EFFECT OF DIFFERENT LEVELS OF SALINITY ON SEED GERMINATION OF FOUR SELECTED TREE SPECIES

Abstract

Salinity is one of the most adverse factors, which restrict the economic utilization of availableland resources in the dry zone of Sri Lanka. The salt affected area in Sri Lanka is estimatedabout 223,000 ha, which comprises 3% of the land area of the Island, found mainly in the dryzone (Vivekanandan, 1989). The most of the salt affected lands are generally barren, with littlewoody vegetation of salt tolerant bushes and herbaceous flora. This resulted in serious soilerosion and land degradation problems, which spreads into adjoining productive agriculturallands too. Therefore it is very important to restore these lands for useful agricultural purposes. Inthis context, the present study was mainly focused to determine the effect of salinity on seedgermination of four selected tree species, namely Castor (Ricinus communis), Ipil-ipil (Leucenealeucocephala), Wood apple (Feronia limonia) and Kottamba (Terminalia catappa) in order tostudy the possibility to regenerate these tree species by direct seeding in salt affected lands.

Four separate pot experiments were conducted by using above four tree species in sand trays. Allexperiments were arranged in a Complete Randomized Design with 5 replicates. 100 seeds wereplanted in each tray for germination. Trays were kept moist with different levels of saline water(i.e. 0.13 (normal water) 4, 8, 12, 16, 24, 32, and 40 (Seawater) mmhos/cm) by diluting seawateras assigned in different treatments throughout the experimental period.

Result revealed that seed germination in control treatments was higher in Wood apple (100%)and Castor (72%) than Kottamba (31%) and Ipil-ipil (13%). Seed germination was decreasedwith increasing level of saline level in Kottamba and Castor. In Kottamba, no germination wasobserved at all when at salinity level increased up tc 16 mmhos/cm while in Castor germinationwas nil when salinity level increased up to 40mmhos/cm. In Wood apple, more than 80% ofgermination was recorded even up to the salinity level of 24 mmhos/cm. Germination was poorin Ipil-ipil even in control treatment and not significantly decreased up to the salinity level of 40mmhos/cm

Therefore, the species can be ranked in order to tolerance to salinity in terms of germination asfollows: Ipil-ipil>Wood apple>Castor>Kottamba.