| High soil salinity levels caused depressing effects on most characters
(Tables 2, 3). Grain
yield, number of spikelets, number of grains and test weight were all significantly
reduced at salinity levels of EC 8.5 and 11.0 mmhos/cm. Thus, reduction
in grain yield mounted to 33% and 68%, respectively (Table
4). It was noted that the reduction in grain yield resulted from marked
reduction in number of spikelets 27% and 42% and number of grains 28% and
44% in the above mentioned salinity levels, respectively. Moreover, 100-grain
weight was depressed by 15% and 47%, respectively. The depressing effects
on 100-grain weight was attributed to the hastening of senescence (ASANA
& KALE 1965; SARIN & NARAYAN 1968) thus reducing the photosynthetic activity
during grain development on the plants. It is noteworthy to mention that
the number of spikes acted independently from the increasing levels of soil
salinity. Another observation was that soil salinity level of EC 6.0 mmhos/cm
was not different in its effects when compared with the control (3.7 mmhos/cm).
In other words, all agronomic characters of the four cultivars were tolerant
to soil salinity conditions upto 6.0 mmhos/cm without any detectable change.
These results agree with previous reprots (BERNSTEIN 1964; MAAS & HOFFMAN
1977) that salinity level of EC 6.0 mmhos/cm is the threshold at which yield
of wheat will decrease upon any increase in salinity beyond the threshold.
The rate of decrease in yield per mmhos/cm in the present study, however,
was much higher (13.6%) than the 7.1% and 5.5% previously reported by the
same authors. The total soil water stress is determined by the algebric sum of soil water tension plus the osmotic pressure of soil solution (BERNSTEIN 1974). As the salinity increases in the soil solution, available moisture in the soil should be increased to lessen the osmotic pressure of the soil solution so that water should be rendered more available for plant use. Under conditions similar to the study, soil moisture should not be reduced to less than 50% of the available water in order to avoid the effects of stress potential due to high salinity levels in the soil solution. It can be concluded that under high salinity conditions: (a) more frequent irrigation should be practiced, (b) cultivars with high salinity tolerance should be used. Literature Cited ASANA, R.D. & V.R. KALE. 1965. Indian J. Pl. Phisiol. 8: 5-22. BERNSTEIN, L. 1974. Agronomy 17: 39-90. Am. Soc. of Agron. Madison, Wis. BHUMBLA, D.R. & N. SINGH 1965. Sci. Cult. 31: 96-97. MAAS, E.V. & G.J. HOFFMAN 1977. J. of the lrrigation and Drainage Division, ASCE. 103: 115-134. SARlN, M.N. & A. NARAYAN 1968. Physiologia Pl. 21: 1201-1209. |
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