Agriculture Reference
In-Depth Information
Other methods that conserve both soil and water are farming on the contour,
bunds, and terraces. Crop rows on the contour tend to slow or stop water movement
down the slope, which means that soil does not move down the slope. Berms or
bunds are like small dams across the field that stop and hold water, thus preventing
it from leaving the field. In some cases soil eroded from higher in the field will be
caught on the up side of the berm, and thus eventually it can be expected that a
terrace will form. Figure 9.6 shows a badly eroded field and rock “dams,” or
berms, made from rocks collected form the field and placed on the contour to
prevent erosion.
Terraces are structures on a hillside where the soil has been removed from the
upper side of a slope and moved to the down side to make a relatively flat piece of
land that can be farmed and that has a reduced risk of erosion. At the down side of
the terrace a steep bank connects with the next lower terrace. This steep bank is kept
protected by permanent grass vegetation and not farmed or tilled.
Note that in all these cases the objective is to prevent soil erosion by preventing as
much water as possible from running down and off a hillside. Water that does not run
off a hillside has only two other options. It can infiltrate into the soil, thereby increasing
soil water, or it can evaporate. In most cases infiltration will be faster than evaporation.
Infiltration must be fast enough to prevent saturation of the soil profile for a period of
time that will otherwise kill the crops planted there. In most situations this is not to be a
particular problem. However, if it is a problem a drainage tile can be used to remove
excess water.
Soil can also be eroded by wind, called wind erosion. It occurs any time wind dis-
lodges soil particles and carries them away or out of a field. In this case keeping the soil
covered and preventing the wind from contacting the soil surface can reduce or elim-
inate erosion. Keep in mind that wind has to be strong and continuous to effectively
dislodge and carry soil away. Generally, the soil must also be dry because water
causes soil particles to stick together, and it has significant weight, thus making it diffi-
cult for wind to carry wet soil.
Prevention of wind erosion is similar to preventing water erosion. Keeping soil
covered with plant residues and growing plants prevent wind erosion. Structures,
usually living trees, called windbreaks used to slow wind speed and keep it off the
ground are effective in stopping wind erosion. It may seem strange but a porous wind-
break does more to prevent wind erosion than does a solid windbreak. A porous wind-
break allows some wind to go through, thus slowing it and allowing suspended soil
particles to fall out. Thus, in this case leaving stubble (plant stalks below the grain
head) in the field after harvest will help prevent wind erosion. Each row of stubble
acts as a windbreak. All windbreaks work best when they are at right angles to the
prevailing wind.
9.10
WATER ON THE THREE FARMS
Water for both Donio and A´da and Octavio come from springs in the mountains some
distance from their farms. Water is piped to the houses by a local authority, and they
Search WWH ::




Custom Search