APPLICATION OF SOIL-IMPROVING MEDIA PRODUCED ON LIGNITE-BASIS ON THE REHABILITATION OF POST-MINING SITES

摘要

This paper deals with the application effects of a lignite-based soil-improving media on sites under extreme harsh conditions like those that occur in areas degraded through mining activities (e.g., on spoil piles). The applied soil-improving media, patented under the commercial name Novihum~R, is artificially produced from German lignite, through oxidative ammonolysis, resulting in enrichment and long-term availability of nitrogen. In February 2002, seeds of the endemic herbaceous plant Atriplex halimus were planted on a vermiculite substrate in a greenhouse. By end of April 2002, the young plants were transplanted to plastic receptors using a kaolin/perlite substrate in 7 variants (of 72 plants each) under different treatments, i.e. by introducing different amounts of the soil-improving media or nitrogen fertilizer. After measuring the plant heights in November 2002, the new plants were transplanted on the slopes of the spoil piles of the kaolin open pit in Kastriani (on Milos Island). Three plots (A, B, C) were prepared for rehabilitation. The substrate in plots A and C was kaolin-rich, whereas in B it was a mixture of kaolin and bentonite. Additionally, in each plot the plants were replanted following different treatment. In plot A, no additional soil-improving media was introduced, whereas in plots B and C 72 g and 144 g of soil-improving media, respectively, were introduced. Twice in the next year (June and October 2003) the plant heights were measured in order to estimate their growth rate. Soil parameters were also measured in order to determine the soil characteristics before and after the planting. The endemic species Atriplex halimus responded well under the arid conditions of Milos Island and it was proven to be a good choice for the specific test. Positively was also judged the use of the kaolin-perlite mixture as a substrate in the greenhouse, since it was simi-lar to the one the young plants would meet to their permanent position in the plots. The obtained results are not totally comparable, due to the differentiation of the substrates: better results were noted in plot B (kaolin and bentonite) followed by the other two plots, which revealed similar results. This is due to the higher ion-exchange capacity of bentonite and the higher bio-availability of the elements K and Mg, positively affecting plant growth. The addition of soil-improving media during planting improved the soil features regarding the total and bio-available nitrogen, since even a year after, a sufficient amount of nitrogen remained. The plants, which in the greenhouse were planted with the addition of soil-improving media, presented an increased growth in comparison to those that received the relevant amount of nitrogen fertilizer. Generally, the plants with the largest amount of soil-improving media revealed the higher growth rates, as well as a more healthful appearance. The same features were also noted later during the measurements of the plant heights in all the plots. The results of this research prove the importance of adding this specific soil-improving media in environmental rehabilitation and generally in the battle against land desertification. Especially in our country, where in many cases the soils are intensely degraded, the application of such materials would be extremely beneficial. On the other hand, several Greek lignite reserves could be exploited for the production of low-cost soil-improving media through oxidative ammonolysis. Such actions will result in the production of a domestic environmental-friendly product with significant added value, as well as the establishment of a market and employment positions.