Type in the number, hit Xy, type in 0. They were not trying to figure out which stars could host a human habitable planet.
Indeed rainfall erosion can be higher in semi-arid areas than in any other climatic zone. This is partly because the rainfall of semi-arid areas has a high proportion of convective thunderstorm rain of high intensity and high erosive power.
It is also because there is poor protective vegetative cover, especially at the beginning of the rainy season.
Some of the soils common in semi-arid areas are particularly vulnerable, either because they have poor resistance to erosion high erodibilityor because of their chemical and physical properties.
An example from Mexico is illustrated in Plate 4. Successful but expensive gully conservation like the Australian example shown in Plate 4. Many measures are directed primarily to one or the other, but most contain an element of both.
Reduction of surface run-off by structures or by changes in land management will also help to reduce erosion. Similarly, reducing erosion will usually involve preventing splash erosion, or formation of crusts, or breakdown of structure, all of which will increase infiltration, and so help the water conservation.
An example is the increasing awareness of the ineffectiveness of terracing programmes alone. Also, we are moving towards the view that the only effective programmes are those which have the full support of the people.
The subsistence farmer cannot afford to respond to philosophical or emotional appeals to care for the soil, and this means that conservation measures must have visible short-term benefits to the farmer.
For the subsistence farmer the benefit he would most appreciate might be increased yields per unit of land, or perhaps better production per unit of labour, or perhaps improved reliabi- lity of yield.
The idea of working together in groups on tasks which require a big labour force is well-established in many countries, particularly for planting or harvesting. The practice can be successfully extended to conservation works. On a fertile soil with good rainfall it may be sensible to invest a lot of labour or money in sophisticated schemes for controlling the run- off, but not in semi-arid areas with low and unreliable yields.
It follows that attempts to eliminate soil erosion completely may be unrealistic, and that some level of erosion may have to be accepted, and also some risk' of soil conservation measures failing.
An example of a realistic approach to the risk of failure are the flood diversion dams built in the People's Democratic Republic of Yemen for spate irrigation schemes. Each end of the diversion is built of stone, or nowadays concrete, with a simple earth centre section. It is accepted that the earth section will be destroyed by big floods but it is cheap to repair or replace Thomas To upgrade the design and construction so that they could withstand the year flood would increase the construction effort beyond what the farmers can provide.
This same approach should be applied to all mechanical conservation programmes in semi-arid areas. The record of soil conservation in north Africa is striking. Heusch concludes that the large conservation programmes in Algeria, Morocco and Tunisia, from towere based on inappropriate technology imported from the totally different conditions of the United States, and the whole effort was a mistake which should not be repeated.
In countries with advanced soil conservation programmes, particularly the USA and Australia, the concept of conservation tillage is the main theme of the recommendations for cropland, and it is also being taken up quickly in other areas, for example southern Brazil.
The application is mainly in mechanized high production farming with good rainfall, or for the control of wind erosion where there is large-scale mechanized cereal production. It is less applicable to low input level crop production, or subsistence agriculture.
The principles are equally effective in any conditions - to maximize cover by returning crop residues and not inverting the top soil, and by using a high crop density of vigorous crops. Conservation tillage also has the advantage of reducing the need for terraces or other permanent struc- tures. However there are several disadvantages which hinder the application of conservation tillage in semi-arid conditions: Surface manipulation such as ridging is discussed in Chapter 5.
The available moisture will be increased if the rooting depth is increased and it has been shown that in some cases deep tillage can help, for example on the dense sandy soils luvisols in Botswana Willcocks Reviewing many studies of experi- ments of depth of tillage on alfisols, El-Swaify finds varied results; deep tillage is beneficial for some crops but not all, and on some soils but not all.
Also deep tillage requires greater draught power which is usually in short supply in semi-arid areas. Ripping or subsoiling can be beneficial, either to increase the porosity of the soil, or to break a pan which is reducing permeability.
The deep placement of fertilizer can also be used to encourage more rooting at depth, but again the application of this technique to subsistence farming will be difficult.
It includes any farming practice which improves yield, or reliability, or decreases the inputs of labour or fertilizer, or anything else leading towards improved land husbandry, which we have defined as the foundation of good soil conservation.
Sometimes there is a long history of traditional farming and soil conservation practices which have been tested and developed over periods of time which are long enough to include all the likely variations of climate.
These traditional practices should give the best long-term result, bearing in mind that the farmer's interpretation of 'best' may be based on reliability rather than maximum yield. But the semi-arid areas are changing rapidly, and the traditional patterns may be no longer relevant.
As Jones says "while tradition may incorporate the wisdom of centuries of practical experience, it may also be inappropriate where recent demographic pressures have already compelled changes - for instance, the abandonment of bush fallowing or migration onto different types of soil or into more arid areas.
There is also the point that the agricultural scientist very often still lacks the recipe for certain success; and you cannot require farmers to adopt new practices that are only 50 percent successful.
Some of the techniques are: Farming on a rade is well established in India Swaminathan In high rainfall areas a common objective is to lead unavoidable surface run-off safely off the land using drains and ditches.
In semi-arid regions the objective is more likely to be to slow down the run-off to non- scouring velocities and to encourage infiltration or deposition of silt, without diverting the run-off. We also submit that composition-based strategy can only produce temporary, rather than sustained, competitive advantage in global competition and this strategy is not without limitations, costs and risks.
While the prior page was more about colonization motivation and methods, this page is more about good planets, hell-hole planets, scouting good planets, and changing hell-hole planets into good planets.
I suppose I am only one of many readers of Fine Woodworking intrigued by an early article about wooden-works clocks (FWW #10). My first efforts were only nominally successful (in large measure because I can be impatient–I wanted to build the whole clockworks and sit back and watch it run).
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What are the advantages and disadvantages of reducing project scope to accelerate a project? What can be done to - Answered by a verified Career Counselor.