A comparison of selected enhanced (coated) and non-enhanced grass seed types for re-seeding of disturbed areas
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Restoration and rehabilitation activities are presently considered to be a major priority in environmental management, whether the activity implies the restoration of neglected cultivated pastures or degraded rangelands due to overgrazing and climatic impacts, or the rehabilitation of the mining and industrial areas. However, the goals are not easily achieved, mainly due to the high input costs, including that of re-seeding activities. Reseeding success is influenced by the quality and effectiveness of the used seed regarding germination and establishment under natural field conditions. If techniques can be developed to enhance the effectiveness of germination and establishment percentage of the seed in restoration and rehabilitation sites, a better cover, density and biomass yield can be expected, which will improve the rehabilitation process. It is known that commercially available grass seed has a better germination percentage and establishment percentage in comparison with seed locally harvested, which may include many impurities such as sticks and stones. The availability of the locally harvested seed types, especially of certain ecotypes adapted to specific environments, can be poor. Advance Seed Company (Krugersdorp, South Africa) has taken commercially available grass seed to the next level by enhancing (coating) the seed with a multitude of different treatments to ensure better handling of the seed in reseeding applications. These treatments also have advantages such as a higher seed to soil contact, growth stimulants included in the treatment, higher seed purity and the protection of the seed against predation by ants and other insects and against harsh chemicals in the soil, which might have an influence on the germination percentage of the seed and the establishment of seedlings. The objective of this study was to investigate whether or not certain enhanced grass seed types of selected grass species will have a better germination and establishment percentage, fresh and dry above-(leaves) and below-ground (root) biomass yield (glasshouse trials) and dry above-ground biomass yields (natural fields trials) in comparison with non-enhanced types. The predation of enhanced and non-enhanced seeds by ants and other insects, as well as the development of the vascular tissue in the transitional region of the seedlings was also investigated. The grasses assessed included enhanced and non-enhanced seed types of Chloris gayana (Rhodes grass), Cynodon dactylon (Couch grass), Digitaria eriantha (Common finger grass) and Eragrostis curvula (Weeping love grass). In the case of E. curvula, four seed types, including the non-enhanced seed type were tested. These included non-enhanced seed, seed treated with "plain coat", enhancement with "organic insecticide on the base of the coat' (Le. insecticide between the enhancement and the seed) and enhancement with "organic insecticide on the base of the coat and as an overspray" (Le. insecticide between the enhancement and the seed, as well as spraying the insecticide over the coated seed). The above mentioned species are commonly used in grass seed mixtures for rehabilitation and restoration purposes. Seeds were supplied by Advance Seed Company. The seed enhancement treatments as well as the non-enhanced seed types were tested under various conditions. The chemical composition of the enhancement treatment used in the coating process is only known by the seed technicians at Advance Seed Company. All the seed supplied by the seed merchant had a purity of >95%. With the application of dormancy breaking in the germination tests the non-enhanced seed types of Chloris gayana had the higher germination percentage of the seed type or the same species. Other differences included the germination percentage being significantly higher for the enhanced seed type of Cynodon dactylon than the non-enhanced seed type. Lower germination percentages were noted in the comparison of the E. curvula seed types, were the non-enhanced seed type had a higher germination percentage in comparison with the enhanced seed types. In the germination tests without dormancy breaking being applied, these results differ. With regard to the establishment percentages, similar statistical differences were noted in both the Coco Peat Moss medium and the Hygromix growth medium. In the above-and below-ground biomass production trials in the glass house the only significant difference were noted in the biomass production of D. eriantha plants. In the case of the dry above-and below-ground biomass yield the plants of the non-enhanced seed types of D. eriantha yielded a significantly higher biomass in comparison with the plants harvested from the enhanced seed type of the same species. With regard to the natural field trials a few significant differences were noted. The results indicated that the enhanced seed types of Chloris gayana and Cynodon dactylon, the non-enhanced seed type of D. eriantha as well as the non-enhanced and "organic insecticide on base and as overspray" enhancement of E cUNula can be used in re-seeding restoration and rehabilitation practices. Eragrostis cUNula enhanced with "plain coat" is not recommended to be used for re-seeding in disturbed areas.