nitrogen and land reclamation

Emironmental Pollution (Serie~ B) 2 (1981) 179 191

N I T R O G E N A N D L A N D R E C L A M A T I O N

S. LANNING • S. T. WILLIAMS

Department of Botany, University of Liverpool, PO Box 147, Liverpool L69 3BX, Great Britain

ABSTRACT

Nitrogen supply is the major limiting factor in most reclamation schemes. A full)" functional nitrogen cycle is dependent on the accumulation of resident soil organic matter from which nitrogen may be released slowly by microbial decomposition. Soil nitrogen transformations including nitrification, mineralisation and immobilisation are discussed, with particular reference to nitrogen transformations in reclaimed land.

The use of legumes in revegetation programmes, their contribution to soil organic matter and transfer of fixed nitrogen to associated grasses is also discussed.

The importance of evaluating the capacity of treated spoil to supply nitrogen in plant-available form is emphasised.

INTRODUCTION

Large areas of derelict and degraded land in Britain are produced by the dumping of industrial wastes. These wastes or spoils are often toxic and generally deficient in organic matter and essential plant nutrients. The successful establishment and maintenance of vegetation on spoils depends on overcoming the environmental factors which restrict plant growth on the material (Bradshaw et al., 1975). The biological objective of any such reclamation programme is to create a functional ecosystem in which the spoil contains sufficient nutrients in circulation to enable satisfactory plant growth. With the exception of phytotoxicity, nitrogen is the major factor limiting plant growth in most spoils, such as metalliferous mine spoils (Johnson & Bradshaw, 1977; Bradshaw & Chadwick, 1979), copper and uranium tailings (Nielson & Peterson, 1973), copper smelter wastes (Goodman et al., 1973; Goodman & Gemmell, 1978), ironstone overburden (Leisman, 1957), pulverised

179 Environ. Pollut. Ser. B. 0143-148X/81/0002-0179/$02-50 ~) Applied Science Publishers Ltd, England, 198 I Printed in Great Britain

Ir(

f(,I

FI I I

cj I I IH

I I I I I I ,[ ...

......

..

I I iJ

i D

I I

P l

i -

....

....

....

J

....

....

....

....

....

. i-

t ........

..........

S

OL

t"

;>

7.

,1¢

q,

q,

:ig.

1.

Gai

ns,

loss

es a

nd

tran

sfor

mat

ion

of n

itro

gen

in

recl

aim

ed l

and.

(A

) w

eath

erin

g; (

B)

prec

ipit

atio

n, d

ust,

aero

sols

; (C

) ab

sorp

tion

of

mm

onia

; (D

) bi

olog

ical

nit

roge

n fi

xati

on; (

E)

addi

tion

of

fert

ilis

er; (

F) c

rop

rem

oval

, gr

azin

g; (

G)

leac

hing

; (H

) de

nitr

ific

atio

n; (

J) v

olat

ilis

atio

n;

K)

amm

onif

icat

ion;

(L

) ni

trif

cati

on;

(M)

imm

obil

isat

ion;

(N

) pl

ant

upta

ke;

(P)

deat

h.

--

gain

s in

nit

roge

n;

loss

es

in

nitr

ogen

; qn

tern

al n

itro

gen

cycl

e'.

NITROGEN AND LAND RECLAMATION 181

fuel ash (Hodgson & Townsend, 1973), fluorspar tailings (Johnson et al., 1976b), colliery spoils (Wilson, 1965; Schramm, 1966; Davison & Jefferies, 1966; Doubleday, 1971a; Williams, 1975) and china clay sand waste (Bradshaw et al., 1975; Lanning & Williams, 1979a). Successful reclamation depends largely, therefore, on the restoration of a functional nitrogen cycle.

In many soils, a self-maintaining system exists when gains of nitrogen balance losses and soil nitrogen transformations (including immobilisation and mineralisation) are in equilibrium. In spoil materials, specific problems arise in the attainment of these equilibria. The mechanisms of gain and loss of nitrogen to and from spoils, or the 'external nitrogen cycle' (Fig. 1) have been dealt with in the reclamation literature and therefore will not be discussed here. Recent work on 'external' nitrogen transformations in spoils includes symbiotic nitrogen fixation (Johnson et al., 1976a; Dancer et al., 1977a,b; Jones & Rees, 1970: Down & Stocks, 1977; Palaniappan et al., 1979), addition of fertiliser (Doubleday, 1974; Williams, 1975; Bradshaw et al., 1975), leaching (Johnson et al., 1976a; Dancer, 1975; Gemmell, 1975; Sheldon & Bradshaw, 1976; Down & Stocks, 1977; Dennington & Chadwick, 1978; Lanning & Williams, 1979b) and volatilisation (Hodgson & Townsend, 1973; Lanning, 1978; Johnson & Bradshaw, 1979). In marked contrast, the behaviour of nitrogen within spoils (the 'internal nitrogen cycle', Fig. 1) has been given less attention, although of fundamental relevance to ameliorative techniques for systems in which the demand for available nitrogen exceeds the supply. We have attempted, therefore, to discuss some of the problems associated with the 'internal' nitrogen cycle in spoils, with particular reference to china clay sand waste and colliery spoil, on which most information is available.

ORGANIC MATTER

Most spoils can supply little or no nitrogen for plant growth due to lack of organic matter (Williams, 1975; Johnson et al., 1976a; Down & Stocks, 1977; Johnson & Bradshaw, 1979). Levels of total nitrogen, which may be regarded as an indicator of organic matter, may be as low as 9 #g g- 1 in some spoils (Table 1), compared with 2000-4000 #gg-1 in, for example, pasture soil (Russell, 1973).

A crucial factor in the development of a functional soil nitrogen cycle in reclaimed land is the formation of resident soil organic matter (humus) from the death and decay of plants and animals. This will provide a store of nutrients which are not easily leached and are released slowly by microbial decomposition in inorganic forms available for plant uptake, provided that these processes are not inhibited by the presence of toxic substances (Johnson et al., 1976a; Quraishi & Cornfield, 1973; Williams et al., 1977).

The nitrogen transformations associated with the decomposition of plant and animal residues include nitrification, mineralisation and immobilisation.

182 S. LANNING, S. T. WILLIAMS

TABLE l TOTAL NITROGEN CONTENT OF SOME SPOIL MATERIALS

Spoil Total Reference nitrogen (l~g g -1)

China clay sand 9-11 Micaceous residue 10-30 Heavy metal contaminated spoil 100~210 Fluorspar tailings 25-230 Lead/zinc waste 33-126 Colliery spoil 730

Bradshaw et al. (1975) Palaniappan et al. (1979) Johnson et al. (1976a) Johnson et al. (1976b) Bradshaw & Chadwick (1979) Reeder & Berg (1977)

NITRIFICATION

Nitrification is the process whereby ammonium-nitrogen is oxidised to nitrite- and nitrate-nitrogen largely by bacterial autotrophs and comprises two main reactions. First, the oxidation of ammonium to nitrite is carried out by Nitrosomonas sp.:

2NH~ + 302 --~ 2NO~ + 4H + + 2H20

Secondly, oxidation of nitrite to nitrate is performed by Nitrobacter sp.:

2NO2- + O 2 ~ 2NO 3

In acidic soils the predominant form of nitrogen available to plants through the microbial mineralisation of soil organic matter is the ammonium ion and in neutral and alkaline soils, the nitrate ion (Pearson, 1958; Jackson, 1967; Gigon & Rorison, 1972). This is because the activity of the nitrifying bacteria is inhibited at a pH of 5.0 or below. Consequently, in some acidic soils little or no nitrification takes place, although slow rates of nitrification have been detected in soils as low as pH4.0 (Weber & Gainey, 1963).

The acidity of many revegetated spoil materials approaches the critical level for inhibition of nitrification. China clay sand waste with pH 5.0 to 5.5 (Bradshaw et al., 1975; Handley, 1976) contained only 20 nitrifying organisms/gram and nitrifying activity was negligible (Prosser, 1975). Similarly nitrification is inhibited in acid colliery spoil and so ammonium is the predominant form of mineral nitrogen (Wilson & Stewart, 1955; Cornfield, 1952; Williams, 1975; Reeder & Berg, 1977). High concentrations of metal ions may also inhibit nitrification at low pH. Nitrification proceeded normally in a sandy loam at pH 7.3 in the presence of 1000ppm copper, but was inhibited at pH5-1 and 5-9 by the same copper concentration (Quraishi & Cornfield, 1973).

Liming of acidic spoils may remove the inhibition of nitrification. Thus Wilson & Stewart (1955) showed that in vegetated colliery spoil with pH4.13 only 2.21 mg NO3-N 100g -1 spoil was detected after 159 days incubation, while in the same


material treated with Ca(OH)2, pH4.45, 26'85mg NO3-N 100g -1 spoil were formed after only 77 days. Williams & Cooper (1976) found large populations of Nitrosomonas and Nitrobacter in neutral colliery spoils and in acid spoils which had received limestone and NPK amendments.

However, the conversion of ammonium to nitrate is not always desirable, especially in spoils with coarse physical texture and low moisture holding capacity, as this will increase loss of nitrogen by leaching. Dancer (1975) showed that more than 98 ~ of nitrate fertiliser applied to bare china clay sand spoil was leached beyond the first 20cm in an average month of rainfall. Reeder & Berg (1977) demonstrated rapid nitrification of ammonium produced via ammonification in incubated soil and vegetated coal-mine spoil. The lack of ammonium or nitrate accumulation in fresh spoil and cretaceous shale was attributed to lack of ammonification or the immobilisation of most of the ammonium by the heterotrophic microbial population. Presumably some loss of inorganic nitrogen could also be attributed to leaching. Similarly, in limed acidic colliery spoils, ammoniacal fertilisers were rapidly nitrified resulting in loss by leaching (Williams & Cooper, 1976).

In order to achieve maximum utilisation of fertilisers, nitrification should be controlled at a rate at which plants can absorb the nitrate produced before it is leached from the spoil. In spoils with an initial neutral reaction, nitrification could be controlled by microbial inhibitors such as N-Serve, or by the use of slow-release fertilisers. In acid spoils, control should be effected by raising the pH of the material to a value not greater than 5.5 and applying nitrogen in the ammonium form (Williams & Cooper, 1976). Such interventions should be made with caution since the uptake of ammonium may lead to a fall in pH of the spoil in the root region which, in certain reclamation sites, may result in heavy metal toxicity due to the increased solubility of, for example, aluminium and manganese (Clarkson, 1966, 1967).

Nitrification may also be inhibited in spoils with a physical texture precluding adequate aeration, since both Nitrosomonas and Nitrobacter are obligate aerobes and sufficient soil oxygen is essential to their activity. Studies on polder reclamation in the Netherlands showed that nitrifying bacteria only increased in numbers after good draining was established (Van Schreven & Harmsen, 1968).

IMMOBILISATION AND MINERALISATION

lmmobilisation denotes the process of conversion of inorganic nitrogen to the organic form during the decomposition of organic residues (Hutchinson & Richards, 1921). Micro-organisms use inorganic nitrogen in the synthesis of cell tissue resulting in organic nitrogen, e.g. amino acids and proteins, which is somewhat resistant to further biological degradation. Micro-organisms effectively

184 s . L A N N I N G , S. T . W I L L I A M S

compete with higher plants for available nitrogen, thus plants may become nitrogen- deficient especially in situations where 'soil' is being created from a skeletal substrate or spoil (Doubleday, 1971b; Goodman & Bray, 1975).

Mineralisation denotes the microbiological transformation of organic nitrogen to the inorganic form. This term may, therefore, include the two processes of ammonification (conversion of organic nitrogen to ammonia) and nitrification (oxidation of ammonia to nitrite and nitrate). This process renders the nitrogen mobile and available, providing secondary soil reactions do not remove the inorganic nitrogen from its mobile state (Bartholomew, 1965).

A condition of dynamic equilibrium exists between the inorganic and organic nitrogen of mature soils. The availability of soil nitrogen to micro-organisms and higher plants is, therefore, largely controlled by the opposing processes of immobilisation and mineralisation, which occur simultaneously and continuously during the decomposition of organic residues in soil (Broadbent, 1965).

Two major factors which determine the balance between immobilisation and mineralisation are (1) pH and (2) C:N ratio of the decomposing substrate.

p H The pH of many unlimed revegetated spoils is low, e.g. colliery spoil may have a

pH as low as 3.5 (Williams, 1975) and china clay sand waste a pH of 4.0 (Bradshaw et al., 1975).

TABLE 2 NITROGEN MINERALISATION FROM INCUBATED COLLIERY SPOILS AND TWO SOILS a

Treatment p H Mi tche l l ' s main p H Upton mineral isable ni trogen mineral isable ni trogen

(gin - 2 to depth o f 18 era) (gin - 2 to depth o f 18 era) -- C a C O 3 + C a C O 3 - C a C O 3 + C a C O 3

Shoddy 4-0 3"0 11.8 6.5 0. l 0"7 Sewage 4-0 6.2 8.4 6.5 0.0 1-2 Control 4.0 2.9 4.8 6-5 1-0 1-2 Lime 5.5 1.4 2.0 7.0 0.5 1.0

Moorland Woodland Soil 4-5 12.7 24.9 6"3 9"3 8"3

a After Williams (1973).

Measurement of net mineralisation of nitrogen in colliery spoils by incubation experiments revealed that very small amounts of nitrogen are released by acid spoils and that treatment with CaCO 3 increases the quality of mineralisable nitrogen formed (Table 2). These results suggest that when the pH is raised, many groups of heterotrophic micro-organisms previously inhibited by the acid conditions, promote the mineralisation of materials that were unattacked (Williams, 1975).

C: N ratio It has been shown that the C:N ratio of plant residues low in nitrogen decreases


during decomposition if mineral nitrogen is available in excess to that contained in the residue (Bartholomew, 1965; Brown & Dickey, 1970; Smith & Douglas, 1971). This may be explained by the occurrence of a net gain in organic nitrogen due to the immobilisation of free soil inorganic nitrogen by the decomposer organisms, while simultaneously a net loss in organic carbon results from carbon dioxide evolution, thus leading to a decrease in C:N ratio. These changes occur early in the decay process, as shown, for example, by experiments on the breakdown of wheat straw (Allison & Klein, 1962). Maximum immobilisation occurred in 20 days and averaged 1.7 ~o of the original weight of straw. This corresponded to a C:N ratio of 25:1. Immediately after maximum immobilisation, mineralisation became the dominant process and nitrogen release occurred.

During the decomposition of organic matter with a low C:N ratio, available nitrogen accumulates.

In many artificially revegetated spoils the nature of the organic matter available for decomposition within the spoil may favour the immobilisation of nitrogen with consequent deleterious effects on the continued growth of vegetation (see next section).

Parnas (1975) developed a model for decomposition based on the assumption that the rate of decomposition of any substrate is proportional to the growth rate of its decomposers. From this model the following points may be predicted.

(1) Addition of extra nitrogen to materials poor in nitrogen increases their rate of decomposition.

(2) Addition of extra nitrogen to a substrate whose initial C: N ratio exceeds the critical value (25:1) causes a decrease in the substrate's C: N ratio during its decomposition.

(3) If the initial C: N ratio is below 25:1, no change in the substrate's C: N ratio will occur with time.

(4) Net mineralisation of organic nitrogen occurs when the substrate has an initial C:N ratio of less than the critical value.

(5) Addition of ammonium ions to such a substrate will increase the rate of organic nitrogen mineralisation, but not necessarily the rate of net mineralisation,

These model predictions suggest that the balance between immobilisation and mineralisation processes in revegetated spoils may be controlled to a certain extent by the judicious use of fertilisers.

USE OF LEGUMES

The availability of nitrogen to the higher plant population depends in part on the nature of the organic matter being decomposed and ultimately, therefore, on the type of plants selected for use in reclamation.


The importance of nitrogen accumulation by both legumes and non-legumes in soil development is well-known (Stevenson, 1965) and the potential value of such plants in the revegetation of devastated areas has received considerable attention. Schramm (1966) showed that generally the only successful colonists of nitrogen- deficient anthracite mine-wastes were either nitrogen-fixing plants or certain ectotrophic mycorrhizal species. Such nitrogen-fixing species as alder and acacia have been used for erosion control (Rothwell, 1973) and it has been shown that the growth of alder can improve surface soil conditions in devastated land, resulting in increased carbon and nitrogen contents, cation exchange capacity and moisture holding capacity (Hashimoto et al., 1973). Natural succession on china clay sand wastes was shown to be dependent on nitrogen accumulation by symbiotic fixation (Dancer et al., 1977a) and the use of forage legumes (Trifoliurn pratense and T. repens) was recommended for use in subsequent reclamation schemes (Bradshaw et al., 1975; Dancer et al., 1977b). Trifoliurn repens and Melilotus alba have also been used in the reclamation of stripmine spoil banks (Leisman, 1957). Lupinus arboreus rapidly colonises micaceous china clay wastes and was shown to increase the concentration of total, inorganic and mineralisable nitrogen in these spoils (Palaniappan et al., 1979). Because it is tolerant of low concentrations of major plant nutrients and fixes atmospheric nitrogen, L. arboreus is a suitable pioneer species for reclaiming wastes of low fertility.

The beneficial effect of legumes on sward development obviously requires release of the fixed nitrogen into the soil and uptake by associated grass species. There is no conclusive evidence, however, for the excretion of nitrogenous compounds from live legume roots and it is generally accepted that the majority of legume nitrogen (about 80 ~) is liberated into the soil after the decay of the nodule-bearing root system (Dilz & Mulder, 1962; Date, 1970; Simpson, 1965). The value of including legumes in a sward is initially, therefore, their contribution to the soil organic matter. Dead legume tissue will provide the soil with a source of organic matter with a low C:N ratio more easily decomposed than roots and herbage derived from grass (Whitehead, 1970; Johnson & Bradshaw, 1979). Net nitrogen release may, therefore, proceed quite rapidly and enable the decomposer population to attack the more recalcitrant litter components. Decomposition rates of clover and grass shoots and roots buried in china clay sand waste were shown to be positively correlated with the initial nitrogen content and inversely correlated with the initial C:N ratio (Table 3). Clover shoots and roots and grass shoots decomposed readily and released nitrogen to the system, but grass roots required an exogenous nitrogen source to reduce their C:N ratio sufficiently to enable nitrogen release (Lanning & Williams, 1979a). Laboratory incubation experiments in which china clay sand waste was amended with clover or grass, shoots or roots and the inorganic nitrogen content monitored, confirmed the field decomposition experiments and showed that clover material rapidly released nitrogen to the system, while grass shoots decomposed more slowly and grass roots required the addition of inorganic

N I T R O G E N A N D L A N D R E C L A M A T I O N 1 8 7

TABLE 3 DECOMPOSITION RATES OF GRASS AND CLOVER SHOOTS AND ROOTS

IN CHINA CLAY SAND WASTE IN RELATION TO THEIR INITIAL C : N

RATIO AND TOTAL NITROGEN CONTENT

Plant Decomposition lnitial total C.'N ratio material rate k* nitrogen content

(~gg- l )

Clover shoots -5.61 31952 15 Clover roots -2-27 6180 100 Grass shoots -1.55 4978 103 Grass roots -0.44 2614 134

k* = regression coefficient of the natural logarithm of the dry weight of remaining litter as a function of time (years).

nitrogen to initiate net nitrogen release (Table 4). Bradshaw et al. (1975) incubated china clay sand waste mixed with grass or grass/clover litter in the presence or absence of 45 ppm ammonium-nitrogen. Net mineralisation of nitrogen occurred in all cases with grass/clover litter, but net immobilisation of nitrogen occurred with grass litter in the sand waste both in the presence and absence of added ammonium- nitrogen (Table 5). The amount of nitrogen was obviously insufficient to satisfy the requirements of the decomposer population. Thus, although in many reclamation sites grass roots constitute the largest proportion of organic matter available for decomposition, their rate of decomposition and net nitrogen release may be retarded by lack of available nitrogen. Jonas (1973), working on surface coal-mining wastes, also found that soil formation requires intense nitrogen fertilisation to facilitate the release of nitrogen, because systematic green fertilisation reduces nitrogen relative to carbon, resulting in a high C:N ratio and the unavailability of nitrogen to plants. Maximum humus formation took place in the first 10 years of reclamation, then an equilibrium was established between the increase and loss of organic matter. Several authors (Reeder & Berg, 1977; Williams & Cooper, 1976) showed that a higher level of nitrogen mineralisation and nitrification was found in vegetated coal-mine spoils as compared with non-vegetated spoils. The contribution

TABLE 4 NITROGEN MINERALISATION FROM INCUBATED CHINA

CLAY SAND WASTE a

Material incubated Mineralisable nitrogen (~gg- ' )

Sand waste 0.67 Sand waste + grass roots 0.62 Sand waste + grass shoots 0.00 Sand waste + clover roots 8.74 Sand waste + clover shoots 25.13

° After Lanning & Williams (1979a).

188 S. L A N N I N G , S. T. W I L L I A M S

T A B L E 5 RELEASE OF NITROGEN FROM RECENTLY RECLAIMED CHINA CLAY SAND WASTES a

Site Sward Inorganic Change in nitrogen after incubation b nitrogen Original Material + Material + plant

material plant debris debris + 45ppm ammonium-nitrogen

M a g g i e Pie G r a s s 12 + 6 - 7 - 5 9 P a r k G r a s s 12 + 4 - 7 - 27 Lee M o o r G r a s s + some clover 16 + 3 9 - 9 - 4 3 S t a n n o n G r a s s + g o o d c lover a n d

g r az ing 53 + 63 + 66 + 44 M a g g i e Pie Or ig ina l s and (contro l ) 2 0 - - + 4 4

a Af te r B r a d s h a w et al. (1975). b I n c u b a t i o n for 14 days a t 25°C .

of organic matter and nitrogen to the vegetated spoil by the alfalfa-dominated vegetation, as well as the physical and chemical breakdown of the spoil material by plant and microbial action, were thought to improve the conditions for nitrogen mineralisation.

POTENTIAL N I T R O G E N - S U P P L Y I N G C A P A C I T Y OF SOILS

In the evaluation of reclamation techniques, it is essential to know the capacity of the treated soil to supply nitrogen in plant-available form. Surprisingly, few studies on this problem have been carried out.

Incubation techniques have proved useful for comparing the effect of different amendments on the ability of reclaimed spoils to supply nitrogen. Handley (1976) compared inorganic nitrogen levels in incubated china clay sand wastes which had been treated with nitrogen fertiliser or in which clover had been growing. He showed that nitrogen was being immobilised in nitrogen fertiliser treatments, but was freely available beneath clover swards. Similarly, sand wastes taken from below clover contained more mineralisable nitrogen than those taken from below grass (Lanning & Williams, 1980). Palaniappan et al. (1979) demonstrated increases in total, inorganic and mineralisable nitrogen in soil under Lupinus arboreus over a five-year period. These results indicated that although most of the increased soil nitrogen was in the organic form, a proportion of this was available for plant uptake.

Williams & Cooper (1976) found that limed and neutral coal spoils amended with shoddy and sewage sludge two years previously released little mineral nitrogen on incubation. Acid spoils, however, similarly ameliorated, released more mineral nitrogen, especially if incubated with calcium carbonate, but released less than unfertilised grassland soil (Table 2). They demonstrated also that unfertilised soil released greater amounts of mineralised nitrogen than either unamended or


amended spoil, even though the total nitrogen contents of the spoils were high when compared with normal soils. The results of incubation studies on coal-mine spoils in Colorado and soil with similar total nitrogen contents, however, indicated that with time nitrogen mineralisation rates and nitrogen mineralisation potentials could approach those found in normal soils (Reeder & Berg, 1977). This emphasises that measurements of total nitrogen alone are inadequate for assessing the nitrogen- supplying power of spoils.

Integrated studies have shown soil biological activity to be more complex and important in ecosystems than perhaps realised by many ecologists (Parkinson, 1976). The behaviour of nitrogen in spoil is clearly very complex and the information from reclaimed land is sparse. More detailed studies of soil nitrogen transformations would facilitate predictions of the potential for maintaining functional nutrient cycling in reclaimed sites.

REFERENCES

ALLISON, F. E. & KLEIN, C. J. (1962). Rates of immobilisation and release of nitrogen following additions of carbonaceous materials and nitrogen to soils. Soil Sci., 93, 383 6.

BARTHOLOMEW, W. V. (1965). Mineralisation and immobilisation of nitrogen in the decomposition of plant and animal residues. In Soil nitrogen, Agronomy, 10, ed. by W. V. Bartholomew and F. E. Clark, 285-306, Madison, Wisconsin, American Society of Agronomy.

BRADSHAW, A. D., DANCER, W. S., HANDLEr, J. F. & SHELDON, J. C. (1975). The biology of land revegetation and the reclamation of china clay wastes of Cornwall. Symp. Br. ecol. Soc., 15, 363-84.

BRADSHAW, A. D. & CHADWICK, M. J. (1979). The restoration of land. Oxford, Blackwell. BROADBENT, F. E. (1965). Organic matter. In Methods ofsoilanalysis, Part 1L Agronomy, 9, ed. by C. A.

Black, D. D. Evans, J. L. White, L. E. Ensminger and F. E. Clark, 1397 1408. Madison, Wisconsin, American Society of Agronomy.

BROWN, P. L. & DICKEY, D. D. (1970). Losses of wheat straw residue under simulated field conditions. Proc. SoiI Sci. Soc. Am., 34, 118-21.

CLARKSON, D. T. (1966). Effect of aluminium on the uptake and metabolism of phosphorus by barley seedlings. PI. Physiol., Lancaster, 41, 165-72.

CLARKSON, D. T. (1967). Interactions between aluminium and phosphorus on root surfaces and cell wall material. PI. Soil, 27, 347-56.

CORNFIELD, A. H. (1952). The mineralisation of the nitrogen of soils during incubation: influence of pH, total nitrogen and organic carbon contents. J. Sci. Fd Agric., 3, 343-9.

DANCER, W. S. (1975). Leaching losses of ammonium and nitrate in the reclamation of sand spoils in Cornwall. J. environ. Qual., 4, 499-504.

DANCER, W. S., HANDLEY, J. F. & BRADSHAW, A. D. (1977a). Nitrogen accumulation in kaolin mining wastes in Cornwall, I. Natural communities. PI. Soil, 48, 153 67.

DANCER, W. S., HANDLEY, J. F. & BRADSHAW, A. D. (1977b). Nitrogen accumulation in kaolin mining wastes in Cornwall, II. Forage legumes. Pl. Soil, 48, 303-14.

DATE, R. A. (1970). Microbiological problems in the inoculation and nodulation of legumes. Pl. Soil, 32, 703-27.

DAVISON, A. & JEEFERIES, B. J. (1966). Some experiments on the nutrition of plants growing on coal mine waste heaps. Nature, Lond., 210, 649-50,

DENNINGTON, V. N. & CHADWICK, M. J. (1978). The nutrient budget of colliery spoil tip sites, I. Nutrient input in rainfall and nutrient losses in surface runoff. J. appl. Ecol., 15, 303-16.

DILZ, K. & MULDER, E. G. (1962). Effect of associated growth on yield and nitrogen content of legume and grass plants. PI. Soil, 16, 229-37.

DOUBLEDAY, G. P. (1971 a). Colliery shales as soil forming materials in North East England. Ph.D. thesis, University of Newcastle upon Tyne.


DOUBLEDAY, G. P. (1971b). Soil forming materials: their nature and assessment. In Landscape reclamation: a report on research into problems of reclaiming derelict land, vol. 1, 70-83. IPC Science and Technology Press Ltd, Guildford published for University of Newcastle upon Tyne.

DOUBLEDAY, G. P. (1974). The reclamation of land after coal mining. Outlook on Agriculture, $, 156-62. DOWN, C. G. & STOCKS, J. (1977). The environmental impact of mining. London, Applied Science. GEMmELL, R. P. (1975). Establishment of grass on waste from iron smelting. Environ. Pollut., 8, 35-44. GIGON, A. & RORISON, 1. H. (1972). The response of some ecologically distinct plant species to nitrate and

to ammonium-nitrogen. J. Ecol., 60, 93-102. GOODMAN, G. T., PITCAmN, C. E. R. & GEMMELL, R. P. (1973). Ecological factors affecting growth on

sites contaminated by heavy metals. In The ecology and reclamation of devastated land, vol. 2, ed. by R.J. Hutnik and G. Davis, 149-73. London, Gordon and Breach.

GOODMAN, G. T. & BRAY, S. A. (1975). Ecological aspects of the reclamation of derelict and disturbed land." an annotated bibliography. Norwich, Geo. Abstracts Ltd.

GOODMAN, G. T. & GEMMELL, R. P. (1978). The maintenance of grassland on smelter wastes in the Lower Swansea Valley, II. Copper smelter waste. J. appl. Ecol., IS, 875-83.

HANDLEY, J. F. (1976). The nitrogen economy of derelict land: studies on the reclamation of china clay waste. Ph.D. thesis, University of Liverpool.

HASHIMOTO, N., KOJIMA, T., OGAWA, M. 8£ SUZUKI, T. (1973). Effects of alder and acacia on devastated land. In The ecology and reclamation of devastated land, vol. 1, ed. by R.J. Hutnik 8£ G. Davis, 357-66. London, Gordon and Breach.

HODGSON, D. R. 8£ TOWNSEND, W. N. (1973). The amelioration and revegetation of pulverised fuel ash. In The ecology and reclamation of devastated land, vol. 2, ed. by R. J. Hutnik & G. Davies, 247-71. London, Gordon and Breach.

HUTCHINSON, H. B. & R1CHARDS, E. H. (1921). Artificial farmyard manure. J. Min. Agric., 28, 398-411. JACKSON, W. A. (1967). Physiological effects of soil acidity. In Soilacidity and liming, Agronomy, 12, ed.

by R.W. Pearson and F. Adams, 43-124. Madison, Wisconsin, American Society of Agronomy. JOHNSON, M. S., BRADSHAW, A. D. 8£ HARWOOD, J. H. (1976a). Plant growth problems of non-ferrous

metal mine wastes. In Land reclamation conference, ed by J. Essex and P. Higgins, 477-500. Thurrock Borough Council, Essex.

JOHNSON, M. S., BRADSHAW, A. D. 8£ HANDLEY, J. F. (1976b). Revegetation of metalliferous fluorspar mine tailings. Trans. Inst. Min. Metall,, 85A, 32-7.

JOHNSON, M. S. 8£ BRADSHAW, A. O. (1977). Prevention of heavy metal pollution from mine wastes by vegetative stabilisation. Trans. Inst. Min. Metall., 86A, 47-55,

JOHNSON, M. S. 8£ BRADSHAW, A. D, (1979). Ecological principles for the restoration of disturbed and degraded land. Appl. Biol., 4, 141-200.

JONAS, F. (1973). Reclamation of areas damaged by mining activity in Czechoslovakia. In The ecology and reclamation of devastated land, vol. 2, ed. by R.J. Hutnik and G. Davis, 379-94. London, Gordon and Breach.

JONES, D. G. 8£ REES. L. (1970). Suitability of Rhizobium trifolii for use as inoculum on acid soils. In White clover research, ed. by J. Lowe, Br. Grassland Soc. Occ. Syrup., 6, 61-70.

LANNING, S. (1978). Decomposition in china clay sand waste. Ph.D. thesis, University of Liverpool. LANNING, S. 8£ WILLIAMS, S. Z. (1979a). Nitrogen in revegetated China Clay Sand Waste, Part 1.

Decomposition of plant material. Environ. Pollut., 20, 149-61. LANNING, S. 8£ WILLIAMS, S. T. (1979b). Nitrogen in revegetated china clay sand waste, Part 2. The effect

of reduced leaching on decomposition and revegetation. Environ. Pollut., 21, 23-33. LANNING, S. 8£ WILLIAMS, S. T. (1980). Nitrogen in revegetated china clay sand waste, Part 3. The use of

clover in revegetation. Environ. Pollut., 21, 89-95. LEISMAN, G. A. (1957). A vegetation and soil chronosequence in the Mesabi iron range spoil banks. Ecol.

Monogr., 27, 221-45. NIELSON, R. F. 8£ PETERSON, H. B. (1973). Establishing vegetation on mine tailings waste. In The ecology

and reclamation of devastated land, vol. 2, ed. by R.J. Hutnik and G. Davis, 103-15. London, Gordon and Breach.

PALANIAPPAN, V. M., MARRS, R. H. 8£ BRADSHAW, A. O. (1979). The effect ofLupinus arboreus on the nitrogen status of china clay wastes. J. appl. Ecol., 16, 825 31.

PARKINSON, D. (1976). The restoration of soil productivity. In The breakdown and restoration of ecosystems. NATO Conference Series 1." Ecology, vol. 3, ed. by M.W. Holdgate and M.J. Woodman, 213-29. New York and London, Plenum Press.

PARNAS, H. (1975). Model for decomposition of organic material by microorganisms. Soil Biol. Biochem., 7, 161-9.

NITROGEN AND LAND RECLAMATION | 91

PEARSON, R. W. (1958). Liming and fertiliser efficiency. Agron. J., 50, 356-62. PROSSER, J. I. (1975). A model system for nitrification. Ph.D. thesis, University of Liverpool. QURAXSnl, M. S. I. & CORNFIELD, A. H. (1973). Incubation study of nitrogen mineralisation and

nitrification in relation to soil pH and level of copper addition. Environ. Pollut., 4, 159-63. REEDER, J. D. & BERG, W. A. (1977). Nitrogen mineralisation and nitrification in a cretaceous shale and

coal mine spoils. Proc. Soil Sci. Soc. Am., 41,922-7. ROTnW~LL, F. M. (1973). Nodulation of various strains of Rhizobium with Robinia pseudoacacia

seedlings planted in strip-mined soil. In The ecology and reclamation of devastated land, vol. 1, ed. by R.J. Hutnik and G. Davis, 349-56. London, Gordon and Breach.

RUSSELL, E. W. (1973). Soil conditions and plant growth. London, Longman. SCnR^MM, J. (1966). Plant colonisation on black wastes from anthracite mining in Pennsylvania. Trans.

Am. Phil. Soc., 56, 1-34. S r~LDON, J. C. & BRADSHAW, A. D. (1976). The reclamation of slate waste tips by tree planting. J. Inst.

Lands. Arch., 113, 31-3. S~MPSON, J. R. (1965). The transference of nitrogen from pasture legumes to an associated grass under

several systems of management in pot culture. Aust. J. agric. Res., 16, 915-26. SMITH, J. H. & DOUGLAS, C. L. (1971). Wheat straw decomposition in the field. Proc. Soil Sci. Soc. Am.,

35, 269-72. S~VENSON, F. J. (1965). Origin and distribution of nitrogen in soil. In Soil nitrogen, Agronomy, 10, ed. by

W.V. Bartholomew and F. E. Clark, 1-42. Madison, Wisconsin, American Society of Agronomy. VAN SCrtREVEN, D. A. & HARMSEN, G. W. (1968). Soil bacteria in relation to the development of polders in

the region of the former Zuider Zee. In The ecology of soil bacteria, ed. by T. R. G. Gray and D. Parkinson, 474-99. Liverpool, Liverpool University Press.

WEBER, D. F. & GAINEr, P. L. (1963). Relative sensitivity of nitrifying organisms to hydrogen ions in soils and in solutions. Soil Sci., 94, 138-45.

WHITEHEAD, D. C. (1970). The role of nitrogen in grassland productivity. Bull. Commonw. Bureau Pastures and Field Crops, 48.

WILLIAMS, P. J. (1975). Investigations into the nitrogen cycle in colliery spoil. Syrnp. Br. ecol. Soc., 15, 259-74.

WILLIAMS, P. J. & COOPER, J. E. (1976). Nitrogen mineralisation and nitrification in amended colliery spoils. J. appl. Ecol., 13, 533-43.

WILLIAMS, S. T., MCNEILLY, T. & WELLINGTON, E. M. H. (1977). The decomposition of vegetation growing on metal mine waste. Soil Biol. Biochem., 9, 271-5.

WILSON, H. A. (1965). The microbiology of strip-mine spoil. Bull. W. Va Univ. agric, exp. Stn, 506T. WILSON, H. A. ~ STEWART, G. (1955). Ammonification and nitrification in a strip mine spoil. Bull. W. Va

univ. agric, exp. Stn, 379T, 16.

nitrogen and land reclamation

Documents