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Years of intensive irrigated farming in the inland valleys of northern Israel have caused secondary salinity in vast areas. Soil salinity/sodicity surveys, conducted after the problem was recognised, showed relatively high levels of sodium adsorption ratio (SAR) in the active soil layers. In a sample of 7 affected fields, 92.5% of the 1584 SAR measurements on cored soil samples had values >5, and 39% had values >15. Two ameliorative approaches were conceived to reverse the evident salinity/sodicity trends in the Yizre’el Valley: (a) a gravitational, newly engineered, subsurface drainage system; and (b) bio-drainage, using eucalypts as a means to control the high water tables. Both approaches were very successful according to the chosen criteria. The drainage system, comprising 3 drain components, effectively controlled excess water from 3 sources: direct infiltration, lateral subsurface flow, and a deep, presumably upward-seeping, artesian aquifer. The groundwater table response to the installation of the applied drainage system was immediate. In the next rainy season, there was an associated and appreciable deep leaching of Cl– and somewhat less of Na+. More than 3000 ha of land has been drained in this way in the past 10 years in the northern, salinity-prone, inland valleys. The bio-drainage approach, tested in 5 different waterlogged and salinity-affected sites in the Yizre’el Valley, also proved very successful. The rates of growth of Eucalyptus camaldulensis provenances was impressive from the first year. In the best plot, in the fifth year, biomass production reached 30 t/ha.year for the Broken-Hill ecotype (NSW) and peaked at 57 t/ha.year for the Hadera (Israel) ecotype. The annual transpiration of selected trees at Nahalal was 1360 mm, or 3 times the local average annual precipitation. The groundwater table dropped to below 3 m in the summer of the fifth year—sufficient to provide saltflushing conditions. In a related study at the Nahalal site, it was demonstrated that E. camaldulensis screens out the salts while consuming soil water. That, coupled with prolonged stresses of salinity and flooding, can be detrimental to eucalypts. In conclusion, despite sodic conditions, which are ‘formal’ by definition and which prevail in much of the area of our northern valleys, drainage, whether conventional or biological, if well-designed and implemented, is a viable means for controlling local hydrology and restraining salinitysodicity trends.

Compared with research on mineral soils, the study of the physical properties of organic soils in the United States is relatively new. Always (1920) and Anderson et al. (1951) considered the value and reclamation of peats in Minnesota and nationally. Davis and Lucas (1959) summarized organic soil formation, utilization, and management in Michigan; however, most of the literature on the detailed physical properties of peat was published from 1956 to 2003. This is true in Europe as well (Parent and Ilnicki 2003), except for a study by von Post (1922) who developed a field method for determining

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Abstract:The bio-drainage-commercial forestry strategy was applied in five plots in the Yizre'el Valley, northern Israel, to evaluate the hydrological and salinity impacts of eucalypt plantations. Each plot contained a mix of 11 selected eucalyptus species/ecotypes. Two plots (Nahalal and Genigar), representing the two extreme waterlogging/salinity conditions in the valley, were selected for in-depth monitoring over a 10-year period to assess the likely environmental improvement through bio-drainage. Despite impressive growth rates of genetically improved Eucalyptus camaldulensis in the year-round waterlogged, slightly saline Nahalal site (650 mm annual rainfall), the water uptake by the trees was insufficient to control the rising water table caused by excessive water inputs, both natural and human. In the more saline, alkaline and drier Genigar plot (450 mm annual rainfall), where rainfall is the only water input, the ground water dropped to below 3 m from soil surface in the fourth year after planting, i.e. deeper than the adjacent ground water levels. Both sites showed appreciable rise in wells that penetrated the 3-to 4-m confining layer. The 10-year salinity (EC) trend of the top layer in Nahalal varied because the drainage was limited by the positive water balance and the above-average spells of dry winters. In and below the 4 m deep layer the EC remained below 1Ð5 dS m 1 throughout the entire 10-year study. The last EC measurement, taken in 2003, showed values not higher than 4 dS m 1 throughout the 6 m soil profile. In Genigar, there was significant leaching of salts from the top layer (1 m) during the 9-year monitoring period, but recently a salts 'bulge' was gradually developed in the 1-5 m strata indicating that the expected downward movement of leached salts was impeded by the 3-4 m deep low-permeability clayey layer that lies over a coarser, far more conductive and notably confined layer, which leads to a perched water body. The last EC measurement at the end of 2003 showed a maximum value of 5Ð5 dS m 1 at 3 m depth. No signs of tree stress were observed in either site, at any soil depth during the 10 years of monitoring. Theoretical considerations do not support the hypothesis that there would be a fatal long-term accumulation of salts in the root zone. The Israeli experience has shown that the bio-drainage technique can effectively lower a shallow water table and reverse salinity trends, provided that the overall water balance is negative, i.e. that the water inputs match the water use by the tree plantation and local drainage characteristics. However, the rate of improvement of the hydraulic, salinity, sodicity and soil physical properties is site specific. Excess fresh water inputs into the plantation, although they create waterlogging conditions, supply unlimited water to the trees, which, in turn, show exceptional growth rates, with usable commercial value.