Carbon and nitrogen reserves of plant residues in agrocenosis of the foreststeppe zone of Krasnoyarsk Region

The aim of research is to determine the reserves of carbon and nitrogen of plant matter entering the agro-soils of the forest-steppe zone of the Krasnoyarsk Region after harvesting crops cultivated using mi-nimum technology. Research was conducted in 2006–2024 in the territory of the Krasnoyarsk and Kansk forest-steppes. The objects of the study are the most common agrocenoses of grain crops, rapeseed, po-tatoes, soybeans and fallow fields in this zone, located on leached chernozems in combination with ordi-nary and podzolized chernozems. The reserves of aboveground plant matter were determined using the method of accounting plots, the reserves of underground plant matter – in the soil layer of 0–20 cm using the monolith method. Carbon in plant matter was determined by the oxidimetric method, nitrogen – by Kjeldahl on the UDK 159 analyzer. When cultivating grain crops, 6.4 to 7.3 t/ha of plant residues are formed annually; in potato agrocenoses – 7.1; soybeans – 8.8; rapeseed – 8.9 t/ha. Most of these residues (more than 71 %) are in the underground part of agrocenoses. Different crops have different C : N ratios in plant residues, cereal crops are characterized as poorly degradable due to a wide C:N ratio (79.2), while soybeans have moderately degradable residues with the lowest C : N ratio (23). The transition of plant residues from aboveground to underground mortmass leads to a narrowing of the carbon-nitrogen ratio from 78 to 61. Grain agrocenoses on average supply up to 2,963 kg/ha of carbon and up to 37.5 kg/ha of nitrogen of plant residues to the soil, potato agrocenoses – about 2,878 kg/ha of carbon and 81 kg/ha of nitrogen, after the cultivation of rapeseed 3,447 kg/ha of carbon and 80 kg/ha of nitrogen enter the soil, the maximum supply of carbon and nitrogen to the soil in the soybean agrocenosis is 3,442 and 142 kg/ha, respectively. During the year of fallowing agrochernozems after the cultivation of grain crops, 60 % of the carbon and 72 % of the nitrogen of plant residues decompose. After 5–8 years of fallowing, the carbon and nitrogen reserves in plant residues are significantly reduced to 54 kg/ha of carbon and 0.6 kg/ha of nitrogen.