A collective farm (kolkhoz) located in the Kzyl Orda region was selected as a study area. The region is in a typical arid continental temperate zone, characterized by a high solar radiation of 0.16 to 0.19 kW/m2, a mean annual temperature of 9°C and annual precipitation of less than 150 mm.
Though the farm has a gross area of 19,000 ha, only 1,900 ha or 10% has been reclaimed for agricultural purposes. Out of the 1,900 ha of reclaimed land which have been cultivated for farming, an area of 600 ha has been abandoned without cropping due to severe salt accumulation. This situation is commonly seen in all the collective farms in the region.
An eight year crop rotation system has been widely practiced in the region. The system is composed of rice cropping for the first and second year, wheat cover-cropped with alfalfa for the third year, alfalfa for the fourth and fifth year, rice for the sixth and seventh year and corn (forage) or fallow for the eighth year. As the soil fertility which was lost during rice planting can be replenished through alfalfa planting, as well as the alfalfa fields being irrigated through percolated water from adjacent rice fields under the system, this system has been recommended by researchers and adopted by farmers in this region. In most rice producing areas in Kazakstan, this cropping pattern has been the basic for design and construction of new rice land development.
Growing rice minimizes salt accumulation in the soil profile through leaching effects in the ponding period. However, there is a possibility that this system has induced waterlogging and salt accumulation in upland areas adjacent to rice fields in and/or out of the irrigation block.
Two sites in an alfalfa field and a nearby deserted field were intensively sampled. Soil samples were measured for electrical conductivity (EC), particle fractions and chemical compositions. Part of the result is shown in Table 9.1.2 Due to high evaporation and less rainfall, the abandoned field was covered with a layer of white salt crust, whereas there was no visual salt accumulation on the soil surface in the alfalfa field. However, EC of the soil saturation extract (ECe) of the alfalfa field was in a range of 15-30 dS/m (decisiemens per meter =millimhos/cm, mhos = ohms-1), around 4 times higher than the critical value demarcating a saline soil. In the deserted field, ECe was as high as 80-100 dS/m, and at least 5 times higher than that in the alfalfa field. The sodium adsorption ratio (SAR = Na/(Ca + Mg)1/2, unit in nmoles per liter) of the saturation extract was higher than 50 for the deserted field and 30 for the alfalfa field.
From the data presented above, the soils both in cultivated and abandoned lands were highly saline. Among other factors that attributed to soil salinization, such as high evaporation, less rainfall and low drainage capacity, the current cropping pattern has its own share of blame. The irrigation water from the Syr Darya River has 1.6 dS/m in EC and 4.5 in SAR. However, in the rotation, paddy rice is usually supplied with excess water with the intention to leach salt from the soil profile, whereas upland crops in the adjacent fields receive no irrigation water from the surface. Thus, ground water is replenished and elevated during ponding when cultivating paddy rice, but concentrated during non-irrigation periods. This allocation of irrigation water has made the ground water more concentrated after each rotation. Affected by the high evaporation rate on the soil surface, salts accumulate in the profile through capillary rise, resulting in soil salinization in the non-rice growing fields.
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