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Ben-Gurion University of the Negev (2018)

Evolution of Agro-Ecosystems in Differently Managed Research Plots in an Arid Loess Area in the Northern Negev

Mor-Mussery Amir

Titre : Evolution of Agro-Ecosystems in Differently Managed Research Plots in an Arid Loess Area in the Northern Negev

Auteur : Mor-Mussery Amir

Etablissement de soutenance : Ben-Gurion University of the Negev

Grade : Doctor of Philosophy (PhD) 2018

Résumé
The current state of many semi-arid to arid cultivated lands, based on their fertility and productivity rates can be termed ‘degraded’ due to long-term overgrazing or unsustainable farming practices. Continuation of these cultivation methods at similar intensities will lead to un-changed or small further decrease of the land Rehabilitation State, a term describing the potential for sustainable further agricultural use. Implementation of conservation management will induce a steady recovery process leading to increased vegetation cover and enhanced soil fertility. The increased vegetation, in turn, enhances litter production, soil fertility, ecosystem engineer activity and landform stabilization, factors that collectively permit achieving appropriate productivity for sustainable agricultural utilization. In contrast, massive soil disturbance, such as improper landform re-modelling or deep tillage, will damage the function of ecosystem engineers, leading to instability, a state where spontaneous recovery becomes impossible. Taking this data and translating it to practical guidelines for the farmer arise four problems : what is the starting point in long-term degraded area, what is the optional (maximal possible) state and what is the most suitable practice to use for reaching the optimal state, relating parameters as climate and erosion. Moreover, how can one represents rehabilitation or degradation processes relying on soil properties with different temporal changes ? Therefore, the hypothesis is that only comparison of the soil properties in controlled cultivation to the common long-term used one, will enable to define the rehabilitation rate of the cultivation. In order to determine the rehabilitation state of different cultivations and the specific mechanisms affecting its value, a comprehensive study was carried out on different cultivated arid loess areas in Project Wadi Attir, the northern Negev, Israel. Soil fertility, productivity, landform stability and biological activity of conserved and heavily grazed rangelands, loess deposits, rocky slopes and agriculture terraces were analyzed before project implementation and during the following five years. Arid environments are characterized not only by low precipitation, but also by high yearly and inter-seasonal heterogeneity. Therefore, in order to calculate the net rehabilitation trend from changes in soil fertility, their values were normalized. A scheme based on two sets of reference plots was used. One control plot resembles the common cultivation in the studied plots, heavily grazed and intensely tilled. Separate plots were defined for the treatments of loess deposit and rocky slope. The second type of reference plots resembles the maximal fertility state achieved in the studied cultivations. The plot chosen in the Project Wadi Attir area was conserved from grazing and located on an abandoned ruminants enclosure overlaid with an ageing manure layer. The ratios between the soil fertility parameters of the studied treatments and their values in the reference plots reflect their net change

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