Abstract <p>The content and stocks of various biogenic elements were determined in a long-term field experiment of 1977 and on experimental plots in fallow and virgin soddy-podzolic heavy loamy soil in the Middle Cis-Urals. The total carbon stocks decreased in the sequence: mixed forest &gt; fallow land &gt; typical crop rotation &gt; continuous barley cultivation &gt; continuous black fallow (from 52.8 to 20.7 t/ha). Total nitrogen stocks ranged from 2.4 to 4.5 t/ha. Soil under the temperate forest contained 0.87% of labile carbon, 478 mg/kg of hydrolyzable nitrogen, and 9.2 mg/kg of mineral nitrogen. The amount of organic carbon and total nitrogen in soil under a 45-year-old fallow was 1.62% and 1568 mg/kg, respectively, due to well-developed meadow vegetation with a large root system. Phosphorus stocks varied between 1.7 and 4.4 t/ha, depending on the type of land use, and potassium stocks were from 30.3 to 74.9 t/ha. Long-term fallow caused a decrease in the content of organic carbon by 29.1%, of difficultly hydrolyzable mineral nitrogen compounds to 544 mg/kg, of organic phosphorus to 205 mg/kg, and of exchangeable potassium to 15.5 mg, as well as a rise in the mineral nitrogen to 30 mg/kg. A crop rotation with two clover fields and black fallow with manure application resulted to an increase in soil fertility to the level of fallow soil. Agrogenic transformations of carbon, nitrogen, phosphorus, and potassium consisted in a reduction in labile organic matter and in an increase in easily hydrolyzable nitrogen at the expense of difficultly hydrolyzable fractions, in available mineral phosphates, and in available potassium.</p>