Objectives Deep plowing is a key measure to improve the soil structure of infertile paddy fields and enhance production capacity. We compared the effects of plowing depths on the yield of the first crop and ratoon rice, and the physical and chemical properties of infertile paddy soil in Jianghan Plain.

Methods Field experiments were conducted in the Jianghan Plain in 2022 and 2023. The plow layer of the paddy fields in this area was 13−22 cm deep. Three plowing depths of 15 cm, 20 cm, and 25 cm were set up in the experiment, with conventional rotary plowing (12 cm) as the control. At the maturity of 1st-crop and ratoon rice, the aboveground parts of the rice plant were collected and divided into stem, leaf, and spike samples, the rice biomass, nutrient accumulation in each part, yield and yield components were investigated. The 0−20 cm soil samples at the beginning, and the 0−10 cm, 10−20 cm, and 20−30 cm soil samples of each treatment at the end of the experiment were collected to analyze the physical and chemical properties.

Results Compared with the control, the plowing depths did not affect the yield of 1st-crop rice in 2022, plowing 15 cm and 25 cm deep increased the ratoon rice yield by 9.58% and 25.15% respectively; In 2023, plowing depth had no significant yield effects on both the first crop and ratoon rice, although plowing 20 cm and 25 cm increase the grain number per panicle or the seed setting rate of both the first crop of rice and the ratoon rice. Compared with control for the first crop rice, plowing depths did not show significant effect on the nitrogen accumulation in all parts of both rice in 2022, and deep plowing reduced the grain N accumulation but increased straw N accumulation of the first crop rice in 2023. Moreover, the straw N accumulation under the 25 cm deep plowing treatment was significantly higher than that under the 15 cm and 20 cm plowing depth treatments. Except that plowing 25 cm deep in 2022 increased the straw P accumulation of the first crop rice, plowing depths had no significant promoting effect on P accumulation in grains, straw, and above-ground parts of both the rice in the two years. In 2022, deep plowing increased the grain K accumulation of the first crop rice, and in 2023, plowing 15 and 20 cm treatments increased the straw K accumulation of the ratoon rice. In most cases, there was no significant difference in the accumulation of N, P and K the above-ground parts of both rices among the three plowing depth treatments. After two years of plowing 20 cm and 25 cm deep, the soil bulk density of 0−30 cm soil layers decreased by 1.80%−5.36%, and the total porosity increased by 2.62%−5.13%, with the most significant effect observed in the 0−10 cm soil layer. The capillary porosity and aeration porosity in 0−10 cm and 10−20 cm soil layers increased by 2.24%−9.41% and 1.52%−6.07% respectively. Plowing 20 cm and 25 cm deep increased the organic matter content in 20−30 cm soil layer. The plowing 25 cm treatment reduced available N and P contents in 0−10 cm soil layer, plowing 15 cm deep reduced the available P content in the 0−10 cm soil layer but increased the available potassium content.