| 其他摘要 | Freshwater scarcity and soil salinity increases are frustrating the sustainable development
of agriculture worldwide, particularly in arid and semi-arid regions. Xinjiang in northwest
China is typical of arid and semi-arid region which is serious affected by two factors. To
address the problems, some measures have been applied. Drip irrigation is considered as
one of the best methods which can increase crop yields; reduced water application;
decreased salinity; and deep percolation. Under drip irrigation, confluence occurs between
pairs of emitters and the area of confluence is termed the ‘overlap zone’, as well as plants
(e.g., cotton) are always grown in the overlap zone between neighboring emitters in a field,
hence knowledge of salinity distributions in the zone is very important for achieving high
crop yields. Salinity increases with times under drip irrigation, it is very important to
understand salt accumulation. In order to understanding water and salinity transport with
drip irrigation, we analysis the problem by combination experiments with simulations. The
conclusions as follows:
1. Research on wetting front dimension with different emitter discharge、different irrigation
volume、different emitter spacing, using the model developed by Schwartzman and Zur
(1986) as a starting point and developed a new empirical model for wetting front
dimension with double-point-source drip irrigation. The following relationship:
where W and W1 denote the widths of the wetting fronts below the dripper and in the
overlap zone, respectively.
2. HYDRUS3-D can successfully simulate both temporal and spatial soil water content
distributions, as well as the salinity distributions with double-point-source drip irrigation under field conditions. Additional simulations with HYDRUS-3D were used to evaluate
the effects of various design parameters on desalinization zone pattern around the overlap
zone. The additional simulation results showed that the area of the desalination zone was:
(1) positively correlated with irrigation volume, following a power function; (2) positively
correlated with discharge rate, following an exponential function; (3) the simulation results
also showed that, for the fine soil type, the horizontal and vertical distances were nearly
uniform, for the coarser soil type, the extent of diatance was far greater vertically than it
was horizontally, as well as desalination also follows.
3. Employed the HYDRUS-3D to determining optimal drip irrigation volumes with the
HYDRUS-3D model for cotton established by dry seeding and planting after
pre-germination under mulch and confirmed by cotton emergency.
4. The lower salt content in high frequency irrigation during the growth period. The
relationship between the frequency winter irrigation and soil salt content has a positive
relation.
5. Compared between observed and simulated, the result showed that the SaltModel can
accuracy predict salt accumulate for the regional.
6. Based on the simulation results, we determined the suitable irrigation schedule including:
irrigation water mineralization 1g/L、irrigation volume 4500m3/ha in growth periods、
winter irrigation 3000m3/ha、water table level is 1.8m. Predict attained the water-salt
balance in 9 year under the irrigation schedule.
Keywords: water and solute transport; drip irrigation with mulch; HYDRUS-3D software;
SaltModel software. |
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