Subsoiling 35 cm in depth improve soil physicochemical properties and increase grain yields of wheat and maize in aquic brown soil

Objectives Current tillage is 20 cm depth, this long-term practice has reduced the thickness of the plough layer, increased the thickness of the plough pan, and affected the growth of crops. Subsoiling in different depths was attempted in this study to provide technical support for field farming management.

Methods A field experiment was conducted in aquic brown soil, Yantai, Shandong Province. Taking conventional tillage 20 cm as control (CK), subsoiling of 30 cm, 35 cm and 40 cm in depth were designed in the experiment. The tillage was conducted before sowing of winter wheat, and all treatments were once applied 1125 kg/hm² of humic acid compound fertilizer (N–P₂O₅–K₂O=18–10–12) with the tillage practice. No tillage was conducted for maize, and chemical fertilizer was top dressed at the jointing stage of maize. At wheat and corn harvest period, soil samples of 0−10 cm, 10−20 cm, 20−30 cm and 30−40 cm in depth were taken to determine the soil organic matter and available N, P and K contents and the soil bulk densities.

Results Compared with CK, the subsoiling treatments of 30 cm, 35 cm and 40 cm increased yields of crops, for wheat the increments were 10.9%, 15.3% and 15.5%, respectively, and for maize they were 12.0%, 14.9% and 9.4%, respectively. The subsoiling treatments effectively reduced the soil bulk density by 0.03−0.18 g/cm³ in the 10−40 cm soil layer, improved the ratio of three phases and the available nutrient contents in the 20−40 cm soil layer (P < 0.05). The soil bulk density in the 0−10 cm soil layer of CK was significantly lower than those of the subsoiling treatments, and those in the 0−10 cm and 10−20 cm soil layers of subsoiling 35 cm treatment was significantly higher than in the others. The lowest soil bulk density in the 0−10 cm and 10−20 cm soil layers of the maize season were all in subsoiling 35 cm treatment, which was significantly lower than in other treatments. After wheat harvest, the minimum R value was between 13.2 and 15.9, and after maize harvest was between 6.03 and 8.81. Subsoiling treatments increased the available P and N contents in 20−40 cm soil layer, with increment of 0.56−37.4 mg/kg for P and 31.9−77.8 mg/kg for N in the 35 cm subsoiling treatment. The available K was increased most significantly by 24.3−100.3 mg/kg in treatment of subsoiling 30 cm. The most significant increase of organic matter content was in subsoiling of 40 cm, with increase of 0.95−0.69 g/kg.

Conclusions Deep subsoiling is effective in reducing soil bulk density, increasing the crop yield of the current and the following season, improving the available nutrient contents of the 20−40 cm soil layer. Comprehensively considering the mechanical consumption and the tillage effect, the 35 cm depth of tillage is recommended for the tested area.