An evaluation of the germination and establishment of three selected coated grass species in different soil types for rehabilitation
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The primary impacts of mining on the environment include the deterioration of soil properties and the loss of vegetation cover and density, often leading to increased erosion. In order to encumber further degeneration of such ecosystems and all subsequent other negative environmental impacts, active rehabilitation practices are often implemented. Active rehabilitation involves the introduction of species by different re–seeding (re–vegetation) methodologies. A higher vegetation cover and density is needed to increase soil quality, combat erosion and contribute to species richness, diversity and ground cover. Several Acts regarding environmental legislation and the conservation of the natural resource in South Africa are used to ensure that sustainable development, rehabilitation and effective environmental management of disturbed areas are enforced. Legislation therefore provides a measure to prevent pollution and ecological degradation, promotes conservation, secure ecologically sustainable development and the use of natural resources, while promoting justifiable economic and social development. Legislation also enforces and regulates the remediation of disturbed ecosystems, such as the rehabilitation of mine tailing areas. Some of this legislation mentioned above is described in the thesis. Species selected for the compilation of seed mixtures for re–seeding and re–vegetation purposes should comply with the standards determined by the regional biodiversity framework where the disturbed area is situated. Only seed of species with non–invasive potential, that are adapted to the specific environmental conditions and have specific genetic traits, should be included in the seed mixture for rehabilitation. Since seed from local ecotype species are often not available, seed companies use seed from especially grass species that might be adapted to the environmental conditions and type of disturbance or degradation to help remediate the poor soil conditions and improve the vegetation cover. The problem is that if the morphological and physiological aspects of the seed type have not been researched properly, it may lead to poor germination and establishment results when used for the rehabilitation of certain degraded and disturbed areas, such as rangelands or mine tailings. Advance Seed Company tries to enhance seed by adding a coating around the caryopsis (grass seed) for better germination and establishment rates. Such seeds are then referred to as “enhanced” or “coated” seed. The term “seed” will be used throughout the dissertation to describe the whole, intact caryopsis (e.g. Anthephora pubescens). The coatings normally refer to the physical enhancements of the seeds by the application of a water–soluble lime–based coating, which may contain nutrients, fungicides, pesticides and other polymers. This study focused on the evaluation of the germination– and establishment rates in four soil types (growth mediums), as well as the activity of three growth enzymes on coated seed of three grass species, namely Anthephora pubescens, Cynodon dactylon and Panicum maximum. Advanced Seed Company provided the seeds for the three selected grass species that were coated with their newly developed certified formulae. Experimental trails were carried out in the laboratory and greenhouses (controlled conditions) at the North West University and in the field (uncontrolled conditions) at the four locations representing the different soil types, namely the clayey and sandy soils at Taaibosbult near Potchefstroom and the platinum (alkaline growth medium) and gold mine tailings (acidic growth medium) near Rustenburg and Stilfontein respectively. Detailed soil analysis was carried out by certified soil laboratories in Potchefstroom and seed purity, viability and quality determined by the Plant Protection Institute in Pretoria. The results from the greenhouse and the field trials differed significantly for all seed types (coated and uncoated) of the three grass species in the four soil types. The germination and establishment rates in both the greenhouse (controlled conditions) and field (uncontrolled conditions) trials were overall very low. The latter can also be ascribed to the competition with other weed species that were present in the soil seed bank before re–seeding, as well as the predation by ants and guinea fowls in especially the field trials of the sandy and clayey soils. Due to the absence of competition in the field trials on the mine tailings, the germination and establishment rates were higher for most grass species. The quality of the seed batches as supplied by Advance Seed Company was not very good. Although the purity was high, many dead seeds were found, especially for Panicum maximum. The germination and establishment rates of Antephora pubescens of the uncoated seed was higher in the sandy, platinum and gold mine tailings soil types in both the uncontrolled field and controlled greenhouse trials and low for both seed types (coated and uncoated) in the clayey soils. Cynodon dactylon had higher germination and establishment rates for especially the gold mine tailings soil in the field trials for both seed types, as well as the sandy soils under controlled conditions in the greenhouse. Both rates were lower in the sand– and clayey soils field trials. The germination rates for Panicum maximum for both seed types were similar for the clay and sandy soil types, but very low in the soils from the mine tailings, especially under controlled conditions in the greenhouse trials. The germination and establishment rates for both seed types of this species were however much higher in the field trials at both the gold and platinum mine tailings, mainly due to the absence of competition. No results for Panicum maximum were obtained from the field trials on the clay soils due to management and maintenance problems. The peroxidise enzyme activity was higher in the coated seed of Antephora pubescens, but lower in both seed types of Cynodon dactylon and Panicum maximum. The alpha amylase enzyme activity was high in the coated seed of Antephora pubescens and both seed types of Panicum maximum, but low in both seed types of Cynodon dactylon. The activity of the lipoxygenase enzyme was higher in all the coated seed of all three grass species that were used in this study. It also appears as if the storage period played a significant role in the germination of the species, especially after and during the seed coating process, as it had a negative effect on the physiology of the seed. In all species, a higher rate of gaseous exchange was observed in the uncoated seed types. However, the water content of the seed types differed between the seed types. Depending on the size and the genetic characteristics of the species, the longevity of the enzyme proteins differed. This is especially observed in the enzyme activity of three enzymes tested, i.e. lipoxygenase, peroxidase and alpha–amylase. The germination rate only improved shortly after being coated and then declined steadily. The germination capacity therefore depends on the length of the storage period. The genetic adaptation of the different species coincided with the four soil types. It is therefore recommended that only species that are adapted to a certain soil type is used in rehabilitation and if the seed is coated, it should be sown shortly after the coating process and not be stored for long periods. It is also recommended to first treat the area with herbicide before any re–seeding takes place, especially if low concentrations of seeds are used.