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In this chapter I am presenting a methodology and basic equations permitting to establish models to monitor water, nutrient and salt distribution in the oasis soil under different irrigation system, to determine the best oasis architecture for an efficient use of resources, to estimate the amount of water really needed by plants and the oasis productivity, to test the efficiency of irrigation and drainage network, to detect the eventual diseases that can attack the three vegetable stories, to predict plant species distribution, to search indicators for environmental planning and ecosystem risk analysis. Finally, a method to scale up or extrapolate results from one stand to all the region have been evoked and a case study have been presented.
In North Africa region, the slogan raised by specialists is "A struggle in favour of oasis safeguard is a struggle against poverty" (Genetic Resources Action International 2002, 2003). In fact, the palm grove of those arid zones are maintained over a complicated water management system. The resources of water are limited which represent a real restraint menace in front of the durable development of the oasis and a menace for the irrigated plants (Association Network for Durable Development of Oases, 2001, 2002; Bob Brac 2002). The rural community of North Africa can not undertake them self in the debate about the biodiversity without discussed the constraints of water resources and soil erosion. The effect of climatic change in the region is characterised by long period of accentuated drought, and abstract
1 introduction brief violent rainfall. Which have caused a decrease of the agriculture product yield, a degradation of the vegetation cover, an hydraulic and wind erosion of soils. Ameliorating the situation and realising a durable development need a scientific study that permits to establish equations describing the best arrangement of tolerant plants for an efficient use of resources and to develop ecosystem risk indicators for the oasis. These indicators can be linked to water resource (which is the key restricting factor for oasis ecosystems), soil resource and climate resource. We must know how the water and the nutrient are distributed inside every type of soil in the region, how they are absorbed by the roots of every species, the influence of local climatic parameter when calculating the drainage and irrigation networks, which irrigation technique to use without wasting water for every type of soil and kind of plants, how to realise effectively the drainage and the leaching, how to conserve the genetic biodiversity reserve inside the oasis?. The set of empirical and theoretical equations that we will present later for many case studies permit to elaborate models that give a response to the above requests, orient the farmer to a best use of rare resources, to realise his plan for an effectual agricultural water management inside the oasis and to safeguard the biodiversity of tolerant plant.
The work presented in this guide put on a scientific support that response to the challenges faced by traditional farmers in the region and proposals for follow up. It is a holder that help them when broaching negotiation at local, regional and international level. In fact, the fight against desertification and rational use of water is being a priority in the political development of North Africa region and worldwide. Also, institutions are tending towards valorizing traditional farming knowledge and products, which help maintain biological diversity (Association Network for Durable Development of Oases, 2001; Genetic Resources Action International 2002, 2003). We can't forget that policy makers in charge of agricultural, water, and biodiversity management are moving in direction of including agriculturist and scientific researchers in fields of cultivation at all decision levels. Finally, the utility of my contribution is more clear when reminding that in North Africa, legislation concerning rational and long-term management of natural resources are enforced and any innovation involving natural resources or agricultural genetic diversity is a subject to an environmental impact assessment with the participation of local communities.
In this guide we will begin by reminding the tendency of the International and regional organizations specialized in nutritious security toward revive traditional know how in agricultural water management and local biodiversity conservation inside the oasis of North Africa. The problems, challenges and occupations of the farming communities working for the oasis ecosystem in North Africa will be discussed. To degage the practical value of my intervention I will resume the objectives of some projects executed or currently under execution in favor of the oasis of North Africa countries. After I will present a set of equations describing water, nutrient and salt distribution for different type of soil that characterized the arid zone of the region, under many irrigation systems used or can be used in the oasis and for every sorts of plant. The interaction soil-plant-atmosphere will be evoked later. Under the same heading we will formulate the solar radiative exchange and the heat and mass transfer inside the oasis. Those equations permits to estimate the biomass productivity of plants, to detect the eventual vegetation diseases by analyzing the leaves optical properties, to calculate the water really needed by plants by determining the evapotranspiration and finally to test the best arrangement between plant (species, density, orientation of rows.) to an efficient use of resources. To scale up a result done in a particular oasis to those of all the region we will present the useful methodology. It can be also used for the problem of extrapolation of data. The results of measurement studies done inside the oasis of the south of Tunisia and models established using the same basic equation will be detailed.
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