s Used for Land Grading
1. Introduction to Land Grading:
Any land used for agriculture requires an even surface for crop production. Land grading consists in reshaping the field surface to a desired grade. Land grading is beneficial both under irrigated and rainfed conditions. Land grading removes humps and depressions interfering with the flow of water on the land surface.
Low spots could cause concentration of water and waterlogging which may affect crop growth, and may also bring harmful salts to the surface. In irrigated agriculture uneven land surfaces need a high head of water to push through the irregularities of the field. This may also cause loss of water as well as soil erosion.
Land grading in irrigated agriculture helps in uniform application of water, better water regulation and saving in irrigation time. Under rainfed conditions, land grading helps in soil and moisture conservation. Either in irrigated agriculture or under rainfed conditions, land grading provides the much needed surface drainage. The terms land grading, land levelling, and land forming are generally used to mean the same thing.
Land levelling need not necessarily mean to bring the surface to perfect level. Many a time a moderate grade is preferable for surface drainage. Depending upon the topography, land levelling requires moving a lot of soil, sometimes over large distances. After the land levelling operations, the land surface requires further smoothing. Land smoothing (also known as land planning or land floating) is the operation that removes the minor irregularities.
Field layout is important both in water management and use of machinery. Due to land fragmentation, a proper layout may be difficult. Land consolidation and proper layout will improve land and labour productivity.
2. Factors Affecting Land Grading:
The land grading operations required for an area depend upon the topography of the area, soil type, soil depth, crops to be grown, source of water supply and method of irrigation.
Based on the initial topography of the land, the layout of the individual fields, irrigation and drainage system needs to be planned. The individual fields should be levelled subsequently as per their requirement. Depending upon the topography, the land may have to be converted into bench terraces.
The depth of the soil restricts the depth of cut in land levelling operations as strata unsuitable for cultivation should not get exposed. The soil texture which influences the infiltration capacity of the soil needs to be considered for giving the final grade to the field. The crops to be grown influence land grading for example, for rice cultivation the land needs to be flat whereas for other irrigated crops mild grades are preferable.
3. Planning and Survey for Land Grading:
The entire farm or the area should be taken into consideration for the purpose of planning land grading operations. Information about the soils, existing field boundaries, water courses, sources of irrigation etc., is to be obtained. A topographical plan of the area with the levels marked is necessary for calculating the earthwork involved in grading and also to decide the layout of the fields.
The topographical survey is carried out as follows:
If a plan of the area is available, it is convenient to draw it on a graph paper to a suitable scale. In case the plan of the area is not available, such a plan can be prepared by chain surveying the area.
The whole area should be divided into squares (referred to as grids) with the help of ranging rods and cross-staff or optical square. The size of the grids adopted are 30 m x 30 m, 15 m x 15 m, or 8 m x 8 m depending upon the size of the field, topography and accuracy of work needed.
For convenience of making the grids, a square corner of the field i.e., one which is a right angle is selected. If there is none, two base lines are made at right angles and their position is marked on the field and as well on the plan.
The first line should be parallel to the base line at a distance of half the proposed grid size. (If the proposed grid size is 30 m x 30 m, this line should be at a distance of 15 m from the base line). Pegs are fixed on the line at the prescribed grid distance.
Similarly pegs are fixed on the line perpendicular to this line and at all grid points. By this procedure, each peg will be at the centre of the square and it is assumed that the level at this peg will represent the level of the entire square.
After the points are marked, readings are taken with the help of the Dumpy Level at all these points with reference to a bench mark and the reduced levels are calculated.
The reduced levels should be marked on the plan and with the help of these levels the contour lines can be drawn. The levels taken at the corners of the squares are used for calculating the earth work involved in the grading operation subsequently.
After the contour plan of the entire area is ready the whole area is divided into fields in accordance with topographical situations (Fig. 13.1) such that each of these plots can be graded to the best advantage. While dividing the area, as far as possible irregularly shaped fields should be avoided, as it is difficult to irrigate and cultivate such fields. Also provision should be made at this time for surface drainage.
4. Construction Procedure for Land Grading:
After the calculations for the desired spot levels have been made, the grid points on the land are marked with the help of pegs. The pegs may be differently coloured or some indication on them may be given to know whether at the particular point earth has to be cut or filled.
It will also be convenient to place bricks or earthen heaps indicating the final level at that point. Taking these as guides, the operator can operate the implements to move the earth in the desired directions. After the earthwork is complete it will be desirable to have a check with the Dumpy level again.
Under some soil conditions, it may be possible that the exposed subsoil as a result of excavation may not be suitable for agriculture. In such cases, the top soil is stock piled separately and spread back after the land grading operations. This will involve moving the soil twice and is therefore done when it is justified from the benefits.
5. Paddy Field Layout:
In case of paddy fields, land levelling is done to obtain a horizontal surface. In addition, layout of the paddy fields is also important for efficient water management.
The layout of paddy fields in a given area initially depends upon the topography but gets modified over a period of time. Several factors like social conditions, land ownership, methods of cultivation, water supply, etc., influence the layout.
An examination of the field layouts in many of the Asian Countries indicates the following problems or difficulties:
1. Because of the irregular layouts followed, considerable land area is lost in bunds (low embankments).
2. Movement of water either for irrigation or drainage becomes difficult.
3. Utilization of rainfall is not up to the maximum possible extent.
The paddy field layouts could broadly be classified, as:
(1) Plot-to-plot, and
(2) Individual plot layout.
There are varied forms and mixed layouts consisting of both of these systems. In individual plot layout irrigation and drainage are easily facilitated, where as in plot-to-plot layout water has to move from one field to another.
The objective of paddy field layout design in relation to water management is to improve the fields to an appropriate form and function for water utilization conditions such as distribution, application and drainage.
At the same time the goal is to achieve highest possible effective use of rainfall, reuse of surface runoff water and reduction of system losses like conveyance and seepage losses. Movement of machinery from field to field also needs to be considered.
In Thailand, paddy field improvement has been attempted in three stages. Ditch and dike development is the first level to ensure an adequate supply of water to each farm by provision of field ditches and drains.
In the next stage termed as extensive development, provision of roads is also made in order to access as many farms as possible. In the third stage, known as intensive development, areas are consolidated and regular plots with roads, irrigation channels and drainage facilities are constructed.
In paddy field layout and improvement, Japan has made significant progress. Fields have been consolidated and laid with irrigation and drainage channels and roads. This has improved the land and labour productivity and also helped mechanization.
6. Equipments Used for Land Grading:
The equipment used for land grading operations may be classified into two groups depending upon the source of power.
These are:
1. Equipment operated with animal power,
2. Equipment operated with mechanical power and
3. Laser Controlled Equipment.
1. Equipment Operated with Animal Power:
Animal power for land grading is economical for medium sized areas and upto a haul of 50 to 60 m.
The different equipment that can be used with animal power are:
i. Metallic Scoop:
This is also sometimes known as buck scraper. This is made up of mild steel sheet in the form of a container, has two handles and arrangement for hitching the bullocks. In this the earth is hauled using the container.
ii. Wooden Buck Scraper:
The wooden buck scraper consists of a wooden plank fitted to a platform and a handle. The movement of earth is facilitated by standing on the platform and keeping the handle down. Wherever the earth is proposed to be dumped, the operator should get down from the platform and the handle may be used for lifting the wooden plank so that the earth is dumped.
2. Equipment Operated with Mechanical Power:
The different equipment operated with mechanical powers that are useful for land grading operations are:
(1) Bulldozers,
(2) Motor graders,
(3) Scrapers,
(4) Tractor mounted blade terracers, and
(5) Land planes and floats.
(1) Bulldozers:
The bulldozer is essentially a crawler tractor with a front mounted blade. The bulldozer is capable of cutting the earth upto 15 cm to 25 cm easily and can move large volumes of earth over short distances efficiently. The bulldozer is not efficient to move earth beyond 30 m of distance. It is also not suitable for fine grading.
(2) Motor Graders:
The motor grader is largely used in the highway construction work. It has a rear mounted engine and a blade mounted on a frame in the front and supported by two front wheels. Because of its flexibility of operation, the motor grader is useful for a wide variety of jobs in land grading. In addition to cutting and filling the motor grader is useful for forming ditches and banks.
(3) Scrapers:
The scraper is an efficient machine for hauling earth over larger distances as compared to the bulldozer. The depth of cut possible with the scraper is, however, less than that of bulldozer. Scrapers are available in different sizes and also both as self-propelled and tractor drawn.
Small wheeled scrapers (also known as Turkish type scraper), which can be used with farm tractors, are convenient for land levelling operations in small farms. These are capable of effecting small cuts and carrying the soil and filling it wherever necessary. Sometimes it is necessary to loosen tight or hard soil by ripping or ploughing before the use of scrapers.
(4) Blade Terracers:
The tractor mounted blade terracer is an easily available equipment used for land grading purposes. It is normally rear mounted even though front mounted models are also available.
The depth of cut and the amount of earth that can be transported is comparatively small in the case of the blade terracer Land levelling operations using the blade terracers are therefore, time consuming.
(5) Land Planes:
Land planes and floats are equipment used to given final touches to a levelling job. The land plane has two or four wheels and adjustable blade located at about the centre of the frame. It is about 10 to 15 m long and this great length makes it possible to finish a field to a uniform smooth surface. Tractors of at least 50 HP are needed to pull the bigger land planes.
The two wheeled type plane hitched to the rear of a tractor is used for final levelling work. It has a movable blade placed at about the centre and is capable of drawing considerable volume of earth. It is usually less than 10 m long, and a medium sized farm tractor can operate it.
There are several designs of the float which is usually used as a land smoothing equipment. It consists of three cross beams fixed to two parallel beams of wood and does not have any wheels. Smaller versions of the float are operated with animal power.
3. Laser Controlled Equipment:
In the recent years laser controlled equipment is being successfully used for land smoothing operations. The laser transmitter placed near the field is mounted on a stand and projects a beam from a revolving head.
The transmitter can be adjusted so that the laser beam is projected on a level or a graded plane as desired. A receiver mounted on the scraper, keeps the scraper blade at the desired elevation of the final field elevation. The operation of the scraper all around the field gives the necessary final elevations.