There exist several simple and cheap means for marking out contour lines, namely the A-frame, the line level and the water tube level. The two level devices may also be employed for marking graded lines.
Making the A-frame:
The A-frame can be made using two pieces of wood about 1.2 m long and one piece about 0.6 m long, a carpenter's level or 0.6 m of string, a stone to be made into a pendulum, and nails or a string to fasten the A-frame together.
°Nail or tie the two long pieces of wood together at one end.
°Set the "legs" of the frame on level ground so that the "feet" are 1 m apart.
°Fasten the short piece of wood to the legs to make an "A".
Using the carpenter's level, check that the crossbar is level, and connect the carpenter's level to the crossbar. (If you will use a pendulum, hang the string from the top of the "A" and put the A-frame on level ground. Mark where the string crosses the crossbar).
Using the A-frame:
°Put leg A on the ground and move leg B forward or backward until the bubble in the carpenter's level floats to the centre (or the pendulum swings to the centre mark).
°Move the A-frame, placing leg A where leg B was before, and repeat the process.
°Move across the hillside along the contour, and place a marking stake every 3 or 5 m.
Using the Water Tube Level:
Using the water level, all that is required are two wooden poles each of approx. 1.8 m length and a clear (transparent) hose pipe of approx. 12 m length.
Employing the Water Tube Level:
Commence at the top of the field slope. Holding one of the two poles, one person remains at the starting point, while a second person moves across the slope over a distance of 10 m with the second pole. There he moves the pole upward or downward until the level of water in the hose pipe reaches the same level on each pole. The two positions are then marked and connected via a scratch mark line using a hoe. This line indicates the position of the contour line.
When the level of water reaches the same level on each pole,
the poles are on the contour.
Reference:
Pacey, A. & A. Cullis (1986): Rainwater harvesting. The collection of rainfall and runoff in rural areas. Intermediate Technology Publications, London/England.
Similarly to the water tube level, a line level may be used. Again, two wooden poles (each 2 m long) and a rope (approx. 11 m long) are required.
Employing the Line Level:
Fix the rope with each end to one pole so that exactly 10 m of rope are between the poles. Mark the middle of the rope at 5 m with knot. Hang the water level next to the knot mark. Then proceed across the slope, surveying 10 m at a time, and mark (scratch) the ground. For marking graded lines, the rope is fixed to different heights on the two poles. For example, for lining out 1% graded lines, the rope has to be fixed on the poles with 10 cm difference, that is at 1 m and 1.1 m height respectively.
Reference:
Hurni, H. (1986): Guidelines for Development Agents on Soil Conservation in Ethiopia.
Centre for Development and Environment, Bern/Switzerland.
The influence of slope and soil cultivation on runoff and/or infiltration can be demonstrated easily in the field with a watering can and small runoff trays.
  
First of all, cover the base of the trays with 25 mm depth of very coarse sand to allow for free drainage of the infiltrated water. Then take enough soil from a cropland to fill the trays. Break up any large clods and remove all pieces of vegetation. For experiments with small trays to be successful, it is essential for the soil in the trays to be in exactly the same condition. Do not compact the soil in the trays. Fill them with loose soil and smooth off the surfaces to exactly level with the sills. From a watering can pour exactly the same volume of water over each tray from a height of about 1 m. Now draw the attention of your audience (e.g. farmers) to the greater amount of water running off from poorly vegetated and/or cultivated soil (and the greater amount of "groundwater" water draining out from the bottom of the well vegetated and/or cultivated soil.) Both, the surface runoff and the groundwater drainage is collected in sets of glass containers placed below the chute (runoff) and bottom pipe (drainage) respectively.
Reference:
Elwell, H.A. (1986): Soil Conservation. The College Press, Harare, Zimbabwe - ISBN 0 86925 624-6
Postal address: Dr. H.A. Elwell, 2 Loerie Lane, Borrowdale, Harare, Zimbabwe.
See also:
Erosion Lanscapes
or
Soil Erosion Demonstrations
Mulch cover measurement by the meterstick method:
This method is well suited for small plots. A meterstick is placed on the soil surface and the total length of mulch (or crop residue) along one edge (side) of the meterstick is measured. Mulch coverage is the total length of mulch divided by the length of the meterstick. Location of measurement is determined randomly (e.g. by throwing the meterstick over one's shoulder into the plot behind). Because mulch is not spread uniformly on a field, the method requires measurements at several locations (5-10) in the field.
Reference:
Hartwig, R.O. and J.M. Laflen (1978): A meterstick method for measuring crop residue cover. Journal of Soil and Water Conservation, 33: 90-91.
Mulch cover measurement by the line-transect method:
This method is similar to the meterstick method. A 10 m long measuring tape is stretched out diagonally across an area, that is crop rows or tillage ridges. The number of times a meter mark is in contact with mulch material under one edge of the tape gives the percent mulch cover. If, for example, 6 of the meter marks have a piece of mulch under them, the cover is 60 percent.
Reference:
McGill, St. (1990): Measuring crop residues. The Furrow, 95: 37.
In order to determine plant root density in the field, soil pits need to be excavated. The pits ought to be dug across crop rows.
In the case of maize root profiles examined in tied ridged and mouldboard ploughed fields in Zimbabwe, the pits were dug across two crop rows (row spacing = 0.9 m) at the time of root sampling. They measured 1.8 m in width and 1.2 m in depth. The surface of the exposed soil profile wall was first smoothed with a putty knife and, subsequently, soil to a depth of approximately 5 mm was brushed off the profile face with a soft paintbrush to expose the maize roots. A 1.0 m x 1.2 m metal frame was then positioned over the cleared maize root profiles with the maize plants always situated in the centre of the frame top. This metal frame was interwoven with thin nylon twine to form a 50 x 50 mm grid pattern. Within each grid square, the position of each 5-mm length of root was noted as a dot on scaled paper. The number of dots per grid square was totalled for each 50-mm-depth increment across a 0.9-m with and converted to root length density (cm cm-3).
Source of image: Root studies
http://www.atinet.org/cati/upda/96/winter/story6.html
Reference:
Vogel, H. (1995): Maize root profiles in gleyic sandy soils as influenced by ridging and ploughing in Zimbabwe. Tropical Agriculture (Trinidad), 72: 120-125.
Prior to deciding upon a herbicide application or when interpreting yield data one ought to determine the actual density of weeds in a particular field. Simple counting frames provide for a quick means for measuring the percentage of the surface covered by small weeds.
 
The device consists of a metal or wooden frame featuring 4 squares of 25 x 25 cm each. With a measurement each square gets one out of 5 possible counts, namely 0 for no weeds, ¼ for ¼ filled with weeds, ½ for ½ filled with weeds, ¾ for ¾ filled with weeds and 1 for total square filled with weeds. Adding up the 4 figures and then multiplying the sum by 25, the weed cover percentage is obtained.
Weed counts made by placing the quadrate at random locations in plots have to be repeated a number of times in order to obtain a reasonably good estimate of the surface area that is covered by small weeds. Quadrates should not be placed completely at random when there are areas within the field which have been influenced by factors other than the treatment, that is rodents, irrigation, equipment, etc.
However, weed counts fail to reflect the practical effect of a few large weeds compared with a large number of small weeds. For rather large weeds the quantity of dry weed biomass per square meter can be determined. The weeds are cut off just above the soil and artificially dried at 105° C. Then the dry matter is weighed and the mass of oven-dry weed biomass per hectare can be calculated.
Reference:
Deutsch, A.E. (Ed.) (1976): Field Manual For Weed Control Research. International Plant Protection Center, Oregon State Univ., Corvallis, U.S.A.
AWC may be estimated from a "universal" soil water characteristic curve derived from a one-parameter model for the soil water characteristic that has shown to fit nicely for a wide range of soils (e.g. for soils in Britain and Zimbabwe).
Reference:
Gregson, K., Hector, D.J., and M. McGowan (1987): A one-parameter model for the soil water characteristic. Journal of Soil Science, 38: 483-486.
The method requires in-situ measurements of soil field capacity (FC). For the latter, the soil is fully wetted to at least 30 cm below the proposed maximum sampling depth, and covered with a sheet of polythene to reduce evaporative losses to a minimum. Soil water content samples are taken at the required depths 48 hours after wetting, and the water content recorded as the FC. Since soil water is determined on a weight basis, the associated soil bulk density (BD) and stone content determinations are needed to convert the result to a volume basis:
WC (% by volume v/v) = WC (% by weight w/w) x BD
that is
WC (%v/v) = Weight of water/weight of dry soil x weight of dry soil/total soil volume
Reference:
Landon, J.R. (Ed.) (1984): Booker tropical soil manual. A handbook for soil survey and agricultural land evaluation in the tropics and subtropics. Booker Agric. Intern. Ltd., Longman Inc., New York, U.S.A.
 
Stable soil aggregate versus structural surface crust
The stability of surface soil aggregates may be directly observed with a simple water coherence test. The test was developed for use in the field to assess the physical behaviour of agricultural topsoils likely to suffer from structural deterioration. To simulate rapid wetting as occuring in the field, approx. 10 g of air-dry 3 to 5 mm aggregates are flood-wetted in a shallow bowl (petri dish) and allowed to stand for up to 10 minutes to ensure complete wetting. Rotary shaking of the receptacle for 1/2 min completes the testing procedure, and, on the basis of a visual key, aggregates are allocated to one of six descriptive classes (very good - good - medium - moderate - low - very low aggregate stability). Although the classification itself is a crude and subjective procedure, the test achieves its main purpose of identifying structurally unstable surface soils in a quick and convenient way.
Reference:
Sekera, F. (1959): Gesunder und kranker Boden.
Ein praktischer Wegweiser zur Gesunderhaltung des Ackers.
Graz/Austria.
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Last updated on 2 September 1998
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