Effect of Lignohumate AM on morphology, yield and commercial quality of Citrus reticulata var. unshiu ‘Kowano Wase’ fruits under the subtropical conditions of Russia

Abstract

Introduction. Against the background of declining soil fertility and increasing abiotic stressors, the use of environmentally safe biostimulants, including humic preparations, represents a promising approach to enhance crop productivity and stress tolerance. Of particular interest is their application in citrus cultivation, given the high sensitivity of these crops to environmental conditions. The humid subtropics of Russia are characterized by considerable variability in temperature and moisture regimes, which significantly affects the growth, development, and fruiting of mandarins. Therefore, the search for agronomic practices aimed at increasing the adaptive potential of plants and stabilizing yields is of high relevance.
Aim. To evaluate the effect of fivefold foliar treatment with the preparation Lignohumate AM on the productivity and commercial fruit quality of mandarin (Citrus reticulata var. unshiu ‘Kowano Wase’) under the humid subtropical conditions of Russia.
Materials and methods. Field experiments were conducted in 2023–2025 at the Subtropical Scientific Centre of the Russian Academy of Sciences (Sochi). The work studied mandarin plants grafted onto Citrus trifoliata rootstock, planted at a spacing of 4 × 1.5 m. Treatments were applied during key phenological stages of plant development.
Results. It was established that the application of Lignohumate AM consistently increased yield throughout all study years. The greatest effect was observed in 2025, when the average yield reached 12.8 kg per tree (212.1 dt/ha), which was 20–25% higher than the control. Under stressful weather conditions (hot and dry summer), the preparation contributed to reducing yield losses, indicating enhanced adaptive potential of the plants. An improvement in commercial fruit quality was also recorded, manifested as an increased proportion of large-sized fruit (≥60 mm) and a decreased share of small-sized fruit.
Conclusion. Thus, fivefold application of Lignohumate AM is an effective agronomic practice that ensures increased yield, greater fruiting stability, and improved fruit quality of mandarin under subtropical conditions.