Cultivation of Miscanthus sacchariflorus in Siberia: application of nitrogen fertilizers

Perennial energy plants, including Miscanthus spp., are cultivated on an industrial scale for bioenergy production and technological purposes. It has been established that high crop productivity is possible even at low costs. In Russia, the problem of growing Miscanthus for biomass production is poorly understood, and the features of fertilizer application for this crop have been practically unstudied. Miscanthus is a new crop for Siberia. The problem of fertilizer application under Miscanthus plantings remains insufficiently studied due to the diversity of climatic and soil conditions, as well as species characteristics of the crop. At the same time, the majority of publications are devoted to the species M. giganteus , which differs from the species M. sacchariflorus in the structure of the root system. The paper presents long-term experimental data on a set of problems associated with the use of nitrogen fertilizers for the Miscanthus crop in Siberian conditions. It has been established that nitrogen fertilizers, without affecting the yield, lead to a decrease in the quality of raw materials due to an increase in the proportion of leaves in the phytomass and an increase in the infestation of rhizomes with fusarium infection; in addition, a decrease in the accumulation of organic matter in the soil is noted when nitrogen fertilizers are applied. The aim of this work is to determine the feasibility of using nitrogen fertilizers under perennial plantings of Miscanthus cultivated in the continental conditions of Siberia: to assess the effect of fertilizers on crop yield, plant infestation by phytopathogens, and the dynamics of organic matter in the soil. The studies were conducted on the territory of the experimental station of the SibNIISR - a branch of the Institute of Cytology and Genetics SB RAS (Novosibirsk Province, Central Forest-steppe of the Novosibirsk Ob Region). The effect of nitrogen fertilizer on the size and structure of the Miscanthus sacchariflorus Soranovsky variety yield was assessed in the initial period of plantation formation (2016-2017) and during its maturity (2018-2022). The plantation with a total area of 0.3 ha consisted of 4 blocks, each of which included fertilizer options N0, N30, N60, N90, N120 in 4-fold repetition. P60K30 was added to all plots. Nitrogen fertilizers in the form of ammonium nitrate were added annually in spring. M. sacchariflorus rhizomes were used as planting material. Aboveground phytomass was harvested from 0.25 m2 plots. Underground phytomass was recorded using the monolith method at the stage of drying of aboveground part of plants. The washed rhizomes were visually assessed for the degree of fungal infestation using standard and modified scales. Total carbon accumulation (Corg) was estimated by comparing the soil under fallow (the original soil on which miscanthus was planted) and under an 8-year-old miscanthus plantation (2023). The amount of carbon accumulated in the mobile fraction of soil organic matter (SOM) during the period of Miscanthus growth was determined by comparing the C-CO2 production by soil samples collected under perennial miscanthus plantings and annual fallow. The intensity of nitrate nitrogen accumulation in the soil was determined in a laboratory experiment under optimal hydrothermal conditions using the generally accepted Kravkov method. Over a 6-7-year period of planting M. sacchariflorus variety Soranovsky, the aboveground phytomass reserve reached an average of 12.0 t/ha, underground - 18.0 t/ha. These indicators are close to the average, typical for this species in the world. Nitrogen fertilizer did not affect the accumulation of phytomass, but contributed to the change in its structural elements. During the period of plantation formation under the influence of nitrogen fertilizer, a decrease in the length of the generative shoot by an average 5 %, the number and biomass of panicles by 35 %, an increase in foliage by 9 % were observed compared to the variant without fertilizers. During the maturity period of the plantation, deviations of the parameters from the unfertilized control became more pronounced, especially at fertilizer doses above N60. In the treatments with the application of nitrogen fertilizers, there was an increase in the incidence of rhizomes with fungal infection (15.5 vs 7.7 % without fertilizers). The main pathogens were fungi of the genus Fusarium - F. oxysporum and F. graminearum . Over 8 years, 150-200 kg C/ha of the mobile fraction of SOM and about 0.05 % of total carbon accumulated annually in the soil under the Miscanthus plantation, which corresponds to the parameters typical of traditional perennial grasses. The rate of carbon accumulation in the soil did not increase with the age of the plantation. The application of N120 resulted in a decrease in the amount of mobile SOM accumulation by approximately 50 % compared to the variant without fertilizers (104 versus 220 kg C/ha per year).