Computer simulation of the soil water regime under an apple orchard in a mountainous area (using the example of the leached chernozem of the experimental agricultural station Gorno-Altaiskoe)

Relevance. Progressive degradation of farmland soils – erosion, salinization, desertification. Aim. To establish features of water-physical properties of leached chernozem under an apple orchard and associated patterns of soil profile moisture distribution in summer period when precipitation deficiency observed. Methods. Moisture content in soil horizons was determined by the gravimetric method. To determine the granulometric composition of soils, the pipette method was used. The soil bulk density was determined by the cutting ring method. For solid phase density determination the pycnometric method was used. The method of graphic interpolation was used for transition the soil texture classification from Russian to international one. Water infiltration modeling into the soil profile was carried out using the HYDRUS-1D program. The parameters of approximating of the water retention curve of soils by the Van Genuchten equation were obtained by the calculation method of pedotransfer functions «Rosetta Lite» of the RETC program, using data on soil density and soil texture. Results. It has been established that the upper well-structured horizons of leached chernozem under an apple orchard have a greater water-holding capacity; their water-retention curves are more flattened. The water retention curve of the more structureless B2k horizon, the soil texture of which is dominated by sandy fractions, is shifted towards lower humidity. During hot and dry summer period the moisture deficiency in the soil was noted only in the upper twenty-centimeter soil column (14 mm). The moisture of the lower horizons, where the bulk of tree roots are concentrated, is satisfactory. The model demonstrates the smallest discrepancies with the moisture values measured during the soil reclamation experiment one day after the start. The downward moisture penetration into the lower soil layers is prevented by low pressure in the clayey A and AB horizons. Selection of input parameters and debugging of the model based on experimental data allows it to be used to simulate further processes occurring in the soil. It was revealed that the formation of positive (upward) water flows, which ensure the “pull-up” of salts and substances from the lower part of the profile to the upper layers during dry periods of the year, has a significant impact on moisture distribution in the chernozem under the apple orchard.