تقييم ثباتية التجمعات وعلاقتها ببعض مكونات التربة في اعالي حوض الفرات

Abstract

Unused soil samples were collected from different regions in the western Iraqi desert, during summer 2011. S0il profiles were morphologically described and classified depending on the USDA Survey Staff 2011. Undisturbed soil samples for the horizons of soils were analyzed. The samples passed through 8 and 4 mm sieves respectively, with its moisture then air dried, afterwards soil aggregates were taken on the sieve of 4 mm to estimate mean weight diameter (MWD), then the soil aggregates passed through 2 mm sieve and remain on 1 mm sieve were taken to estimate water stable aggregate (WSA), while micro aggregate stability were estimated by using Stokes law, once the existence of bonds and once when removed. The most important results can be summarized as follow: 1 – According to the report of British Environment Agency, the aggregates stability of desert soils are sustainable or have high sustainability when using MWD and WSA index, when samples were pre - wetted by steam, and rated non-sustainable to high sustainability when samples are immersed. However when using a percentage of dispersion DR the soil aggregates are unstable. 2 – There is no significantly statistical correlation for each soil property individually with MWD, Which decreased exponentially and significantly with the clay percentage increasing, when pre-wetting the samples by immersion with r2 values equal 0.31, and logarithmic decrease with pre-wetting by steam and under 10 cm tension with r2 values about 0.35 and 0.18 respectively. Significant exponential increase in MWD with increasing the percentage of gypsum in soil particle sizes less than 0.25, 0.25 – 0.5, 0.5- 1, 1-2 and 2–4 mm, and according to the power function in soil aggregates size less than 2 mm with r2 values ranged between 0.39 - 0.51. MWD decreases with increasing the percentage of lime in soil particles size 2 -4 and 4 -8 mm with r2 0.42 and 0.43 respectively in according to power function, however MWD decreases linearly with increasing in organic matter in the soil passed through 2 mm sieve at immersion pre-wetted with r2 values about 0.25. The values of r2 increase from 0.30, 0.27 and 0.20 for soil separates group, and the physical and chemical properties groups respectively, to 0.65 when overlapping all soil properties groups above as average for three wetting methods. The overlapping of lime, gypsum and organic matter groups and the groups of total properties gave r2 equal to 1.00. The soil indicate that related to MWD were trended to be the same MWD trend but with some differences in regression analysis slop and r2 values. 3 - The results showed that linear increasing WSA with increasing of clay percentage in soil with r2 about 0.60 under immersion, and decreased with increasing in silt with r2 0.44 and 0.24 under immersion and steam pre – wetting respectively, there is also significant correlation between WSA and sand under steam pre-wetting with r2 0.33. While WSA increase significantly with gypsum increasing as linear function in soil particles less than 0.25, 0.5 – 1 and 1 – 2 mm with r2 equal to 0.23, 0.28 and 0.20 respectively. The determination coefficient of soil separates group as an average for the two wetting methods 0.52, 0.12 and 0.29 for a physical and chemical groups respectively, and become 0.66 under overlapping of the above groups of properties, while overlapping groups of lime ratios, gypsum and organic matter give r2 equal to 1.00, the same result are obtained when the all studied properties overlap. 4 - The results showed that the DR increased as logarithmic function with increasing of gypsum percentage in soil particles size less than 0.25 and 2 mm, and linearly in remain soil particles size with r2 ranged between 0.38-0.61. The ASC index values decreased due to gypsum increment with power function relation for the aggregate soil size less than 0.25 mm, and liner relation for soil aggregate size 0.25 – 0.5 mm, and exponentially for the rest of soil particles size with r2 ranged between 0.50 - 0.81. CFI index decreases according to power function in soil particles size less than 0.25 mm with gypsum increase, and linearly in soil size 0.25 – 0.5, 2 – 4 and less than 2 mm, and as exponentially in soil size particles 0.5 – 1 and 1 – C 2, and as logarithmic function in soil aggregate size 4 – 8 mm with r2 ranged between 0.58 – 0.79. CDI index increases with gypsum increase according to logarithmic function soil aggregate size less than 0.25 and 4 – 8 mm, and according to the power function with in soil particles size 0.25 – 0.5, while there is linear an increase in the other soil size with r2 0.5 - 0.69. ASC index increased with increase in lime according to the power function in soil size 0.25 – 0.5 mm, and exponentially in soil size less than 2 mm. On the other hand, there is significant and exponential increases in soil size 0.5 – 1 and 4 – 8 mm with r2 ranged between 0.44 - 0.53. There is significant increase in CFI index with lime increase according to linear function of all soil particles size with r2 ranged 0.33 to 0.72. There are also linear and significant decreases in soil size less than 0.25 mm and exponentially decreases for the rest soil sizes with r2 ranged between 0.34 -0.78. The overlapping of soil micro aggregate stability indices and soil properties was similar to MWD and WSA indices. 5 - Results showed the possibility of predicting MWD and WSA for the rapid and slow pre-wetted method from the perception of some values of soil properties like the bulk density, electric conductivity and soil pH once, and another time from the realization of above values and percentage of soil separates. Results reveal good fitness between predicted and actual values. 6- Results show that the standard error of the method of pre-wetted by steam to simulate the week breakdown powers, when used to estimate MWD lower than the method of immersion and under 0.10 m tension pre-wetted at the 39 and 9% respectively. Besides the arrangement of the soil aggregate stability indices according to the variation coefficient was as the followings: WSAv < DR < MWDv < MWDc < WSAf < CDI < ASI = RSI < SI< MWDf < ASC < CFI While arrangement according to the ability indices to reflect the stability case as follows: WSAf > WSAv > CFI > CDI > DR > ASC > MWDf > MWDv > ASI > SI > RSI > MWDc