Viacheslav Eremeev

An established Estonian field experiment was used to evaluate potato productivity in 2013–2017 and soil properties in the following springs (2014–2018). Seven cropping-system treatments were arranged in four blocks. Soil organic carbon (SOC), total nitrogen (TN), ammonium-lactate-extractable phosphorus (P-AL), stoichiometric ratios, tuber dry-matter yield and starch yield were analysed by blocked factorial ANOVA accounting for block and rotation structure. Treatment affected SOC, TN, C/N and N/P, but not P-AL or C/P; year × treatment interactions occurred for SOC, TN, P-AL, C/N and C/P. Organic management had higher SOC (15.2 vs. 13.6 g kg⁻¹) and TN (1.23 vs. 1.00 g kg⁻¹) than conventional management, whereas P-AL was similar. Year, treatment and their interaction affected both productivity measures. Five-year mean dry-matter yields were 6.04–6.68 t ha⁻¹ in the organic treatments and the unfertilised conventional treatment, and 8.79–10.75 t ha⁻¹ in the mineral-fertilised conventional treatments. Mineral nutrient supply was associated with higher productivity. These results represent five seasons rather than long-term temporal trends.

Summer cover crops can improve soil fertility and contribute to nitrogen (N) supply in temperate cropping systems, yet the effects of mixture composition and sowing timing remain insufficiently documented. This study evaluated biomass production and N accumulation of five multispecies cover crop mixtures grown in Estonia during 2024–2025 under two sowing dates per year. Aboveground biomass, botanical composition, and carbon (C) and nitrogen concentrations were measured to assess productivity, species contributions, and residue quality. Earlier sowing was generally associated with higher biomass and N accumulation, with first-sown mixtures producing, on average, 38.7% more biomass than later-sown mixtures. Mixture performance was strongly shaped by species composition and competitive hierarchies. Total N accumulation of the cover crop mixtures ranged from 42 to 275 kg N ha⁻¹ depending on mixture composition and sowing time, with mixtures dominated by common vetch (Vicia sativa L.) achieving the highest values. Oat (Avena sativa) dominated and contributed substantially to biomass in mixtures lacking competitive legumes, whereas sunflower (Helianthus annuus) and maize (Zea mays) performed less well under delayed sowing. Low-growing species such as Persian clover (Trifolium resupinatum) produced little biomass when grown with highly competitive species. Legumes exhibited lower C:N ratios than non-legumes, while mixture-level values remained moderate, suggesting residue quality with potential for favourable decomposition and nutrient release in summer cover crop systems under temperate conditions.

Long-term site-specific studies describing changes in the phenotypic variability of Phytophthora infestans populations allow quantitative predictions of pathogen spread and possible outbreaks of epidemics, and provide key input for regional resistance breeding programs. Late blight samples were collected from potato (Solanum tuberosum) breeding fields in Estonia during a twelve-year study period between 2001 and 2014. In total, 207 isolates were assessed for mating type and 235 isolates for metalaxyl resistance and 251 isolates for virulence factors. The frequency of mating types strongly fluctuated across the years, whereas the later period of 2010–2014 was dominated by the A2 mating. Despite fluctuations, both mating types were recorded in the same fields in most years, indicating sustained sexual reproduction of P. infestans with oospore production. Metalaxyl-resistant and intermediately resistant strains dominated in the first years of study, but with the progression of the study, metalaxyl-sensitive isolates became dominant, reaching up to 88%. Racial diversity, characterized by normalized Shannon diversity index decreased in time, varying from 1.00 in 2003 to 0.43 in 2013. The frequency of several virulence factors changed in a time-dependent manner, with R2 increasing and R6, R8, and R9 decreasing in time. Potato cultivar resistance background did not influence the frequency of P. infestans mating type, response to metalaxyl, and racial diversity. However, the diversity index decreased in time among isolates collected from resistant and susceptible cultivars, and remained at a high level in moderately resistant cultivars. These data demonstrate major time-dependent changes in racial diversity, fungicide resistance, and virulence factors in P. infestans, consistent with alterations in the control strategies and popularity of potato cultivars with different resistance.

For finding more sustainable cropping systems, this study on how the farming system influences the yield and quality of potato tubers was carried out with long-term crop rotation experiment. The long-term five-field crop rotation field trial was established with the following farming system treatments: organic farming system treatments: Org I (organic control), Org II (organic crop rotation with winter cover crops) and Org III (organic crop rotation with winter cover crops and the addition of composted cattle manure); conventional farming system treatments: N0 (conventional system without fertilizers), N50 (conventional system with fertilization, N50P25K95), N100 (conventional system, N100P25K95) and N150 (conventional system, N150P25K95). The average yield (based on 3 trial years) of conventional systems was 25% higher, compared to organic systems. However, in organic systems, the yield was the most stable. The most fluctuating cropping system was the most intensively managed N150. In each trial year, the yield differed statistically and it varied from 4.7 t ha⁻¹ up to 10.9 t ha⁻¹. Org I had the same dry matter yield as the N0 system, where chemicals were used, meaning that using chemicals for plant protection but no fertilizer for growth improvement had no positive effect. In each year, the yield in Org III system was similar to N50 system. Regarding the tubers per plant, there were no differences between farming systems but there was a significant difference between the trial years. The tubers in conventional systems had a lower starch content than the organic systems. It is possible to conclude that if cover crops and manure are used, organic farming practices provide just as good results as the conventional farming with low nitrogen level.

Soil microbes play a key role in the nutrient cycling by decomposing the organic material into plant-available elements and also by maintaining the soil health. The study of soil microbial hydrolytic activity (SMA) was carried out in a long-term crop rotation (barley undersown (us) with red clover, red clover, winter wheat, pea and potato) experiment in five different farming systems during 2014–2018. There were two conventional systems, with chemical plant protection and mineral fertilizers, and three organic systems, which included winter cover crops and composted manure. The aim of the present study was to evaluate the effect of the (i) cropping system and (ii) precrops in rotation on the soil SMA. The soil microbial hydrolytic activity was significantly affected by yearly weather conditions, farming system, and crops. In all farming systems, the SMA was the lowest after dry and cold conditions during early spring in 2018. In unfertilized conventional systems, the considerably lower SMA is explained by the side effects of pesticides and low organic residuals, and we can conclude that the conventional system with no added fertilizer or organic matter is not sustainable, considering soil health. In each year, the SMA of organic systems with cover crops and composted manure was 7.3–14.0% higher compared to all farming systems. On average, for both farming systems, the SMA of all the rotation crops was positively correlated with the SMA values of precrops. However, in conventional farming systems, the effect of undersowing on the SMA of the precrop was smaller compared to organic systems.

This study aimed to investigate the soil organic carbon (SOC) sequestration rate and soil organic matter (SOM) composition in conventional rotational cropping with mineral fertilization compared with organic cover cropping with and without composted manure addition during 2008–2018 to specify the SOM stabilization under different farming systems. The SOC proportion in particulate organic matter (POM) (63–2000 µm) and mineral-associated organic matter (MAOM) (−1 y⁻¹) in the organic treatment with cover crop and composted manure. Across all treatments, 57.3%–77.8% of the SOC stock was in the MAOM fraction. Mineral N fertilization increased POM-C concentration by 19%–52% compared with the unfertilized control. Under the organic treatments, the POM-C concentration was 83%–95% higher than the control. The MAOM-C concentration increased by 8%–20%. The mineral N fertilization and organic treatments (with and without cover crops and composted manure) increased the SOC stock proportion of POM. The highest proportion of SOC stock related to POM was in the cover cropping system, reducing the proportion of C related to the MAOM fraction, but the addition of composted manure with cover cropping also increased the proportion of C in MAOM. Compared with MAOM, the POM had a less resistant organic matter composition, and the POM resistance was higher in organic than conventional treatments. In general, the recalcitrance of SOM increased with SOC concentration. The POM fraction had higher aromaticity (or degree of decomposition) than the MAOM fraction. The aromaticity in POM and MAOM fractions was higher in the organic farming system and depended on mineral N fertilization and cover cropping, but the effect of manure was not significant. Although the SOC sequestration rate was higher under manure addition, resulting in the highest formation of both POM and MAOM in the soil, manure addition had little effect on overall SOM composition compared with cover crops.

The increase in the cultivation area of cruciferous oilseed crops and the use of short crop rotation has resulted in the enhanced spread of several major pests in Northern latitudes. There is currently limited information about incidence and severity of Alternaria black spot disease (Alternaria brassicae) on the main oilseed crop, spring oilseed rape (Brassica napus), in the Northern Baltics. Thus, spring oilseed rape and five alternative cruciferous oilseed crops were selected and their resistance to black spot disease was evaluated in field conditions during two growing seasons. We hypothesized that spring oilseed rape is more susceptible to Alternaria black spot disease than other alternative cruciferous oilseed crops. Both growing seasons were warmer and drier compared to the long-term average, and were thus suitable for A. brassicae development and assessments. In both years, incidence of Alternaria black spot infection was recorded on all cruciferous species, yet the disease development differed considerably among the crops. During both growing seasons, black mustard (B. nigra) plants were the most infected. Based on our observations during warm growing seasons we conclude that alternative oilseed crops such as Sinapis alba, Eruca sativa and Raphanus sativus are more resistant to the Alternaria black spot infection than the traditional oilseed crops and thus, possess a great potential to grow with limited chemical disease control in Northern Baltic conditions.

The pathogen Erysiphe cruciferarum is an increasingly serious threat to cruciferous oilseed crops worldwide. In the present study, the severity of powdery mildew was evaluated on spring oilseed rape (Brassica napus) and five alternative oilseed crop species (B. juncea, B. nigra, Sinapis alba, Raphanus sativus, Eruca sativa). The main aim of the study was to identify plant species that are less susceptible to powdery mildew for possible application as cover crop, in trap cropping or seed production. Powdery mildew assessments were conducted in two growing seasons that were characterised by unusually warm and dry conditions for northern temperate climatic conditions. In both growing seasons, a heavy powdery mildew infection (over 80%) was recorded on B. napus and B. nigra plants, indicating that E. cruciferarum is an important pathogen for oilseed crops in northern Baltics. However, three other cruciferous species S. alba, E. sativa and R. sativus showed full resistance to powdery mildew, and thus, even under strong powdery mildew pressure, they can be cultivated without pesticide application in northern Baltic conditions. We suggest that in changing climatic conditions powdery mildew is expected to become a more serious problem in cruciferous oilseed crops in northern Europe, especially under intensive short-rotation farming practices.

The size distribution of wheat-grain starch granules has an impact on the yield of fine flour. The aim of the study was to compare the impact of conventional (mineral fertilizers, pesticides) and organic farming treatments (cover crops, composted cattle manure) on (i) the size distribution of starch granules, (ii) the level of the first break whole and fine flour yield. The grain samples of winter wheat cv Fredis were taken from a long-term field crop rotation experiment established in 2008 at the Estonian University of Life Sciences in Tartu County (58°22′ N, 26°40′ E) on Stagnic Luvisol soil. The weather conditions during the grain filling period of winter wheat had a strong impact (p < 0.001) on the grain starch granule size distribution. The proportion of starch granules with a smaller diameter (C-type granules) was higher in years with a longer grain filling period. The size distribution of starch granules was not influenced by farming system. The increased proportion of C-type granules increased the fine flour yield significantly. Fertilisation with organic manure and twice with mineral nitrogen increased significantly the mean diameter value of different starch granules.