ROCZNIKI GLEBOZNAWCZE (SOIL SCIENCE ANNUAL) T. XLIX NR 1/2 W ARSZAW A 1998 5 -1 6
ALINA KUSIŃSKA
ELEMENTAL COMPOSITION OF HUMIC ACIDS
AS AN INDICATOR OF THEIR PROPERTIES
AND STRUCTURE
Department o f Soil Science, Warsaw Agricultural University - SGGW
INTRODUCTION
In the study o f soil humus im proved m ethods to investigate m ore precisely the characteristics and structure o f humus (both physico-chem ical m ethods and indi cators) are still needed. The early study on hum ic acids parameters proved that their elem ental com position is specific for soils o f significant genetic difference. Later work show ed how ever that elem ental com position, esp ecially w hen expres sed in terms o f w eight percentage, cannot be fully useful for com parisons o f typologically related soils [R oszyk 1962, Kusińska 1979, U sak iew icz 1983, Turski et al. 1987, Turski 1988]. M any authors have, on the other hand, su ccessfu lly em ployed this index for determining the effect o f different agrotechnical m eans on the structure o f soil humus [K leszczycki et al. 1967, Turski, et al. 1970, N azarova 1975, Flis-Bujak 1978, Gonet 1989, G ołębiow ska et al. 1990]. The presentation o f elem ental com position using atom ic per cents and particularly in the form o f atom ic ratios H:C and 0 :C gave better interpretation p ossib ilities. N um eric values o f the atom ic ratio H:C allow for the assessm ent o f hum ic acids structure because these values are inversely proportional to aromatization degree o f organic com pounds.
The purpose o f this work was to demonstrate the effect o f selected crop plants grown follow in g varying agricultural system s on the structure o f soil hum ic acids. A s the indicator, elem ental com position o f hum ic acids was em ployed in this study.
THE PLACE, SCOPE AND OBJECTIVE
Elem ental com position o f hum ic acids isolated from three static experim ental fields were studied. In the experim ents, different crop species grown had been (am ong others, potato, rape, m aize, rye and flax), follo w in g different agricultural
6 A. Kusińska
system s (m onoculture, crop rotation after grow ing grass, unrestricted rotation, and fiv e-field rotation system ).
O b je ct I - E x p e r im e n ta l F ie ld o f W A U in S k ie r n ie w ic e (C en tral P o la n d ) A static experim ent was initiated in 1923 on lessives soils originated from a light clay, with admixture o f sand in its superficial layer. The arable horizon contains 0 .5 0 -0 .7 4 % organic carbon, 0.0 5 0 -0 .0 6 7 % o f total nitrogen, 4 - 1 0 mg P205 and 6 .0 -9 .5 mg K20 in 100 g o f soil. Soil pH (KC1) ranges 5 .5 -7 .0 in
lime-treated plots and 4.0^4.5 in the non-lim ed plots [Góralski 1984].
R ye and potato have been grown in (a) many years monoculture, (b) unrestric ted rotation without legum inous plants and with 75% proportion o f cereals (R0) and (c ) follo w in g the five-field rotation with a legum inous plant and manure w hile grow ing root crops (R5). Additional factor studied was the effect o f lim ing.
O b je ct II - E x p e r im e n ta l F ie ld o f W A U in C h y lic e (C en tral P o la n d )
This experim ent had been established in 1981 on degraded black earth formed from a dusty light clay with sand in its superficial layer; the arable layer contains on the average 0.9% o f organic carbon, 0.079% o f total nitrogen, 20.5 mg P205
and 8.5 mg K90 in 100 g o f soil. Soil pH(KC1) ranges from 5.3 to 5.9 [Gawrońska et al. 1990].
M aize was grown (a) in monoculture lasting up to 9 years; and follow in g two types o f crop rotation: (b) the five-field system with a root crop and a legum inous plant (R5) and (c ) in crop rotation preceded by grass (R CT) - four years o f grass grow ing - winter wheat - maize.
O b je ct III - E x p erim e n ta l F ie ld o f T e c h n ic a l-A g r ic u ltu r a l A c a d e m y o f O ls z ty n in B a lc y n y (N o rth P o la n d )
This experim ent had been started in 1967 in lessives soils developed from a dusty light clay. The arable layer contains on the average 0.74% o f organic carbon, 12.1 m g P20 5 and 9.2 mg K90 in 100 g o f s o il. Soil pH (KC1) is about 6.0 [Zawiślak
et al. 1988].
Ten crop species were cultivated in (a) monoculture (lasting 21 years) and (b) fiv e-field rotation system (R5) with a root crop and a legum inous plant. For the present study m aize, flax, rape and potato were selected. An additional factor studied was the effect o f fungicides.
The study has lasted for three years. Soil sam ples were taken three times at grow ing season from the arable soil layer. In order to isolate humic acids, joint sam ples were prepared.
H um ic acids were extracted from soil with use o f 0.5 M NaOH solution within the atm osphere o f nitrogen. Humic acids were precipitated from the alkaline extract by acidification o f the later to pH = 1. Preparations containing humic acids were rectified from the excess ash com ponents through electrodialysis and then they were dried in a vacuum drier. Elemental com position was determined using the C H N Perkin-Elmer auto-analyzer. The results o f the analyses were recalcula ted considering absolutely dry ashless matter o f humic acids.
Elemental composition ofhumic acids.. 7
Sym bols used throughout the paper:
M2-5 m o n o c u ltu r e la ste d 2 - 5 y ea rs R5 fiv e - f ie ld ro ta tio n s y s te m M3-6 m o n o c u ltu r e la ste d 3 - 6 y e a rs H A h u m ic a c id s
М б-9 m o n o c u ltu r e la ste d 6 - 9 y ea rs H A -M e m a iz e crop h u m ic a c id s M l 9-21 m o n o c u ltu r e la sted 1 9 -2 1 yea rs H A -F fla x crop h u m ic a c id s M66-68 m o n o c u ltu r e la ste d 6 6 - 6 8 yea rs H A -R p rape cro p h u m ic a c id s Rg crop ro ta tio n after g r o w in g grass H A -P p o ta to cro p h u m ic a c id s Ro u n restricted crop rotation sy s te m H A -R rye cro p h u m ic a c id s
RESULTS
Hum ic acids sam pled from in soil under the rye and potato crops in Skiernie w ice (Table 1) contained from 44.95 to 52.45% (w eight per cent) o f carbon, from 4 .9 0 to 5.68% o f hydrogen, from 3.66 to 4.74% nitrogen and fróm 3 7 .6 0 to 45.96% oxygen. The effect o f the system o f cultivation em ployed on elem ental com p osi tion o f H A depended on the crop. In the rye crop, relatively the highest con cen trations o f carbon, hydrogen and nitrogen were found in H A from the five-field rotation system (R5). Sm aller amounts o f these elem ents were found in H A from the m onoculture and much smaller - in the unrestricted rotation (R 0).W hen considering oxygen content, the descending rank was reverse: R5 <- ^ 6 6 - 6 8 < R0.
In the potato crop, the largest carbon amount was found in H A from the m on ocu l ture, follo w ed by the unrestricted rotation and, finally, the fiv e-field system .
The concentration o f H, N and О was reverse and thus the values o f H:C, 0 :C , N:C were increased and the experim ent variants ordered in a descending order were: R5 > M6 6 . 6 8 > R0. In general, humic acids from the rye crop had slightly more
carbon and less - oxygen. The degree o f their particles’ internal oxidation was also lower.
The effect o f lim ing on the elem ental com position was more obvious in H A from the rotation system s as compared with the monoculture. On the average, rye and potato crops lim ing resulted in an insignificant decrease in carbon and hydrogen content, w hile the content o f oxygen and the degree o f H A particles’ internal oxidation increased.
The content o f carbon in humic acids from C hylice varies betw een 4 3 .5 6 - 49.78% ; that o f hydrogen: 4 ,9 1 -6 .1 1 % , oxygen: 4 0 .96 -45 .9 3% ; and nitrogen: 3 .9 9 ^ .5 7 % (Table 2). Hum ic acids from the 9-year old m onoculture contained, com paring with both younger monoculture, and R5 rotation system , less carbon
and nitrogen and more oxygen and hydrogen. As a consequence, the indices: H:C and 0 :C increased their values w hile the index N:C decreased its value. The longer a m onoculture lasted the low er was the degree o f internal oxidation o f H A particles w h ile their formula weight was growing. Different was elem ental com position o f H A sam pled from the R5 and Rg system s: hum ic acids from the R5 variant
contained a relatively highest concentration o f carbon and the least amounts o f oxygen and hydrogen and, consequently, the H:C and 0 :C indices reached minim um in this variant w hile the degree o f particles’ internal oxidation reached its m axim um . H um ic acids from the Rg variant had contrary characteristics: they contained m inim um amounts o f carbon, and relatively highest concentrations o f hydrogen and oxygen. The atomic ratios: H:C, 0 :C and N:C reached in this last
°°
TABLE 1. Elemental composition of humic acids, degree o f internal oxidation and basic formula weight - Experimental Field in Skierniewice
S ystem C o m b i nation С H N 0 H:C 0 : C N :C W C h em ical form ula Form ula w eigh t R ye M66-68 N P K 4 9 .0 7 33 .5 8 5.24' 4 2 .6 9 4.19 2.46 4 1 .5 0 2 1 .0 2 1.27 0 .6 3 0.0 7 3 0 .2 0 2 c I4h17o 9n 343 C aN PK 4 9 .1 7 3 2 .6 2 5.66 44.71 3.82 2.15 4 1 .3 5 20 .5 3 1.37 0 .6 3 0 .0 6 6 0 .0 8 6 ^15H 21^10^ 375 R o N P K 4 7 .8 7 3 1 .7 7 5.68 4 4 .8 2 3.73 2.15 4 2 .7 2 2 1 .2 6 1.41 0 .6 7 0 .0 6 8 0,131 ^15^ 21^ 10^ 375 C aN PK 46.61 32.85 4 .9 0 4 1 .1 5 4 .0 7 2.46 4 4 .4 2 2 3 .5 4 1.25 0 .7 2 0.075 0 .4 0 5 c13h17o 10n 34 7 R 5 N P K 5 2 .2 6 35.0 8 5 .40 4 3.23 4 .7 4 2.74 3 7 .6 0 18.95 1.23 0 .5 4 0 .0 7 8 0 .0 8 2 C13H1907N 298 C aN PK 5 1 .4 2 3 4 .4 0 5.49 4 3 .7 0 4 .2 6 2.41 3 8.83 19.49 1.27 0 .5 7 0 .0 7 0 0.0 7 3 ^ M ^ g O g N 328 Potato M66-68 N P K 5 0 .6 7 33.95 5.48 4 3 .7 7 3.75 2 .17 4 0 .1 0 20 .1 1 1.29 0.5 9 0 .0 6 4 0 .0 8 7 ^ 1 6 ^ 2 (p 9 ^ 37 0 C aN PK 52.45 35 .8 6 5 .12 4 1 .8 8 3 .96 2.31 3 8 .4 7 19.79 1.17 0 .5 5 0 .0 6 4 0.1 2 8 ^ 1 6 ^ 1 8 ^ 9 ^ 368 R o N P K 4 7 .8 7 31.77 5.68 4 4 .8 2 3.73 2.15 4 2 .7 2 2 1 .2 6 1.41 0 .6 7 0 .0 6 8 0.131 C 15H 21°10N 375 C aN PK 46.61 32.85 4.9 0 41.15 4 .0 7 2 .4 6 4 4 .4 2 2 3 .5 4 1.25 0 .7 2 0.075 0 .4 0 5 ^ 13^ 17^ 10^ 347 R 5 N P K 4 7 .7 9 31 .9 9 5.55 44.2 9 4.6 8 2.65 4 1 .9 8 2 1 .0 6 1.38 0 .6 6 0.0 8 3 0.181 c12h17o 8n 303 C aN PK 4 4 .9 5 3 0 .5 6 5.43 43.93 3.66 2 .1 2 4 5 .9 6 2 3 .3 9 1.44 0.7 7 0 .0 6 9 0.301 C 14H 21°11N 379
*In numerator: data in weight per cent; in denominator: atomic per cent as counted regarding ashless matter. ( 2 - 0 + 3- N ) - H „ „ XI 4 .
W = --- --— C, H, N, О in atomic per cent
A . K u s iń s k a
Elemental composition of humic acids.. 9
T A B L E 2. E lem en tal c o m p o sitio n , degree o f internal oxidation and basic form ula w eig h t o f hu m ic acid s under m aize sp ec ies - Experim ental F ield in C h y lice*
S y s tem С H N 0 H:C 0 : C N :C W C h em ical form ula Form ula w eig h t Мб-9 4 6 .0 5 3 0 .8 7 5 .58 4 4 .5 3 3 .99 2 .25 4 4 .3 8 2 2 .3 5 1.44 0 .7 2 0 .0 7 3 0 .2 2 4 C14H20O10N 3 6 2 .0 Мз-6 4 8 .1 8 3 2 .8 7 5 .3 0 4 3 .0 0 4 .4 6 2 .6 2 4 2 .0 6 2 1 .5 0 1.31 0 .6 5 0 .0 7 9 0 .2 3 9 C13H16O8N 3 1 4 .0 M2-5 4 7 .4 9 3 2 .3 8 5.3 2 4 3 .1 7 4 .5 7 2 .7 0 4 2 .6 2 2 1 .7 5 1.33 0 .6 7 0 .0 8 3 0 .2 4 4 C12H16O6N 2 7 0 .0 Rs 4 9 .7 8 3 4 .9 0 4.91 4 0 .9 6 4.35 2 .6 0 4 0 .9 6 2 1 .5 3 1.17 0 .6 2 0 .0 7 4 0 .2 8 3 C13H16O8N 3 1 4 .0 R g 4 3 .5 6 2 8 .2 0 6 .1 1 4 7 .0 9 4 .4 0 2.41 4 5 .9 3 2 2 .3 0 1.67 0 .7 9 0 .0 8 5 0 .1 6 8 C12H20O9N 3 2 2 .0 * R em arks - se e T able 1.
variant highest values as compared with HA from the remaining objects w hile the energy o f their particles’ internal oxidation was the low est.
H um ic acids from the B alcyny soil (Table 3) contained 4 1 .9 1 -5 1 .7 0 % carbon, 5.2 7 -6 .5 4 % hydrogen, 3.89-4.75% nitrogen and 3 8 .93 -4 7.6 5% oxygen. In this experim ent, the effect o f cultivation system , crop species and fungicides use on the elem ental com position o f humic acids was studied. An explicit differentiation o f elem ental com position was observed, regardless the system o f cultivation, in H A originated in soils under different crops. Considering the mean content o f carbon, hum ic acids may be ordered as follow s (descending order): H A -F > H A -C M e > H A -R > H A-P (50.7 > 50.2 > 4 6 .1 > 44.1, respectively). The order regarding the content o f hydrogen, nitrogen and oxygen was quite reverse (H: 5.4 < 5.5 < 6.0 < 6.1; N: 4.1 < 4.2 < 4.3 < 4.4; and O: 39.8 < 4 0 .0 < 43 .6 < 45.4). W h ile analyzing the above data, one may com e to a conclusion that there are two similar groups o f humic acids: one com prising from the soil under flax and m aize crops and the other under rape and potato. The mean values o f the H:C, 0 :C , N:C indices are 1.3, 0.6 and 0.075 respectively for the first group and 1.6 , 0.75, 0.083
for the other. The effect o f cultivation system on the HA elemental com position in the two groups is, also, different. M aize and flax crops grown in m onoculture have caused a decrease in carbon and hydrogen content in HA; on the other hand, nitrogen and oxygen concentrations were increased, as compared with the rotated variants. The H:C and N:C indices had similar values in HA extracted from the soils o f the two system s o f cultivation, w hile the 0 :C index had som ew hat higher values in H A from the monoculture system . In the second group o f humic acids, grow ing rape in monoculture has increased the content o f carbon and nitrogen; and it has decreased the concentration o f hydrogen and oxygen. The H:C, 0 :C and N:C indices were lowered as compared with the monoculture. G rowing potato crop in m onoculture did not influence the carbon amount in HA; but the con cen tration o f hydrogen and nitrogen was low er and that o f oxygen - higher, com paring H A from .the rotation system s. G rowing crop plants in m onoculture resulted in
10 A. Kusińska
T A B L E 3. E lem en t co m p o sitio n , degree o f internal oxidation and basic form ula w eig h t o f hu m ic acids - A gricultural Experim ental Station B a łcy n y
S y s tem F u n g i cid es* С H N 0 H:C 0 :C N :C W C h em ical form ula F orm ula w eig h t M a ize Mi9-21 + 4 9 .5 7 33777 5.27 42775 4.41 2 Ш 4 0 .7 5 2 0 .8 5 1.26 0 .6 2 0 .1 0 7 0 .2 0 1 C13H16O8N 3 1 4 - 5 0 .1 0 3 3 .2 3 5.65 4 4 .5 9 4 .1 8 2 3 T 4 0 .0 7 19.87 1.35 0 .6 0 0 .0 7 0 0 .0 6 3 C14H19O9N 345 R5 + 4 9 .9 3 Т Ш 5.48 43777 4 .3 5 Z 4 9 4 0 .2 4 Ж Т 7 1.31 0.61 0 .0 7 4 0 .1 2 7 C13H18O8N 3 1 6 - 5 1 .2 9 Ж 5.58 4 4 .1 8 4 .0 9 3 9 .0 4 19.46 1.30 0 .5 7 0 .0 6 8 0 .0 4 9 C15H19O8N 341 Flax M l 9-21 + 4 8 .8 9 T L 9 3 5.45 43777 4.31 T Ä 3 4 1 .3 5 Ж Я 7 1.33 0.63 0 .0 7 4 0 .1 5 9 C14H18O9N 3 3 4 - 5 1 .5 6 3 4 .6 8 5.41 4 3.31 3 .8 9 Т 2 Б 3 9 .1 4 19775 1.25 0 .5 7 0 .0 6 5 0 .0 8 6 C15H19O9N 3 5 7 R5 + 5 0 .6 8 Т Ш 5 5 .6 0 4 4 .2 6 4 .1 4 Z 3 9 3 9 .5 8 T977Ü 1.32 0 .5 9 0.071 0 .0 6 9 C14H19O8N 3 2 9 - 5 1 .7 0 33779 5.38 4 3 .2 0 3 .9 9 Z 3 5 3 8.93 19.66 1.24 0 .5 7 0 .0 6 8 0.091 C15H18O8N 3 4 0 R ap e M19-21 + 5 0 .2 9 3 3 ^ 3 5.51 4 3 .9 0 4.21 Z 4 T 3 9 .9 9 2 0 .0 6 1.31 0 .6 0 0 .0 7 2 0 .1 0 3 C u H is O s N . 3 2 8 - 4 9 .2 0 3 Z 4 9 5.71 4 4 .8 5 4 .5 0 2 3 4 4 0 .5 9 2 0 .1 3 1.38 0 .6 0 0 .0 7 2 0 .0 9 3 C13H18O8N 3 1 6 R5 + 41.91 Ж 7 0 6 .3 6 4 8 .2 8 4 .0 8 T 2 2 4 7 .6 5 7 Z S Ö 1.81 0.85 0 .0 8 3 0 .1 4 9 C12H22O10N 3 4 0 - 4 3.11 TT7Z0 6.47 4 8 .6 4 4.31 Z 3 5 46.11 2 1 .1 8 1.79 0 .78 0 .0 8 6 0 .0 2 8 C12H21O9N 32 3 Potato M l 9-21 + 4 3 .8 4 Ж Б 7 5.95 4 6 .3 4 4 .5 8 T 5 9 4 5 .6 3 2 2 J 9 1.62 0 .7 9 0 .0 9 0 0 .2 1 7 Ci 1H18O9N 2 0 8 - 4 4 .5 2 2 9 .4 7 5.78 4 5.51 4 .1 8 T I E 4 5 .5 2 U M 1.54 0 .7 7 0.081 0 .2 3 4 C12H19O10N 3 3 7 Rs + 4 1 .9 5 2 6 .3 6 6 .5 4 Ш П 4 .7 5 2 3 7 4 6 .7 6 7ZJ55 1 .8 6 0 .8 4 0 .0 9 7 0 .1 0 6 C10H19O9N 2 9 7 - 4 6 .0 7 Ж 7 Ч 6 .08 4 6 .7 8 4 .1 2 Г 2 5 4 3 .7 3 2 1 .1 8 1.57 0.71 0 .0 7 6 0 .0 7 8 C13H21O9N 3 3 5
Elemental composition of humic acids...
_______________77
F IG U R E 1. D iagram s o f m ean valu es o f atom ic ratio H:C and 0 : C in hum ic acid s in three experim en ts: Ch - C h y lice, В - B a łcy n y , SK - S k iern iew ice
elevation o f the degree o f internal oxidation o f H A particles. The application o f fungicides increased the level o f carbon and oxygen and (insignificantly) also nitrogen in HA. Thus, increased becam e, even though not significantly, the atom ic ratios. The use o f fungicides resulted, also, in increased energy o f internal oxidation o f particles and - in lowering o f H A particles formula w eight. The effect o f fungicides was comparable in the both system s o f cultivation.
In order to compare the elem ental com position o f soil from the three experi mental centers, and to assess the effect o f crop cultivation system on the structure o f hum ic acids, diagrams were prepared illustrating the atom ic ratios H:C and 0 :C (Fig. 1).
Hum ic acids from the soil under monoculture as compared with the rotation system s were characterized by lower values o f H:C and 0 :C indices. Hum ic acids extracted from soil under monoculture contained more aromatic com ponents. The ever highest discrepancy in H:C between monoculture and a rotation system was observed in the C hylice field. The actually high values o f H:C in the R(T variant
12 A. Kusińska
F IG U R E 2. D iagram s o f m ean values o f atom ic ratio H:C and 0 : C in hum ic acid s extracted from soil eith er under m onoculture (M ) or under crop rotation (R)
F IG U R E 3. D iagram o f m ean valu es o f atom ic ratio H:C and 0 : C in hum ic acid s extracted from soil under different crops: flax (F), rye (R), m aize (M e), potato (P) and rape (R p)
Elemental composition ofhymic acids.. 13
indicate that these hum ic acids contain mainly the ring carbohydrates. The relati v ely m ost aromatized were hum ic acids from the soil o f Skierniew ice. H um ic acids from the B alcyny field were intermediate. This differentiation may have its source, excep t o f crop sp ecies, in the environmental conditions that differed to som e extent betw een the objects and, also, in the age o f particular experim ents.
Figure 2 show s diagrams o f H:C and 0 :C in hum ic acids extracted from soil o f particular crops grown either in m onoculture or fo llo w in g a rotation system . In m onoculture, the H:C value was decreased, regardless o f the crop sp ecies, yet the decrease was different. The least was the difference in H:C betw een monoculture and a rotation system when crops o f rye, flax and maize were grown; the difference w as relatively the highest w h ile grow ing rape. It was intermediate in the case o f potato crops. In the diagrams presented, visible is also the effect o f crop sp ecies on the elem ental com position and structure o f hum ic acids (Fig. 3). The m ost aliphatic structure was that in humic acids from the variants with potato and rape crops grown follow in g a rotation system . The mean values o f H:C and 0 :C indices indicate that, regardless the cultivation system em ployed, grow ing o f flax and rye results in a more profound aromatization o f humic acids w hile grow ing o f potato and rape contributes to a higher aliphatization. Growing o f corn gives intermediate results considering the structure o f humic acids.
DISCUSSION
The presentation o f elem ental com position o f hum ic acids using atom ic per centage and particularly so - atom ic ratios H:C and 0 :C gave im proved p o ssib i lities to interpret the results. Numeric values o f H:C atom ic ratio allow for the assessm ent o f hum ic acids structure, because those values are inversely proportio nal to the degree o f aromatization o f organic com pounds. The aromatic rings coupled with aliphatic chains containing up to 1 0 atoms o f carbon correspond to
H:C ratio value from 0.7 to 1.5. The ratio reaches from 1.5 to 1.7 in cy clic hydrocarbons, and in chain hydrocarbons it is near 2 [van Krevelen 1950]. T hese indices were used w hile studying humus by V isser [ 1983], K awatsukaet al. [1978], Turski [1988], G onet [1989], G ołębiow ska et al. [1990].
In this paper, the values o f atomic ratios H:C and 0 :C as reported by van K revelen proved to characterize w ell enough the humic acids o f different grow ing system s and from under different crop sp ecies. The diagrams (Figures 1 - 3 ) suggest that m onoculture acts towards aromatization o f hum ic acids particles in grow ing o f any crop sp ecies. This effect was the least in the case o f grow ing rye: the H:C ratio in hum ic acids is extrem ely variable and the 0 :C ratio has the sam e value both in hum ic acids from m onoculture and those from rotated crops. A lso, G ołęb iow ska et al. [1990] did not find significant differences in elem ental co m position o f H A from a rye crop grown in m onoculture and that grown under rotation. The use o f another extractant by the author o f this paper resulted in obtaining higher values o f H:C ratio. Flis-Bujak [1978] found rather small d iffe rentiation in the elem ental com position o f H A from crop rotations o f varying share o f cereals. This last-m entioned author reports C:H ratio values betw een 1.12 and 1.22 for soils under rotated crops and betw een 1.15 and 1.42 - for cereal m on o culture; som e tendencies may be detected from these data in H A structure, the author explains this fact by „lower hydrogenation” o f hum ic acids particles.
14 A. Kusińska
The aromatization o f HA particles observed under monoculture o f crop plants depends on increased portion o f aromatic com pounds rather than a higher con cen tration o f aromatic rings. This can be concluded from the obtained in this paper values o f the H:C ratio exceeding 1 in all preparations o f hum ic acids sam pled from monoculture.
CONCLUSIONS
1. The use o f atomic ratios values: H:C, 0 :C and N:C for interpretation o f hum ic acids elem ental com position results proved valuable for com parison purposes in the professional rotation system s.
2. The elem ental com position o f humic acids was dependent on cultivation system , the species o f crop plant as well as environmental conditions.
• Humic acids in the soils under monoculture are characteristic o f lower values of H:C and 0:C ratios and thus - increased portion of aromatic elements. • Mean values of H:C and 0 :C ratios as found for humic acids in soil under
different crops indicate that, regardless of the cultivation system used, flax and rye crops cause the origin of more aromatized humic acids, while growing of potato and rape causes a more profound aliphatization o f humic acids ; growing of com results in an intermediate characteristics o f humic acids structure. • The effect of fungicides on elemental composition was similar both in mono
culture and in crop rotation systems; application of fungicides resulted in increased proportion of carbon, oxygen and insignificant increase in nitrogen, and consequently a slight increase in the value of atomic ratios: H:C, 0 :C and N:C.
• The effect of liming on elemental composition of humic acids was more visible in crop rotated soil than in soil under monoculture. The application of lime resulted in insignificant drop of carbon and hydrogen content; the content of oxygen and degree of internal oxidation of humic acids particles also incre ased.
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G A W R O Ń S K A A. et al. 1990: L ong-term m onoculture o f m aize versus b io lo g ic a l properties o f soil. A g ro k e m ia es tal a j tan, 39 (3 -4 ): 4 3 0 .
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Elemental composition of humic acids.. 15
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16 A. Kusińska
A. Kusińska
SKŁAD PIERWIASTKOWY KWASÓW HUMINOWYCH
JAKO WSKAŹNIK W OKREŚLENIU ICH WŁAŚCIWOŚCI
I STRUKTURY
Katedra Gleboznawstwa SGGW w Warszawie
STRESZCZENIE
Badano w pływ różnych system ów uprawy niektórych gatunków roślin na skład pierw iastkow y kw asów hum inowych. Żyto, ziem niaki, kukurydza, rzepak i len uprawiano w monokulturze i w trzech typach zmianowań: zm ianow anie dow olne bez obornika i rośliny m otylkow ej, zm ianow anie 5-p olow e z obornikiem pod ok opow e i z rośliną m otylkow ą i zm ianow anie po trawach (4-letnia uprawa traw nasiennych). Próby gleby do badań kw asów hum inowych pobrano z trzech pól dośw iadczalnych, a m ianow icie ze Skierniew ic, Chylić i z B ałcyn (k. O lsztyna). W interpretacji w yników składu pierw iastkow ego KH zastosow ano wartości ilorazów atom ow ych H:C, 0 :C i N:C. K wasy hum inowe z gleb spod upraw m onokulturow ych w porównaniu do zm ianowań charakteryzują się niższym i wartościam i ilorazów atom owych H:C i 0 :C , co św iadczy o w iększym udziale w ich strukturze elem entów arom atycznych. Uprawa żyta i lnu niezależnie od system u uprawy w pływ a na tworzenie się KH bardziej zarom atyzowanych, nato miast uprawa ziem niaków i rzepaku powoduje tworzenie się kw asów hum ino w ych z dużym udziałem zw iązków alifatycznych. Uprawa kukurydzy zajmuje m iejsce pośrednie w opisanych strukturach kw asów hum inowych.
D r hab. A lin a K u siń sk a D e p a rtm e n t o f S o il S cien ce
W a rsa w A g ricu Itural Un i ve rs i ty (S G G W ) R a k o w iec k a str. 2 6 /3 0 , 0 2 -5 2 8 W arsaw , P o la n d
