Transformations of Nitrogen and its Availability to Plants in Coal Mine Soils

Shah, Syed Sabir Hussain (1988) Transformations of Nitrogen and its Availability to Plants in Coal Mine Soils. PhD thesis, University of Glasgow.

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The work of this thesis is concerned with the study of some aspects of nitrogen cycling in coal mine soils. A survey of sites in Central Scotland was made to assess which parts of the N cycle function in coal mine soils. 90 samples of widely varying properties were taken and various properties measured. The mineral N status of the waste material was low. Carbon dioxide evolution and nitrogen mineralization rates showed that a high level of carbon, but little nitrogen was turned over. Nitrification was measurable only on about half of the sites studied and was highly pH dependent, being inhibited below pH 5.0. However, even on sites above this pH, nitrification was not always measured which suggests that the introduction of nitrifying bacteria into the spoil was also an important factor. Some nitrogen was lost due to the fixation of ammonium by the clay minerals and much more was lost during incubation due to immobilization. The urease and amidase activities measured were similar to those in agricultural soils which suggests that the use of urea or amide-N fertilizers may be possible on these coal mine soils. Significant correlations of carbon turnover, urease activity, amidase activity and nitrification rate with each other, suggest the importance of organic matter for both microbial activity and enzyme stabilization. A laboratory incubation experiment was carried out to study the fate of nitrogen added as ammonium sulphate, urea or chicken manure in five selected samples of coal mine soils with different properties. Two samples showed no net mineralization of N at any stage in either the control, ammonium sulphate or urea treated samples. Two samples which were collected from the plots of an established organic manure trial, showed N mineralization rates comparable to agricultural soils suggesting the favourable effect of organic amendments in the long term on the establishment of N cycling. There were large losses of N in the first weeks of incubation, which were generally greater in the manure treated samples, where up to 69 % of added N was lost. These losses were attributed to a combination of ammonium fixation and immobilization. In the later stages of the incubations there was a clear contribution to mineralization from the chicken manure. Mineralization and nitrification rates were significantly improved by manure addition in all samples, especially in the acid soil where these processes did not occur with ammonium sulphate or urea addition. The manure not only increased the pH of the acid soil, but may have also added nitrifying bacteria to the soil. In general however, it would seem that these transformations of nitrogen species can occur in coal mine soils if other conditions, particularly pH, are suitable. A field experiment was set up to study nitrogen response on a reclaimed site for two years in 1986 and 1987. Seven rates of N fertilizer ranging between 0 and 150 kg N/ha as ammonium nitrate were added to triplicate plots. An attempt was also made to study the herbage response to N both in the presence and absence of added P and K, and to compare urea with ammonium nitrate. Nitrogen fertilizer significantly improved the herbage yield in both years, which was also reflected generally in higher N, P, and K contents in the herbage. In addition P and K tended to increase the yield of herbage when applied with N but their effect was not significant. Vegetation responded equally to both N fertilizers with no significant differences in herbage yield.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Keywords: Soil sciences, Biogeochemistry
Date of Award: 1988
Depositing User: Enlighten Team
Unique ID: glathesis:1988-77674
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 14 Jan 2020 11:53
Last Modified: 14 Jan 2020 11:53

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