Several factors are involved in the incidence of blossom-end rot (BER) in tomato fruit, but the main one is insufficient Ca uptake and transport through the plant, resulting in Ca deficiency in the fruit. Sprays of Ca-containing products are considered to be a possible measure to overcome the local Ca deficiency in tomato fruit. Therefore, the main objective was to evaluate the effectiveness of additional Ca supply to tomato fruits for increasing Ca content and reducing fruit damage. Sprays of five different commercial preparations containing (Brexil Duo, Calmax Zero N, Ca(NO₃)₂, CaCl₂) or promoting (Greenstim) Ca uptake were tested using BER-sensitive large-fruit variety ‘Beorange’. The experiment was conducted in the commercial greenhouse ‘Getlini EKO’, Latvia, during the autumn–spring season of 2020/2021 under controlled conditions, eliminating the adverse impact of external factors. The results revealed that none of the preparations were effective in increasing Ca content, preventing BER, and did not promote the tomato yield. As good agricultural practices were followed in the greenhouse to manage BER, we concluded that a non-marketable yield of around 15% should be expected for ‘Beorange’ when grown under artificial light, possibly due to the impact of abiotic stresses and genetically determined susceptibility.

The present study was carried out to evaluate the leaf nutrient status of commercially grown strawberries in Latvia during 2014–2022. The results of N, P, K, Ca, Mg, S, Fe, Mn, Zn, Cu, Mo and B in 200 strawberry leaf samples from different strawberry-producing farms were analysed over three periods: 2014–2016, 2017–2019, and 2020–2022. According to leaf analyses, plant fertilization was only partly well managed by the growers. During the research period, strawberries in Latvia were generally sufficiently supplied with N, P, K, Mg, Fe, Mn, Mo, and B, while the level of Ca, S, Zn, and Cu was considered low. The deficiency of these nutrients was characteristic for more than 50% of the samples. Since Ca, S, Zn, and Cu are essential for berry formation and quality and contribute to stress resistance; their deficiency could be one of the limiting factors for strawberry yield. The significant positive correlations found between nutrients, including deficient ones, confirmed their close relationship in the uptake process and the importance of sufficient supply. The results clearly indicated that fertilization could currently be an issue that limits the strawberry harvest in Latvia, and adequate provisions of Ca, S, Zn, and B should be the main focus.

Inconsistent results on the effects of humic substances (HS) on yield and nutrient status of important food crops, including oilseeds, confirm the need for further research on different HS products to match their use to actual field conditions. The aim of this study was to evaluate the effect of foliar application of commercially produced peat- and vermicompost-derived HS preparations on nutrient status and yield of spring oilseed rape (Brassica napus). The field experiment was carried out in Stende State Cereals Breeding Institute, Latvia, during the vegetation season of 2012, using the spring oilseed rape cultivar ‘Perfect’. Although foliar sprays of HS were applied during the critical stages of crop development from rapid growth to flowering, they were ineffective in improving the supply of the deficient nutrients (N, K, B, Zn, Cu) in leaves. Moreover, both tested HS products caused a decrease in Cu and B content in the seeds, which resulted in a negative trend in oilseed rape seed yield. Therefore, the conducted experiment demonstrated that foliar application of both HS preparations was ineffective to promote nutrient status and did not contribute to spring oilseed rape yield.

Urban trees are vital for air pollution mitigation, but their function is often compromised by exposure to particulate matter (PM), which impairs physiological processes and reduces growth. Enhancing tree resilience is therefore essential for maintaining their ecosystem services in polluted urban environments. This study examined the early growth and biochemical responses of Norway spruce (Picea abies) and Norway maple (Acer platanoides) seedlings to foliar PM exposure and assessed whether biochar (BC) soil amendment can alleviate PM-induced stress. Seedlings were cultivated outdoors under three treatments: Control (no treatment), PM (foliar exposure to particulate matter), and PM + BC (PM exposure with 10% biochar added to the substrate). Results revealed that Norway maple showed significant biochemical sensitivity to PM, including substantial reductions in chlorophyll and increases in antioxidant activity. However, Norway spruce showed more moderate pigment changes but reduced height growth. BC modulated oxidative and phenolic responses (TPC, TFC, MDA) and partially mitigated PM-induced stress, although its effectiveness varied by species. For Norway spruce, BC significantly enhanced resilience by restoring height growth, stabilizing pigments, and reducing oxidative stress compared with treatment using PM alone. In contrast, for Norway maple, BC failed to restore chlorophyll levels and increased oxidative and phenolic activity, yielding mixed outcomes. Despite physiological differences between the two species, multivariate PCA consistently showed that PM-treated seedlings diverged from the control cluster, whereas PM + BC-treated seedlings were closer to the controls, with mitigation substantially stronger in Norway spruce. These findings demonstrate that biochar can reduce PM-induced stress, but its successful implementation depends fundamentally on selecting appropriate species traits and understanding their specific metabolic response strategies.