Document Type : Original Article
Authors
Pedology Dept, Desert water resources and land, Desert Research Center, Egypt
Abstract
Due to the importance of Maryout region for its potential rehabitation and calcareous soil reclamation, three sites pertaining wide range of soil salinity from 250 to 2.5 dS/m were selected to model salts leaching. In order to obtain a sound basis for field reclamation under different conditions, a leaching experimental model was undertaken laboratorial using three soil columns simulating these three sites which varying mainly in salinity levels to assess the effect of several factors on the effectiveness of salt removal. The experiment was performed twice with and without removal of CaCO3. There are four problems were investigated based on the experiment; the evolution of leachates salinity with time, monitoring the changes of ion loses and changes of chemical composition of drained leachates, the effect of leaching process on particle size distribution and fine particles migration at each salinity level, and the probabilities of Calcic horizon formation. Also the study emphasized on the influence of carbonate removal on leachates salinity. Results showed that the counts of required leachates for salinity minimizing were 20, 15 and 12 with total leachates volume 1552, 1055 and 732 cm3 during leaching periods (hr:m) 10:48, 7:41 and 5:59, respectively. Soil texture was clay loam (CL) at the first location, clay (C) at the second site except for the middle layer which has sandy clay loam (SCL) texture, while at the third location soil texture was clay loam (CL) at surface and clay (C) at subsurface. Results of particle size distribution indicated that lime removal in general increased percentage of fine particles in contrast in course ones. After leaching of free lime columns fine particles percentages were decreased at surface horizons of extremely and highly saline soils more than slightly saline column. Clay particles immigrated after leaching downward which increase their content at last horizons by 22.7 and 7.1% for first and second columns, respectively. The electrical conductivity values of the second drained leachate fractions were reduced significantly by about 77.8%, 57.1% and 15.6%, respectively. After the experiment was turned off the stable salinity level for whole leachates were 0.74, 0.44 and 0.16 dSm-1, respectively. Thus, leaching succeeded in removing about 99.7 %, 98.2 % and 93.6% from the total salt content. Results indicated that the ionic loss was orderly as Na+, Cl-, Ca++, Mg++ then K+ in descending order in whole drained leachates, where removed cations essentially were in chloride or sulfate forms. Estimated rates of CaCO3 deposition for the studied soils were 19.9, 16.4 and 9.5 g/m3/year, respectively. Dominant lime horizons will receive 0.76, 0.64 and 0.37% of carbonate after 500 years at the studied sites, respectively, which indicate unsuitable conditions for Calcic horizon formation during that period. The model tried to simulate field conditions associated to leaching of salty calcareous soils, but nutrients levels have to be carefully monitored to sustain healthy plant growth, and it is usually not advisable to leach if the resulting soil will be sodic or alkali, where such soils should receive amendments before being leached.
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