401the furrows between ridges. The width of the ridge and furrow is dependent on the
specific water and heat conditions. In the area with an annual rainfall of 300–400
mm, V-shaped furrow is often used due to insufficient hydrothermal conditions. A
V-shaped furrow is a naturally formed furrow of two adjacent ridges, which has a
width of zero. The main function of ridge-furrow with film-mulching is harvesting
rainwater. The ridge and furrow itself has a capability to collect precipitation from
surface to bottom of the ridge. With film-mulching, the precipitation on the ridge
surface is collected to the bottom of furrows, and then is infiltrated into soil through
small holes on the film. Thus, useless precipitation during light rains in the non-
mulched fields is efficiently overlapped to maize root zones in the film mulched
ridge-furrow cropping (Jiang and Li 2015 ; Li et al. 1999a).
Plastic film mulch on ridge-furrows can effectively reduce water evaporation
from soil. Compared to un-mulched cultivation, plastic film mulch prepared before
the previous winter increases the water storage in 2 m-depth soil profiles by 43 mm
at maize sowing time (Liu et al. 2009 ). Plastic film mulch also significantly increased
soil moisture during the early growth of maize. But at the peak time of maize grow-
ing, this effect of increasing soil moisture is usually not significant. In some cases,
plastic mulch even reduces soil moisture compared with no mulch (Li et al. 1998 ,
2005 ; Liu et al. 2014b; Wang et al. 2014 ). Liu et al. (2014b) once assessed the effect
of plastic film mulched ridge-furrow copping to conseve rainwater in soil under
non-maize-cropped condition. They found that in one growing season plastic film
mulched ridge-furrow cropping increased soil water contents in the 170 cm-depth to
the field capacity, and conserved 100 mm more rainwater in soil than un-mulched
ridge-furrow cropping.
Plastic film mulch can effectively enhance temperature in the topsoil. This func-
tion of the plastic film mulch expands maize planting to the areas where previously
maize was not a profitable crop due to low yield under insufficient rainfall and low
temperature conditions. The effect of plastic film mulch in increasing soil tempera-
ture mainly occurs in the early stage of crop growth (seedling and jointing) (Liu
et al. 2009 , 2014b; Zhou et al. 2009 ; Wang et al. 2014 ; Hai et al. 2015 ). At a site
with annual temperature of about 6.6 °C and precipitation of about 300 mm, found
that daytime soil temperature in the 0–15 cm was 3.0 °C higher in mulched than
un-mulched plots throughout maize growing season in the absence of maize grow-
ing (Hai et al. 2015 ). However, in the presence of maize growing, daytime soil tem-
perature in the same depth increased by 2.8 °C in mulched relative to non-mulched
plots, only in the early growth (before jointing) but not in the late growth (Hai et al.
2015 ). This indicates that during the late growth when soil surface is mostly shaded
by canopy, the plastic mulch effect in increasing soil temperature is not significant.
The increasing effect of film-mulching on soil temperature is the key to plant maize
in high altitude areas with a lack of heat. In the areas with an average annual rainfall
of only 300 mm, average annual temperature of 6.5 °C, and altitude of 2400 m
above sea level, maize was completely unable to grow without film-mulching; the
application of ridge-furrow with film-mulching made maize yield reach to 6–7 t ha−^1 ,
5–10 times more than conventional uncovered cultivation (Liu et al. 2009 ; Zhou
et al. 2009 ). In a continuous four-year experiment, it was found that the lower limit
Integrated Dryland Agriculture Sustainable Management in Northwest China