Ridge-furrow irrigation was birthed and developed in accompany with ridge-furrow
intercropping fields. The ridge-furrow configuration is built by shaping the soil surface
with alternate ridges and furrows along the contour. In ridge-furrow irrigation, the flow
water only transports on furrows and supplies water to crops. The flow water on furrows
infiltrates into ridge-furrow configuration by capillarity forces, and lateral infiltrated water
volume must meet the needs of the plants grown on the ridges of soil or raised beds.
Improper ridge-furrow irrigation design and management in fields has some disadvantages,
such as interference infiltration, higher deep water percolation, and lower irrigation
uniformity. Soil water dynamics and distribution under ridge-furrow configuration can
provide guidance to design the appropriate width ratio of furrows to ridges in ridge-furrow
intercropping fields. Soil infiltration characteristics in ridge-furrow irrigation were
investigated in laboratory experiment by using rectangular soil chambers. Soil water
movement was numerically simulated by using HYDRUS-2D software. The effects of
variables—soil physical properties, cultivation technique parameters, and irrigation
technique parameters—on irrigated soil infiltration process and wetting patterns were
quantitatively evaluated. The optimized artificial neural networks model was developed to
predict soil infiltration characterization under ridge-furrow irrigation. The appropriate
width ratio of furrows to ridges under ridge-furrow irrigation was investigated by
optimized method and simulated calculation, which provide theoretical guidance to
irrigation technique optimization and management in field experiments. The mainly results
are as follows:
(1) Soil water movement equation was revised to simulate water infiltration in
ridge-furrow irrigation based on variably saturated flow theory. Soil hydraulic parameters
in heavy loam soil and sandy loam soil were deduced. The initial and boundary conditions
were determined in ridge-furrow irrigation. Soil water movement equation was solved by
using HYDRUS-2D software and accurately simulated soil water dynamics under ridge-furrow irrigation. There were higher simulated precision in cumulative infiltration
and wetting distances, while a low simulated precision was shown in soil water distribution
in ridge-furrow irrigation through the hydrodynamic model.
(2) The effect of different variables on soil water distribution and cumulative
infiltration was investigated by using numerical simulation. Soil texture had a significant
effect on soil water distribution and cumulative infiltration during the same ridge-furrow
irrigation event. Ridge-furrow irrigation design and optimization is relied on soil texture,
and the irrigation method should be implemented in finer soil. Film-covering furrow
regulated water distribution between ridges and furrows. The vertical infiltration distance
was significantly reduced, while lateral infiltration distance was increased. Film-covering
furrow should be implemented in ridge-furrow irrigation fields. Furrow size had an effect
on soil water distribution and cumulative infiltration. We should select narrow furrows for
crops with deep rooting depth and wide furrows for crops with shallow rooting depth.
Furrow water depth had an effect on lateral infiltration distance and cumulative infiltration.
Lateral infiltration distance and cumulative infiltration tended to increase with increase of
furrow water depth. The higher furrow water depth is recommended in ridge-furrow
irrigation to improve water use efficiency and irrigation uniformity.
(3) The effect of different variables on soil infiltration characteristics and infiltration
models were quantitatively evaluated by using statistical methods. Ridge-furrow irrigation
was conducted in laboratory experiment, and the path analysis method was applied to
quantify the effect of variables on cumulative infiltration. The results showed that 51.62%,
47.2%, 38.12%, and 6.44% of variability in cumulative infiltration was explained by total
variations in wetted perimeter, bulk density, flow section area, and initial soil water content.
The principal component variables were bulk density and wetted perimeter under
ridge-furrow irrigation. The performance of four infiltration models—Philip model,
Kostiakov model, Kostiakov-Lewis model, and Horton model—was investigated on the
basis of evaluation indices. The Kostiakov-Lewis model provided the best description of
the relationship between cumulative infiltrations with infiltration time. A furrow
cumulative infiltration model taking wetted perimeter into consideration was developed.
The validations by experimental data indicated that the variation of cumulative infiltration
against infiltration time could be effectively simulated by the furrow cumulative infiltration
(4) The spatial moment analysis method was applied to quantify the effect of variables
on the wetting pattern. The results showed that the wetting pattern was like an ellipse with a long axis in the horizontal direction. The longitudinal coordinate of the mass center of the
ellipse, z c , the long axis, σ x , and the minor axis, σ z , were increasing with the increase of
initial soil water content, respectively, and the area of the ellipse was also increasing.
Initial soil water content had a minor effect on the ellipse characteristics compared with
other variables. Soil texture had a significant effect on the ellipse characteristics. z c , σ x , and
σ z were increasing with the increase of furrow size, and the area of the ellipse was also
increasing. σ x and σ z were increasing with the increase of furrow water depth, and the area
of the ellipse was also increasing. However, z c was decreasing with the increase of furrow
water depth because of higher water depth. The eccentricity of higher furrow water depth
was greater and lateral infiltration distance was further.
(5) Back propagation artificial neural network (BP-ANN) model in ridge-furrow
irrigation was established based on water moments data to predict irrigated soil infiltration.
The Bayesian arithmetic was used in the BP-ANN model. The results showed that the
optimized BP-ANN model is reasonably accurate and can provide an easy and efficient
mean of estimating complex soil water distribution in ridge-furrow irrigation.
(6) The method of determining the appropriate width ratio furrows to ridges was
proposed in ridge-furrow irrigation. Soil water distribution in different ridge widths was
simulated in ridge-furrow irrigation by using numerical simulation. The appropriate width
ratio of furrows to ridges was determined by soil water content matching principle. The 60
cm: 75 cm and 60 cm: 70 cm width ratio of furrows to ridges are recommended in heavy
loam soil and sandy loam soil in ridge-furrow irrigation, respectively. These results can
provide guidance to reasonable design of irrigation design and field extension in
ridge-furrow intercropping fields.
Key words: ridge-furrow irrigation; HYDRUS-2D; infiltration; wetting pattern; width
ratio of furrows to ridges