The aim of the research was to determine selected biochemical and physical characteristics and yielding of fruits in apple varieties (Malus domestica Borkh) such as Gala Schniga, Beni Shogun (Fuji) and Ligol, M.9 rootstock growing in the Wielkopolska region, Poland. high-performance liquid chromatography (HPLC) analysis revealed differences both in the profile and contents of soluble sugars and other metabolites detected in fruits of the tested apple varieties. The highest total saccharide content was found in fruits of cv. Gala Schniga, while leaves and shoots of this variety showed the lowest contents. Electron paramagnetic resonance (EPR) spectroscopy revealed the lowest contents of semiquinone radicals in apple fruits and the highest in leaves of apple trees. All organs of Schniga Gala apple trees were characterized by the highest levels of these radicals. Besides, gas chromatography-mass spectrometry (GC-MS) analysis of abscisic acid (ABA) revealed the highest levels of this molecule in shoots of apple trees, especially the Beni Shogun variety, while in fruits the levels were the lowest. Ligol fruits had the highest content of ABA. The percentage of injury observed after a low-temperature treatment and estimated on the basis of electrolyte leakage, was shown to be the lowest in fruits of the Beni Shogun variety. In turn, the lowest average yield of apple fruits was recorded for the Ligol and Fuji varieties, with the highest in the case of the Gala Schniga variety. At the same time, a significant variability in the average weight of fruits was observed; the highest average mass of fruits was recorded for the Ligol variety, while it was lowest for Gala Schniga. Additionally, firmness evaluation of the fruits revealed that the firmest fruits were harvested from Gala apple trees, before the Beni Shogun and Ligol varieties. A significant variability was recorded in the red blush on fruit surfaces of the tested varieties, with Ligol fruits having the weakest blush. Altogether, these results indicate that fruits of the analyzed apple varieties differed both in terms of their biochemical composition and physical characteristics.

Sour cherry (Prunus cerasus L.) is one of the most important fruit crops in Poland and ‘Łutówka’ is the dominant cultivar in commercial orchards. The experiment was carried out in 2007–2013 in three orchards; in each of them, three levels of fertilization were applied: 0 N kg ha⁻¹, 60 kg N ha⁻¹, and 120 kg N ha⁻¹. The activity of dehydrogenase and protease in the soil was studied depending on nitrogen fertilization. The abundance of soil microorganisms was assessed: bacteria, fungi, actinomycetes, and nitrogenous bacteria (Azospirillum and Azotobacter) in the years during the experiments carried out with fertilization of 60 kg N ha⁻¹ in all orchards. The enzyme activity of dehydrogenases increased after the use of 60 kg N ha⁻¹ from 3.8 to 6.7 (cm³ H₂ 24 h⁻¹ kg⁻¹ DW soil), but a further increase in the dose to 120 kg N ha⁻¹ caused a decrease in activity to 5.1 (cm³ H₂ 24 h⁻¹ kg⁻¹ DW soil). The activity of proteases was dependent on nitrogen fertilization, but to a large extent it was related to the course of climatic conditions. There is no relationship between the growth and the activity of proteases. The yield and selected quality parameters of the cherry fruits were associated with both dehydrogenases and proteases. The use of lower doses of nitrogen fertilizers allows for maintaining biological balance in the soil and a more efficient use of nutrients, contributing to less environmental pollution.

Foliar fertilization makes it possible to quickly provide plants with essential nutrients, mainly micronutrients, which can significantly improve the quality of yields. The aim of this study was to evaluate the effect of foliar fertilization with fertilizers containing calcium and microelements on yielding and fruit quality of highbush blueberry (Vaccinium corymbosum L.). A two-year study was carried out in western Poland in an experimental highbush blueberry production plantation. During the growing season the bushes were treated several times with the following foliar fertilizers: Armurox, BioCal, and Stymjod. The experiment assessed bush growth vigor, yield, fruit quality characteristics, sugar, organic acid, and health-promoting substance content. It was found that as a result of fertilizing highbush blueberry bushes with foliar fertilizers, the leaf blade area and plant yield increased significantly. The fruits collected from those bushes were characterized by a higher mass, firmness, and TSS content. This also applies to blueberry fruit after storage. Foliar fertilization had no significant effect on the content of chlorophyll a and b in the leaves of northern highbush blueberry, on fruit coloration, the content of sugars, ascorbic and citric acids, and the phenolic compounds in them.

Both mycorrhizal and Trichoderma spp. fungi are known for antagonistic effects against certain biological pathogens causing apple replant disease (ARD). The aim of this study was to assess the effectiveness of the bioinoculants based on endomycorrhizal and Trichoderma spp. fungi on the biological properties of soil as well as the parameters of the apple tree growths in a fruit tree nursery under replantation conditions. A two-year experiment was conducted on Jonagold apple trees grafted on to M.9 rootstock in western Poland. The trees were planted in the replant soil—from areas used for the production of apple trees, and in the crop rotation soil, that had not been used for nursery purposes before. A mycorrhizal inoculum and preparations containing Trichoderma spp. fungi were applied to the replant soil. Biological properties of the soil and the growth of the aerial and underground parts of the apple trees were assessed. The enzymatic (dehydrogenases and protease) and respiratory activity of the replant soil was significantly lower than that of the crop rotation soil. The apple trees grew worse when exposed to the ARD conditions. The effectiveness of applied bioinoculants in mitigating the effects of replantation in the nursery were shown. Both the treatment mycorrhization and the application of bioinoculants containing Trichoderma spp. increased the respiratory and enzymatic activity of the replant soil. The growth of the root system and the aerial parts of the trees (including leaves) was much better after the combined use of both types of fungi than in the replant soil that had not received the fungal treatment.

Humic acids are plant biostimulants, which can be used in horticulture as an effective and relatively inexpensive alternative to chemical means of production. The aim of the study was to assess how the fertiliser containing humic acids affected the growth, yield, and quality of strawberry fruits. In 2021, an experiment was conducted on two-year-old strawberry bushes (Fragaria× ananassa (Duchesne ex Weston) Duchesne ex Rozier) of the ‘Rumba’ cultivar growing on a horticultural farm in northern Wielkopolska, Poland. During the growing season, the soil was fertilized by the mineral fertilization and the bushes were sprayed two, three, or four times with the Humi Brown Gold fertiliser containing humic acids. In the experiment, the soil enzymatic activity, biometric parameters of strawberry leaves, fruit yield and fruit quality was assessed. It was determined that, in the experimental treatments where foliar fertilisation had been applied, the activities of proteases and dehydrogenases as well as soil respiration increased by more than double and were significantly higher than in the variants where soil fertilisers had been applied. The strawberry bushes treated with the humic acids fertiliser developed more than 60% larger surface leaves, bloomed more intensively and gave a higher yield. Fruits with significantly higher firmness were harvested from such bushes, with higher weight and extract content than those where the soil fertiliser had been applied. The difference was several tens of percent. This leads to the conclusion that the foliar application of humic acids could be an effective alternative to mineral fertilisation in strawberry plantations.

The technology of producing fruits containing an increased amount of elements essential for the health of the human body, including silicon, has become very important in recent years. Due to the popularity of apple tree cultivation in Europe, appropriate research has been undertaken. The aim of the experiment was to determine the advisability of foliar silicon nutrition in apple tree cultivation. Apple cultivars ‘Gala Schniga’, ‘Ligol’ and ‘Topaz’ were studied and treated with three different doses of silicon (100, 200, 300 mg SiO₂·L⁻¹). The treatments were performed five times during tree growth in the third year of cultivation from early June to late July. Foliar application of silicon did not improve the evaluated tree growth parameters. It significantly influenced, in the highest analysed concentration, a better fruit yield (12%), a higher yield coefficient, depending on the concentration, from 16 to 18%, a better fruit quality (weight and size) and a more extensive red blush. The considered cultivars differed in the growth and yield of trees in the third year of cultivation. ‘Topaz’ grew strongest and ‘Ligol’ yielded the best. The highest yield coefficient was found for the Topaz’ cultivar. The fruit of ‘Topaz’ had the biggest blush and ‘Gala Schniga’ the biggest sugar content. Macro- and micro-nutrient nutritional status of trees were no better, except for iron and copper in leaves, and at some concentrations of applied silicon also zinc and copper in fruit.