Subsoiling depth affects the morphological and physiological traits of roots in film-mulched and drip-irrigated cotton

Abstract

Subsoil compaction is increasingly a problem. Subsoiling breaks up the soil, removes compaction, and improves root growth. However, it is unclear whether subsoiling depth affects root growth and physiological functioning of film-mulched and drip-irrigated cotton, which has a shallow root system (< 60 cm). A 2-year experiment (2019–2020) was performed under field conditions (soil texture was sandy loam from 0 to 40 cm and clay loam from 40 to 60 cm) to determine the morphological and physiological traits of the root system at different subsoiling depths: no subsoiling (NS, control) and subsoiling to 30 (S30), 40 (S40), and 50 (S50) cm. The root/shoot ratios were significantly higher for the S30 and S40 treatments than for the control (p < 0.05). The dry matter levels over the 2 years were 24.2% higher in S40 plants than in controls and 20.7% higher than in the others subsoiling treatments. The average 2-year yields (676.9 g m–2) were 24.3%, 11.9%, and 1.4% higher in S40 plants than in controls, S30, and S50 plants. At different soil depths of 0–60 cm, the average 2-year root length density (RLD) of all subsoiling treatments was 0.5 cm cm−3 in the top 20 cm of soil, 14.0% higher than that from 20 to 40 cm and 344.2% higher than that from 40 to 60 cm. However, RLDs of the NS and S30 treatments were highest at 0–20 cm, while S40 and S50 maximum RLDs were in the 20–40 cm layers. The RLD, average diameter of roots, and surface area density of roots were significantly higher in the S40 and S50 treatments than in the S30 and NS treatments (p < 0.05). Compared to NS, subsoiling reduced the levels of malondialdehyde and abscisic acid in roots; improved superoxide dismutase, peroxidase, and catalase activities in roots, and increased the levels of gibberellic acid and indole-3-acetic acid in roots. Our results provide evidence that could help optimize subsoiling depth in film mulching and drip-irrigated cotton in Xinjiang.