Comparative analysis of water-physical and agrochemical indices of soil in Volga delta fallows of various ages

The purpose of the research was to determine agrochemical and physical changes occurring on the fallow lands of the Volga delta, taken out of active economic turnover in different years, to establish the worthwhileness of their returning to agricultural production. The objects of research were fallow lands of different ages. In the course of the research conducting, it was revealed that on a short-term fallow (8-9 years old), the values of the soil compaction density in the upper level were the smallest - 1.31-1.75 t/m3. On long-term (24-25 years old) and middle-term (16-17 years old) fallow there was recorded the soil compaction up to 1.55-2.01 t/m3 in the upper levels, and significant decomposition of soil up to 0.85-1.10 t/m3 in the lower levels. In the water-deficient conditions of the Volga delta, all types of agricultural land were stressed due to very high summer air temperatures and low rainfall. A linear correlation (r=0.71) was established between the soil moisture reserves and the number of plants. Comparing the moisture reserves in the soil on different fallow plots, one can note a short-term fallow as the richest in moisture. Within spring period the largest soil moisture reserves of 860.3 m3/hectare were defined on the short-term fallow lands. In old-aged fallows in the summer, the natural moisture content of the soil decreased on average to 3.9-4.2 %, discouraging seed germination and plant growth. An increased content of the amount of water-soluble salts in the soil was revealed in all fallow plots, especially at the end of hot summer. The fallow stage of the development of soil processes is associated with the restoration of soil fertility. The content of humus, easily hydrolysable nitrogen, labile phosphorus and exchangeable potassium increased in line with the age of fallow.