Soil cover and humus state of armable soils of the Volga Republic of Tatarstan

The purpose of the study is to assess the dynamics of the humus state of arable soils in connection with the distribution features of soil types and subtypes in the municipal regions of the Volga region of the Republic of Tatarstan (RT). The territory of the Volga region occupies 1014.3 thousand hectares, which is about 15% of the area of the Republic of Tatarstan. The Volga region includes 8 municipal districts: Apastovsky, Buinsky, Verkhneuslonsky, Drozhzhanovsky, Zelenodolsky, Kaybitsky, Kamsko-Ustinsky and Tetyushsky. The results of soil and agrochemical surveys conducted by the Federal State Budgetary Institution CAS “Tatarsky” over the past 35 years are summarized. For the first time, arable soils of the studied region were examined for humus content in 1986-1990. (IV cycle of agrochemical examination). The determination of humus was carried out according to the method of I.V. Tyurin as modified by TsINAO (GOST 26213-91). It has been established that the soil cover of two municipal districts (Buinsky and Drozhzhanovsky) is dominated by highly fertile chernozems, and the remaining six districts are dominated by gray forest soils. A comparison of the distribution of the main soil types in the Volga region and in the Republic of Tatarstan as a whole shows that the region under study appears to be a miniature copy of Tatarstan: in both cases, gray forest soils are dominant, and chernozems are subdominant. It is noted that over 35 years, the area of arable land in the region has decreased by 57 thousand hectares, presumably due to the withdrawal of less fertile land from agricultural use. It is indicated that this circumstance to a certain extent stabilized the humus state of the soils remaining in the arable land. The weighted average content of humus in the arable layer according to the cycles of agrochemical survey of soils in the studied region varied from 4.42 to 4.82%, however, these fluctuations turned out to be statistically insignificant (r = -0.06). There was a positive correlation and the highest degree of dependence of the weighted average humus content on the total share of chernozem and dark gray forest soils (R²=0.96).