Effect of soil water content changes caused by ridge-furrow plastic film mulching on the root distribution and water use pattern of spring maize in the Loess Plateau

Ridge-furrow plastic film mulching (RFPM) is an efficient planting technique for rainwater harvesting in rainfed regions of the Loess Plateau, China. However, relevant data on root water use patterns under RFPM remain sparse. To clarify the water use pattern of roots under this planting technique and determine the root characteristic parameters related to water absorption, this study conducted a two-year field experiment using spring maize with three treatments: flat planting (FP), and RFPM with two different ridge:furrow ratios (40 cm:70 cm and 70 cm:40 cm). Hydrogen and oxygen stable isotopes (δD and δ18O) of different water sources were measured, and the MixSIAR model was used to quantify the contributions of different water sources to spring maize root water uptake. The results showed that the root characteristic parameters of spring maize under the three treatments decreased with increasing soil depth and were mainly distributed in the shallow (0–20 cm) and middle (20–60 cm) soil layers. Compared to FP, under RFPM the distribution proportions of the root characteristic parameters in shallow soil were higher, which may be related to the increase in shallow soil water content. The main water-absorbing soil layers of spring maize under the three treatments were the same: 0–20 cm, 20–40 cm, 40–60 cm, 40–60 cm, and 0–20 cm in the V6, V12, R1, R3, and R6 growth stages, respectively. However, compared to FP, under RFPM the water use proportion of spring maize of shallow soil increased, especially under the larger ridge to furrow ratio, and correlation analysis showed that this phenomenon might be related to the RFPM increasing the proportion of the spring maize root characteristic parameters in shallow soil. Correlation analysis further showed that the root length density and root surface area density might be the key characteristic parameters for determining root water uptake.