Literature analysis revealed the most important characteristics of soil structure for irrigation. Soil structure is appeared in soils which have texture heavier than sandy loam. The aggregates by the size 2–3 mm are the most favorable for crop productivity. It is important that aggregates have pores which size is from 0.1 to 30 micrometers. In these pores the conditions for preserving available moisture for root growing and bacteria activity are created. One of the indices of soil structure quality is aggregate water stability due to cementation of texture fractions by recently precipitated organic matter. At the present time, there is no the theory of formation mechanism of soil structure. Among the existing hypotheses there is the hypothesis of the influence of amphiphilicity of organic matter on aggregate formation. Aggregate water stability is the most important for irrigated soils because any irrigation method has some negative effect on soil structure which appears in the chemical and physical impact of water entering soil. Chemical impact mainly caused by cation-anion composition of water and can be characterized through such indices as SAR (sodium absorption ratio) and EC (electrical conductivity). Fine texture soils which contain clay minerals with high ratio of smectite (montmorillonite) should be irrigated by water with minimal content of sodium. Physical impact of water is related to the rate of its distribution in soil. High rates have negative effect on soil structure and facilitate its destruction. Thereby, slow entering of water into soil is preferable for soil structure preserving which is manifested in speed limit of water flow in irrigation furrow to 0.15 m/sec, raindrop fall speed to 4 m/sec at mean diameter 0.4 to 1.0 mm, intensity of water discharge to a value comparable to the absorption rate of the soil.
Keywords: soil structure, water stability, organic matter, amphiphilicity, irrigation, water quality, surface irrigation, sprinkling, drip irrigation.
