Soil sealing and crusting is a serious soil degradation problem in Ukraine's North-Western Region. It causes significant declines in crop yield (up to 60 per cent) if appropriate measures to mitigate this negative impact of crust formation are not taken in proper time. The methods, widely used in Ukraine to alleviate this problem, are mainly mechanical harrowing and hoeing. In order to effectively reduce the negative influences of soil crust, Ukrainian farmers spend additional resources and money for labor, fuel, machinery and special equipment.

This problem of soil sealing and crusting has attracted a lot of attention by soil scientists in the former Soviet Union, Europe and the USA. Their research mainly discusses data about soil sealing and crusting as a consequence of poor soil structure and its dependence on soil texture peculiarities. In Ukraine, especially in its North-Western region, little attention has been paid to this problem. In our research, conducted in this region during 1999-2005, we studied the generally accepted reasons for soil sealing and crust formation as well as a number of a less studied aspects of this problem. Among them are (1) the influence of increased soil organic matter content on soil sealing and crusting processes; (2) the role of the soil absorbtion complex and exchangeable cations (Ca, Mg, Fe, Al, K, Na) and their influence on these processes; (3) implementation of conservation tillage (4) the application of lime and gypsum on the soil plots studied and (5) the contents of mobile aluminum and iron in the soil particles and their influence on sealing and crusting.

Results of our research lead us to the conclusion that those soils of North-Western region of Ukraine which are less susceptible to sealing have high percentage of soil particles within the size range 5-2 mm in diameter. Particles of this size comprise about 60 per cent of the entire soil aggregate structure. Those soils susceptible to sealing and crusting have at least 20 per cent content of fine particles and loamy particles (< 0.01 mm) in their aggregate structure. The better the soil structure, the higher the water resistance coefficient of the soil structure, the less the probability of the soil sealing and forming a crust.

Our experimental field work with increased doses of organic fertilizer applications has shown that organic matter helps to improve soil structure and after drying, soil is less susceptible to sealing and crusting. Soil surface mulching with straw and sand resulted in no observation of soil crust on investigated soil plots.

Conservation tillage, followed by lime and gypsum application, has shown a lesser degree of soil crusting, an increase in soil infiltration and an increase in seedling emergence. As a result, crop yields have risen by 15-25 per cent.

Some researchers indicate that the amount of mobile aluminum and iron in the soil affects the soil crusting process. We applied Al2 (SO4)3 and Fe2 (SO4)3 to investigated soils. We paid special attention to 1-0.25 mm soil particles and particles less than 0.002 mm in diameter. According to our research, the ratio of these particles in the soil is most responsible for soil sealing and crusting processes. Only 5-15 per cent of mobile iron and 5-27 per cent of aluminum are combined with colloidal particles, and 70-85 per cent of these elements are held by soil particles of 1-0.25 mm. We are making an assumption, based on obtained results that mobile iron and aluminum tend to concentrate in soil particles 1-0.25 mm. However, other researchers' findings suggest that both elements concentrate evenly throughout all ranges of soil particles. One of our other assumptions suggests that mobile Fe and Al tend to coagulate smaller particles and form them into larger ones, thus helping to improve soil structure and form soil aggregates 1-2 mm in size, which are resist crusting.

Based on our research, in order to prevent soil sealing and crusting of the soils of the North-Western region of Ukraine we recommend: (1) implementing methods of conservation tillage; (2) applying lime and gypsum to degraded soils; (3) applying increased doses of organic fertilizers to improve soil structure; (4) mulching soil and (5) applying Al2 (SO4)3 and Fe2 (SO4)3 to degraded soils.