Dual effect of fruit tree cultivation on soil physical characteristics

Soil bulk density, hardness, moisture and surface soil aggregation composition were measured in <10-, 10~20- and >20-year-old orchards in Weibei Region. The results showed that soil bulk density in the 0~30 cm soil layer decreased with increasing orchard age. However, bulk density below the 30 cm layer increased with increasing orchard age, exceeding the 1.30 g?cm^-3 upper limit for healthy garden soils. Soil bulk density in the 10~30 cm soil layer was lower in orchards than in croplands. Soil hardness increased sharply below the 30 cm soil layer, almost reaching the 1 000 kPa upper limit of soil quality standard for healthy root growth. Soil hardness in the 17.5~27.5 cm soil layer is lower in orchards than in croplands. Soil aggregation status was poor in surface soil of orchards. Most water-stable aggregates in the orchard soils were in 0.5~0.25 mm range class. Contents of water-stable soil aggregates >0.25 mm increased with increasing age of orchards. Water-stable soil aggregates contents in 20-year-old orchards were two times higher than those in 10-year-old orchards. Fruit trees have a dual effect on soil physical characteristics. Soil physical conditions was generally improved in topsoil (0~30 cm), but worsen in subsoil (<30 cm) with increasing orchard age. As latent degradation of subsoil in orchards affected the healthy growth of fruit trees, any such degradation should be carefully monitored.