• Plastic increased total plant 15N uptake rather than Open. • More residual 15N was recovered in 0–120 cm soil under Plastic than under Open. • The ridge was the main N fertilizer source for plant uptake. • Lateral N movements from furrow to ridge and from ridge to furrow were observed.

Plastic film mulching has commonly been used for adaptation to water scarcity and for increasing agricultural productivity on the semiarid Loess Plateau of China. However, the effect of plastic film mulching on cropland soil water and thermal regimes on the semiarid Loess Plateau of China is not well understood. This study simultaneously monitored the dynamics of the soil water content and the soil temperature with high resolution in a ridge cultivation system with plastic film mulching (RS) and a flat cultivation system without plastic film mulching (FS) during the maize (Zea mays L.)-growing season. We found that, in general, the soil temperature and soil water content were significantly different among the ridge under RS (RS-ridge), the furrow under RS (RS-furrow) and FS throughout the maize-growing season (P < 0.05). Plastic film mulching increased the near-surface soil temperature by approximately 1°C throughout the study period. RS significantly increased the soil water content during the dry period (May to June), especially within the middle soil layer (30–60 cm), compared to FS. The lowest monthly average soil water content was found at a depth of 30–60 cm layer in FS during the dry period (May and June). The water depletion was found within deeper (100–160 cm) soil layers in May but the water storage in the same layer of FS in June increased although it was the dry period, which differed from RS. The RS practices showed a longer period of water supply from the deeper soil layer (100–160 cm) in May and June for meeting maize water demands during the early growing stage rather than in only May for FS. During June (dry period), the water storage at a depth of 0–60 cm was greater in RS than in FS, and the reverse was true at a depth of 60–160 cm. The results indicate that the dry soil layer at a depth of 30–60 cm formed during June in FS likely reduced water movement from deeper layers to the topsoil layer, and hence constrained the availability of surface soil water for meeting maize water requirements during the early growing stage (dry period). Our study suggests that RS tends to significantly increase surface soil water availability by restraining the formation of a dry soil layer during the early maize-growth stage primarily under dry conditions, and thus enhances maize productivity in the semiarid Loess Plateau of China.

• We evaluated the effect of a ridge mulched system (RM) on soil water and inorganic N. • RM increased soil water storage and decreased evapotranspiration during the pre-silking stage. • RM increased soil inorganic N in the topsoil under the ridge and reduced N leaching. • RM led to high inorganic N accumulation in soil after three years maize cultivation.