ROCZNIKI GLEBOZNAWCZE T. X X X III, NR 1/2, WARSZAWA 1982
ZBIGNIEW PRUSINKIEWICZ, JADWIGA JÓZEFKOWICZ-KOTLARZ
DYNAMICS OF AMMONIA VOLATILIZATION FROM THE UREA APPLIED IN FERTILIZATION OF POOR FOREST SOILS AND THE
POSSIBILITY OF REDUCING THE NITROGEN LOSSES
BY SIMULTANEOUS APPLICATION OF POTASSIUM CHLORIDE1
D epartm ent of Soil Science, In stitu te of Biology Nicolaus Copernicus U niversity, Toruń
INTRODUCTION
The ever increasing demand for timber necessitates an intensification of forest production. One of the means leading to achieving this aim is m ineral fertilization of forest. Increasing use of fertilizers has been observed in world forestry for the last few decades [2, 3]. In Poland about 250 thousands ha of forest soils are fertilized every year. Subject to fertilization are in the first place the poorest and degraded soils and sites affected by industry [24].
In our climatic zone of particular importance is nitrogen fertilization. One of the nitrogen fertilizers m ost frequently used in forestry is urea. Thanks to its relativy easy manufacturing, high content of pure elem ent (46% N) and low hygroscopicity and corrosive activity and low toxiticity for animals, this product is w ell suited for aerial application.
Some properties of urea, however, are less advantageous. Thus for instance it has been demonstrated in Sweden on vast statistical m aterial that growth increments in pine effected by urea nitrogen were by 25-40% lower than those obtained by application of equivalent doses of ammonium salpetre [39]. A n s o r g e et al. [1] observed that in ferior effect of urea on light sandy soils occurred only when it was applied without cover and there was no rainfall w ithin 5 -1 0 days after treatment.
It seems that differences in the effectivity of the two fertilizers are largely due to loss of gaseous ammonia forming in the course of enzy matic hydrolysis of urea in soil medium. As to the size of these losses 1 The study was carried out in the fram ew ork of the problem coordinated by the Forest Research In stitu te — W arsaw, Poland.
20 Z. Prusinkiewicz, J. Józefkowicz-Kotlarz
from forest soils, there is discordant information in literature. The va lues given by various authors range from several to about 50%) of the urea nitrogen introduced into the soil [9, 22, 31, 32, 45, 46]. Such great differences no doubt are due to different climatic, soil or floristic con ditions etc, but some part in them m ay be played by the different research methods used.
So far there have not been any studies on ammonia volatilization from urea fertilized forest soils under conditions prevailing in Poland, hence there are on grounds for assessm ent of the resulting losses.
The main aim of the experim ents described in this paper was to obtain materials on loss of nitrogen (size of loss, its dynamics) under conditions of urea fertilized m iddle-aged pine stand in Cladonio-Pinetum. These low -productivity sites, showing as a rule signs of anthropogenic degradation, occupy in some regions of our country considerable areas. The study was also aimed at elucidating the effect of potassium chlo ride applied sim ultaneously w ith urea on the size of ammonia volatili zation. In characterizing the sites, special attention was paid to those properties of soils which can affect ammonia volatilization and which them selves can be subject to various modifications under the influence of the fertilizers applied. Thus studies were made of the dynamics of changes in pH and in sorption properties of soil humus and of the changes in the numbers of microorganisms with special stress of urease- producing bacteria and fungi. Also the activity of nitrification processes was assessed in order to obtain niformation on the possibility of addi tional loss of nitrogen in the form of nitrates, which are easily washed out of the soil. The studies of the sorption properties of the soils and the microbiological analyses were executed on our initiative by P o- k o j s k a [34] and S t e f a n i a k [43] respectively. The results of si multaneous lysim etric studies w ill be presented in a separate publi cation.
THE RESEARCH AREA
The investigations were conducted in the northern part of Bory Tucholskie (Tuchola Forests). From the geomorphological point of view the area represents the proximal part of an outwash plain (the m eeting line of the outwash plains of the Brda and the Wda rivers) elevated about 150 m asl, in places slightly eolically undulated and varied by channel lakes and kettles of various sizes. The experim ental area was selected in the forest inspectorate Przymuszewo (distr. Lubnia, section 301) in a 72-year-old pine stand of yield class IV in Cladonio-Pinetum. The herb layer is dominated by lichens — Cladonia sylvatica, Cl. ran-
Dynamics of ammonia volatilization., 21
Dicranum undulatum, Dicranum scoparium and others species. Among
small shrubs and herbaceous plants the most noteworthy are Calluna
vulgaris, Vaccinium vitis idaea, Vaccinium m yrtillus, Deschampsia jlexuosa, but they occur rather scantily. There are, on the other hand,
frequent patches devoid of herb layer altogether and covered solely by fallen pine needles.
The soil in the area has been defined as weakly podzolized rusty soil, impoverished and degraded because of transitory farming, sheep grazing and raking out of the litter. Parent material of the soil are outwash sands, partly windblown in their upper layers. Ground water is found at about 15 m depth. The set of genetic horizons of this soil can be presented by symbols: Ao — Aeh — Ahp — В — В/С — С — D. The type of humus is xeromor in the form characteristic of degraded sites. Horizon Ao varies from 3,5 to 6.5 cm in thickness (average 4.5 cm). In the litter subhorizon the organic matter content amounts to about 92% and the C/N ratio is about 44:1; in the lower subhorizons of the forest floor both these values gradually decrease. The potential cation exchan
ge capacity (CECP) of the whole forest floor layer reaches about 55 kval/ha [34].
The climatic data for the experim ental period (16 April 1977 — 15 July 1977) were obtained from the Station of Institute of M eteorology and Water Management at Chojnice, about 32 km from the experim ental area. The mean temperatures at that time were: in the second half of April 6.4°, in May 10.9°, in June 16.1°, in the first half of July 15.4°C and except for June were lower than the overall means for these months. The total rainfall for April to July 1977 was 304 mm and was higher than the overall mean for that period (212 mm).
The moisture content of the forest floor layer determined in the field varied from 43 to 76% over the experim ental period.
METHODS
Standard doses of fertilizers were hand applied in the experim ental area: on 16 April 1977 granular urea (92 kg N/ha) and on 18 April 1977 60% potassium chloride (100 kg K/ha). Four variants were obtained: “O” (control), “N ”, “K ” and “N + K ”. The amounts of ammonia volatili zing from the soil as a result of hydrolysis of urea were determined in variants “N ” and “N + K ” in five replications. The static m ethod was used, consisting in absorbing gaseous NH3 in 1 N H3P 04 under m etal chambers (1 0X1 0X20 cm) open at the bottom and pressed down into the soil 3-4 cm deep in places devoid of ground flora. To reduce varia tions in temperature the chambers were protected against direct solar
22 Z. Prusinkiewicz, J. Józefkowicz-Kotlarz
radiation w ith conical tin foil covers. The ammonia sorbed in phosphoric acid was determined by K jeldahl’s method. The experim ents were con ducted without interruption for 90 days (16 April — 14 July). The exposition time in April was 24 hours each time, and later, when the intensity of NH3 release decreased, it was extended to serval days, so that the amounts of ammonia adsorbed were always analytically deter minable.
The microbiological studies were carried out by O. Stefaniak, who cooperates w ith us. Soil dilutions were sprayed on to selective agar-agar media and the results were calculated to 1 g of fresh soil. The first samples for microbiological analyses were taken at the end of March 1977, i.e. before fertilization; the follow ing samples were taken two w eeks after fertilization (end of April) and further on until September at 4-week intervals. At the same times O. Stefaniak also determined the intensity of nitrification processes on the grounds of the amount of N -N 03 produced in N-NH 4-containing mineral liquid medium inoculated w ith the soil under study. The nitrates were determined colorimetrically w ith difenylsulfonic acid.
Measurements of pH (in H20 and KC1) were taken for each fertili zing variant once a month from April until October 1977.
The soil m aterial for studies of cation exchange capacity and of the composition of exchange cations was taken [34] from all fertilizer com binations on 15 June 1977, i.e. two months after fertilization. The cation exchange capacity and its dependence on pH were determined for each humus horizon and subhorizon separately by the method described by H e l l i n g et al. [11]. The real cation exchange capacity (CECr) was read each time for a given pHH O value from the curve expressing the relation C EC r = f (pH). The main exchange cations (Ca2+, Mg2+, K +, N a+) was determined spectrophotom etrically after extraction in IN CH3COONH4 solution. The exchangeable N H + was extracted w ith 10% NaCl solution (pH 2.5) according J a c k s o n [13] and determined by K jeldahl’s method. The saturation degree (Vr) of the sorption complex was calculated from the sum of the exchangeable bases (S) and the real cation exchange capacity (CECr) according to the equation:
v r = — --- 100.
CECr RESULTS
L o s s e s o f a m m o n i a n i t r o g e n . The ammonia release was the m ost intensive in the second week of the experim ent (Fig. 1). The total losses of nitrogen over the second week were 11.7% in variant “N ” and 8.3% in variant “N + K ” in relation to the amounts introduced in the dose of urea. The m aximum daily losses were noted in the 12th
Dynamics of ammonia volatilization... 23
Fig. 1 Cum ulative curves showing the dynamics of am monia volatilization from forest soil fertilized w ith urea and urea -f potassium chloride
day after fertilizer applying. They amounted to 2.7 and 1.9% respecti vely. This means that during that day an average of more than 300 mg
of NH3 (in one replication even 425 mg) was emitted from each square metre of plot “N ” and more than 200 mg of NH3 from each square metre of plot “N + K ”. After reaching that culmination, the intensity of ammo nia volatilization in both variants decreased rapidly, but vestigial losses were still observed even in the final stage of the experim ent, especially in the plot not treated w ith potassium chloride. The total nitrogen losses throughout the 3-month experim ental period reached 25.0% in variant “N ” and 20.1% in variant “N + K ” in relation to the nitrogen introduced onto the soil in the urea dose applied. This difference is statistical signi- ficat at P < 0 .0 5 level.
R e a c t i o n . As a result of the urea fertilization the reaction of the organic horizon, at first strongly acidic, became transitionally neu tralized (Fig. 2). An increase in pH v/as noted in all subhorizons of the organic horizon in the urea-treated plots nearly im m ediately after treatment, but the maxima of pH increments in the deeper subhorizons were a few weeks delayed compared with the A ob subhorizon. In sub horizons А оь and A of the reaction (pHHa0 ) reached, and in some places
even considerably exceeded, the value of 6.0 whereas in subhorizon A oFH — 4.5 pH. The neutralizing effect of urea in subhorizons A oL and Aof could be detected as long as 6 m onths after fertilization; in subho rizon A oFH the reaction returned to its initial values already after 4 months.
In soil treated w ith urea and potassium chloride jointly the rise in pH was frequently som ewhat less than in the variant w ith urea alone. The difference in the soil reaction betw een the two variants was the most distinct in subhorizon A oF (Fig. 2).
24 Z. Prusinkiewicz, J. Józefkowicz-Kotlarz
Fig. 2 The effect of fertilization w ith urea and w ith urea + potassium chloride on pH changes in xerom or humus
Dynamics of ammonia volatilization., 25 In the plot treated w ith potassium chloride alone a tendency towards increased acidity was noted.
S o r p t i o n p r o p e r t i e s o f h u m u s . As a result of the inc rease in pH value, the real cation exchange capacity of the organic horizon in urea-fertilized plots increased considerably. Consequently, the ammonium ions forming during hydrolysis of urea could be easily sorbed without elim inating from the complex other exchangeable bases, but nearly only hydrogen ions. In soil fertilized w ith urea only, ammo
nium cations came up in some cases to the first place in the organic sorption complex, ahead even of calcium (Table 1).
The sorption took a different course w ith potassium ions, which in the plot treated with potassium chloride alone entered the sorption complex m ainly in the place of other exchangeable bases (particularly calcium). In variant “N + K ” potassium elim inated besides exchangeable bases also part of hydrogen ions, whereas the ammonium ion, though sorbed in smaller quantities than in the urea fertilized plot, was distri buted more uniform ly throughout the entire humus profile including the humus containing soil horizons (Table 1).
U r e o l y t i c m i c r o o r g a n i s m s . The introduction of urea into the soil caused in the upper organic soil horizons (AoL nad A oF) a rapid increase in the numbers of all bacteria, among them also those active in ureolysis (Fig. 3). The response of ureolytic fungi, on the other hand, was weak and became m anifest only after the bacteria began to subside. In both fertilizer combinations the numbers of bacterial cells exceeded m any tim es those found in the control. Similar regularities were found in urea-fertilized soil under a spruce stand (Picea mariana) by R o- b e r g e and K n o w l e s [37, 381. In variant “N + K ” the numbers of ureolytic bacteria were generally somewhat smaller than in “N ”. The dynamic developm ent of the populations of these microorganisms con tinued only until June, and then was followed by a marked reduction in their numbers.
N i t r i f i c a t i o n . An extrem ely low activity of nitrifying pro cesses is one of the typical characteristics of soils in Cladonio-Pinetum forests. Increased concentration of ammonium ions due to ureolysis in the fertilized soil resulted in only a very slight increase of that activity (Fig. 4). No clear difference was found between the effect of urea alone and urea with potassium chloride. S t e f a n i a k [43] accounts for this condition by the nearly complete absence of nitrifying microflora, which in the soils under study does not find suitable conditions for its development. Our m onthly tests of lysim etric waters in the plots representing the particular fertilizer combinations have also shown that
Tne effect Ox fertilisation witn urea arid potassium chloride on the exchangeable cations and the cation exchange capacity of the humus /mval/100 g of dry organic matter/
T a b l e 1
rO CO
Variant Horizon C a 2+ MS2* K+ Na+ r a t4 3 CECr
Vr AoL 1 4 .0 1 .5 1 .3 0.6 1.8 1 9 .7 30.1 6 5 .4 0 A oP 12.5 1 .4 2.0 O.S 1 .7 1 8 .4 3 2 .0 5 7 .5 /control/ A oPH 15 .2 1.8 1 .9 1.0 1.8 2 1 .7 4 1 .4 5 2 .4 Ahe 9 .6 2,0 2.1 1.1 3.1 1 7 .9 50.1 3 5 .7 A hp 6 .9 1 .7 1 .9 1 .4 4 .9 1o,8 6 1 .5 2 7 .3 AoL 1 4 .4 1 .3 1.8 0 .7 1 9 .0 3 7 .7 4 3 .3 7 3.1 A oP 14eS 1 .7 1 .7 1.2 22.1 4 1 .5 53.1 7 8 .2 IT A oPH 20.2 2 .9 1.8 1.1 1 2. 1 3 3.1 5 1 .7 7 3 .7 Ahe 12.9 1 .4 1 .9 1 .3 1 0.6 23 .1 5 8 .0 4 3 .4 Ahp 1 2 .4 2 .4 2 .4 2.2 6.6 26.0 6 3 .2 41 .1 AoL 11.0 1.6 4 .7 0.6 1*6 1 9 .5 2 9 .3 6 5 .4 AoP 11 .5 1 .4 5 .0 0 . 7 1 .4 2 0 .0 3 0 .9 6 4 .7 К A oPH i6.a 2 .5 5 .2 1 .4 1 .4 2 7 .3 4 2 .0 6 5 .0 Ahe 7 .5 1 .7 2.6 0 .9 3 .4 iS.1 52.1 3 0 .9 Ahp 9 .3 2,1 2 .3 1 .4 4 .3 1 9 .9 6 3 .0 3 1 .6 A oL 12.2 1 .5 9 .2 1.2 6 .7 3 0 .8 36 .8 8 3 .7 A oP 10.5 1 .3 12.8 1 .3 8 .5 3 4 .4 3 9 .4 8 7 .3 Ы+Х A oPH 12.0 1 .4 9 .8 1.2 7 .5 3 1 .9 4 7 .0 6 7 .9 A he 11.6 1 .7 9 .4 1 .5 6 .9 3 1 .3 5 4.8 57.1 Ahp 15 .2 2.2 6.8 2.2 8.2 3 4 .6 65.1 53.1 Z . P ru si n k ie w ic z , J. Jo z e fk o w ic z -K o tl a rz
Dynamics of ammonia volatilization. 27
Fig. 3 The effect of fertilization w ith urea and w ith urea + potassium chloride on the dynam ics of the num bers of ureolytic bacteria In the A 0l and A 0f
suibho-rizons of xerom or hum us
Fig. 4 The effect of fertilization w ith urea and w ith urea + potassium chloride on the dynamics of nitrification in the A 0l and A 0f subhorizons of xerom or
28 Z. Prusinkiewicz, J. Józefkowicz-Kotlarz
only vestigial amounts of nitrates are washed down from the uppermost holoorganic horizon to mineral soil.
DISCUSSION
Urea is easily soluble in water (779 g in 1 litre E^O at 5°C). Urea [CO(NH2)2] by itself is sorbed to only a small extent even in soils with a w ell developed sorption complex, for it is a very weak base with a dissociation constant 1.5 • 10-14 [5, 12]. After being introduced into the soil, urea becomes hydrolysed, being transformed first into (NH4)2C 03 and then into NH4OH and H2C 0 3. The latter being unstable compounds, they decompose into water and volatile products NH3 and C 0 2.
Ureolysis is catalysed by urease — an enzyme produced by many microorganisms and also by higher plants. Urease in soil can be in tracellular — inside the cells of ureolytic microorganisms, and extra cellular — released from dead and decomposed cells of plants and m ic roorganisms and partially adsorbed by mineral and organic soil colloids. L l o y e l and S h e a f е е [16], Z a n t u a and B r e m n e r [47] and P e t t i t et al. [29] think that extracellular urease adsorbed in soil is protected against microbiological degradation and does not lose its acti vity. P a u l s o n and K u r t z [28] and S a r i g u m b a and F i s к e 1 [41] inferred from special experim ents that hydrolysis of urea in soil depends in the first place on extracellular urease.
Urease is more effective in neutral than in acid medium^. According to N ô m m i k [22], a decrease in pH results in inactivation of urease. P i n e and A l l i s o n [30] point out that maxim um activity of that enzyme occurs at pH 7. The intensity of urea decomposition is also greatly affected by temperature (optimum ca. 30 °C) and moisture con tent of the substratum. According to O v e r r e i n and М о е [27], the effectiveness of ureolysis at 28°C was 5.4 times greater than at 4°C. At low moisture contents ureolysis proceeds more slow ly, but in spite of this, losses of gaseous ammonia are greater than at m oderately high moisture contents.
It has been found by a number of investigators [38, 7] during in cubation under laboratory conditions that hydrolysis of urea added to samples of acid forest floor layers from soils under coniferous stands proceeds very rapidly. Complete decomposition of doses of the order of 500 kg urea per ha, took about 3 days. Under non-optimal field condi tions ureolysis m ust proceed somewhat more slow ly. However, according to O v e r e i n [25] in Norway even urea doses of the order of 1000 kg N/ha in sites w ith mor humus were hydrolysed w ithin a few days. In the case studied maxim um losses through ammonia volatilization were noted towards the end of the second week from the date of urea treat m ent (Fig. 1),
Dynamics of ammonia volatilization.., 29 J u n g [14] and H ü s e r [12] point to the specific nature of urea transformations in forest soils w ith mor humus and to the insufficiency of research in this domain. According to N ô m m i k [21], a certain part of the ammonium nitrogen forming in the course of ureolysis m ay be fixed w ith the products of lignin decomposition. S a 1 o n i u s nad M a h e n d r a p p a [40] have found that the unexchangeable binding of ammonium nitrogen takes place m ainly in the A oL subhorizon and decreases in the deeper subhorizons of the forest floor layer. O v e r r e i n [26] demonstrated that nitrogen applied to forest humus in the form of ammonium chloride was subject to insolubilization to a much lesser extent than urea nitrogen. Part of the nitrogen may become im mobilized in the cells of microorganisms, whose number greatly in creases after urea treatment, especially in A oL and A oF subhorizons. However, as revealed by the studies of M a i and F i e d l e r [17] the quantities of immoblilized nitrogen are not large enough to have adverse effect on the nutrition of pine.
The decomposition of urea in soil is associated w ith a change in pH. It is due to the fact that during ureolysis ammonium base and carbonic acid are formed. The substratum becomes neutralized, for NH4OH is more intensely dissociated in water (Kb = 1.73 • 10“5) than H2C 03 (Ka = 4.45 • 10“7). The somewhat smaller increase of pH observed in some cases in soil treated w ith urea and potassium chloride jointly, can probably be acconuted for by the m anifestation of a certain part of potential acidity — as is the case in laboratory measurements of exchange acidity of soil samples treated with KC1 solution.
The increase in pH of most urea fertilized farm soils is usually of short duration, as the ammonia produced in them is subject to intensive biological oxidation to nitric acid, which causes another increase in hydrogen ion concentration [18].
The results of the present work demonstrate that in the forest soils under study the activity of nitrification processes is extrem ely low — both before and after urea treatment. For that reason higher pH values persisted for more than six months. This observation is in line w ith those of other authors on the transformations of urea in forest mor humus [25, 20]. On the other hand, L e u b e et al. [15] testing soils under a 105-year-old pine stand, fertilized for 5 yeards running with large doses of urea, found a considerable degree of transformation of ammonia into nitric acid.
Thanks to the negligible activity of nitrification processes, the losses of nitrogen due to the washing down of nitrates beyond the soil profile do not play any singnificant role in the case in question. It follows therefore that in this situation there cannot be any problem of pollution of ground waters with nitrates, which m ust be taken into account in salpetre fertilizing.
30 Z. Prusinkiewicz, J. Józefkowicz-Kotlarz
In contrast to N-NO3, losses of nitrogen in the form of gaseous
ammonia are high. In spite of the increase in cation exchange capacity due to change in pH [33], in the urea fertilized plot they reached 25°/o in relation to the nitrogen introduced. Though lower than the maxim um losses reported by some authors, losses of that order constitute a serious economic problem.
In this context it becomes of particular importance that applying potassium chloride directly after urea resulted in a marked reduction of ammonia volatilization, which in the “N + K ” variant was only 20% instead of 25% in the “N ” variant.
W a t k i n s et al. [46] found a reduction in NH3 losses, when ammo nium chloride was applied together w ith urea onto forest soil. C a r r i e r and B e r n i e r [7] report the effect of potassium-magnesium sulphate on inhibiting the decomposition of urea and on diminishing ammonia volatilization.
P o b i e d o v and L e b i e d i e v [32], who also found a reduction in losses of ammonia due to MgCl2 applied together w ith urea, think that the effect of that salt consists in inhibiting the enzymatic soil pro
cesses. It follows however from the extensive studies of B r e m n e r and D o u g l a s [4], T a b a t a b a i [44] and M i s h r a and F 1 a i g [19] on the inhibiting effect of various mineral and organic substances on urease that potassium, magnesium, chloride and sulphate ions do not show such inhibitory properties.
In the light of our studies it seems probable that the supposed m e chanism of the advantageous effect of KC1 (and possibly also of NH4CI and MgCl2) consists in:
— counteracting too radical a rise in pH — since urease is less active in acid than in neutral or basic medium;
— partial dislodging of ammonium ion from the uppermost to some what deeper horizons of the humus profile, whose sorption capacity would not otherwise be utilized. Mobilization of soil ammonium nitrogen effected by various chlorides has also been demonstrated in the experi ments of S i n g h et al. [42] and H e i l m a n [10].
Although the reduction of nitrogen losses by 5% found in our experim ents is not great, it should not be disregarded, considering that it was achieved w ithout additional expenditure and that growing amounts of urea are applied in forests each year.
To raise the productivity of forest soils studied in this work and similar soils in other areas it is needed in the first place to apply nitro gen and potassium, and in some parts also m agnesium fertilization [35, 36]. The current practice of aerial fertilization of forest solis w ith nitro gen and potassium consists in spilling the whole area to be fertilized first w ith one and then with the other fertilizer. The interval between the two operations is usually ca a fortnight, which maks interaction of
Dynamics of ammonia volatilization.. 3 i the two fertilizers in soil difficult or impossible. If urea fertilization was follow ed by potassium fertilization w ith no more than one day interval, which does not require any additional expenditure, it would be enough to achieve substantial improvement in the utilization of the fertilizer nitrogen.
In connection w ith the problem under discussion it should be added that other methods of reducing ammonia volatilization from urea, such as using ureo-formaldehyde preparations, or urea with supplement of substance of low permeability to water, m ay be more effective, but for the time being at least, they are too expensive to be w idely used in forestry
CONCLUSIONS
1. Losses of nitrogen due to ammonia volatilization from urea applied in a m iddle-aged pine stand in Cladonio-Pinetum amounted to 25°/o at a dose of 200 kg of urea per hectare.
2. Potassium chloride applied im m ediately after urea markedly re duces ammonia volatilization.
3. For sandy forest soils requiring nitrogen nad potassium fertili zation it is recommended to arrange fertilization so that urea spilling should be followed im m ediately by potassium chloride spilling.
4. Our studies point out that the supposed mechanism of the bene ficial effect of KC1 consists perhaps in dislodging the ammonium ion from the uppermost to som ewhat deeper horizons of the humus profile and in counteracting too radical a rise in soil pH.
5. The increase in pH value of the humus horizons of forest soils has a twofold significance from the point of view of ammonia volatilization from urea:
— it increases, it, as it accelerates ureolysis and favours excessive concentration of ammonia in the uppermost layer of litter;
— it considerably increases the cation exchange capacity of forest humus, which helps sorb larger amounts of ammonium ion and reduce losses.
6. Fertilization of soils in dry pine forest sites (Cladonio-Pinetum) w ith urea doses commonly used in aerial fertilization (200 kg of urea/ha) does not cause activation of nitrification processes, and so there is no danger of ground water pollution.
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[13] J a c s o n M. L.: Soil chemical analysis. P ractice Hall, Inc. 1962, 498 pp. [14] J u n g J.: Vergleichende Ü berprüfung verschiedener Stickstoff Verbindungen
auf ihre chemische Reaktion m it Rohhumus und die photom etrische Erfaassung dieses Reaktionseffektes. Z. Pflanzenernähr. Düng., Bodenkunde 85,2, 1959, 104-112.
[15] L e u b e F., H ö h n e H., F i e d 1 e r H. J.: Einfluss stark er Harnstoffgaben auf Ernährung, W achstum nud H arzertrag eines K iefernatbestandes. Beiträge f. d. F orstw irtschaft 3, 1975, 111-117.
[16] L l o y e l A. B., S h e a f e e M. J.: Urease activity in soils. Plant and Soil 39, 1973, 71-80.
[17] M a i H., F i e d l e r H. J.: W irkung von H arnstoff- und K alkam m onsalpeter- Düngung auf die M ikroflora und den Stickstoffum satz im Kiefernrohhum us. Zbl. Bakt. II Abt., 132, 1977, 551-572.
[18] M a t z e l W., H e b e r R.: Grundlagen fü r den effektiven Einsatz von H arnstoff als Stickstoffdüngem ittel. Tagungsber. Akad. Landw irtschaftsw iss. DDR, 1978, 287-293.
[19] M i s h r a M. M., F l a i g W.: Inhibition of m ineralization of urea nitrogen in soil. P lant and Soil 51, 3, 1979, 301-309.
[20] N a k o s G.: Interactions of nitrogen fertilizers and forest humus. I. Fir and Black Pine. Soil Biol. Biochem. 8, 1976, 379-383.
[21] N ö m m i k H.: Assessment of volatilization loss of ammonia from surface — applied urea on forest soil by N15 recovery. P lant and Soil 38, 1973, 589-603.
Dynamics of ammonia volatilization... 33 [22] N ô m m i k H.: The effect of pellet size on the am m onia loss from urea
applied to forest soil. P lan t and Soil 39, 1973, 309-318.
[23] N ô m m i k H.: F u rth e r observations on am m onia loss from urea applied to forest soil w ith special reference to the effect of pellet size. P lan t and Soil 45, 1976, 279-282.
[24] O r z e s z e k T., R o z w a ł k a T.: Low -productivity forests in Poland, (in Polish), Polsk. Tow. Leśne Poznań, 1978, 1-16. W: Problem y lasów niskopro-
dukcyjnych na przykładzie Puszczy Noteckiej.
[25] O v e r r e i n L. N.: Immobilization and m ineralization of tracer nitrogen in forest raw hum us I. Effect of tem perature on the interchange of nitrogen after addition of urea-, am monium-, and n itra te - N15. P lant nad Soil 27, 1967, 1-19.
[26] О v e r r e i n L. N.: Imm obilization and m ineralization of tracer nitrogen in forest raw humus. II. Effect of tem perature and incubation tim e on the in terchange of urea-, am moinum-, and n itate- N15 under waterlogged conditions. P lan t and Soil 32, 1970, 207-220.
[27] О v e r r e i n L. N., М о е P. G.: Factors affecting urea hydrolysis and am m onia volatilization in soil. Soil Sei. Coc. Amer. Proc. 31, 1967, 57-61. [28] P a u l s o n К. N., K u r t z L. T.: Locus of urease activity in soil. Soil Sei.
Soc. Amer. Proc. 33, 1969, 897-901.
[29] P e t t i t N. M., S m i t h A. R. J., F r e e d m a n R. B., B u r n s R. G.: Soil urease: activity, stability and kienetic propetries. Soil Biol. Biochem. 8, 1976, 479-484.
[30] P i n с к L. A., A l l i s o n F.: Adsorption and release of urease by and from clay m inerals. Soil Sei. 91, 1961, 183-188.
[31] P o b i e d о V V. S., L e b i e d e v E. A.: Volatile ammonia losses from the nitrogen fertilizers applied in forests, (in Russian) Agrochimija 3, 1976, 26-31. 32 P o b i e d o v V. S., L e b i e d i e v E. A.: The effect of nitrification inhibitors
on the volatile nitrogen losses from fertilizers applied in forests, (in Russian) Tartu, 1977, 69-73. W: Prim ienienije m ineralnych udobrenij w lesnom cho-
zjajstwie.
[33] P o k o j s k a U.: Tte pH-effects on the catioin exchange capacity of the forest hum us of mor type, (in Polish) Polskie Tow. Gleb. Prace Kom. Nauk. 11/12, 1979, 219—224. M ateriały sympozjum nt. Fizykochemiczne właściwości gleb różnych ekosystemów. Sękocin 28-29. XI. 1978.
[34] P o k o j s k a U.: The effects of urea and potassium chloride fertilization on the cation-exchange properties of the xerom or humus in lichen pine forest
(Cladonio-Pinetum). Roczniki Gleboznawcze 32} 3, 1981, 131-142.
[35] P r u s i n k i e w i с z Z. : Abschätzungsmögliichkeitön der Em ährungsbedigungen auf den K iefem standorten an Hand einer kom plexen A usw ertung der Na de 1 an a 1 y s endat en. Gemeinsame Regional taguing der IUFRO -A rbeitsgruppen S1.02—06 und S1.02—07, Wien, 6-9 Mai, 1980. Mitt. ol. Forestl. B undesversu chsanstalt, Wien, 140, 1981, 109-115.
[36] P r u s i n k i e w i c z Z.: A new m ultivariate approach to foliar analyses for diagnostic purposes in m ature Scots pine stands. Forest Ecol. Manage. 4, 1982,
101-115.
[37] R o b e r g e M. R., K n o w l e s R.: Ureolysis, im m obilization and mtnifi cation in Black Spruce (Picea mariana Mill.) humus. Soil Sei. Soc. Amer. Proc.
30, 1966, 201-205.
[38] R o b e r g e M. R., K n o w l e s R.: The ureolytic m icroflora iim a Black Spruce
(Picea mariana Mül.) humus. Soil Sei. Soc. Amer. Proc. 31, 1967, 76—79.
[39] R o s v a i l О.: Prognosfunktioner for beräkninig av gödslingseffekter. Särtryck 3 — R oczniki G leboznaw cze 1—2/82
34 Z. Prusinkiewicz, J. Józefkowicz-Kotlarz
ur Föreningen Skogsträdsförädling och In stitu tet för skogsförbättring, arsbok 1979, 70-130.
[40] S a l o n i u s P. O., M a h e n d r a p p a M. K.: Microbial respiration and exchangeable ammonium in podzol organic horizon m aterials treated w ith urea. Can. J. For. Res. 5, 1975, 731-734.
[41] S a r i g u m b a T. I., F i s k e l l J. G. A.: Urea transform ation in two acid sandy soils. Soil and Crop Sei. Soc. of Florida Proc. 35, 1975, 150-153. [42] S i n g h B. R., A g a r w a l A. S., K a n e h i r o Y.: Effect of chloride salts on
ammonium nitrogen release in two haw aiian soils. Soil Sei. Soc. Amer. Proc. 33, 1969, 557-560.
[43] S t e f a n i a k О.: The effect of the fertilization w ith the urea and potassium chloride on the m icroflora of hum us horizons in Cladonio-Pinetum. (in Polish) In press.
[44] T a b a t a b a i M. A.: Effects of trace elem ents on urease activity in soils. Soil Biol. Biochem. 9, 1977, 9-13.
[45] V o l k G. М.: Gaseous loss of ammonia from prilled urea applied to slash pine Soil Sei. Soc. Amer. Proc. 34, 1970, 513-516.
[46] W a t k i n s S. H., S t r a n d R. F., D e b e l l D. S., E s c h J. Jr.: Factors influencing ammonia losses from urea applied to northw estern forest soils. Soil Soc. Amer. Proc. 36, 1972, 354-357.
[47] Z a n t u a M. I., B r e m n e r J. M.: Production and persistance of urease activity in soils. Soil Biol. Biochem. 8, 1976, 369-374.
Publications on the behaviour of urea in forest soils w ith hum us of the mor type are scattered throughout a large num ber of journals. For that reason a compara tively long list of the more im portant sources has been included.
Статьи, рассматривающие поведение мочевины в лесны х почвах с гумусом типа мор, разбрасаны в многих науч.ных ж урналах. По этой причине здесь приведен сравнительно обширный список важ нейших источников. 3 . П Р У С И Н К Е В И Ч , Я . Ю З Е Ф К О В И Ч -К О Т Л Я Ж ДИНАМИКА ПОТЕРЬ ГАЗОВОГО АММИАКА ИЗ МОЧЕВИНЫ ПРИМЕНЯЕМОЙ В УДОБРЕНИИ БЕДНЫХ ЛЕСНЫХ ПОЧВ, И ВОЗМОЖНОСТЬ УМЕНЬШЕНИЯ ЭТИХ ПОТЕРЬ ОДНОВРЕМЕННЫМ ВНЕСЕНИЕМ КАЛИЙНОЙ СОЛИ К аф едра почвоведения, Институт биологии при Университете им. Н. Коперника в Тору ни. Р е з ю м е Потери азота вследствие илетучивания аммиака из мочевины, высеянной в средневозрастном лишайниковом сосняке составили 25°/о при дозе в 200 кг мо чевины на гектар. Улетучивание продолжалось 3 месяца, но своего максимума оно достилго к концу второй недели со дня внесения мочевины (рис. 1). К алий ная соль применённая непосредственно после высева мочевины, явно уменьшила потери газового аммиака. В связи с этим на песчаных лесных почвах, требую щих азотных и калийных удобрений, следует рекомендовать такую органи зацию работы, которая даёт возможность высеивания калийной соли сейчас же после мочевины.
Dynamics of ammonia volatilization... 35 Произведённые исследования показывают, что механизм благоприятного воздействия КС1 заклю чается по всей вероятности в вытеснении аммониевого иона из самых поверхностных в несколько более глубокие горизонты гуму- сово профиля почвы и в противодействии слишком радикальному увеличению pH пчовы. Повышение pH перегнойных горизонтов лесных почв имеет двойное и взаимопротивопоставляющееся значение с точки зрения его влияния на по тери газового аммиака из мочевины: — способствует увеличению этих потерь, так как ускоряет процессы уреолиза и вы зы вает образование слишком высоких концентраций аммиака в подгоризонте A oL; — значительно увеличивает погло тительную способность лесного перегноя, что даёт возможность сорбции повы шенного количества аммониевого иона и содействует понижению потерь. Удобрение почв сухих лиш айниковых сосняков общеприменяемыми в мас совом авиаудобрении дозами мочевины (200 кг на гектар) не вызы вает активи зации нитрификационных процессов (рис. 4), благодаря чему не существует опасность загрязнения грунтовых вод нитратами.
Z. PRU SIN K IEW ICZ, J. JÓ ZEFK OW ICZ-K OTLARZ
DYNAMIKA STRAT GAZOWEGO AMONIAKU Z MOCZNIKA STOSOWANEGO W NAWOŻENIU UBOGICH GLEB LEŚNYCH I MOŻLIWOŚĆ ZMNIEJSZENIA
TYCH STRAT PRZEZ RÓWNOCZESNY WYSIEW SOLI POTASOWEJ Zakład Gleboznawstwa, Instytut Biologii UMK w Toruniu
S t r e s z c z e n i e
S traty azotu w skutek ulatniania się am oniaku z mocznika wysianego w śred- niowiekowym drzew ostanie sosnowym n a siedlisku 'boru suchego Cladonio-Pinetum wyniosły 25°/o przy dawce 200 kg mocznika na hektar. U latnianie trw ało 3 m ie siące, lecz m aksim um osiągnęło pod koniec drugiego tygodnia od daty wysiewu (rys. 1). Sól potasowa zastosowana natychm aist po m oczniku w yraźnie zm niej szyła straty gazowego am oniaku. W związku z tym na piaskow ych glebach leś nych w ym agających nawożenia azotem i potasem należy zalecać organizowanie nawożenia w sposób umożliwiający wysiew anie soli potasowej n atychm iast po moczniku.
Przeprow adzone badania w skazują, że m echanizm korzystnego działania KC1 polega na w ypieraniu jonu amonowego z najbardziej powierzchniowych do nieco głębszych poziomów profilu próchnicznego i n a przeciw działaniu zbyt radykalne mu wzrostowi pH gleiby. Wzrost w artości pH próchnicznych poziomów gleb leś nych ma dwojakie i przeciw staw ne znaczenie z punktu widzenia wpływu na stra
ty gazowego am oniaku z mocznika:
— przyczynia się do powiększenia tych strat, gdyż przyspiesza procesy ureoii- zy i sprzyja pow staw aniu nadm iernych koncentracja am oniaku w podpozło mie AoL,
— znacznie powiększa kationow ym ienną pojemność próchnicy leśnej, co umoż liwia sorbowanie zwiększonych ilości jonu amonowego i powoduje obniżenie strat. Nawożenie gleb suchych siedlisk borowych daw kam i mocznika powszechnie stosowanymi w masowym naw ożeniu lotniczym (200 kg nawozu na hektar) nie powoduje uaktyw nienia procesów nitryfakacji (rys. 4), dnięki czemu nie m a nie bezpieczeństwa zatruw ania wód gruntow ych azotanam i.
P ro /, d r hab. Z b ig n iew P ru sin k ie w icz
Z akład G leb o zn a w stw a UM K T o ru ń , ul. S ien k iew icz a 30
