Effects of subsoiling depth, period interval and combined tillage practice on soil properties and yield in the Huang-Huai-Hai Plain, China

Compaction layers are widely distributed in the Huang-Huai-Hai Plain, China, which restrict root growth and reduce yields. The adoption of subsoiling has been recommended to disrupt compacted soil layers and create a reasonable soil structure for crop development. In this paper, the effects of subsoiling depth (30, 35 and 40 cm), period interval (2 or 3 years) and combined pre-sowing tillage practice (rotary cultivation or ploughing) on soil condition improvement was studied on a tidal soil in the Huang-Huai-Hai Plain. Seven tillage patterns were designed by combining different subsoiling depths, period intervals and pre-sowing. The evaluation indicators for soil condition improvement were as follows: thickness of the plough layer and hard pan, soil bulk density, cone index, soil three-phase R values, alkali nitrogen content, crop yield, and economic benefits. The results showed that subsoiling can significantly improve the soil structure and physical properties. In all subsoiling treatments, the depth of 35 or 40 cm at a 2-year interval was the most significant. The thickness of the plough layer increased from 13.67 cm before the test to 21.54–23.45 cm in 2018. The thickness of the hard pan decreased from 17.68 cm before the test to 12.09–12.76 cm in 2018, a decrease of about 40.07%. However, the subsoiling combined pre-sowing tillage practice, that is, rotary cultivation or ploughing, was not significant for soil structure and physical properties. For all subsoiling treatments, the soil bulk density, cone index and soil three-phase R values of the 15–25 cm soil layer were significantly lower compared to single rotary cultivation. Subsoiling was observed to increase the soil alkaline nitrogen and water contents. The tillage patterns that had subsoiling at the depth of 35–40 cm at a 2-year interval combined with rotary cultivation had the highest alkali nitrogen and water contents, which increased by 31.08–34.23% compared with that of the single rotary cultivation. Subsoiling can significantly increase the yield both of wheat and corn, as well as the economic benefits. The treatment of subsoiling at the depth of 35 cm at an interval of 2 years combined with rotary cultivation had the highest annual yield and economic benefits. For this treatment, the annual yield and economic benefits increased by 14.55 and 62.87% in 2018, respectively. In conclusion, the tillage patterns that involved subsoiling at a depth of 35 cm at a 2-year interval along with rotary cultivation are suitable for the Huang-Huai-Hai Plain.