Effectiveness of coated seed in the establishment of herbaceous species on different mined substrates as influenced by pH and salinity

Abstract

Mining throughout the world is needed, especially coal mining to satisfy our need for electricity, and our entire economy is therefore dependant on mining. Competition exists for resources between mining and agriculture, since the rehabilitated land’s agricultural potential is changed after mining and it is yet to be proven that the land will reach the same potential again. Mining produces by-product tailings materials, waste products and slurry disposed in large dams. These tailings can in addition to the physical disturbance of the soil structure due to the physical mining progress cause the soil quality to deteriorate. The decline in soil quality makes it very difficult for plants to survive and these areas usually have no or very little plant growth. These areas that are mined, needs to be rehabilitated and made productive by law (Mining and Petroleum Resources Development Act 28 of 2002 (MPRDA)). The most commonly accepted practice to rehabilitate these mined areas is to establish pastures on them once the topsoil or subsoil is replaced. The rehabilitation of these mined areas with pastures can be difficult and is a timely process especially in open cast mining where large areas of land have been cleared. Deep shaft mining in gold and platinum industry result in the substrate to be brought to the surface and once processed the discarded material is placed in waste disposal sites where rehabilitation is required which includes the re-vegetation with grass. Coating is the science that incorporates information from various agricultural companies, for example; seed, pesticide and fertilizer companies. Coating seed is done by adding polymers, nutrients, fungicides, fillers and insecticides to the outer layer of the seed. These treatments can improve the germination and emergence of species, depending on the soil it is planted in, therefore it can improve the establishment of these species. The main aim of the coating of coated seed is to overcome most of the environmental challenges, to increase the success rate of germination and emergence of these seed and to give a seed the best chance of survival. The first aim was to determine the emergence percentage of six species, Chloris gayana, , Cynodon dactylon, Cenchrus ciliaris, Digitaria eriantha Eragrostis curvula and Medicago sativa, (coated and uncoated) in substrates with different salinity’s (0.05M , 0.1M and 0.15M ) and pH’s (3, 5 , 7 and 9). The second aim was to determine the emergence percentage of the same species (coated and uncoated) in nine different mine substrates. The third aim was to determine the dry matter production, leaf area and root production in substrates with different salinity concentrations. The fourth and final aim was to determine the dry matter production, leaf area and root production in substrates with different pH’s. Three species was used, namely Chloris gayana, Eragrostis curvula and Medicago sativa. The species were planted in silica sand placed in 400 mm tall and 150 mm wide pots. Two irrigation water treatments were tested, with different salinity’s (0.05 M and 0.09 M NaCl) and water with different pH (3, 5, 7 and 9). It was concluded for study 1 that there was no significant difference in emergence between D. eriantha, E. curvula and M. sativa. Cenchrus ciliaris and C. dactylon had higher emergence percentage in acidic soils while C. gayana being sensitive to acidic and alkaline soils. In study 1 the highest emergence for most of the species were when the soil moisture was at field capacity. Coated seed had a higher emergence for C. cilliaris, C. dactylon and E. curvula, while uncoated seed had higher emergence for C. gayana and D. eriantha. There was no notable difference for E. curvula. In the salinity trials all the emergence decreased as the salinity concentration increased. Cenchrus ciliaris, C. dactylon and E. curvula are very sensitive to saline soils and it is therefore not recommended to use these species in these soils. Coated C. gayana and M. sativa had a higher emergence percentage compared to the uncoated treatments of the species. Uncoated D. eriantha had a higher emergence percentage compared to the coated treatment. In the second study it was concluded that the low pH and high aluminium levels prevented any species from growing in the coal discard substrate. Coated seed had a higher emergence for C. ciliaris in gypsym- and andalusite substrates, C. gayana in gold > 2% pyrite-, platinum-, fluorspar- and andalusite substrates and for D. eriantha in platinum substrate. Coated seed had a definitely advantage in M. sativa with higher emergence percentage in red sandy loam-, gold < 2% pyrite-, platinum-, gypsum- and fluorspar substrates, compared to uncoated seed. Coated seed also had a higher emergence for E. curvula in all the different substrates. Uncoated seed in all the different species had a higher emergence percentage in kimberlite due to kimberlites coarse texture. The texture prevented any seed to substrate contact.