Irrigation increases agricultural productivity and inevitably affects soil properties. When irrigation water is of a good quality and does not cause soil salinity or sodicity or contamination, and when there is no soil erosion, a gradual increase in soil fertility under irrigation conditions is, as a rule, expected. However, studies in various countries present examples of a gradual decline in soil fertility under long‐term freshwater irrigation due to leaching of organic matter and exchangeable cations. It is known that ploughing and agricultural activities modify natural soil formation processes and soil fertility. Irrigation enhances soil formation processes but also causes soil leaching. This paper presents data on the impact of long‐term freshwater irrigation on soil fertility for different climatic zones of Mexico, assessed by comparing some agrochemical properties of irrigated and non‐irrigated soils. This comparison shows that irrigation generally has a positive effect on soil fertility in arid conditions and a negative effect in semi‐arid, semi‐humid and humid tropical zones. Therefore, when planning and applying irrigation to crops, it is necessary to take into account not only crop water requirements, but also the need to preserve and improve soil fertility. © 2019 John Wiley & Sons, Ltd.
The transport parameters were determined for the 18 O isotope (in the form of H 2 18 O), the Br -ion, and atrazine in intact columns of allophanic Andosol (Mexico State, Mexico). A one dimensional model for the convective dispersive transport of chemicals with account for the decomposition and equilibrium adsorp tion (HYDRUS 1D), which is widely applied for assessing the risk of the chemical and bacterial contamina tion of natural waters, was used. The model parameters were obtained by solving the inverse problem on the basis of laboratory experiments on the transport of the 18 O isotope, the Br -ion, and atrazine in intact soil columns at a fixed filtration velocity. The hydrodynamic dispersion parameters determined for the 18 O and Br -ions in one column were of the same order of magnitude, and those for atrazine were higher by 3-4 times. The obtained parameters were used to calculate the transport of these substances in another column with dif ferent values of the water content and filtration velocity. The transport process was adequately described only for the 18 O isotope. In the case of the Br -ion, the model significantly underestimated the transport velocity; for atrazine, its peak concentration in the column was overestimated. The column study of the transport of the three chemical compounds showed that transport parameters could not be reliably predicted from the results of a single experiment, even when several compounds were used in this experiment.
Water release from reservoirs to improve the environmental condition of floodplains is of great relevance. Thus, the aim of this study was to propose a method to assess ecological drawdowns from power station reservoirs. An example of its application for the Volga River downstream area is presented. The efficiency of the quantitative assessment of ecological water discharge from the reservoir of the Volgograd hydroelectric power station is analyzed and discussed in relation to the improvement of the environmental condition of the Volga-Akhtuba floodplain, which covers an area of 6.1 × 10 3 km 2 . It is shown that a decrease of spring-summer flooding worsened significantly its environmental condition, i.e. biodiversity decreased by 2-3 times, soil fertility declined by 25%, floodplain relief deformation occurred and the productivity of semi-migratory fish decreased by more than 3 times. The economic benefit accumulated from river flow regulation was 300 × 10 6 USD in 2011, and economic damage related to the deterioration of the ecological situation was estimated at 400 × 10 6 USD in the same year. It is impossible to fully satisfy the needs of all the participants in the water-economic complex in the assessment of the environmental flows. Priority should be given to environmental requirements. It was found that assessing the ecological drawdowns confirmed the possibility of improving the floodplain environment by reducing between 15-20% the electricity production. This would allow conserving the region's biodiversity and increasing about 60-80% the natural vegetation productivity. This will prevent deformation of the floodplain relief and doubling the productivity of semi-migratory fish.
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