The system of shelterbelt forests is a long-lasting ecological framework of an agrarian territory. Their main function is to prevent the degradation of arable soils, improve the microclimate of fields, and preserve the stability and biological diversity of landscape. However, the presence of forest belts complicates field cultivation, and along their borders zones (strips) of depression in crop development could formed, reducing the productivity of lands. This impedes field-protective afforestation, and, consequently, the solution of the problem of reliable protection of land resources. The aim of the work is to establish the causes and regularities of formation of depressive zones in agrocenoses, and to determine the possibility and methods of suppressing their development. The research has been conducted for 8 years in the experimental-production system of 30 to 53-year old 2 to 4-row forest belts of Betula pendula ROTH, Pinus silvestris L., Ulmus laevis PALL. and other species on the automorphic chestnut soil of the Kulunda steppe (the Altai territory) by the generally accepted methods. It was found that the depressive zone in agrocenoses is the least wide for relatively sparse forest belts of birch and pine, and also for forest belts with marginal rows of xerophytic shrubs (3-7 m in total on windward and leeward sides), and the largest (up to 25-30 m) for elm and poplar (Populus laurifolia LEDEB.), i. e. for plantations of hydrophylous tall species with dense crowns. It is 1-3 m wider on the leeward side of forest belts, where more snow is deposited in winter and soil moisture is better in spring. The increase in height and density of stands, influencing the length and intensity of day-time soil shading, stimulates the expansion of the zone. Crop depression is more pronounced in wet years. The increased amount of atmospheric precipitation during the cold season, as well as at the beginning of the growing season and during the reaping season till the onset of stable cold weather also contributes to it. The development of depressive zones is suppressed by abundant precipitation during the period of active growth of field crops. Thus, the formation of depressive zone in agrocenoses of shelterbelt forests depends on many factors. Under arid conditions, the most effective factors are the need for soil moisture and moisture availability for the stand. The most active expansion of the tree root system in the field and the suppression of crops occur in wet years and during the periods with high soil moisture in the absence or weakened competition of field crops. To reduce damage to their productivity, it is necessary to implement a set of coordinated organizational, silvicultural and agrotechnological measures aimed at increasing moisture availability and limiting the expansion of tree root system of forest belts in the field.
