الملخص الإنجليزي
Salinity and water scarcity are the major abiotic factors limiting agricultural
production in the world, particularly in arid and semi-arid regions like Oman.
Capillary barrier (CB) is one of the potential techniques which can mitigate both
the salinity and water scarcity problems. CB is a composition of two soil layers
having distinct differences in textural and, therefore, hydraulic characteristics. This
study aimed to investigate the effect of structured substrates (both native soil and
potting media substrates) on plant growth and production, water-saving, and
mitigating salinity problems.
The first part of the study focused on the effect of layered potting media on the
growth and production of marigold. Marigold seedlings were grown in a layered
potting medium as well as in mixed potting media. For each layered media, there
was a mixed medium of the same substrates. Several vegetative, reproductive, and
physiological parameters were measured. Generally, layered media resulted in
better vegetative and reproductive growth of marigold than mixed media.
The second part of the study explored the best layered potting media on mitigating
salinity stress of marigold plants. The best three configurations of layered media in
the previous study were selected to test their effect on mitigating salinity stress of
marigold plants. These configurations were: (Vermiculite-Perlite-Vermiculite),
(Vermiculite-Sand-Vermiculite), and (Vermiculite-Perlite-Peat moss). Each medium
was treated with three salinity levels of irrigation water (ECi= 3 dS m-1, 6 dS m-1and
9 dS m-1) in addition to the control (Desalinated, ECi ≈ 0.6 dS m-1). Several
vegetative, reproductive, and physiological parameters were measured. The results
showed that the presence of sand in the middle layer was more efficient in reducing
salt accumulation in the root zone than perlite, which reflected positively on
marigold growth. Peat moss was also an efficient substrate in reducing salt buildup. However, marigold roots could not penetrate the peat moss substrate due to
the acidity property of the peat moss. Marigold is very sensitive to pH changes.
Overall, layered (Vermiculite-Sand-Vermiculite) medium was the best for growing
marigold under salinity stress.
The third part of the study focused on the unique naturally formed CB discovered
in the reservoir bed of the Al-Khoud dam, Oman. This naturally formed CB
structure in the soil (sediments) resulted in capturing large quantities of water
during reservoir ponding. The infiltrated water has been preserved by capillarity in
the cascade of silty blocks at a depth of 0.5 to 2.5 m, such that wild plants were able
to utilize this in-block moisture, despite prolonged periods of drought and high
VI
temperature. This study aimed to replicate and test the impact of this unique CB on
mitigating the salinity stress of marigold plants grown under an open field
condition. Seedlings of marigold plants were selected as a model-plant and grown
in both structured and unstructured soil. The plants were subjected to three
salinity levels of irrigation water (ECi= 3 dS m-1, 6 dS m-1, and 9 dS m-1) in addition
to the control (Desalinated, ECi ≈ 0.6 dS m-1). Several physiological, vegetative, and
reproductive growth parameters were measured in each treatment. The results
showed that the structured soil significantly improved all plant parameters
measured and helped in reducing the effects of salinity stress on the growth and
production of the marigold under arid-climate field conditions. The results also
showed the capability of structured soil in water-saving and improving water use
efficiency (WUE).
The fourth part of the study focused on investigating the effect of the naturally
formed CB on mitigating salinity problem of tomato plants. The plants were
subjected to three salinity treatments (ECi= 3 dS m-1, 6 dS m-1, and 9 dS m-1) in
addition to control (Desalinated, ECi ≈ 0.6 dS m-1). Several physiological, vegetative,
and reproductive growth parameters were measured in each treatment. The
results showed that growing tomato in the structured soil required less water for
irrigation. The results showed that most vegetative, reproductive, and physiological
parameters of tomato grown in the unstructured soil were negatively affected as
salinity level increased. There was no significant reduction in most vegetative,
reproductive, and physiological parameters of tomato grown in the structured soil.
This study suggests that artificial substrate and soil structuring can be used to save
irrigation water, ameliorate salinity stress and improve plant growth. Further
research for extended period of time is needed to evaluate the long-term impact of
structured media on crop growth and yield and the economics of crop cultivation.
