Soil Microbiology in Land Reclamation. Volume I – Soil Microbial Development

Dennis Parkinson
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There are two reports in Volume I: Visser, S., C. Griffiths and D. Parkinson, 1984. Reinstatement of biological activity in severely disturbed soils: Effects of mining on the microbiology of three minespoils after amendation and planting. 283 pp. Abstract: Soil microorganisms and their activities are the major vectors in the decomposition of plant litter and the subsequent transformation and flow of such essential plant nutrients as nitrogen and phosphorus. The end result of their activities is the stabilization of soil organic matter upon which the development of a self-sustaining vegetative cover is based. Consequently, a project was initiated with the following objectives in mind: 1. to determine the immediate effects of coal and bitumen mining on a variety of soil microbiological factors. 2. to provide detailed information on the rates of redevelopment of biological activity when various organic and inorganic amendments are applied singly to various minespoils and subsequently planted with different herbaceous and woody plant species. The effects of surface mining on soil microbial populations, microbial activity and decay potential were studied in a prairie grassland, a subalpine spruce-fir forest and a jack pine forest (oil sands) in Alberta. In general, mining drastically changed the composition of the bacterial and fungal communities and caused significant reductions in bacterial, actinomycete numbers, lengths of fungal hyphae, microbial respiration, microbial biomass C and ATP. However, the decomposition of cellulose filter paper placed in the field for two to three years was more rapid in the mined than unmined sites. The decrease in soil microbial activity after mining was attributed to the loss of organic matter since microbial biomass C and soil organic matter in revegetated subalpine minesoils were observed to be highly correlated. Procedures for improving the microbial status of the prairie grassland and subalpine coal minespoils and the oil sands tailings were studied by treating each one with three different organic or inorganic amendments and then planting each with four different plant species. The grassland spoil was treated with topsoil, anaerobically-digested sewage sludge, gypsum or left untreated and planted with fall rye, crested wheatgrass, Russian wild-rye or rambler alfalfa. The subalpine minespoil and oil sands tailings received fibrous peat, sewage sludge, mineral fertilizer or no amendment. The plant species tested on the subalpine spoil included slender wheatgrass, white spruce, alsike clover and laurel leaf willow while those on the tailings sand were slender wheatgrass, sainfoin, jack pine and bearberry. Individual plant species were studied on each amendment treatment. The response of mixtures of plant species or combinations of amendments were not examined. The effects of amendation and plant growth (fall rye on the grassland minespoil; slender wheatgrass and white spruce on the subalpine spoil; and slender wheatgrass and jack pine on the tailings sand) on soil microbial development were monitored over three to four years. Application of sewage sludge or topsoil to the grassland spoil was highly effective in increasing microbial activity and biomass C, particularly in the upper 5 cm of the amended spoil. The development of microbial activity and biomass appeared to be linked to primary production since both parameters increased as shoot production by fall rye increased. The increased microbial biomass maintained itself for at least one year after fall rye failed, but its metabolic activity was reduced to pre-planting levels. The decay of filter papers appeared to be related to density of plant cover rather than amendment type with decomposition in the topsoil and sewage sludge treatments being faster than that in the gypsum and control treatments. No significant treatment effects on filter paper decay were measured after growth by fall rye ceased, while the decay potential in the topsoil and sludge treated spoil increased as plant cover by rambler alfalfa increased. The N2 fixation potential of rambler alfalfa was not significantly affected by amendation, although measurements were highly variable. The microbial status of the subalpine and oil sands spoils was most improved by the addition of peat while treatment with sewage sludge or fertilizer was less effective. The effects of amendation and planting were restricted mainly to the top 5 cm of the treated spoils. Although C02 efflux from the unplanted, peat amended minespoils increased substantially over the four year term of the study, loss on ignition estimates indicated no significant loss of stable organic matter from this treatment. The fast growing, highly productive slender wheatgrass was more effective in stimulating the development of microbial activity and biomass C in the variously treated minespoils than the slow growing white spruce or jack pine were, again suggesting that plant productivity and soil microbial productivity are closely related. Rates of microbial development appeared to be dependent on the input of root exudates, sloughed root material and dead roots and shoots from the primary producers, which, in the case of slender wheatgrass, was particularly high in the sewage sludge treatment. During the first two years after planting, cellulose filter paper placed in the subalpine spoil decomposed most rapidly in the sewage sludge treatment regardless of vegetation type, while those placed in the oil sands minespoil decayed fastest in the sewage sludge and fertilizer treatments planted with slender wheatgrass. Over the long term (four years), cellulose decay potential of the amended and planted subalpine spoil was not significantly altered, but the decay potential of the sludge treated sand planted with slender wheatgrass was considerably reduced. In both minespoils, the short term decomposition (one year) of slender wheatgrass leaves was faster than that of stems. Alsike clover leaves decayed more rapidly than slender wheatgrass leaves in the subalpine minespoil whilst sainfoin leaves decayed more slowly than slender wheatgrass leaves in the oil sand minespoil. Neither grass nor legume litter decomposition was significantly affected by amendation. The decay rates of filter paper could not be extrapolated to predict decay rates of plant litter. The N2 fixation capacity of alsike clover was not significantly influenced by amendation, but sewage sludge inhibited N2 fixation by sainfoin after the third growing season.

Visser, S., J.C. Zak, R.M. Danielson, C. Griffiths and D. Parkinson, 1984. Reinstatement of biological activity in severely disturbed soils: Effects of different amendments to three different minespoils on selected soil physical and chemical properties and on plant growth. 120 pp. Abstract: Three different minespoils (prairie grassland, subalpine and extracted oil sands) were each treated with three different organic or inorganic amendments and then planted with four different plant species. Amendation effects on some of the soil chemical characteristics and on plant growth were then monitored over 2 and 3 years respectively. Application of topsoil was most effective in reducing the high sodium adsorption ratio characteristic of the prairie minespoil . It also promoted the best growth by rambler alfalfa. Fall rye and crested wheat were most productive in the sewage and topsoil treated spoil, while russian wild rye was most stimulated by the sewage sludge treatment. Gypsum was observed to be the least effective of the amendments tested. Crested wheat, russian wild rye and rambler alfalfa, once established, behaved as long-term cover crops, but fall rye was found to be short-lived (2 years). The poor fertility status of the subalpine and oil sands spoil was most improved over the long term by the addition of sewage sludge. The slender wheatgrass, alsike clover, white spruce and willow planted in the subalpine soil, and the slender wheatgrass, sainfoin, jack pine and bearberry planted in the extracted oil sands were generally most productive in the sewage sludge treated spoils. The slow growing woody perennials (white spruce, bearberry) also performed well in the peat amended spoils, but low extractable P levels in the peat may have suppressed growth by the faster growing species. Mineral fertilizer stimulated shoot production by the grass, clover and willow in the subalpine spoil, but ellicited a poor response from plants grown in the tailing sand. Much of the fertilizer applied to the sand had leached out of the rooting zone by the end of the first growing season. Slender wheatgrass followed the same growth pattern as fall rye and did not reseed readily. Heavy metals introduced with the sewage sludge were not significantly concentrated in plant tissue over the short term. The N2-fixing legumes (clover and sainfoin) were observed to be least sensitive to low soil N levels.