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sur le développement des zones arides et semi-arides

Titre : Properties of dark anthropogenic soil layers and influence of charcoal on crop growth in the Negev desert

Auteur : Bor, A.

Université de soutenance  : Wageningen University

Grade : Master of Science (MS) 2010

Résumé
Research into the sustained fertility of Terra Pretas in the humid tropics has led to the discovery of enriched levels of charcoal. At Horvat Haluqim, an Iron Age desert village in the Central Negev Highlands (Israel), dark anthropogenic soil layers containing pieces of charcoal have also been found. The objective of this study was twofold. The first objective was to assess the differences in chemical and physical soil properties between the anthropogenic and the non-anthropogenic soil horizons at Horvat Haluqim and to assess whether they could be attributed to charcoal fertilization. The observed differences were compared to the effects of charcoal that have been reported for soils in the humid tropics. The second objective was to identify possible beneficial effects, in terms of chemical and physical soil fertility, of the addition of charcoal on crop production in the Negev soil and to compare this to the reported effects of addition to the soils in the humid tropics. The anthropogenic soil horizons have significantly lower mean bulk density (1.21g cm-3) compared to non-anthropogenic soil horizons (1.39 g cm-3). The anthropogenic horizons also have more often a weak structure compared to the non-anthropogenic horizons. These differences are not related to the charcoal content of the soil horizons, because the charcoal content of the soil is very low, ranging from 0.06 to 0.19% and is comparable between the anthropogenic and non-anthropogenic horizons, even though there is a distinct difference in colour. Furthermore, the soil horizon with the highest charcoal content does not have the lowest bulk density or the weakest structure. No differences were found in pH, EC and cumulative infiltration between the anthropogenic and non-anthropogenic soil horizons from Horvat Haluqim. Charcoal addition to the soil in the pot experiment slightly increased soil pH and EC, but water retention decreased. Charcoal additions to soils in the humid tropics usually lead to an increase in pH that is much larger than the increase that was observed in this study. A pot experiment with wheat was conducted with the anthropogenic and non-anthropogenic soil from Horvat Haluqim with or without the addition of charcoal and ash. The addition of charcoal led to significant lower crop growth and biomass production compared to the control. This was most likely caused by N deficiency, since charcoal has a high C/N ratio, which can lead to N immobilization. In contrast to what was found in this study, charcoal addition to highly weathered soils of the humid tropics often leads to increased crop growth and biomass production due to reduced Al availability and the addition of nutrients. The dark colour of the anthropogenic soil horizons at Horvat Haluqim is not due to the presence of charcoal and in that sense they are not comparable to the Terra Pretas in the humid tropics. The creation of ‘Terra Pretas’ in arid regions with loess soils through addition of charcoal, as has been done in the humid tropics, shows no great potential, since it decreases water retention and can lead to N deficiency.

Mots clés : anthropogenic horizons / horizons / charcoal / soil fertility / crop production / soil properties / soil ph / nitrogen / desert soils / israel

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