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Abstract ~~-_ .._---~--- .__..... --- 118 5_ s~y Salt affected soils are those having excessive concentrations of soluble salts and/or exchangeable sodium sufficient to interrupt the growth of roost crop plants, either directly due to the osmotic and specific-ion toxicity effects or indirectly by changing the physicochemical properties of the soil such as, poor water permeability, poor aeration a.nd root penetration problems. The area of salt affected soils in Egypt amounts to 800.000 ha (2 million feddans) concentrated in the northern and eastern part of the Nile Delta. In addition. the problem of salinity began to appear and did affect the production of further 400.000 ha by varying degrees. The present work aims at studying the effect of using two different types of soil conditioners (Bitumen emulsions and polyacrylamide solutions) at different application rates on some hydrophysical and chemical properties of some sa It at f ec t.ed soi Is of Egypt- With this respect, three salt affected soils were chosen in the presented study namely; A) saline non sodie clay soil from the Agricultural Experimental Station of the NRC at Shalakan. Qualubia Governorate, B) saline,sodic clay soil from Sakha, Kafr El-Sheick Governorate a~q C) sodie clay soil from Tal EI-Kebeir, Sharkia Governorate. Examined soil conditioners were a) a locally prepared Bitumen Emulsion (Bit I): 25% active material was prepared in the filed from the Egyptian raw materials. Bitumen (penetration 60/70) is produced by the EI-Nasr petroleum company. at Suez and the non ionic commercial type emulsifier (Misrofir 810) is produced by Misr Petroleum Company, Factory of Alexandria. b) Humofina Bitumen Emulsion. HA (Bit II): 50% active material produced by Lapofina, Petrclfina, Brussels, Belgium. C) Humofina polyacrylamide (PMll I) a low Mol.wt PAM solution (Mol.wt 150.000-200.000) 16% active material produced by Lapofina, Petrofina, Brussels, Belgium and d) a locally prepared polyacrylamide (PAM II) a highly Mol.wt (mol.wt 1.360.000) 10% active material prepared in the laboratories of NRC. Cctiro. Egypt. The rates of ---’._- -_._------- 119 application in weight of active material of the conditioner per 100 g of the dry soi.l-were0•.25, 0.5 and 1.0 for Bit and 0.1 and 0.2 for PAM. The optimal conditions to make the soil conditioning such as suitable initial and final soil moisture content were 10-15% and 30-35% (on weight basis), respectively. Some physical and chemicdl characterists of the affected soils under study as influenced by conditioners were determined. salt soil The results obtain can be summarized as follows: 1-’Effect of soi 1 conditioners on some physical properties of the salt affected soils: 1. Stability of soil structure: a- Micro aggregation 1- Soil micro structure expressed as percentages of increase in the structural unit> 2 u . > 5 u , > 20 u. and > 50 u in diameter was improved in the three examined salt affected soils by conditioning. The effectiveness of both types of soil conditioners on improving soil micro structure was enhanced by increasing the amountB of conditioners applied. At the same appl ication r-ate of PAM, the higher the Mol.wt is. the more stable is the soil microstructure. 2- Idices which related both mechanical and micro-structural anaLysis with the state of structurization or dispersion namely; the structure factor. the aggregation index. the dispersion ratio and the dispersal index indicate the beneficial effect of soil conditioners on improving soil micro structure and on reducing its dispersability. 3- A considerable increase in the fraction silt plUS clay not detached and remained in water stable structure units> 0.02 mm in diameter was obtained. The response of this parameter to the treatments was similar to that of the micro aggregation. 1Ij j - ~-_.~-~--_ .. _._--- -~--_._--- ----- .- .. --_._--_.~ 120 b- Macro aggregate stability: 1- Data of the size distribution of water-stable structural units after wet sieving of the three soils indicate improving of soil aggregation with conditioning and with the amount of conditioners appiied. Th response to PAM depends on its Mol.wt. The polymer having high Mol.wt is more effective than that having the lower one. 2- Soil conditionerE: increased the percentage of water stable structural units> 0.84 rom, > 0.21 rom, and > 0.105 rom in diameter. Conditioning the soil enhanced the formation of the stable structural uni ts > 2 rom in d t ame t.er at the expense of the smaller ones. Formation processes increased with increasing the amount of conditioners applied and the Mol.wt of PAM. 3- The Mean weight diameter (MWD) of the stable structural units increased with increasing the application rate of the conditioner and the Mol.wt of PAM. The response of the MWD to the applied conditioners conside with that of the stable structural units. 2. Volume expansion of the soil: 1- Soil swelling -measured by its water content - on weight basis - at a hydrostatic suction of 15 mb or by the change in its volume due to wetting to this particular suction - was decreased by soil conditioning. 2- The change in this soil property also increased with increasing the amount of conditioners applied. Polyacrylamide having the Mol.wt of 1.360.000 was more effective than that having the Mol.wt of 150.000-200.000. 3- The response of hoth the saline sodie and the sodie soil to soil conditioning was more clear than that in the case of the saline soil. By using 1.0% Bit and 0.2% PAM II. The decrease in the swe llabil i ty of the sa 1ine sodie and the sodic soi 1 reached about, 30 and 50%. respectively. In the saline soil. this decrease reached only about 13 and 20% by treating the soil with the aforementioned conditioners, respectively. ~I Ii I II I, ----~-----_ .. - ----~----- -- ---------- ~-- _.----- -------------- I :, 121 3. Hydraulic properties of soil under saturated conditions: 1- Conditioning caused better changes in the hydraulic properties of soils. Consequently, the water movement through the soil under saturated conditions would be facilitated. 2- The data indicated an increase in the hydraulic conductivity, intrinsic permeability and mean diameter of soil pores with soil conditioning. The change in all the parameters under investigation using both type of soil conditioners increased with increasing the amount of conditioners applied. The response of the parameters to conditioning process was higher using PA.M having high Mol.wt relative to that having low ones. 3- Transimissivity of the layered conditioned soils for vertical flmo1 increased with the amount of conditioners applied and took the same trend as that of the other hydraulic properties. With this respect. the studied conditioners could be arranged in the following decreasing order: PAM II > PAM I > Bit II ~ Bit 1. 4-~ The positive relation between soil micro structure and its permeability as affected by soil conditioning was insured from calculating some indices namely; probable permeability, potential permeabi 1ity and act.uel permeabi 1i ty. 4. The possibility of usina the conditioned salt affected soils as drain filters: Using the aggregate size distribution curves. the three soils treated with different application orates of the examined conditioners had been evaluated as filter materials for drains according to some set of filter criteria recommended by Terzahi (1941), Juusela (1958), Winger and Ryan (1970), Spadd 1ing (1970) and USDA (1971) to assure a higher permeabi 1ity i:!Il1lediatenleyar drains and to prevent its silting. According to the USDA (1971), the acceptable filters were: the saline soil treated with 0.5 and 1.0% bit or 0.1 and 0.2% PAM, the saline or the sodie soils treated with 1.0% Bit, the saline sodic soil treated with 0.2% PAM I or 0.1 and -~ --- - --- ~---~- - -_.----- -~.~----~ I \ \ Ii ---------------- 122 0.2% PAM II and the sadie soil treated with the high Mol.wt PAM at the rate of 0.2%. Because the hydraulic conductivity of the conditioned soils with PAM was at least 10 times that of the untreated ones regardless of the application rate of the conditioner or its Mol.wt - they could be considered as suitable filter mat.erial (Winger and Ryan, 1970). On the other hand, adeque t e hydraulic conductivity was insured when the saline soil was conditioned with 0.25, 0.50 and 1.0% Bit. Moreover, treating either the saline sadie or the sodic soil with 1.0% Bit can achieve the goal. Conditioning the saline soil with at least 0.25% Bit or 0.1% PAM would assure a suitable filter criteria according to Terzaghi (1941), Jllusela (1958) and Spaddling (1970). On the other hand, classification of the treated saline sodic or sadie as a drain filter according to Spaddling (1970) is in good aggreement with those of Terzaghi (1941) or Juusela (1958) with minor exceptions. ’These exceptions include the effective-ness of the 0.1% high Mol.wt PAM in the saline sodic soil and 0.25% Bit I in the sodic soil. Conditioning the soil situ and reusing the obtained stable structural units as drain filters can replace gravels or other filter materials and save their costs and the expenses of their transportation and grading. 2. Effect of soil conditioners on some chemical properties of salt affected Boils: 1- All the paramet.ers under study, i.e. soil pH, electrical conductivity, soluble ions in the saturation paste extract, effective CEC, exchangeable Na and surface area of the soil were decreased by soil conditioning. 2- The higher the application rate of the conditioner was, the lower were the values of the mentioned properties. 3- the studied conditioners were arranged according to their efficil~ncy in the following descending order: PAM (Mol.wt 1.360.00’0 > PAM (Mol.wt 150.000-200.000) > Bit II (Petrofina, imported) ~ Bit I (locally produced). - -~-----~- ----~-~---- - --------- --------------~----- 123 4- Gypsum requirements of the ~aline ~o~ic.and the sadie soils were decreased by SOli condItIonIng. Instead of about 21 and 35 Tons/Fed for the saline sadie and sodic soils, respectively, gypsum requirements were reduced to reach about 13 Tons/Fed for the saline sodic’soil and 20 Tons/Fed for the sadie one using either 1.0% Bit or 0.2% PAM. Therefore. using gypStun for reclaiming of saline sodie and sadie soils would be facilitated by conditioners application. Obtained results were discussed on the basis of the following: 1~ The aggregating action of both types of soil conditioners and the formation of interparticle bridges which depends on : a) The mode of migration of active electrically charged micelles of bitumen ~ as large organic molecules to points of contact between soil particles or elay tactoids. This is not only a matter of applied quantity of the conditioner but also of the dilution of its emulsion, t.he dispersion of emulsifier rno lecules. the mois1.ure content of the soi I and eventually of the method of incorporation. b) The external and or internal adsorption of PAM molecules and their distribution on or into clay tactoids. This is mainly affected by the polymer Mol.wt and the specific viscosity of its solution. Hence, the particles will be fixed so tightly together that the amounts of particle rearrangement possible may be restricted and the swellability of the soil will be largely impeded. Therefore. soil hydraulic properties will be improved and water movement through the soil will be greatly enhanced. On the other hand. the coating effect of the conditioner used (thickness and hardness) may decrease either the contact between soluble salts in the soil and the water used for extraction or the diffusion of water through the obtained aggregates especially with the hydrophobic Bit. This will lead to a decrease in quantities of dissolved salts in the soil solution by varying degrees according to the type of conditioner used lI --- -~ ~----------------~- ------- -----------_._- ~---- 124 and its application ra.te. The effect of PAM Mol.wt on coating thickness and hardness must be taken into considerations. The partially covering of soil particles and tactoids and the occupation of the active sites of the fixed cations by the applied products will lower either the cation exchange capacity of the soil or its exchangeable cations. Thus, gypsum requirements of the soil will be decreased. |