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Aims Saprotrophic soil fungi participate in biomass mineralization, inhibit pathogen development and promote plant growth. Pathogens accumulate in soil and decrease crop yields. The structure of fungal communities is determined mainly by the organic matter content and pH of soil. Little is known about the influence of crop rotation and long-term monoculture on saprotrophic fungi that decompose plant roots and crop residues as sources of soil biomass. Methods Fungal communities that promote plant growth (arbuscular mycorrhizal fungi (AMF), yeasts, Trichoderma spp.), cellulolytic fungi and pathogenic species were analyzed in a 6-year crop rotation system (maize – spring barley – peas – winter rapeseed – winter wheat – sugar beets) and in 50-year maize monoculture. Fungal DNA was extracted from the rhizosphere and plant roots, and the ITS2 region of fungal rDNA was analyzed by high-throughput sequencing. In both treatments, weeds were controlled chemically (terbuthylazine + mesotrione + s-metolachlor) or mechanically. Results A total of 311 fungal species were identified. The biodiversity of soil fungi, in particular AMF and yeasts, was higher in monoculture than in crop rotation. Maize pathogens were more frequently identified in monoculture, whereas species of the genus Trichoderma were more prevalent in crop rotation. Herbicides clearly increased the abundance of cellulolytic fungi of the phyla Mucoromycota and Mortierellomycota, Mortierella spp. and Minimedusa polyspora. The abiotic properties of soil were affected by the cropping sequence. The content of organic carbon (Corg) and the availability of P and Mg decreased in monoculture. Maize yields were bound by a strong positive correlation with the availability of macronutrients and Corg in soil, as well as a weak positive correlation with the abundance of Trichoderma spp., Mucoromycota and Mortierellomycota. Conclusions Fungi exert a complex and ambiguous effect on maize biomass yields, whereas a decrease in the macronutrient content of soil in monoculture strongly decreases maize yields. In the long term, the cropping sequence considerably influences the structure of the soil microbiome which can be a reservoir of unique species and species that minimize the negative effects of monoculture in agroecosystems. Graphical Abstract

The aim of this study was to evaluate, in 3 experiments, seedling emergence and sensitivity to temporary soil water deficit in 24 sugar beet cultivars. Seeds were sown in 2012 and 2013 in containers (60x40x15 cm) filled with a soil classified as Luvisol (with 65% field water capacity) and placed in an phytotron. For 2 weeks, until the first counting of seedlings, the temperature was maintained at 10°C, and then it was raised to 15°C to simulate the temperature increase occurring in the spring period in the field. At the first stage of the study, the number of emerged seedlings was counted 14 and 21 days after sowing. After the following 2 weeks, in the second pair of leaves unfolded stage, the plants were not watered for 6 days to evaluate on day 7 their sensitivity to soil moisture deficit. The above cycle was repeated, and the plants were not supplied with water over a period of 6 successive days. At the end of that period, the seedlings were counted, and the ratio of surviving seedlings to the number of seedlings before the first water deficit was calculated again. Under controlled conditions, high emergence capacity (14 days after sowing) was noted in cv. Janosik, Julietta, and Silvetta, whereas very high final emergence capacity (21 days after sowing) was observed in cv. Agent and Julietta. Sugar beet cv. Huzar, Lukas, and Expert were the least sensitive to soil moisture deficit and they can, therefore, be recommended for cultivation in areas prone to water deficit at the beginning of the growth season. Among the conventional cultivars of sugar beet, there are also cultivars with a low susceptibility to drought that increasingly more often causes problems in regions of intensive production of root crops.

The paper presents the findings of 6-year (1993–1998) investigations obtained in the field static experiment continued since 1967. This experiment concerned the estimation of the crop yield and its structure, and root technological quality under the conditions of crop rotation and extreme shortening of the rotation, i.e. monoculture. Investigations have proved that under agroclimatic conditions of north-eastern Poland it is possible to obtain 60 t of roots per ha in a naturally correct crop rotation, while in a long-term monoculture – 33 t, and 36 t and 19 t of top, respectively. The differences in monoculture crops occurred as a result of a plant loss during germination by 5.6%, and a smaller unit weight per root by 41.6%. The applied procedures of plant protection by herbicides and fungicides improved the root and top crop and favored the maintenance of plant density. A lowering of saccharose content in roots from 15.7% in the crop rotation to 15.0% in monoculture was recorded, and of sugar yield in the technological process from 13.0 to 12.3%, respectively. A high white sugar yield was obtained in crop rotation – 7.89 t per ha, while in monoculture it was only 4.06 t, i.e. 48.5% less.