MEDIUM REACTION AND CHEMICAL SOIL MELIORATION
The important factor that affects crops growth and development is the medium reaction, acidity or alkalinity. In view of this it is important to make continuous observations for the soil reaction to place crops in fields according to one or another reaction and also to practice measures on the chemical soils melioration. Research is conducted on 10 reference plots laid in different soil-climatic zones of North Ossetia-Alania and when total agrochemical survey. Thus we may conclude that the reaction of the soil solution (pH) in different soil types and subtypes on reference plots is in the range from 4,3 to 7,5 of the salt extract that is from highly acidic to alkalescent. The most acid needy the chemical melioration (liming) are soddy slightly-podzolized and gray forest podzolized soils. The total agrochemical survey results show that for 50 years the soil reaction has undergone significant changes. So the period between the first (1965-1968) and the third (1973-1977) survey cycles is characterized with declining the proportion of neutral soils from 78 to 55% and increasing the areas with acid reaction from 19 to 33% due to application of physiologically-acid mineral fertilizers and lack of soils liming. After the fourth cycle (1978-1982) the areas of acid arable soils decreased to 26%. However when stopping liming after 1992 the areas of acid arable soils again began to increase and according the results of the tenth completed survey cycle (2006-2013) were 33% (more that 60 thousand ha) that require liming.