| Forestry training manual for the Africa region |
Total time 3 to 4 hours
- To have a forester trainee teach the other trainees how to build a rustic transit,
- To have the trainees build rustic transits,
- For the trainees practice use of transit by laying out the area in which to plant trees during Session 28.
The trainee for whom this is a special project instructs the other trainees in building a rustic transit. The trainees practice using the rustic transit for contouring by laying out an area to be used the following day. It is necessary for the trainees to learn how to construct and use these practical measuring devices, as in many cases more sophisticated equipment will not be available.
1. Building a Rustic Transit
Board 2 m (h) X 3 cm (w) X 2 cm (1)
Pole 2 m long (bamboo is good for this)
Small piece of wood 2 cm (h) X 4 cm (w) X 40 cm (1)
1 wing nut, 6 cm long
1 plumb line
1 weight (bowling ball is too big)
A piece of cloth - marker
Bottle cap - sight
Stakes for surveying
Exercise 1 Building a Rustic Transit
Total time 3 to 4 hours
The trainee for whom this is a special project shows how to build and use a rustic transit and lay out the area.
1. The trainee presents a lecture about rustic transits. (example of lecture follows)
2. Using newsprint and a completed transit, the trainee shows the others how to construct
3. The trainees construct a transit either individually or in groups of three depending upon the method used.
4. The trainees practice using a transit.
5. In the area designated by the technical trainer, the trainee lay out the area to be used for tree planting the following day.
Trainer’s Note: The technical trainer should monitor this session very closely. It will be necessary to work with trainees from the time they get the assignment to be sure the proper materials are available and being used.
Plowing along the contour is an agricultural practice to aid in erosion control. By plowing with the contour, soil erosion can be reduced by as much as 50%. Contour lines are generally incorporated with other erosion control measures such as strip cropping, crop rotation, agro-forestry, diversion ditches and diversion terracing.
Diversion terraces are widely used in Africa to catch surface run-off and allow its safe exit from the field. The terraces are constructed along the contour at intervals down the slope. The distance between terraces varies depending upon the slope of the land. The terrace is raised to a height of 50 - 70 cm with a width of 1 meter. The up slope side of the terrace has a channel 50 cm wide and 30 cm deep which catches surface run-off. This channel has a gradual slope of 0.25 - 0.50 percent off to one side of the field. The channel should be covered with a low growing grass to reduce erosion in the channel itself. The terraces should be vegetated with bunch grass, trees or naturally covered by weeds.
Contours can be laid out using rustic or modern instruments. Rustic instruments can be constructed easily and cheaply. Three people are generally needed to lay out the contour lines. Using rustic methods, about 4 - 6 ha/day can be marked as opposed to 15 20 ha/day with a tripod surveyor's level. These figures vary depending on the uniformity and slope of the land.
Laying out the Contours
The first step is to measure the slope of the field in degrees or percent. The steepness of the slope will determine the distance between terraces. The steeper the slope, the closer the terraces the less the gradient, the farther apart the terraces. Slope can be measured using a protractor, abney level or surveyor's level. The protractor will give degree slope while the latter will be percent slope. Tables are available in most areas which indicate terrace spacing in relation to slope and soil type.
After determining the slope and the terrace spacing, the marking can be started. Start from the highest point in the field and measure down the slope your calculated terrace interval to your first point. It is important to always measure this distance directly down the slope. This direction may not coincide down the border of the field. If this distance is not measured directly down the slope, the terraces will not have uniform distances between them. This may mean starting from the middle of the field (fig.8) from point "A" and measuring down slope towards point "B".
Point "B" is the starting point. From here you mark the contour towards the borders of the field.
When you arrive at point "C", you measure to your next terrace to point "D", directly down slope.
Using the rustic instruments, points can be marked every 10 or 15 meters. The points are marked by driving a stake into the ground. Using a surveyor' e level, points can be placed every 20 - 25 meters. A helpful way to measure these distances is to tie a light weight rope between the sighting instrument and the sight rod.
Once all the contour e are marked, you will see that some stakes may not be in line. It will be necessary to adjust some points in order to have a smooth plow line. For example, a sharp "V. in the contour will cause water to collect and leak through the terrace. It will also be harder for the farmer to plow his field.
The terraces can be constructed with a tractor, horse, oxen or by hand. The tractor is most efficient because it can throw more soil. When using animals, it is necessary to follow up with hoes to raise the terrace and also deepen the channel in front.
The actual plowing is done by throwing soil toward the stakes on both the uphill and downhill side. Two passes with a tractor on each side are usually sufficient. Three or four passes with animals on each side are recommended. The last pass with either method should be on the uphill side to clean out the diversion channel.
Vegetation should be established as soon as possible. Bunch grasses can be planted from cuttings or by seed. The grass in the diversion channel can be seeded or left to natural weed growth. Trees can also be planted on the terraces in conjunction with the bunch grasses.
SOME WAYS TO USE YOUR RUSTIC TRANSIT
You will be using this level to aid you in making contour level terraces. These are for the protection of soil in crop fields. This method is not recommended for over 13% slope.
Example: This is a Contour line.
You take the rustic transit and sight over the sight arm to the mark on the sight pole (which is ten meters away in this example).
Some ways to use the rustic transit
You can also incorporate a drainage slope into the contour terraces>This would be to disperse water caught in the ditches of the contour terraces. For example, you decide on .5% slope for drainage. For every 1% slope at 10 meters distance from sight pole to rustic level, you move the mark on the sight pole up or down (depending which way the slope runs). In this case, with .5% slope drainage at 10 meters distance, you would move mark up or down 5 cm.
For .5% elope, drain off channel, move sight line 5 cm every 10 meters between the two men (up or down depending on which way you want the water to run).
You can control 50% of your erosion by running your rows of crops along the contour line. The contour line does not need to be long.
Another Rustic Level that could be built.
Rustic Level: A-Frame
A rustic level is a tool that can be made of simple materials, easy to use and simple to construct. The materials can be anything that is readily available, such as lumber (l X 2's or 2 X 2's) or poles cut from local vegetation.
The dimensions do not have to be exact. The cross arm should be placed about half-way up. The string with the end weight should be hung from a nail placed in the juncture where the two legs meet. Consideration should be given to bolting together all pieces to facilitate easy transportation.
To calibrate the level, choose a semi-level spot of ground and pound a couple of 6" - 8" stakes halfway into the soil at a distance equal to the spread of the level's legs. Place the level on the stakes and make a pencil mark where the plumb line comes to rest. Then reverse the level and make a second mark. The level mark is halfway between these marks.
To make contours along a hillside, simply put a stake at the starting point. Then place one of the legs of the level on the stake and the other in the direction you wish to travel. Then move the latter leg up or down hill until the plumb line comes to rest on the level line. Mark that spot and move on. Put one of the legs on the stake you just placed.
Some information contained here is extracted from Soils, Crops, and Fertilizer Use by David Leonard, Peace Corps Reprint R-8.