|Keywords (Extracted from title, table of contents and abstract of thesis)
soil-plant relationships, salt-affected wastelands, seed germination, salt tolerance, allelopathic effects, weeds, kallar grass, saline wastelands, amelioration process, atriples crassifolia, cyndon dectyion, dismostacya bipinnata, eleuaine flagellifera, prosopis juliflora, sporobolus arabicus, suaeda truticosa
A survey of undisturbed saline wastelands and kallar grass (Leptochloa fusca (L.) kunth) fields was undertaken to study species distribution in relation to soil conditions and changes in species composition during amelioration process. Seven community types: Atriples crassifolia, cyndon dectyion, Dismostacya bipinnata, Eleuaine flagellifera, prosopis juliflora, sporobolus arabicus, and suaeda truticosa were recognized, in the undisturbed natural vegetation. The soils under these communities showed significant variations with respect to texture, salinity and sod city. Desmostachya had wide ecological amplitude and was found in soils ranging from normal to highly saline-sodic. On the contrary, Atriplex crassifolia prosopis juliflora were retricted to slightly saline-sodic and Eleusine flagellifra to salt-free soils. Cynodon dactylon. Sporobolus arabicus and suaeda fruticosa had relatively wider distribution but their field cover was greatly influenced by variations in soil salinity. Suaeda fruticosa preferred saline- soils while cynodon dactyon and sproobolus arabicus attained good cover in soils with low to moderate salinity.
Seed germination and growth responses of plant species to salinity were highly variable. Salt tolerance (Electrical conductivity (EC) causing 50% relative-to â€“ control loss in growth) of these species ranged between 9.0-48.0 ms/cm. the species studied may be arranged for salt tolerance in the decreasing order as: suaeda fruticosa (48.0) Kochia indica (38.0) Atriplex crassijolia (22.3), sporobolus arabicus (21.7), polypogon monspeliensis (13.7), cynodon dactylon (13.2), and Desmostachya bipinnata (9.0). Although soil salinity played important role field distribution of different species, salt tolerance of a species was not always related to salinity of the habitat.
The undisturbed soils were generally saline, sodic and alkaline. Growth of kallar grass caused marked decrease in salinity and sodicity of soil . as a result of soil improvement, a successive invasion of plant species was observed at different stages after growth kallar grass. Many plant species in addition to those representing natural flora, colonized the fields of kallar grass. The invading species formed dense patches eliminating kallar grass. The analysis of soils sampled from weed patches and adjacent kallar grass showed no marked differences in salinity or nutrients. The elimination of kallar grass from weed patches was not attributable to soil conditions. Thereby suggesting the presence of some interference mechanism.
To quantify the degree of interference and explore its mechanism, kallra grass was in mono- and mixed â€“cultures with five important weed species at different salinity and watering levels. In mixed-cultures, the growth of kallar grass was drastically affected at high salinity (Ec = 16 ms/cm) by suaeda fruticosa at low salinity (Ec = 6 ms/cm) by cynodon dactylin, and by dochia indica at both salinity levels. In contrast, dallar grass growth was not affected when intercropped with sporobolus arabicus or desmostachya bipinnata. The intensity of competition differed between competing species and soil conditions, especially salinity status. The concentrations of nutrients such as N,P,K, and in kallar grass or competing species were little affected due to competition. However, total uptake of these nutrients by kallar grass was significantly reduced in the presence of competing species.
Further, aqueous extracts, organic material decaying in soil, and lea hates from amended soils inhibited seed germination and growth of kallar grass to varying degree depending on weed species. The experimental data clearly indicated allelopathic interference by weeds against kallar grass as well as its autointoxication mechanism. Interference from invading species and autointoxication were identified as more probable causative factors for decline in productivity of kallar grass in its older stands.
The distribution and coexistence of plant species was related to a complex of factors including soil properties and biological interactions among plant species the relative importance of such factors has been discussed in the light of information already available in literature. The impact of different components of environment was best interpreted as additive.