Changes in surface structure (crusting) after application of sewage sludge and pig slurry to cultivated agricultural soils in Northern Italy

Geoderma, 30 (1983) 35--53

35

Elsevier Science Publishers B.V., Amsterdam -- Printed in The Netherlands

CHANGES IN SURFACE STRUCTURE (CRUSTING) A F T E R APPLICATION OF SEWAGE SLUDGE A N D PIG SLURRY TO CULTIVATED AGRICULTURAL SOILS IN NORTHERN ITALY

M PAGLIAI, E.B.A. BISDOM and S. LEDIN

C N.R. --Institute for Sod Chemzstry, 78-Pisa (Italy) Netherlands Soil Survey Institute, 6700 AB Wagenmgen (The Netherlands) Department of Soil Sciences, Swedish University of Agricultural Sciences, S-75007 Uppsala 7 (Sweden) (Accepted for publication February 17, 1983)

ABSTRACT

Pagliai, M., Bisdom, E.B.A. and Ledin, S., 1983. Changes in surface structure (crusting) after application of sewage sludge and pig slurry to cultivated agricultural soils in northern Italy. Geoderma, 30: 35--53. The first results of a cooperative research project on changes in cultivated agricultural topsoils after treatment with sewage sludge and pig slurry are discussed for a silty clay soft (Vertic Xerochrept) and a sandy loam soil (Typic Psammaquent) Such changes are expressed in the surface structure, including crusts, of the soils and have a direct effect on their fertility. To measure these changes, special attention was paid to porosity characteristics, especially increases in porosity after application of organic manures to agricultural soils with crusting problems. Light microscopy, SEM-EDXRA (scanning electron microscopy -- energy dispersive X-ray analysis) and Quantimet (electro-optical image analysis) were applied and allowed quantitation and visualisation of pores. Initial results clearly demonstrate that the porosity of the topsoil increased after treatment with urban refuse or pig slurry and that crusting decreased.

INTRODUCTION

This cooperative research project of IWGSUSM (International Working Group on Submicroscopy of Undisturbed Soil Materials) was started to determine the effect of the application of livestock effluents and sewage sludges on the structure of Italian softs with crusting problems. Soft crusting in cultivated softs is one of the most dangerous phenomena in Italy both from an agronomic and a soil erosion point of view. The main effects of a soil crust are: reduction of water infiltration, increase in run-off, reduction of gas exchange between the soft and atmosphere, and interference with seed germination. Many authors have studied the structure and the mechanism of formation of soil crusts (McIntyre, 1958; Evans and Buol, 1968; Epstein and Grant, 1973; Falayi and Bouma, 1975; Pagliai and La Marca, 1979; Pagliai et al., 0016-7061/83/$03.00

© 1983 Elsevier Science Publishers B.V.

3~ 1981b; Jongerms, 1981). According to the mechamsm of formation, two types of crusts can be distinguished, 1.e. those formed as a result of raindrop impact (structural crusts), and those formed by translocation of free particles and their deposition at a certain distance from their original location (deposltional crusts) (Chen et al., 1980). The principal reason for crust formation in cultivated soils is poor stablht y of soil aggregates upon which the impact of raindrops causes d e t a c h m e n t of constituents. The lnstablhty of aggregates is higher the lighter the t ext ure of the soft and the lower its organic matter content. This small a m o u n t of orgamc matter IS caused by a severe shortage of manure and by intensive cultivations whmh replaced the traditional farming rotations. Moreover, heavy rainfall followed by a strong and dry wind is normal in the Po area of northern Italy and the d e c o m p o s i t m n rate of orgamc matter is high m the Italian chmate. For these reasons, sources of orgamc matter had to be found, i.e. hvestock effluents and sewage sludges In which the organic m at t er accounts for about 50% of the sludge dry matter. The area with intensive cultivation Is increasing m Italy and due to a severe shortage of manure, the use of sewage sludge and pig slurry has become increasingly popular. This study has been carried out with an m situ investigation of unhardened soil peds and crusts by SEM (scanning electron microscope) and by examination of soil materials m thin sectmns with the hght microscope, SEM-EDXRA (scanning electron microscope -- energy dispersive X-ray analyzer) and Quantlmet 720 (electro-optical image analyzer). Special attention was paid to the upper 5 cm of the soft, especially to porosity changes related to the application of manure and sewage sludge. The present paper ~s the hrst of a serms Only some of the samples have been examined with all techmques so far, vlz. the upper part of a silty clay soft --treated with 300 m 3/ha of pig slurry -- by hght microscopy, SEMEDXRA and Quantlmet, and a sandy loam soil -- treated with c o m p o s t of anaerobic sludge and the organic fractions (20--80%} of urban refuse (CANS m Table I) -- by light microscopy and Quantnnet. Samples of control plots of both soils were also investigated with the light microscope and Quantlmet. EXPERIMENTAL PLOTS AND SAMPLING Two soils with a strong t e n d e n c y to form surface crusts were chosen for experunents with pig slurry and sewage sludge. A silty clay soil (Vertic Xerochrept) and a sandy loam soil (Typm Psammaquent) were planted with corn in May 1980. Pig slurry was applied in June to the silty clay, about one m o n t h after the corn was sown, whereas the sewage sludge had been ploughed i n t o ' t h e sandy loam before May 1980. This ex p er imen t with silty clay soils was carried out on four plots of 1 ha each 1 ha represented the control of the Vertic X e r o c h r e p t and the other 3 ha were treated with different amounts of pig slurry. 1 ha of the silty clay soil received 100 m 3, a second 200 m ~ and the third experimental plot 300

37 m 3 of livestock effluent. Surface samples of the Vertic Xerochrept were taken at the end of September. The experimental plots on the sandy loam soil (Typic Psammaquent) were each 500 m:. Six of these plots were studied, viz. one control plot, four plots which were given different types of sewage sludge, and one plot that was treated with manure. The four sewage sludges differed in composition and were applied in quantities that were equivalent to 50 tons/ha of manure on an organic carbon basis. The four sludges consisted of aerobic sludge (AS), anaerobic sludge (ANS), a c o m p o s t of aerobic sludge and the organic fraction ( 4 0 - - 6 0 % ) of urban refuse (CAS), and a compost of anaerobic sludge and the organic fraction (20--80%) of urban refuse (CANS). The sixth plot was treated with manure (M). Surface samples of the sandy loam soil were taken four months after the application of the sewage sludges, I.e. at the beginning of September. SEM S T U D Y OF U N H A R D E N E D SOIL M A T E R I A L

A scanning electron microscope (SEM) study was made of small pieces of the uppermost part of the silty clay soil which was treated with 300 m3/ ha pig slurry. The secondary electron images (SEI) of pieces of the treated soil were compared with pieces of the crust of the control soil, i.e. in and below the dense part of its surface crust. The pieces of soil were attached to stubs with silver, coated with gold to give conductivity to the insulating material and studied by SEM. To obtain the right position of the soil pieces on the stubs these were oriented with the help of stereo microscope and examined with a Jeol 25S3 scanning electron microscope. A surface sample of the control plot was broken with pliers to observe the microstructure of the crust (Fig.l). Three microlayers were distinguishable (Fig.la), viz. a very thin t o p part, a middle part which was much thicker, and a lower part of which only the upper section and surface is portrayed in the foreground. These three microlayers had different compositions. The top part was comprised of fine clayey particles (Fig.lb) which were arranged in platy and other structures. Silt-sized particles were dominant in the middle microlayer of the crust which was rather clean and fairly free from adhering clay particles (Fig.lc). A mixture of coarser and finer particles is distinguishable in the lower part of the crust (Fig.ld). The crust had formed on nearly horizontal soil surfaces and the following mechanism of crust formation could be envisaged. Raindrop impact is believed to be the principal force in the formation of this type of crust which was called structural crust in the introduction. The raindrops, when hitting the very top of the soft, separate the finest particles from the silt and sand which may also move over short distances. The smallest particles such as single clay minerals, somewhat larger entities and organic materials, are kept in a dispersed state as long as the rain continues. Water fills every pore and stands a few millimetres above the surface of the soil because the

38

39

infiltration rate is so low that accumulation of water takes place. When the rain stops, the finest material sediments on t o p of the silt and sand particles. These coarser particles function as a filter and do not allow small particles to follow the downward movement of percolating water. When the soil dries, all particles are brought closer together and kept that way by attraction forces and in the dry state these will affect the clay particles strongest. Small particles can be brought very close to each other and Van der Waal's forces will be active; the formation of cation bridges and edge-surface attraction is also possible. As long as the crust is dry the short range attraction forces will remain active. When 300 m3/ha pig slurry is put onto the silty clay soil, SEM micrographs show that crust formation will continue and that the process as such remains the same. However, straw fragments (Fig.2a), pig hairs (Fig.2b) and other organic materials are able to break up the crust (Fig.2c). The results can be compared with secondary electron images (SEI) of the crust in the control soft, a t o p view of which is given at the same magnification in Fig. 2d. To allow a continuous view of the upper 0.6 mm of the crust in the control plot, a photo-montage was made (Fig.3). The very thin t o p part with fine clayey material is somewhat less expressed than in Fig.lc and maximally a few microns thick. It is underlain by the relatively clean middle part of the crust up to about 0.15 mm depth. This microlayer of silt-sized particles, without many adhering clay particles, is followed by the lower part of the studied crust in which a mixture of particles occurs. LIGHT MICROSCOPY

OF THIN SECTIONS

Undisturbed soil samples were taken from the upper 5 cm of a Vertic Xerochrept {silty clay soil) and of a Typic Psammaquent (sandy loam soil). At sampling time, m September, the softs were so dry that further shrinkage was almost negligible. Both the control samples and the samples treated with pig slurry (silty clay soft) or sewage sludge (sandy loam soil) were airdried at room temperature. Samples were subsequently impregnated and made into thin sections. The larger part of the upper 5 cm of both softs is portrayed in Figs.4 and 5 (Vertic Xerochrept) and Figs. 6--9 (Typic Psammaquent). Samples treated with organic material are shown in Figs. 5 and 9.

Fig.1. SEM micrographs of u n i m p r e g n a t e d crust of the control plot on silty clay. The fine clayey material of the Vertic Xerochrept is o n l y a f e w m i c r o n s thick at the surface (a). Detail of the fine clayey material (b). The very thin surface part of the crust is underlain by relatively clean silty particles (c). A m i x t u r e of silt and clay can be found in the lower part of the crust (d).

40

c~

o

c~

I

v

0

~

41

mm

.0,4

01

-0.s -0.2

-06

.03

Fig.3. SEM view o f a b o u t 0.6 m m crust. The s a m e d i f f e r e n t i a t i o n as given in Fig. I can be discerned, viz. a very thin surface layer, r a t h e r clean slit u n d e r n e a t h , and a m i x t u r e o f silt a n d clay particles b e l o w 0.15 m m d e p t h . U n t r e a t e d soil

42 LIGHT MICROSCOPY OF THE SILTY CLAY SOIL No c o n t i n u o u s very thin t o p part is distinguishable m the surface crust o f the Vertic X e r o c h r e p t m Fig. 4 at this small m a g m f l c a t l o n . The same part of the crust, however, was clearly indicated on SEI t a k e n b y SEM ( F i g . l ) and p r o v e d to be a few microns think. A p r o n o u n c e d p l a t y s t r u c t u r e (Fig.4) is present in the c o n t r o l plot o f the silty clay soil as indicated by the subh o r i z o n t a l fractures. S o m e o r i e n t a t i o n o f the soil particles was seen with crossed polarizers at t h e t o p o f the soil and adjacent to the h o r i z o n t a l fractures.

750 ~m

Fig.4. Platy structure in untreated silty clay crust of a Vertm Xerochrept. Differences in structure are difficult to estabhsh at this small hght mmroscopic magnification Plane polarized light (a) and crossed polarizers (b) A representative area o f a thin section f r o m soil t r e a t e d with 300 m3/ ha o f pig slurry is s h o w n in Fig.5. C o m p a r e d with t h e u n t r e a t e d soil, a sigm f i c a n t increase in p o r o s i t y was discernable. This was t h o u g h t t o be the case after land spreadings o f pig slurry b u t has n o w been wsualised. Usually, all the large pores had an irregular shape. T h e adhesion o f soil particles t o organic materials s e e m e d evident. Cracks and m i c r o c r a c k s were also f o r m e d in the thin crust and these are o f i m p o r t a n c e for i m p r o v e d w a t e r infiltration.

43

Fig. 5. The silty clay crust of Fig.4 was broken after treatment with pig slurry and conslderable macroporosity developed. Plane polarized hght (a) and crossed polarizers (b).

LIGHT MICROSCOPY OF THE SANDY LOAM SOIL

Light microscopy of the Typic Psammaquent shows more variability in structure than the silty clay soil. A certain microlayering can be observed in Fig.6, starting with coarser material and ending with clayey material at the t o p and at the end of a cycle of sedimentation. On the present surface of the soil, just above the latest sedimented clay lammella, the start of a new sedimentation cycle can be discerned and is indicated by a microlayer of sandy material. A small gully-like structure is present in the lower half of Fig.6a. The topography of the soil surfaces in the experimental plots is virtually flat and it has been indicated above that the impact of raindrops is considered to be the main force that separates the soil particles in poorly stable aggregates. Fig.6, however, demonstrates that small-scale sedimentation processes also do occur in furrows and puddles. Entrapped air may be present below a surface sealing of m u d d y material, and vesicles can form (Fig. 7). In this case, carbon dioxide liberated by biological activity from organic material added to the soil, may play a role in the formation of vesicles. Such vesicles can collapse at deeper levels (Fig.7a) or remain intact (Fig.8). One difference between the b o t t o m part of the two figures is the presence of a clay lammella in Fig.8 and its absence in Fig.7. It should be noted

44

Fig 6 T w o u n d i s t u r b e d layered crusts m s a n d y loam o f an u n t r e a t e d T y p m P s a m m a q u e n t A n e w cycle is started at t h e surface w i t h the d e p o s i t i o n o f s a n d y material Near t h e bott o m o f the m i c r o g r a p h t h e r e is a gully-like s t r u c t u r e , a possible origin of w h m h is described in t h e t e x t . Plane polarized light (a} and crossed polarizers (b)

Fig.7. Vesicles and sealing-layer m sandy loam Collapsed vesmles at the bottom of the micrograph. Plane polarized light (a) and crossed polarlzers (b). Untreated T y p m Psammaquent

45

I

750 ~m

J

Fig.8. Uncollapsed vesicles in Typic Psammaquent These are present above a clay lamella in the centre of the micrograph Plane polarized light (a) and crossed polarizers (b). Untreated soil.

Fig.9. Sandy loam of a Typic Psammaquent treated with sewage sludge. Macro-porosity ~s mainly visible in the form of vertical cracks or channel-shaped pores Plane polarized light (a) and crossed polarizers (b).

46

that Miller (1971) and Kemper and Miller (1974) regard the presence of vesicles in the topsoil as an indication of an unstable and transitory structure helped by a poor stability of soil aggregates. The other types of pores m Figs.6--8 are often elongated in a subhorizontal direction. These pores have irregular walls. The elongated pores are well expressed underneath the lammellae with fine soil material in Figs.6 and 8, while they also occur at the b o t t o m part of Fig.7. A special type of pore, related to the collaps of vesicles, is also discernable in the latter figure. When the sandy loam was treated with sewage sludge (Fig.9) considerable changes occurred in the surface part of the Typm Psammaquents. Part of the centre of the silty clay crust on the surface of the soil and the silty layer underneath have newly formed pores. Channel-type pores are, for example, visible at the right hand side of Fig.9b. These pores could also be observed in the field and are therefore regarded as predominantly natural ones. Frequently, however, such channel-type pores or cracks are regarded as artificial, caused by drying during sample preparation or by movements during sampling. Q U A N T I M E T M E A S U R E M E N T S O F T H E L A R G E R P O R E S IN T H I N S E C T I O N S

Larger pores, with diameters larger than 30 pm, were measured in the upper 5 cm of the silty clay soil and the sandy loam soil using combmed light mmroscopic and Quantimet techniques. These techmques were described by Jongerius (1974, 1975), Jongerius et al. (1972, 1979), Ismail TABLE I Effect of treatments on porosity of the soil surface layer (0--5 cm), data are the means of three and five replications, respectively for the silty clay soil and for the sandy loam soil Treatments

Rounded pores

Irregular pores

Elongated pores

Total porosity

(%)

(%)

(%)

(%)

0.3 3.0

2.8 18.7

67 9.4

9.8 (± 1.1) 31.1 (± 2.3)

24 1.2

8 2 20.5

7 3 11.4

17.9 (± 1.6) 33.1 (± 1.2)

Sdty clay sod Control 300 m~/ha of plg slurry

Sandy loam sod Control CANS

C A N S stands for : C o m p o s t of anaerobm sludge and the organic fraction of urban refuse (20--80%). The q u a n t i t y applied was e q m v a l e n t to 50 t o n s / h a of manure on an organic carbon basis Numbers between parentheses represent the standard error

47

(1975) and Murphy et al. (1977a, b). Such Quantimet measurements of porosities in thin sections were correlated by Bouma et al. (1977, 1979) with the saturated hydraulic conductivity of heavy clays. Quantimet measurements are usually necessary to characterise pore systems in thin sections. Some of the results of such measurements are given in Table I for the silty clay and sandy loam soft, 1.e. porosity characteristics of the upper 5 cm of the control plots and of treated plots. Although this is a rather rough approach to porosity measurements, the table serves to illustrate some differences between the porosities of the control and treated plots. These measurements will be refined when more thin sections become available and submicroscopic imaging can be used on a larger scale, i.e. backscattered electron scanning images (BESI) which are measured by Quantimet (Bisdom and Thiel, 1981; Jongerius and Bisdom, 1981). CONTROL

80

ORGANICALLY TREATED

SILTY CLAY SOIL

60

ELONGATED PORES D

IRREGULAR PORES

[~

ROUNDED PORES

40 u3 LU

nO

20

,,,

0

~

8e

~

60

er

Z

SANDY LOAM SOIL

w

~-

40

20

30 50 500>500

30 50 500>500Jura

F i g . 1 0 . D i s t r i b u t i o n o f t h e size and s h a p e of p o r e s larger than 3 0 # m t r e a t m e n t w i t h organic m a t t e r

before and after

48 The total porosity of the studied mmrographs, made with a light microscope, was determined by Quantimet and shape groups of pores distinguished, viz. rounded, Irregular and elongated pores. Such shape groups can be found by measuring the area (A) and the perimeter (Pe) of the pores and by working with A / P e 2 ratios. Rounded pores have A / P e 2 ~ 0.04, irregular pores A / P e 2 from 0.04 to 0.015, and elongated pores have A / P e 2 ,~ 0.015 (Bouma et al., 1977). The pores of each shape group were subsequently subdivided into three size classes, viz.30--50 urn, 50--500 ~m and > 500 pm (Fig.10). This was done for rounded and irregular pores according to the equivalent pore diameter, whereas the width, calculated from area and perimeter data, was used for elongated pores. In the present study only prehminary results of Quantimet measurements can be given . The measurements confirm that plots treated with organic debris have a higher porosity than control plots. The total porosity increased from 9.8% (control plot) to 31.1% (plot treated with 300 m3/ha of pig slurry) m the Vertic Xerochrept and from 17.9% (control plot) to 33.1% (plot treated with anaerobic sludge and urban refuse) m the Typic Psammaquent (Table I). The treated plots contained less pores larger than 500 pm than the control plots (Fig.10), whereas the number of pores smaller than 500 pm increased in the size classes 30--50 ~m and 50--500 urn. Quantimet measurements also mdmated that the decrease in pores larger than 500 #m was principally given by the reduction of elongated pores with respect to the control. This means that the organic fertilizers were able to reduce cracks which originated by shrinkage (Paglim et al., 1981a). When rounded pores of Table I are compared with percentages of rounded pores m Fig.10, it is shown that large rounded pores occur mainly m plots of the silty clay soils which were treated with pig slurry, whereas they were present in the control plot of sandy loam soils. The percentage of irregular pores increased in all organically treated plots with one exception; pores larger than 500/~m m the sandy loam soil treated with sewage sludge. BACKSCATTERED THIN SECTIONS

ELECTRON

SCANNING

IMAGES OF POLISHED BLOCKS

AND

Backscattered electron scanning images (BESI) were made of one sampleblock of silty clay treated with 300 m 3 of pig slurry. This block represented the upper 5 cm of a Vertic Xerochrept of which the surface crust had become broken and more porous. The present BESI micrographs only represent a few examples of what can be done with this submicroscopic technique on polished blocks and thin sections. High quality micrographs can be obtained of various materials and porosities (Bisdom and Thiel, 1981). With this technique one can easily obtain images of such quality that even pores with a diameter smaller than 0.1 um become measurable by Quantimet (Jongerius and Bisdom, 1981). If in situ microchemical analysis is also neces-

49

F i g . l l . Backscattered electron scanning image (BESI) of the silty clay crust treated with pig slurry. Organic matter may take up a position which breaks the crust.

sary, a number of submicroscopic techniques are available (cf. review articles by Bisdom, 1981a, b). The present sample-block forms part of a series of which thin sections are currently being made. These allow microscopic and submicroscopic visualisatlon of the effects of crust formation and destabilisation processes, if present. For the m o m e n t only a few micrographs are given of the surface of the loosened crust ( F i g . l l ) , of part of the former crust at various magnifications (Fig.12), and of pig slurry which was found 2 to 3 cm below the surface of the Vertic Xerochrept (Fig.13). These and other BESI images indicate that the organically treated crust is very heterogeneous in a horizontal and vertical direction. CONCLUSIONS

Light microscopy, electron microscopy and Quantimet 720 were used to study the behaviour of surface crusts of Vertic Xerochrepts and Typic Psammaquents in experimental plots from Italy before and after treatment with pig slurry and sewage sludge. Only the initial part of our cooperative research project has been completed and therefore only first results are discussed in this paper. SEM observation of unhardened pieces of untreated crust from the silty clay soil demonstrated that the upper 0.6 mm of the 5 cm thick surface crust could be subdivided into three microlayers. The uppermost microlayer was comprised of clayey material and was only a few micrometres thick. The underlying silty microlayer was a b o u t 0.15 mm thick. The lower microlayer consisted of a mixture of predominantly silt and clay. The microlayers are thought to have formed as a result of raindrop impact and the effects of wetting and drying of the soil together with small-scale sedimentation processes. Light microscopy of the 5 cm thick surface crust of the sandy loam soil demonstrated the existence of various cycles of sedimentation. Each cycle

k

51

Fig.13. Pig slurry (a) and (b) has also been found some centimetres b e l o w the surface. A vaxiety of forms in the organic matter are indicated by BESI.

started with coarser material and ended with clayey material. Microlayering, although observed by SEM, was far less present in silty clay soil. Sub-horizontal fractures indicated the presence of platy structures in the crusts of Vertic Xerochrepts. Porosity changes, going from untreated to treated plots, can be observed on micrographs from light microscopy or electron microscopy. The attention in mainly attracted by larger pores and cracks but it is hard to obtain good insight into the total porosity if no Quantimet techniques are involved. As a consequence mistakes can be made. In the present case only rough Quantimet measurements are involved because additional thin sections must be prepared for combined BESI and Quantlmet investigation. It is clear, however, that the increased porosity, after treatment of the soil crust with organic matter, could be documented by Quantimet and light microscopy. Pores larger than 500 ~m decreased in number after treatment of the crust, largely because of a reduction in elongated pores. The percentage of irregular pores increased in most organically treated plots. Future research will concentrate on the study of all samples with more emphasis on submicroscopic techniques to supply backscattered electron scanning images for Quantimet measurement of capillary and larger pores. More secondary electron images will also be made of unhardened soil materials in treated and untreated crusts. When all thin sections are ready in the three laboratories, more light microscopic information will also become available. The combination of the three techniques will allow better insight mto the effects of different organic materials on crust formation, especially on porosity development.

Fig.12 BESI o f the crust of a Vertic Xerochrept treated with pig slurry (a). Some organic fragments of pig slurry axe visible. Microporosity can also be studied by Quantimet if the black pores are measured in micrographs (b) to (d).

52 REFERENCES Bisdom, E B A., 1981a A review of the apphcation of submmroscopic techniques m soil micromorphology, I. Transmissmn electron microscope (TEM) and scanning electron mmroscope (SEM). In. E.B.A Bisdom (Editor), Submmroscopy of Soils and Weathered Rocks. 1st Workshop of the International Working-Group on Submmroscopy of Undisturbed Sod Materials (IWGSUSM) 1980, Wageningen Centre for Agricultural Publishing and Documentation (Pudoc), Wagenmgen, pp 67--116_ B,sdom, E.B.A., 1981b. A revxew of the application of subm,croscopm techmques m sod m,cromorphology, II. Electron microprobe analyzer (EMA), scanning electron m,croscope -- energy dispersive X-ray analyzer (SEM-EDXRA), laser mmroprobe mass analyzer (LAMMA 500), electron spectroscopy for chemical analysis (ESCA), ion mmroprobe mass analyzer (IMMA), and the secondary ion m,croscope (SIM) In_ E B.A Blsdom (Editor), Submmroscopy of Soils and Weathered Rocks. 1st Workshop of the Internatmnal Working-Group on Submmroscopy of Undisturbed Soil Mater,als (IWGSUSM) 1980, Wagemngen. Centre for Agr,cultural Pubhsh,ng and Documentat,on (Pudoc), Wagenmgen, pp 117--162 Bisdom, E B A and Thml, F., 1981 Backscattered electron scanning images of porosities m thin sections of softs, weathered rocks and o,l-gas reservoir rocks using SEMEDXRA In E.B.A Bisdom (Editor), Submmroscopy of Soils and Weathered Rocks. 1st Workshop of the Internat,onal Working Group on Submicroscopy of Undisturbed Soft Materials (IWGSUSM) 1980, Wageningen. Centre for Agricultural Pubhshmg and Documentation (Pudoc), Wageningen, pp 191--206. Bouma, J., Jongerius, A., Boersma, O , Jager, A and Schoonderbeek, D , 1977_ The function of different types of macropores during saturated flow through four swelhng sod horizons. Soil Scl Soc. Am J., 41(5) 945--950 Bouma, J , Jongerms, A and Schoonderbeek, D., 1979. Calculation of saturated hydrauhc conductivity of some pedal clay soils using micromorphometric data Soil Sci Soc. Am J , 4 3 ( 2 ) 261--264. Chen, Y., Tarchltzky, J , Brouwer, J., Morro, J and Bantu, A , 1980. Scanning electron microscope observations on soil crusts and their formation, Soil Scl, 130(1) 49--55. Epste,n, E and Grant, W J , 1973 Soil crust formatmn as affected by ra,ndrop impact. In Ecological Studies, 4 Phys,cal Aspects of Soil Water and Salts in Ecosystems, pp 195--201 Evans, D D and Buol, S W, 1968 Micromorphologmal study of sod crusts Soil Sci. Soc Am J , 3 2 . 1 9 - 2 2 Falayl, O and Bouma, J , 1975 Relationships between the hydraulic conductance of surface crusts and soil management m a Typic Hapludalf Soft Sci. Soc_ Am J., 39: 957--963 Ismad, S_N_A., 1975 M,cromorphometric soil-porosity characterization by means of electro-optical image analysxs (Quant,met 720) Neth. Soil Surv Inst., Wageningen, Soil Surv Pap., 9. 104 pp Jongerms, A , 1974. Recent developments in soil mmromorphology. In G.K Rutherford (Editor), Soft M,croscopy Proceedings of the Fourth International Working-Meeting on Soil Mmromorphology, Kingston, 1973. The Limestone Press, Kingston, Ont., pp 67--83 Jongerms, A , 1975. Micromorphometrm soil analysis by means of Quantimet 720. In Fortschr,tte der quantltatxven Bildanalyse, Vortrage des IMANCO-Symposmms, pp. 161--185 Jongerms, A , 1981_ Mmromorphological applications ,n agricultural research. Interna,renal Working-Meeting on Soil Mmromorphology. London, 1981. In press

53 Jongerius, A. and Bisdom, E.B.A, 1981. Porosity measurements using the Quantimet 720 on baekscattered electron scanning images of thin sections of soils. In E.B A. Bisdom (Editor), Submieroscopy of Soils and Weathered Rocks. 1st Workshop of the International Working-Group on Submicroscopy of Undisturbed Soil Materials (IWGSUSM) 1980, Wageningen. Centre for Agricultural Publishing and Documentation (Pudoc), Wageningen, pp 207--216 Jongerms, A , Schoonderbeek, D. and Jager, A., 1972 The appheatlon of the Quantimet 720 in soil micromorphology The Mmroscope, 20 243--254. Jongerms, A., Schoonderbeek, D. and Bouma, J , 1979 Micromorphometrm image analysts of flow patterns in swelling clay softs. In Proceedings of the QuantlmetSymposmm on Advances of Quantitative Image Analysis. Microsc. Acta, Suppl, 3 115--120

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