The water stability of aggregates in various size classes separated from 18 samples of red soils under different managements, and the mechanisms responsible for the formation of water-stable soil aggregates were studi...The water stability of aggregates in various size classes separated from 18 samples of red soils under different managements, and the mechanisms responsible for the formation of water-stable soil aggregates were studied. The results showed that the water stability of soil aggregates declined with increasing size, especially for the low organic matter soils. Organic matter plays a key role in the formation of water-stable soil aggregates. The larger the soil aggregate size, the greater the impact of organic matter on the water stability of soil aggregates. Removal of organic matter markedly disintegrated the large water-stable aggregates (> 2.0 mm) and increased the small ones (< 0.25-0.smm) to some extent, whereas removal of free iron(aluminium) oxides considerably destroyed aggregates of all sizes, especially the < 0.25-0.5 mm classes. The contents of organic matter in water-stable aggregates increased with aggregate sizes. It is concluded from this study that small water-stable aggregates (< 0.25-0.5 mm) were chiefly cemented by Fe and Al oxides whilst the large ones (> 2.0 mm) were mainly glued up by organic matter. Both free oxides and organic matter contribute to the formation and water stability of aggregates in red soils.展开更多
In the Tunisian arid zones, where the soils are sandy and very poor in organic and mineral matters, wind erosion process is very active and triggered the departure of the thinnest elements of the soil and the appariti...In the Tunisian arid zones, where the soils are sandy and very poor in organic and mineral matters, wind erosion process is very active and triggered the departure of the thinnest elements of the soil and the apparition of dune building. Facing to these situations, many simple and efficient practices for combating desertification had been tested since many years in the Tunisian arid zones. The mulching of the olive mill wastewaters is one of these techniques. Otherwise, an olive mill wastewaters spray experimental device, with these respective doses of 50 m3/ha, 100 m3/ha and 200 m3/ha next to a witness parcel without OMW, has been putted in place since 1995 in the Chammakh-Zarzis, Tunisia. The mulching of the OMW, in the southern Tunisian regions constitutes an interesting alternative for the controlled and rational evacuation of this polluting sewage on the one hand and for the soil cohesion improvement by： （i） the increase of the organic matter rate which raised, in proportion to the dose, from 0.06% to 1.27% after 10 years of OMW mulching, and （ii） the improvement of the soil structural stability or ~＇the mean weight diameter＂ where the aggregation rate superior to 2 mm is increased until 34% with the dose of 200 m3/ha. Therefore, that treatment will bind the sand particles and thereof control of sandstorms is gained. Indeed, the results in wind tunnel tests on the soil treated with these different doses of OMW showed that the threshold friction velocity u,t was raised from 8.5 m/s to 12 m/s for 50 m3/ha and 200 m3/ha, respectively.展开更多
Studies conducted over several decades have shown that the freeze-thaw cycles are a process of energy input and output in soil, which help drive the formation of soil structure, through water expansion by crystallizat...Studies conducted over several decades have shown that the freeze-thaw cycles are a process of energy input and output in soil, which help drive the formation of soil structure, through water expansion by crystallization and the movement of water and salts by thermal gradients. However, most of these studies are published in Russian or Chinese and are less accessible to international researchers. This review brought together a wide range of studies on the effects of freezing and thawing on soil structure. The following findings are summarized： i） soil structure after freeze-thaw cycles changes considerably and the changes are due to the mechanical fragmentation of soil coarse mineral particles and the aggregation of soil fine particles; ii） the particle size of soil becomes homogeneous and the variation in soil structure weakens as the number of freeze-thaw cycles increases; iii） in the freezing process of soil, an important principle in the variation of soil particle bonding is presented as： condensation →aggregation→ crystallization; iv） the freeze-thaw cycling process has a strong effect on soil structure by changing the granulometric composition of mineral particles and structures within the soil. The freeze-thaw cycling process strengthens particle bonding, which causes an overall increase in aggregate stability of soil, showing a process from destruction to reconstruction.展开更多
文摘The water stability of aggregates in various size classes separated from 18 samples of red soils under different managements, and the mechanisms responsible for the formation of water-stable soil aggregates were studied. The results showed that the water stability of soil aggregates declined with increasing size, especially for the low organic matter soils. Organic matter plays a key role in the formation of water-stable soil aggregates. The larger the soil aggregate size, the greater the impact of organic matter on the water stability of soil aggregates. Removal of organic matter markedly disintegrated the large water-stable aggregates (> 2.0 mm) and increased the small ones (< 0.25-0.smm) to some extent, whereas removal of free iron(aluminium) oxides considerably destroyed aggregates of all sizes, especially the < 0.25-0.5 mm classes. The contents of organic matter in water-stable aggregates increased with aggregate sizes. It is concluded from this study that small water-stable aggregates (< 0.25-0.5 mm) were chiefly cemented by Fe and Al oxides whilst the large ones (> 2.0 mm) were mainly glued up by organic matter. Both free oxides and organic matter contribute to the formation and water stability of aggregates in red soils.
文摘In the Tunisian arid zones, where the soils are sandy and very poor in organic and mineral matters, wind erosion process is very active and triggered the departure of the thinnest elements of the soil and the apparition of dune building. Facing to these situations, many simple and efficient practices for combating desertification had been tested since many years in the Tunisian arid zones. The mulching of the olive mill wastewaters is one of these techniques. Otherwise, an olive mill wastewaters spray experimental device, with these respective doses of 50 m3/ha, 100 m3/ha and 200 m3/ha next to a witness parcel without OMW, has been putted in place since 1995 in the Chammakh-Zarzis, Tunisia. The mulching of the OMW, in the southern Tunisian regions constitutes an interesting alternative for the controlled and rational evacuation of this polluting sewage on the one hand and for the soil cohesion improvement by： （i） the increase of the organic matter rate which raised, in proportion to the dose, from 0.06% to 1.27% after 10 years of OMW mulching, and （ii） the improvement of the soil structural stability or ~＇the mean weight diameter＂ where the aggregation rate superior to 2 mm is increased until 34% with the dose of 200 m3/ha. Therefore, that treatment will bind the sand particles and thereof control of sandstorms is gained. Indeed, the results in wind tunnel tests on the soil treated with these different doses of OMW showed that the threshold friction velocity u,t was raised from 8.5 m/s to 12 m/s for 50 m3/ha and 200 m3/ha, respectively.
基金supported by the Natural Science Foundation of China(No.41301070)the National Key Basic Research Program(973 Program) of China (No.2012CB026106)+2 种基金the West Light Program for Talent Cultivation of Chinese Academy of Sciences(toDr.ZHANG Ze)the Scientific Research Foundation for the Returned Overseas Chinese Scholars,China Ministry of Education(to Dr.ZHANG Ze)the Scientific and Technical Projects of the Transport Department of Gansu Province,China(No.2014-03)
文摘Studies conducted over several decades have shown that the freeze-thaw cycles are a process of energy input and output in soil, which help drive the formation of soil structure, through water expansion by crystallization and the movement of water and salts by thermal gradients. However, most of these studies are published in Russian or Chinese and are less accessible to international researchers. This review brought together a wide range of studies on the effects of freezing and thawing on soil structure. The following findings are summarized： i） soil structure after freeze-thaw cycles changes considerably and the changes are due to the mechanical fragmentation of soil coarse mineral particles and the aggregation of soil fine particles; ii） the particle size of soil becomes homogeneous and the variation in soil structure weakens as the number of freeze-thaw cycles increases; iii） in the freezing process of soil, an important principle in the variation of soil particle bonding is presented as： condensation →aggregation→ crystallization; iv） the freeze-thaw cycling process has a strong effect on soil structure by changing the granulometric composition of mineral particles and structures within the soil. The freeze-thaw cycling process strengthens particle bonding, which causes an overall increase in aggregate stability of soil, showing a process from destruction to reconstruction.
