f t Ö C Z N i k l G L E ß O Z I S i A W C Z E , 'Г. X X X I I , NH 3, W A R S Z A W A 19Ö1
U R SZ U L A P O K O JSK A
THE EFFECT OF UREA AND POTASSIUM CHLORIDE FERTILIZATION ON THE CATION-EXCHANGE PROPERTIES
OF THE XEROMOR HUMUS IN LICHEN PINE FOREST
(CLAD O N IO -PIN ETU M f
D ep a rtm en t o f S o il S cien ce, In stitu te o f B iology, C op ern icu s U n iv ersity o f Toruń
IN TRO DU CTIO N
A erial fertilization of pine forests growing on poor, often degraded soils, derived from sands has been carried on the north of Poland for the last few years. Due to very low clay fraction content in those soils, th eir sorption capacity depends m ostly on the quantity and quality of humus. It is on the sorption properties of the hum us th a t depends the soil capacity for retention of n u trien ts introduced w ith the m ineral fertilizers and for securing them against washing them away from the upper p art of the soil profile. On the other hand, the m ineral fertilizers m ay have a modifying effect on the sorption properties of the humus. This effect m ay be connected w ith a considerable increase in salt con centration in the soil solution or w ith altered soil reaction.
The present work was aimed at studying the effect of urea and KC1 fertilization on the cation-exchange properties of the xeromor humus.
C H A R A C T E R IST IC S OF ST U D Y AREA
The investigations were carried out in the experim ental area of the D epartm ent of Soil Science, Institute of Biology, Copernicus U niversity in the Forest D istrict Lubnia (Forest Inspectorate Przymuszewo) in Bory Tucholskie (Tuchola Forests). The soils occurring there are ru sty podzolized soils derived from deep loose sands The humus of these soils has been referred, in accordance w ith the classification of P r u s i n
132 U. P ok ojsk a
k i e w i c z [7], to the xerom or type, subtype dis-mor (with signs of degradation). The organic horizon (AoL+ A oF+ A oFH) averages 4 cm in thickness. The hum us horizon (Alp), about 10 cm in thickness, bears traces of form er ploughing. In its upper portion occurs subhorizon A le (1—2 cm) w ith sign of podzolization. The hum us supplies in the particu lar horizons of the profile tare as follows : A oL 11.6 t/h, in A ^F 7.3
t/ha, in Aofh 9.9 t/ha and in A lp 30 t/ha. The experim ental area is grown
w ith lichen pine forest (Cladonio-Pinetum).
The experim ental area was divided into plotsy each differently fer tilized : plot “K ” was fertilized w ith KC1, plot “N ” w ith urea, plot “N + K ” w ith urea and KC1 and plot “O” was control. The treatm en t was repeated twice : in June 1976 by aeroplane and in A pril 1977 by hand, except for plot “K ”, which was fertilized by hand only. The doses applied at aerial fertilizing were about 50 kg of each fertilizer per hectare, and at hand fertilizing 200 kg/ha. The m easurem ents of pH in horizon Ao after treatm e n t w ith urea (plot “N ” and “N + K ”)
carried out by P r u s i n k i e w i c z and J ó z e f k o w i c z [8] revealed
a considerable drop in hum us acidity (by more th an 2 pH units). 4-6 m onths after the treatm ent, the hum us acidity retu rn ed to about starting value.
M ETH OD S
2 and 14 m onths after hand treatm ent, hum us samples were taken for analysis from horizons A 0 (with division into subhorizons) and A lp. Air dried samples were homogenized and strained through a 1 mm sieve. Hygroscopic w ater, roasting losses and pH in distilled w ater and 1 N KC1 were determ ined in the samples.
Exchangeable m etallic cations (Ca, Mg, K, Na) were determ ined in
1 N CH3COONH4 extract, pH 7, exchangeable NH+4 in 10e/o NaCl extract,
pH 2.5 ;[3]. The hydrolytic acidity (Hh) was determ ined by K appen’s m ethod using 1 N (CH3COO)2Ca, pH 8.2. The sum of exchangeable basic cations and Hh was accepted as the total cation-exchange capacity (CECt) revealed at pH 8.2. Moreover, in samples from the control plot, exchangeable H+ and Al3+ constituting jointly the exchange acidity, w ere determ ined in BaCl2 ex tract by the potentiom etric titratio n m ethod [4]. The sum of exchangeable basic cations and exchange acidity was regarded as the real cation-exchange capacity (CECr). D irect hum us CEC determ inations were also made at pH 2.0, 4.0, 6.0 and 8.0 applying repea
ted saturation of samples w ith strongly buffered barium solution [2].
The effect of the fertilization on the cation binding energy of the hum us was tested by extracting the samples w ith distilled w ater and w ith 0.03 N CH3COOH.
Ca, К and Na were determ ined by flam e emission spectrophotom etry, Mg by AAS method, and NH+4 by distillation w ith NaOH.
E ffe c t o f urea and p otassiu m ch lorid e on CEC of hu m u s 133
R E SU L T S A N D D IS C U S S IO N
C a t i o n - e x c h a n g e p r o p e r t i e s o f t h e x e r o m o r h u m u s (n o n - f e r t i l i z e d )
The specific properties of xerom or hum us are presented in Table 1 and 2 (plot “O”). The hum us under study is highly acid. The percentage base satu ration (V) calculated in relation to CECt is very low and
decreases from subhorizon A ob (ca 18%) to horizon A lp (ca 6.5%). The
composition of exchangeable basic cations is dom inated by calcium (ca 70%). The percentage of Mg2+, K + and NH+4 ions generally ranges from 7 to 10%. The percentage of Na+ is the lowest (generally 2-4%). In horizon A lp the percentage of Ca2+ decreases in favour the rem aining cations.
The CEC of the hum us under study strongly depends on the hum us reaction (Fig. 1). The shape of the graphs of CEC as a function of pH
Fig. 1. T he CEC of the xerom or typ e hu m u s as a fu n c tio n of pH
suggests th a t the character of the acid groups deciding on the sorption capacity of hum us changes gradually from strongly acid groups, which ionize at pH 2, to groups whose acid character is only very slightly
m arked and which ionize only in alkaline reaction (pH 8).
Of course, in n atu ral conditions the cation-exchange capacity of strongly acid hum us of the xerom or type does not correspond to the
со l ' a b l e 1 С a t i. о n - о X с h : i n , • p r o p e r t i o ; : o f x o r o m o r h1 un i j :i 2 mci'; i ï i a f U*:r Го r t i U :vi trion
/me an v . t l u o r , p e r 1 0 0 g ma rus о Г a s h l o n r ; o r g a n i c « u b n l a n c o / P l o t i i o r i z o u R o a n t i n g ]0Ü3C3 % pH E x c h a n g o n b J e b a u le*, c a t i o n u h n u ;/ I 0 0 g i'K C h J i ru* / 1 0 0 g V uJ L - • 100% r:icct C * К N a 4 , l 4 m e / 1 0 0 g rV? r c e r i t a ' ' “ Г о a c t i o n h2o K C l т с / 1 ti o r g a n i c з и Ь в t a n c e C a M e К I J a N H „ ••0" A o L 9 4 . 7 4 . 0 7 3 . 1 5 1 4 . 0 1 . 5 1 . 8 0 . 6 1 . 8 1 9 . 7 7 1 0 9 \ 9 i c a . ; 1 1 8 . 2 AoF 9 1 . 5 3 . 7 5 2 . 7 7 1 2 . 4 1 . 4 2 . 0 0 . 8 1 . 7 1 3 . i 6 B 0 11 4 9 1 ; I . 4 1 4 ) . 7 1 2 . 2 AoFI1 4 6 . 7 3 . 4 6 2 . 6 9 1 5 . 2 1 . 8 1 . 9 1 . 0 1 . 8 2 1 . 7 7 0 8 9 S a 166.0 W 7 . 7 1 1 . 6 A 1 P 1 . 9 6 4 . 1 1 3 . 5 0 6 . 9 1 . 7 1 . 9 1 . 4 4 .9 16.8 41 1 0 11 8 2 9 24 3.6 2 о 0 . 4 6 . 4 "К" A o L , 9 2 . 9 4 . 0 9 2 . 9 9 1 1 . 0 1.5 4 . 7 0 . 6 1 . 6 1 9 . 4 5 7 8 2 4 3 8 1 0 2 .1 i ? i . 5 16.0 AoF 8 8 . 0 3 . 7 9 2 . 6 3 1 1 . 5 1 . 4 5 .0 0 . 7 1 . 4 2 0 . 0 50 7 25 3 7 141.6 16 1 . b 12.4 AoF H 43. 1 3.54 2.61 16.3 2 . 5 5 . 2 1.4 1.4 2 7. 4 61 9 19 5 5 162.4 ;'*0').0 13.1 A 1 P 2.11 4.44 3.30 9.8 2.1 2 . 3 1.4 4 . 2 19.8 49 11 12 7 21 2 2 3 . 4 2 4 3 . 2 8 . 1 "N ” AoL 9 4 .9 5 .3 3 4 . 1 3 14.4 1.8 1.8 0 . 7 19.0 37. 7 38 5 5 2 50 6 3 . 7 101.4 37. 2 AoF 8 6 . 7 4.96 3. 49 14.0 1.7 1.7 1. 2 22.1 4 1. 5 36 4 4 3 53 103.7 150.2 27 .6 AoF H 39.0 3.65 2. 6 9 20. 2 2 . 9 1.8 1. 2 12.1 38.2 53 8 5 3 32 13 1.3 2 2 0 . 0 17. 4 A 1 P 1.37 4.25 3.49 12.4 2 . 4 2 . 4 2 . 2 6 . 6 2 6 . 0 43 9 9 8 2 5 ?•; 4. 5 2 9 0 . 5 9 . 0 "N+K" AoL 9 5 .0 4.82 3.59 12.1 1.5 9 . 2 1.2 6 . 7 30.7 39 5 30 4 22 7-3.9 106.6 28 .8 AoF 8 9 . 8 4.6 3 3.20 10.5 1Л 12. 8 1 . 3 0 . 5 34.4 30 4 37 4 25 109.8 144.2 2 3. 3 AoF H 48. 6 4.25 2 .9 3 12.0 1 .3 9 . 8 1 . 2 7 . 5 31.8 33 4 31 4 24 163.7 195.5 16. 3 A 1 P 1.48 4.46 3 . 3 7 15.2 2 . 2 6 . 8 2.1 8 . 2 34 .5 4 4 6 20 6 24 307.6 342.1 1 0 . 1 U P o k o js k a
E x c h a n g e ab le b a r.ic c a t i o n a „ r .^r _ a , w о PI« * H o rizo n П о « « » , p«______ С , I Mg I К I Па К I S I ^ % H?0 KC1 m e/100 s o rg a n ic s u b s ta n c e m e/100 g Ch Mg К Па NH^ AoI 96 . (■ 3.92 3*02 10.4 1 .5 1 .5 0 .4 1 .2 1 5 .0 69 Ю 10 3 9 6 5 .9 8 0 .9 1 9 .5 AqF 9 1 .F 3 .8 3 2 .3 8 1 1 .7 1 .6 1 .2 0 .4 1 .2 1 6 . 1 73 10 7 2 7 9 6 . I 112.2 1 4 .3 Аорн 6 5 . Ł 3.46 2 .6 3 1 2 .3 1 .7 1 .6 0 .7 1 .0 1 7 .3 71 10 9 4 6 1 4 5 .5 162.8 1 1 .9 А1г 2 .1 1 4.2 3 3 .5 3 0 .1 2 .1 1 .8 1 .0 2 .9 1 5 .9 51 13 «1 6 18 2 2 3 .5 2 3 9 .4 6 .6 "Kr AoJ 9 4 . c 3.86 . 3. 07 0 . 7 1 . 4 1. 7 0 . 3 1.6 13.7 64 10 12 2 12 8 4 . 1 97. 8 14 . 0 A ^ 8 5 . 7 3.76 2 . 7 6 10.1 1 . 4 1 . 3 0 . 4 1. 9 15.1 67 9 9 3 13 12 4. 0 139.1 10.3 AoPH 53 .' 3.62 2 . 6 9 1 2. 7 1 . 7 1.6- 0 . 8 1.2 18 .0 71 9 9 4 7 157.1 175.1 1 0 . 3 A1p i . 9 ° 4.18 . 3.5 2 7 . 5 1 . 9 3 .0 1 .0 3 .3 16.8 45 11 18 6 20 2 1 7 . 4 2 3 4. 2 7 .1 «N* AoL 9 6 .c 4.2 0 3.3 1 12.1 1 .9 1 .6 0 .4 1 .6 1 7 .6 69 11 9 2 9 5 9 .5 7 7 .1 2 2 .8 AoF 9 0 .p 3.94 2 .9 4 11.7 1 .9 1 .3 0 .5 1 .8 17.1 63 10 8 3 10 8 7 .3 104.4 16 .4 AoPII 5 7 ,3 3,52 2 ,7 1 12#2 1,6 0 ,8 1 ,8 1 8 ,0 68 9 9 4 10 1 3 4 .8 152.8 11.8 An 1 .4 3 4 .3 3 3 .8 8 11,1 2 .4 2 .5 1 .5 2 .2 1 9 .7 56 12 13 0 11 1 9 9 .8 2 1 9 .5 9 .9 ■ M * AoT 96» 1 4.2 5 3 .3 3 1 2 .4 2 .1 2 .4 0 .4 1 .3 : 19.1 65 11 13 2 9 5 3 .5 7 2 .6 2 6 .4 A0> 8 8 .1 4 .0 9 2 .9 6 1 3 .6 1 .7 3 .7 0 .6 2 .1 2 1 .7 63 8 17 3 10 9 0 .7 11 2 .4 2 3 .9 aoFH 4 5 - 4 3*35 2 *82 13*° 4 *9 1*° 2 3 *1 60 T 21 4 8 146.9 170 .0 i3 .6 A ^ 1 .6 ? 4 .3 6 3 .6 9 1 1 .2 2 .2 4 .0 1 .3 3 .4 2 2 .1 51 10 18 6 15 2 2 1 .4 2 4 3 .5 C a tio n -o x c h a n g a p r o p e r t i e s оГ x o ro n o r humu» 14 m o n th s a f t e r f e r t i l i z a t i o n /m ean v a lu o n p e r 100 g o f a sh le a t? o rg a n ic s u b s t a n c e / T a b l e 2 E ffe c t of ur ea an d p o ta ss iu m c h lo rid e on C KC of h u m u s 1 3 5
136 U. P ok ojsk a
T a b l e 3
E x c h a n g e ab le b a s i c and a c i d i c c a t i o n s and CECr and Vr v a lu o s / d a t a f o r c o n t r o l p l o t i n m e/100 g o r g a n ic s u b s t a n c e /
H o riz o n s He x A1ex CECr - S+Hex +A1ex VT = _S__«100JS C£CV
AoL 1 9 . 7 5 . 1 5 - 3 30.1 6 5 .4
AoF 1 8 . 3 8 . 1 5 . 6 3 2 .0 5 7 .2
AoFH 2 1 . 7 11 < 3 8 . 4 4 1 .4
A1P 1 6 . 8 7 . 6 3 7 . 1 6 1 .5 c- i » J
soil pH. CECr can be calculated as the sum of exchangeable basic cations (S), and exchangeable hydrogen (He*) and alum inium (Ale> ). The CECr of the xerom or hum us (Tab. 3) is 3-5 times lower than the CECt (Table
1). The percentage base satu ratio n (Vr) calculated in relation to CECr
is therefore considerably higher th a n value V (Table 1). Leaving out of account such g reat differences in the assessm ent of cation-exchange capacity of the hum us would lead to grave errors. The necessity of distinguishing betw een CECr and CECt has been pointed out by other authors [1, 9].
A nother notew orthy observation is the exchangeable alum inium content in the hum us samples. The predom inance of A lc* over the rem aining cations in horizon A lp is in line w ith the predom inant role of exchangeable A1 in strongly acid soils found by U l r i c h [0]. In the organic horizon A 0y on the other hand, the Ale£ fraction is much lower.
E f f e c t o f K C 1 f e r t i l i z a t i o n
One application of KC1 on plot “K ” at a rate of 200 kg/ha effected the least changes in the hum us sorption properties compared w ith the other fertilized plots.
Two m onths after fertilization in horizon A 0 exchangeable K+ avera ged 2.5 the initial content (Table 1). In horizon A ip the increase in K+ content was m uch smaller. Moreover, the hum us from plot “K ” showed a slight decrease in Ca2* and NH+4 content. The la tter observation as well as the fact th a t the sum of exchangeable basic cations increased b u t very slightly after fertilization suggest th a t a large p art of K+ have been adsorbed by the humus at the expense of elim inating other basic cations. The percentage base saturation2 of the hum us in plot “K ” rem ained v irtu ally the same as in control.
2 S in ce in som e of the plots treated, hum us pH increased considerably, the p ercen ta g e b ase satu ration w a s a lw a y s ca lcu la ted in rela tio n to CECr
E ffect of urea and potassiu m ch lorid e on CEC of hum us 137
The fertilization did not change the hum us reaction to any signific ant extent (Table 1). Consequently, its CECr did not significantly change. A comparison of the num ber of K+ equivalents introduced w ith the fertilizers (ca 2680 e./ha) w ith the num ber of those retain ed in A 0 and
A lp horizons (ca 1000 e./ha) suggests th a t the acid xerom or hum us was
unable to adsorb even the com paratively low dose of potassium applied on the plot.
A replication of the analyses 14 m onths after fertilizing (Table 2) showed no longer distinguishable differences between control hum us and hum us from plot “K ”. Since the soils under study are deficient in potassium, its loss from the adsorbing complex is probably due m ainly to it being taken up by plant roots. The variation in exchangeable potassium content in the hum us under study at different times after treatm en t has been presented in Fig. 2.
F ig. 2. C h an ges in e x c h a n g e a b le K+ co n ten t in hu m u s u n der stu d y e ffe c t
by K C1 fertilization 1 — e x c h a n g e a b l e K + i n p l o t , , 0 ” a t tw o t i m e s ; e x c h a n g e a b l e K + i n p l o t ,,K ” : 2 — tw o m o n t h s a f t e r f e r t i l i z a t i o n , 3 — 14 m o n t h s a f t e r f e r t i l i z a t i o n F ig . 3. C h a n g e s in e x c h a n g e a b le N H +4 c o n te n t in h u m u s u n d e r s tu d y e ffe c te d b y u re a f e r t iliz a t io n 1 — e x c h a n g e a b le N H +4 in p lo t , , 0 ” at tw o tim es; e x c h a n g e a b le N H +4 in plot ,.N ” : 2 — tw o m o n th s a fte r fe r tiliz a tio n , 3 — 14
m o n th s a fte r fe r tiliz a tio n
E f f e c t o f u r e a f e r t i l i z a t i o n
Two m onths after fertilization the effects of urea treatm en t are very clear (Table 1). Increase in pH was observed compared w ith control : in the surface horizons (AoL and A oF) by more than one unit, in the deeper horizons (A oFH and A lp) somewhat less. Compared w ith the high
pH values found directly after applying urea [8], two months after fertili
zation it is considerably lower, w hich indicates a slow, re tu rn of the reaction to the pre-treatm en t state. This transitional increase in hum us pH ,however, seems very im portant for CEC of the humus.
1 3 8 U. Pokorska
Urea fertilization effected a great (average 10-fold) increase in
exchangeable NH+4 content (Fig. 3). The content of the rem aining
exchangeable basic cations did not significantly change. This suggests th a t NH+4 ions did not displace the rem aining exchangeable basic cations, but thanks to increased hum us pH and to the rise in ionization degree of acid groups, they took the place of hydrogen. Consequently, the percentage base saturation of the humus from plot “N ” averages twice th a t of nonfertilized humus.
Considering the fact th a t the loss of nitrogen in the form of gaseous
ammonium on plot “N” am ounted to ca 25% [8], it has been calculated
th a t the applied dose of urea corresponds to ca 5000 equivalents of
NH+4/ha. The am ount of exchangeable NH+4 determ ined in A 0 and A lp
am ounts to 5014 e./ha. In th a t case the am ount of nitrogen introduced into soil and th a t retained by the hum us surprisingly agree.
The analyses made 14 m onths after fertilization (Table 2) show only
slight differences in hum us properties from plots “N ” and “O” . The exchangeable NH+4 content is b u t very slightly higher compared w ith control (Fig. 3). Since after urea fertilization no fixation of nitrogen
by the hum us under study was found [6], it should be presum ed ûhat
the m ajor p art of th a t elem ent had been taken up by plants during the year and incorporated in the biological cycle.
E f f e c t s o f j o i n t K C 1 a n d u r e a f e r t i l i z a t i o n
A fter applying joint KC1 and urea fertilization (plot “N + K ”) it was observed th a t pH, the sum of exchangeable basic cations and the per centage base saturation increased m arkedly, though som ew hat less than in plot “N ” (Table 1). That was due solely to the effect of urea, since KC1 fertilization does not cause such changes in humus. Increased real cation exchange capacity of the xerom or humus, caused by increase in pH, facilitated the sorption of a larger qu antity of K+ than would have been possible after fertilization w ith KC1 only. At the same time, the sorption of K+ ions lim ited to a certain extent th a t of NH+* ions (cf. Figs 2, 3 and 4).
The comparison of the q u antity of K+ and NH+4 introduced into the soil w ith m ineral fertilizers w ith the ions determ ined as exchangeable cations dem onstrated th a t the hum us of plot “N + K ” adsorbed the total num ber of K+ and one half of NH+4.
14 m onths after fertilization the hum us of plot “N + K ” still showed elevated pH, exchangeable K+ content higher than control and a certain increase in the quantity of exchangeable cations not introduced w ith
fertilizers (Table 2). As a result, values S and V are elevated. F ertili
E ffect of urea and p otassium ch lorid e on CEC of hum us 139
F ig . 4. C h a n g e s in e x c h a n g e a b le K + a n d N H +4 c o n te n t in h u m u s u n d e r s tu d y e ffe c te d b y KC 1 a n d u re a f e r t iliz a t io n
h a ch u re d e sig n a tio n lik e in F ig. 2 and 3
C h a n g e i n c a t i o n b i n d i n g e n e r g y o f x e r o m o r h u m u s e f f e c t e d b y f e r t i l i z a t i o n
The effects of m ineral fertilization on the cation binding energy were revealed by the results of extraction of the samples w ith distilled w ater and 0.03N CH3COOH (Table 4).
Only 11-18% of the total num ber of exchangeable basic cations pass into w ater ex tract from non-fertilized humus. The p articu lar cations, however, show m uch variation in th eir capacity for w ater extraction. Distilled w ater extracts only several per cent of the exchangeable di valent cations (Ca2+, Mg*4-), w hereas more than 50% of the total num ber
of exchangeable K+ and NH+4 are w ater-extractable. 0.03 N CH3COOH is
a stronger extractant. It extracts from non-fertilized hum us about 40% of the sum of exchageable basic cations, including an average of 90%
exchangeable NH+4, 79% K +, 57% Mg*\ 25% Ca2+. The analysis of both
extracts has revealed th a t a large p art of the exchangeable m onovalent cations is very weakly bound w ith the hum us under study.
The same extractions carried out two m onths after treatm en t yielded results somewhat different than expected. W hat was expected was a fu rth er increase in the percentage fraction of w ater-extractable K + (after KC1 fertilization) and NH+4 (after urea fertilization). It became evident, however, th a t the hum us from plot “K ” liberates only little more potassium to the w ater extracts than th a t of the control. Though
140 U. P okojska
T a b l e 4
B asic c u tio n s in w a te r and 0 .0 3 N CH^COOH e x t r a c t s / а о p e rc e n ta g e o f e x c h a n g e a b le c a t i o n s / o f th e huaius c o l l e c t e d two m onths a f t e r f e r t i l i z a t i o n
P lo t 3ub-h o riz o n W ater e x t r a c t s 0.0 3 N CH3COOH e x t r a c t s
Ca Mg К Na KH4 S Ca Kg К Na nh4 S «•0" AoL 4 10 54 24 89 18 32 66 70 27 91 43 >0 3 8 66 26 77 18 20 47 100 32 100 33 AoF H 3 10 44 28 29 11 22 57 66 33 70 34 » K„ AoL 3 6 38 29 76 19 26 45 66 37 95 43 AoF 2 5 39 39 29 15 15 31 77 44 83 30 AoF H 2 5 32 21 12 10 20 35 59 39 76 33 "N" Aol, 2 2 27 22 30 18 16 37 61 34 96 60 V 1 3 24 8 19 12 16 33 50 15 53 41 V l i 2 4 23 16 20 Э 20 35 54 29 70 39 " M ” AoL 2 3 37 35 37 21 19 41 S3 50 90 GO AoF 2 3 13 26 22 14 14 31 66 47 31 52 AoF H 2 4 21 27 17 12 17 30 75 47 74 50
after urea fertilization w ater extracts m ore NH+4, this is due to a large
extent to the increase in solubility of the hum us saturated w ith N Hf4
(the extracts are coloured). The same effect of urea on some hum us fractions solubility was observed in plot “N + K ”, w here considerable rise in K + and NH+4 concentration in w ater extracts was observed. A part from the absolute increase in ion concentration in the w ater extracts, in each case the percentage of w ater extractable K+ and NH+4 (calcula ted in relation to exchangeable K* and NH+4) after fertilization was sm aller than control (Table 4). It follows th a t the m ajor p art of nutrients derived from fertilizers is com paratively quickly sorbed by hum us and in this w ay secured against washing down by rainfall.
It is also interesting to not how fertilization affects the binding energy of cations which have not been introduced w ith fertilizers. Analyses of w ater extracts and of 0.03 N CH3COOH revealed th a t urea fertilization is followed by m arked reduction in the capacity for extrac tion of these cations. Evidence of th a t is the considerable reduction in relation to control of the quantity of w ater-extractable Ca2\ Mg2+, K + and Na+ in the hum us of plot “N ” (Fig. 5). This shows th a t a side effect of urea fertilization is increased binding energy of above cations by humus. This presum ption is in line w ith the observations of O t c h e r e - B о a t e n g et al. [5], who noted th a t for some tim e after urea fertiliza
tion the washing down of basic cations from organic horizon was considerably inhibited.
E ffect of urea and potassiu m ch lorid e on CEC o f hum us 141
F ig . 5. C o m p a ris o n o f w a te r - e x tr a c ta b le c a tio n s f r o m h u m u s o f p io t “ O ” a n d o f p lo t “ N ”
C O N C L U S IO N S
The reported experim ents confirm the essential effect of pH on the cation-exchange properties of humus, noted by a num ber of authors. Taking this correlation into account is of particu lar im portance in estim ating the capacity of strongly acid hum us of forest sandy soils for sorption of fertilizer constituents.
W ith fertilizers which do not cause increase in hum us pH, e.g. KC1, sorption of extra cations is impeded and proceeds at the cost of dis placem ent of p a rt of the exchangeable basic cations. On the other hand, fertilization which causes an increase in hum us pH, e.g. urea, results eo ipso in an increase in the real cation-exchange capacity of humus. This enables the hum us to adsorb large quantities of cations introduced into soil w ith fertilizer and a t the same time increases its energy of binding the other basic cations. W hen both fertilizers are used jointly, the effect of the component causing increase in pH is predom inant. In applying fertilizers, it is th a t component th a t should be applied first on account of its favourable effect on CEC.
R E F E R E N C E S
[1] C o l e m a n N. T. , W e e d S. B. , M c C r a c k e n R . J. : C a tio n -e x c h a n g e c a p a c ity a n d e x c h a n g e a b le c a tio n s in P ie d m o n t s o ils o f N o r th C a ro lin a . S o il. S ei. Soc. A m . P ro c . 23, 1959, 146-149.
[2] H e l l i n g Ch. S., C h e s t e r s G. , C o r e y R . В . : C o n s tr ib u tio n o f o rg a n ic m a tte r a n d c la y to s o il c a tio n -e x c h a n g e c a p a c ie y as a ffe c te d b y th e p H o f
th e s a tu r a tin g s o lu tio n . S o il S ei. Soc. A m e r. P ro c . 28, 1964, 517-520. [3 ] J a c k s o n M . L . : S o il c h e m ic a l a n a ly s is . P r e n t ic e - H a ll 1962.
{4] M e h 1 i с h A . : C h a rg e c h a ra c te riz a tio n o f so ils . 7 th I n te r n . C o n g re s s o f S o il
142 Ü. Pokojskâ
[5] O t c h e r e - B o a t e n g J., B a l l a r d Т. M. : U rea fe r tiliz e r s e ffe c ts on d is s o l v e d n u trien t co n cen tra tio n s in som e fo rest soils. S o il Sei. Am . J. 42, 1978, 503-508.
[6] P 1 i с h t a W. : E ffect of fertilization w ith urea and potassium salt on som e n itro g en form s in h u m u s of th e x ero m o r typ e. S p raw ozd. z prac w y k o n a n y ch w ram ach tem atu w ę z ło w e g o i zad an ia nr 09.10.01.02.10, 1980.
[7] P r u s i n k i e w i c z Z. : P o lish n o m en cla tu re and m orp h ogen etic c la ssific a tio n of ofrest hum us a g a in st the b ackground o f m ain con tem p orary ten d en cies in th e w orld p ed ology. M ateriały z k o n feren cji „P róchnica g leb leśn y ch — aku m u lacja, rozkład, w ła śc iw o śc i, k la s y fik a c ja ”. W arsaw —T oruń 1979, P art 2, 291-304.
[8] P r u s i n k i e w i c z Z., J ó z e f o w i с z-K o 1 1 a r z J. : D yn am ics of am m onia v o la tiliz a tio n from th e urea ap p lied in fe r tiliz a tio n of poor forest so ils and the p o ssib ility of red u cin g th e n itrogen lo sses by sim u lta n eo u s a p p lication of p o ta ssiu m chlorid e. Rocz. gleb ozn . (in press).
[9] U l r i c h B. : K a tio n en a u sta u sch — G le ic h g e w ic h te in B öden, Z eitsciir. f. P fl D üng., B od en k u n d e 113, 1966, 141-159.
и . POK O JSK A
W PŁYW N A W O ŻE N IA M OCZNIKIEM I SO L Ą PO T A SO W Ą N A W ŁAŚCIW O ŚCI K A T IO N O W Y M IEN N E PR Ó C H N IC Y KSEROM O R W BORZE SU C H Y M
C L A D O N IO -P IN E T U M
Z akład G leb o zn a w stw a In sty tu tu B io lo g ii U M K w T oruniu S t r e s z c z e n i e
B ad an ia przep row ad zon o na p o w ierzch n i d o św ia d cza ln ej Z akładu G leb o zn a w stw a In sty tu tu B io lo g ii U M K w L e śn ic tw ie L u bnia w B orach T u ch olsk ich . W y stę pują tam g le b y rd zaw e b ie lic o w a n e z p róch n icą typ u k serom or. P o jem n o ść sorp c y jn a tej p róch n icy w zg lęd em k a tio n ó w jest zn a czn ie u za leżn io n a od odczynu. P rzy n a tu ra ln y m siln ie k w a śn y m o d czy n ie realn a p ojem n ość je st 3-5 razy m n ie j sza od p ojem n ości p o ten cja ln ej, ob liczon ej jako sum a w y m ie n n y c h k a tio n ó w za sad ow ych i k w a so w o ści h y d ro lity czn ej.
N a w o żen ie solą p ota so w ą KCl n ie w y w o ła ło za u w a ża ln y ch zm ian odczynu próch n icy. S orp cja jo n ó w K+ b yła utru d n ion a i od b y w a ła się w zn aczn ej m ierze kosztem w y p iera n ia z k o m p lek su sorp cyjn ego p o zo sta ły ch k a tio n ó w o ch arak terze zasad ow ym . N a w o żen ie m o czn ik iem w y w o ła ło zn aczny w zrost pH próch n icy. U w a ln ia ją c e się p odczas h yd rolizy m oczn ik a k a tio n y N H+4 były w zw iązku z tym sorb ow an e g łó w n ie w m ie jsc e k a tio n ó w w o d orow ych . N ie ob serw o w a n o desorpcji k a tio n ó w o ch arak terze zasad ow ym , p rzeciw n ie , w zro sła siła ich w ią za n ia przez próchnicę. P rzy łą czn y m n a w o żen iu solą p otasow ą i m o czn ik iem d ecy d u ją cy w p ły w n a p rzeb ieg p rocesów sorpcji w y w ie r a ł m ocznik. W zw iązk u z p o zy ty w n y m od d z ia ły w a n ie m m oczn ik a n a p ojem n ość sorp cyjn ą p róch n icy przy sto so w a n iu k ilk u n a w o zó w ce lo w e jest w y sie w a n ie m oczn ik a w p ierw szej k olejn ości.
D r U rsz ula P o k o js k a I n s t y t u t Btolo glt UM K T o r u ń , ul. S i e n k i e w i c z a 30
