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Mobilisation of nutrients in a Sitka spruce (Picea sitchensis) (Bong.) Carr.) forest floor II. Interaction of leaching with lime and fertilizers under laboratory conditions
Forest Ecology and Management, 3 (1980/1981) 229--236 Elsevier Scientific Publishing Company, Amsterdam -- Printed in The Netherlands
229
M O B I L I S A T I O N O F N U T R I E N T S IN A S I T K A S P R U C E ( P I C E A S I T C H E N S I S ) (BONG.) C A R R . ) F O R E S T F L O O R II. I N T E R A C T I O N O F L E A C H I N G W I T H L I M E A N D F E R T I L I Z E R S UNDER LABORATORY CONDITIONS
M.L. CAREY*, E.P. FARRELL** and D.M. McALEESE**
*Forest and Wildlife Service, Sidmonton Place, Bray, Co. Wicklow (Ireland) **Department of Agricultural Chemistry and Soil Science, University College, Belfield, Dublin 4 (Ireland) (Accepted 27 October 1980)
ABSTRACT Carey, M.L., Farrell, E.P. and McAleese, D.M., 1981. Mobilisation of nutrients in a Sitka spruce (Picea sitchensis (Bong.) Carr.) forest floor. II. Interaction of leaching with lime and fertilizers. Forest Ecol. Manage., 3: 229--236. Samples of Sitka spruce (Picea sitchensis (Bong.) Carr.) litter incubated at 12°C were leached periodically with water following addition of lime and fertilizers over a period of 94 days. The leachates were examined for levels of N, P and K. The results showed that nitrogenous fertilizers are easily leached from Sitka spruce forest floor material and that their application results in a significant release of phosphorus and potassium. Phosphorus and lime application, although not leached out as easily, resulted in a significant increase in the release of nitrogen and potassium from the forest floor. In general the quantities of nutrients released from the forest floor following the application of lime and fertilizers appear small relative to the overall nutrient cycle.
INTRODUCTION The effects o f fertilizer n i t r o g e n , p h o s p h o r u s and lime o n the m o b i l i s a t i o n o f n u t r i e n t s f r o m Sitka spruce (Picea sitchensis (Bong.) Carr.) f o r e s t f l o o r material have b e e n r e p o r t e d in an earlier p a p e r (Carey et al., 1 9 8 1 ) . In three e x p e r i m e n t s , n i t r o g e n m o b i l i s a t i o n was m e a s u r e d in the t r e a t e d forest f l o o r samples using a s o l u t i o n o f N KC1, a practice c o m m o n in m a n y o t h e r studies of this kind (Viro, 1 9 6 3 ; N 5 m m i k , 1 9 6 8 ; Overrein, 1 9 6 7 , 1 9 7 0 ; Williams, 1972). P h o s p h o r u s m o b i l i s a t i o n was m e a s u r e d b y treating the samples with a s o l u t i o n o f 3 N H2SO4. A l t h o u g h b o t h e x t r a c t a n t s give s o m e i n d i c a t i o n o f w h a t t h e end result m a y be t h e y suffer f r o m a disadvantage in t h a t t h e y o n l y reflect t h e levels o f e x t r a c t a b l e n u t r i e n t s at a particular p o i n t in t i m e in t h e test material a n d provide little i n f o r m a t i o n o n the actual a m o u n t s t h a t m a y
0378-1127/81/0000--0000/$02.50 © 1981 Elsevier Scientific Publishing Company
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be released or on their rates of release. In an a t t e m p t to fill this void some researchers have set up leaching type experiments in which water is passed through the material in question and the subsequent leachate analyses for nutrients. Foremost amongst these have been the studies of Cole and Gessel (1963), Beaton et al. (1969), Riekerk (1971) and McColl (1973). This report describes one such experiment in which samples of a Sitka spruce forest floor were leached with water following treatment with fertilizers and lime, and the leachates subsequently analysed for their concentrations of nitrogen, phosphorus and potassium. MATERIALS AND METHODS
The forest floor sample material was similar to that described in the earlier paper (Carey et al., 1981). Moist samples, each weighing 40 g (12 g dry weight), were placed in PVC rings, 7 cm diameter and 8 cm deep, one end of which had been covered with a double layer of fine nylon netting secured by means of elastic bands. Samples and their containers were placed in petri dishes and the treatments {Table I) applied to the surface and washed in lightly with distilled water.
TABLE I Experimental treatments Treatment
Weight of c h e m i c a l (mg)/sample
E q u i v a l e n t rate o f active n u t r i e n t (kg/ha)
Control Ground rock phosphate NaH2PO42H20 CaNH4NO 3 NH4NO 3 CaCO 3
0 265 193 295 219 1922
0 100 100 200 200 5000
P P N N CaCO3
N ]~. T h e rates p e r s a m p l e were based o n t h e surface area o f t h e s a m p l e s as o p p o s e d to their dry matter content.
Samples and petri dishes were then incubated at 12°C for 94 days. On day 11, 28, 52, 73 and 94 all samples were removed from the incubator for a period of 6--7 h. During this time sufficient distilled water was added slowly to each to provide a total leachate of 200 cm 3. The quantity of water necessary to achieve this was usually about 210--220 cm 3. This quantity approximates with the estimated average throughfall for a period of similar duration in the forest from which the sample material was obtained. The leachates were then filtered and stored at 4°C for chemical analysis.
231
Chemical analysis All leachates were filtered before analysis. Total water soluble nitrogen, phosphorus and potassium were determined as outlined in Carey et al. (1981). Total nitrogen was not fractionated. RESULTS AND DISCUSSION
The effects of the various fertilizer treatments, and time of incubation on the quantity of nitrogen in the leachates at leaching date are shown in Figs. 1 and 2. The pH of the forest floor samples after leaching are given in Table II. Nitrogen content of the leachates varied significantly between some of the leachings and also as a result of all fertilizer treatments, and there was a significant interaction between the two factors. In addition to calcium carbonate and rock phosphate applications increasing the quantity of nitrogen in the leachates, the effect of sodium dihydrogen orthophosphate in this respect during the earlier part of the experiment is particularly striking. After 52 days and three leachings practically twice as much nitrogen had been obtained from the leachates of this treatment compared with the controls (Fig. 2). This is consistent with results obtained by Viro (1963) who also used sodium dihydrogen orthophosphate. Although the results suggest therefore that the addition of phosphate causes a release of nitrogen from the test material, it is possible that it is the sodium ion rather than the orthophosphate which is actually responsible for the effect. For instance, Agarwal et al. (1971) found that the sodium ion had the ability to displace NH~-N in a mineral soil with a high organic carbon content. It is also possible that the release of nitrogen is due to the effect of increased alkalinity on the dissociation of soil water which may result in an increase in both organic matter and nitrogen mineralisation as suggested by Laura (1976). This hypothesis is supported by the data in Table II which show that the addition of NaH2PO4 did T A B L E II p H o f f o r e s t f l o o r s a m p l e s f o l l o w i n g l e a c h i n g w i t h w a t e r a n d various fertilizer t r e a t m e n t s Fertilizer treatments
Control G r o u n d r o c k p h o s p h a t e 100 NaH2PO 4 100 CaNH4NO3200 NH4NO3200 CACO3500
Date of s a m p l i n g (days) 11
28
52
73
94
3.9 3.9 4.2 3.9 3.9 7.1
4.0 4.2 4.3 4.5 4.4 6.9
4.2 4.3 4.1 4.8 4.5 6.9
4.2 4.2 4.2 4.8 4.7 6.7
4.3 4.4 4.2 4.7 4.7 6.8
SE = 0.03 ( d a t e a n d t r e a t m e n t m e a n s ) ; LSD (5%) = 0.10.
232
300 CaNH4N03
o-...-o
200
E 100 o o T"
0
°
Lsos,o 0
, 11
, 28
, 52
, Day 73
P , 94
Fig. 1. Nitrogen c o n t e n t of leachates. T r e a t m e n t details are given in Table I.
600. 500 400
E
300
. , ~ . ~
,/
....... 0 " ~ ' ~ . . . . . . "'"
sCaN NH4N
"13
o o p z
E C~
GRP
..t~:
Ca
50
~
~
+
.....
NaP
40. 30, 20
10, 0
.I
11
.-
I
28
J
52
A
73
|
94
Fig. 2. Cumulative nitrogen c o n t e n t o f leachates. T r e a t m e n t details are given in Table I.
233 TABLE III Water soluble inorganic phosphorus content of leachates Fertilizer treatments
Leaching date (days) 11
Control (cumulative) CaNH4NO3 (cumulative) NH~NO3 (cumulative) CaCO~ (cumulative)
0.67 (0.67) 1.21 (1.21) 1.90 (1.90) 0.50 (0.50)
28 1.93 (2.60) 2.33 (3.54) 2.22 (4.12) 0.77 (1.27)
52 0.44 (3.04) 1.70 (5.24) 1.91 (6.03) 1.77 (3.04)
73 0.55 (3.59) 1.07 (6.31) 1.19 (7.22) 1.32 (4.36)
94 0.36 (3.95) 0.50 (6.81) 0.28 (7.50) 0.64 (5.00)
SE = 0.07. LSD (5%) = 0.14 (does not refer to cumulative data). result in a small, though significant, increase in pH for the first two leaching periods. Whatever the cause of the nitrogen release, the results are somewhat in contrast to those obtained in the earlier experiments (Carey et al., 1981), where it was f o u n d that the addition of o r t h o p h o s p h a t e (as the potassium dihydrogen form) had little, if any, effect on the levels of N KCl-extractable nitrogen. It could be postulated t ha t the o r t h o p h o s p h a t e , or its carrier ion, or b oth together, stimulate mineralisation of nitrogen which in this experimerit was leached out by water but in the earlier experiments was re-immobilised. A similar explanation could be put forward for the positive effect of lime on nitrogen release in this e x p e r i m e n t and its negative effect in this regard r ep o r ted previously (Carey et al., 1981). There were no significant differences between the data for the two sources of nitrogen. When the figures are com pa r ed with the controls, the recovery of applied nitrogen (assuming no mineralisation) is in the order of 85% (allowance being made for the fact that the treatments were applied on an area basis whereas the results are expressed on a dry m at t er basis). Both nitrogen treatments and lime application increased the pH of the forest floor leachates significantly. The effects of applied nitrogen and lime on the inorganic phosphorus content of the leachates are shown in Table III. The cumulative figures for each t r e a t m e n t and time of leaching/incubation affected the inorganic phosphorus c o n t e n t o f the leachates significantly. The time × t r e a t m e n t interaction was also found to be significant. The main effect of bot h forms of nitrogen and lime was to increase the phosphorus contents of the leachates up to a b o u t day 52 after which their effects in this regard, although still significantly better than the controls, t ended to decrease. This decrease was highly significant for the three treatments. Whether this is due to the fact that most of the applied nitrogen and very likely much of the applied lime had been leached away at this stage of the e x p e r i m e n t can only be speculated upon.
234
]" LS D 5O/o E 1Go "o 0 0
--.50
Ca
o~
GRP O
E~o 1"0. 0
,
,
,
,.., a y n
11
28
52
73
N 94
Fig. 3. P o t a s s i u m c o n t e n t of leachates. T r e a t m e n t details are given in T a b l e I.
The effect of the different treatments on the potassium content of the leachates are shown in Figs 3 and 4. It is apparent that all treatments with the exception of the orthophosphate significantly affected the quantity of potassium in the leachates and that these effects varied significantly with time during the course of the experiment (the time X treatment effect being also highly significant). Both forms of applied nitrogen had the greatest effect on the mobilisation of potassium for the first two leachings. Thereafter, the potassium content of the leachates from the samples treated with nitrogen was significantly lower than the controls. 40 +Ca
.+/......s =
/
jo
o
//.o
o
~
+
NaP
E Day 0
I
11
an
o
28
52
|
a
73
94
Fig. 4. Cumulative potassium content of leachates. Treatment details are given in Table I.
235 S o d i u m d i h y d r o g e n o r t h o p h o s p h a t e , a l t h o u g h it initially increased the potassium c o n t e n t o f the leachates significantly, fell b e h i n d the c o n t r o l s in this regard f r o m the s e c o n d leaching onwards. The e f f e c t o f g r o u n d r o c k phosphate, on t h e o t h e r hand, was far m o r e persistent, the d i f f e r e n c e b e t w e e n the c o n t r o l s and t r e a t e d samples being still significant a f t e r the final leaching. T h e e f f e c t of lime o n t h e p o t a s s i u m c o n t e n t o f the leachates also lasted for the d u r a t i o n o f the e x p e r i m e n t a l t h o u g h it t o o gradually decreased in effectiveness with time. CONCLUSIONS These results, a l t h o u g h t h e y d i f f e r s o m e w h a t f r o m t h o s e r e p o r t e d in the earlier paper, nevertheless indicate t h a t considerable changes m a y o c c u r in the n u t r i e n t d y n a m i c s o f a Sitka spruce f o r e s t f l o o r following the a d d i t i o n of fertilizer materials and lime. B o t h papers clearly illustrate the p r o b l e m s t h a t arise in r e l a t i o n t o t h e i n t e r p r e t a t i o n o f results f r o m i n c u b a t i o n experim e n t s and, in particular, their e x t r a p o l a t i o n to what might h a p p e n u n d e r the c o n s i d e r a b l y d i f f e r e n t c o n d i t i o n s pertaining in the forest. In general, the results s h o w t h a t n i t r o g e n o u s fertilizer materials are easily leached f r o m Sitka spruce f o r e s t floors and t h a t in t h e i r m o v e m e n t t h r o u g h t h e y m a y bring a b o u t a small, b u t significant, release o f native p h o s p h o r u s and potassium. Phosphorus and lime application, a l t h o u g h n o t leached o u t as easily, result in a significant increase in t h e release o f n i t r o g e n and p o t a s s i u m f r o m the forest floor. A l t h o u g h the a d d i t i o n o f lime and fertilizers bring a b o u t significant changes in the n u t r i e n t d y n a m i c s o f the f o r e s t floor, the quantities of n u t r i e n t s included a p p e a r small relative to the overall n u t r i e n t budget. ACKNOWLEDGEMENTS G r a t e f u l a c k n o w l e d g e m e n t is e x t e n d e d t o the F o r e s t and Wildlife Service for financial aid and t o Miss Rachel Reid for assistance in the chemical analyses. This s t u d y is based o n part o f a larger s t u d y carried o u t b y M.L. Carey at University College, Dublin. REFERENCES Agarwal, A.S., Singh, B.R. and Kanehiro, Y., 1971. Ionic effects of salts on mineral nitrogen release in an allophanic soil. Soil Sci. Soc. Am. Proc., 35: 454--457. Beaton, J.D., Harapiak, J.T., Speer, R.C. and Gardiner, R.T., 1969. Release of plant nutrients from forest soils humus treated with nitrogen and sulphur fertilizers. Can. Soc. Soil Sci. Annu. Meeting, pp. 1--15. Carey, M.L., Farrell, E.P. and McAleese, D.M., 1981. Mobilisation of nutrients in a Sitka spruce (t~'cea sitchensis (Bong.) Carr.) forest floor. I. Influence of lime and fertilizers. Forest Ecol. Manage., 3: 209--227. Cole. D.W. and Gessel, S.P., 1963. Movement of elements through a forest floor as influenced by tree removal and fertilizer additions. In: C.T. Youngberg (Editor), Forest Soil Relationships in North America. Proc. 2nd. N. Am. For. Soil Conf. Oregon State Univ. Press, Corvallis, pp. 95--104.
236 Laura, R.D., 1976. The effects of alkali salts on carbon and nitrogen mineralisation of organic m a t t e r in soil. Plant Soil, 44: 587--596. McColl, J.C., 1973. E n v i r o n m e n t a l factors influencing ion transport in a Douglas fir forest soil in western Washington. J. Ecol., 61: 71--83. N ~ m m i k , H., 1968. Nitrogen mineralisation and t u r n o v e r in Norway spruce (Picea abies (L) Karst) raw h u m u s as influenced by liming. 9th Int. Cong. Soil Sci., Adelaide, 2: 533--545. Overrein, L.N., 1967. I m m o b i l i s a t i o n and mineralisation of tracer nitrogen in forest raw humus. I. Effects of t e m p e r a t u r e on the interchange of nitrogen after addition of ureaa m m o n i u m - and nitrate-N L5. Plant Soil, 27: 1--19. Overrein, L.N., 1970. Tracer studies on nitrogen immobilisation--mineralisation relationships in forest raw humus. Plant Soil, 32: 478--500. Riekerk, H., 1971. The m o b i l i t y of phosphorus, potassium and calcium in a forest soil. Soil Sci. Soc. Am. Proc. 35: 350--356. Viro, P.J., 1963. Factorial e x p e r i m e n t s on forest humus decomposition. Soil Sci., 95: 2 4 30. Williams, B.L., 1972. Nitrogen mineralisation and organic m a t t e r d e c o m p o s i t i o n in Scots pine humus. Forestry, 45: 177--188.
229
M O B I L I S A T I O N O F N U T R I E N T S IN A S I T K A S P R U C E ( P I C E A S I T C H E N S I S ) (BONG.) C A R R . ) F O R E S T F L O O R II. I N T E R A C T I O N O F L E A C H I N G W I T H L I M E A N D F E R T I L I Z E R S UNDER LABORATORY CONDITIONS
M.L. CAREY*, E.P. FARRELL** and D.M. McALEESE**
*Forest and Wildlife Service, Sidmonton Place, Bray, Co. Wicklow (Ireland) **Department of Agricultural Chemistry and Soil Science, University College, Belfield, Dublin 4 (Ireland) (Accepted 27 October 1980)
ABSTRACT Carey, M.L., Farrell, E.P. and McAleese, D.M., 1981. Mobilisation of nutrients in a Sitka spruce (Picea sitchensis (Bong.) Carr.) forest floor. II. Interaction of leaching with lime and fertilizers. Forest Ecol. Manage., 3: 229--236. Samples of Sitka spruce (Picea sitchensis (Bong.) Carr.) litter incubated at 12°C were leached periodically with water following addition of lime and fertilizers over a period of 94 days. The leachates were examined for levels of N, P and K. The results showed that nitrogenous fertilizers are easily leached from Sitka spruce forest floor material and that their application results in a significant release of phosphorus and potassium. Phosphorus and lime application, although not leached out as easily, resulted in a significant increase in the release of nitrogen and potassium from the forest floor. In general the quantities of nutrients released from the forest floor following the application of lime and fertilizers appear small relative to the overall nutrient cycle.
INTRODUCTION The effects o f fertilizer n i t r o g e n , p h o s p h o r u s and lime o n the m o b i l i s a t i o n o f n u t r i e n t s f r o m Sitka spruce (Picea sitchensis (Bong.) Carr.) f o r e s t f l o o r material have b e e n r e p o r t e d in an earlier p a p e r (Carey et al., 1 9 8 1 ) . In three e x p e r i m e n t s , n i t r o g e n m o b i l i s a t i o n was m e a s u r e d in the t r e a t e d forest f l o o r samples using a s o l u t i o n o f N KC1, a practice c o m m o n in m a n y o t h e r studies of this kind (Viro, 1 9 6 3 ; N 5 m m i k , 1 9 6 8 ; Overrein, 1 9 6 7 , 1 9 7 0 ; Williams, 1972). P h o s p h o r u s m o b i l i s a t i o n was m e a s u r e d b y treating the samples with a s o l u t i o n o f 3 N H2SO4. A l t h o u g h b o t h e x t r a c t a n t s give s o m e i n d i c a t i o n o f w h a t t h e end result m a y be t h e y suffer f r o m a disadvantage in t h a t t h e y o n l y reflect t h e levels o f e x t r a c t a b l e n u t r i e n t s at a particular p o i n t in t i m e in t h e test material a n d provide little i n f o r m a t i o n o n the actual a m o u n t s t h a t m a y
0378-1127/81/0000--0000/$02.50 © 1981 Elsevier Scientific Publishing Company
230
be released or on their rates of release. In an a t t e m p t to fill this void some researchers have set up leaching type experiments in which water is passed through the material in question and the subsequent leachate analyses for nutrients. Foremost amongst these have been the studies of Cole and Gessel (1963), Beaton et al. (1969), Riekerk (1971) and McColl (1973). This report describes one such experiment in which samples of a Sitka spruce forest floor were leached with water following treatment with fertilizers and lime, and the leachates subsequently analysed for their concentrations of nitrogen, phosphorus and potassium. MATERIALS AND METHODS
The forest floor sample material was similar to that described in the earlier paper (Carey et al., 1981). Moist samples, each weighing 40 g (12 g dry weight), were placed in PVC rings, 7 cm diameter and 8 cm deep, one end of which had been covered with a double layer of fine nylon netting secured by means of elastic bands. Samples and their containers were placed in petri dishes and the treatments {Table I) applied to the surface and washed in lightly with distilled water.
TABLE I Experimental treatments Treatment
Weight of c h e m i c a l (mg)/sample
E q u i v a l e n t rate o f active n u t r i e n t (kg/ha)
Control Ground rock phosphate NaH2PO42H20 CaNH4NO 3 NH4NO 3 CaCO 3
0 265 193 295 219 1922
0 100 100 200 200 5000
P P N N CaCO3
N ]~. T h e rates p e r s a m p l e were based o n t h e surface area o f t h e s a m p l e s as o p p o s e d to their dry matter content.
Samples and petri dishes were then incubated at 12°C for 94 days. On day 11, 28, 52, 73 and 94 all samples were removed from the incubator for a period of 6--7 h. During this time sufficient distilled water was added slowly to each to provide a total leachate of 200 cm 3. The quantity of water necessary to achieve this was usually about 210--220 cm 3. This quantity approximates with the estimated average throughfall for a period of similar duration in the forest from which the sample material was obtained. The leachates were then filtered and stored at 4°C for chemical analysis.
231
Chemical analysis All leachates were filtered before analysis. Total water soluble nitrogen, phosphorus and potassium were determined as outlined in Carey et al. (1981). Total nitrogen was not fractionated. RESULTS AND DISCUSSION
The effects of the various fertilizer treatments, and time of incubation on the quantity of nitrogen in the leachates at leaching date are shown in Figs. 1 and 2. The pH of the forest floor samples after leaching are given in Table II. Nitrogen content of the leachates varied significantly between some of the leachings and also as a result of all fertilizer treatments, and there was a significant interaction between the two factors. In addition to calcium carbonate and rock phosphate applications increasing the quantity of nitrogen in the leachates, the effect of sodium dihydrogen orthophosphate in this respect during the earlier part of the experiment is particularly striking. After 52 days and three leachings practically twice as much nitrogen had been obtained from the leachates of this treatment compared with the controls (Fig. 2). This is consistent with results obtained by Viro (1963) who also used sodium dihydrogen orthophosphate. Although the results suggest therefore that the addition of phosphate causes a release of nitrogen from the test material, it is possible that it is the sodium ion rather than the orthophosphate which is actually responsible for the effect. For instance, Agarwal et al. (1971) found that the sodium ion had the ability to displace NH~-N in a mineral soil with a high organic carbon content. It is also possible that the release of nitrogen is due to the effect of increased alkalinity on the dissociation of soil water which may result in an increase in both organic matter and nitrogen mineralisation as suggested by Laura (1976). This hypothesis is supported by the data in Table II which show that the addition of NaH2PO4 did T A B L E II p H o f f o r e s t f l o o r s a m p l e s f o l l o w i n g l e a c h i n g w i t h w a t e r a n d various fertilizer t r e a t m e n t s Fertilizer treatments
Control G r o u n d r o c k p h o s p h a t e 100 NaH2PO 4 100 CaNH4NO3200 NH4NO3200 CACO3500
Date of s a m p l i n g (days) 11
28
52
73
94
3.9 3.9 4.2 3.9 3.9 7.1
4.0 4.2 4.3 4.5 4.4 6.9
4.2 4.3 4.1 4.8 4.5 6.9
4.2 4.2 4.2 4.8 4.7 6.7
4.3 4.4 4.2 4.7 4.7 6.8
SE = 0.03 ( d a t e a n d t r e a t m e n t m e a n s ) ; LSD (5%) = 0.10.
232
300 CaNH4N03
o-...-o
200
E 100 o o T"
0
°
Lsos,o 0
, 11
, 28
, 52
, Day 73
P , 94
Fig. 1. Nitrogen c o n t e n t of leachates. T r e a t m e n t details are given in Table I.
600. 500 400
E
300
. , ~ . ~
,/
....... 0 " ~ ' ~ . . . . . . "'"
sCaN NH4N
"13
o o p z
E C~
GRP
..t~:
Ca
50
~
~
+
.....
NaP
40. 30, 20
10, 0
.I
11
.-
I
28
J
52
A
73
|
94
Fig. 2. Cumulative nitrogen c o n t e n t o f leachates. T r e a t m e n t details are given in Table I.
233 TABLE III Water soluble inorganic phosphorus content of leachates Fertilizer treatments
Leaching date (days) 11
Control (cumulative) CaNH4NO3 (cumulative) NH~NO3 (cumulative) CaCO~ (cumulative)
0.67 (0.67) 1.21 (1.21) 1.90 (1.90) 0.50 (0.50)
28 1.93 (2.60) 2.33 (3.54) 2.22 (4.12) 0.77 (1.27)
52 0.44 (3.04) 1.70 (5.24) 1.91 (6.03) 1.77 (3.04)
73 0.55 (3.59) 1.07 (6.31) 1.19 (7.22) 1.32 (4.36)
94 0.36 (3.95) 0.50 (6.81) 0.28 (7.50) 0.64 (5.00)
SE = 0.07. LSD (5%) = 0.14 (does not refer to cumulative data). result in a small, though significant, increase in pH for the first two leaching periods. Whatever the cause of the nitrogen release, the results are somewhat in contrast to those obtained in the earlier experiments (Carey et al., 1981), where it was f o u n d that the addition of o r t h o p h o s p h a t e (as the potassium dihydrogen form) had little, if any, effect on the levels of N KCl-extractable nitrogen. It could be postulated t ha t the o r t h o p h o s p h a t e , or its carrier ion, or b oth together, stimulate mineralisation of nitrogen which in this experimerit was leached out by water but in the earlier experiments was re-immobilised. A similar explanation could be put forward for the positive effect of lime on nitrogen release in this e x p e r i m e n t and its negative effect in this regard r ep o r ted previously (Carey et al., 1981). There were no significant differences between the data for the two sources of nitrogen. When the figures are com pa r ed with the controls, the recovery of applied nitrogen (assuming no mineralisation) is in the order of 85% (allowance being made for the fact that the treatments were applied on an area basis whereas the results are expressed on a dry m at t er basis). Both nitrogen treatments and lime application increased the pH of the forest floor leachates significantly. The effects of applied nitrogen and lime on the inorganic phosphorus content of the leachates are shown in Table III. The cumulative figures for each t r e a t m e n t and time of leaching/incubation affected the inorganic phosphorus c o n t e n t o f the leachates significantly. The time × t r e a t m e n t interaction was also found to be significant. The main effect of bot h forms of nitrogen and lime was to increase the phosphorus contents of the leachates up to a b o u t day 52 after which their effects in this regard, although still significantly better than the controls, t ended to decrease. This decrease was highly significant for the three treatments. Whether this is due to the fact that most of the applied nitrogen and very likely much of the applied lime had been leached away at this stage of the e x p e r i m e n t can only be speculated upon.
234
]" LS D 5O/o E 1Go "o 0 0
--.50
Ca
o~
GRP O
E~o 1"0. 0
,
,
,
,.., a y n
11
28
52
73
N 94
Fig. 3. P o t a s s i u m c o n t e n t of leachates. T r e a t m e n t details are given in T a b l e I.
The effect of the different treatments on the potassium content of the leachates are shown in Figs 3 and 4. It is apparent that all treatments with the exception of the orthophosphate significantly affected the quantity of potassium in the leachates and that these effects varied significantly with time during the course of the experiment (the time X treatment effect being also highly significant). Both forms of applied nitrogen had the greatest effect on the mobilisation of potassium for the first two leachings. Thereafter, the potassium content of the leachates from the samples treated with nitrogen was significantly lower than the controls. 40 +Ca
.+/......s =
/
jo
o
//.o
o
~
+
NaP
E Day 0
I
11
an
o
28
52
|
a
73
94
Fig. 4. Cumulative potassium content of leachates. Treatment details are given in Table I.
235 S o d i u m d i h y d r o g e n o r t h o p h o s p h a t e , a l t h o u g h it initially increased the potassium c o n t e n t o f the leachates significantly, fell b e h i n d the c o n t r o l s in this regard f r o m the s e c o n d leaching onwards. The e f f e c t o f g r o u n d r o c k phosphate, on t h e o t h e r hand, was far m o r e persistent, the d i f f e r e n c e b e t w e e n the c o n t r o l s and t r e a t e d samples being still significant a f t e r the final leaching. T h e e f f e c t of lime o n t h e p o t a s s i u m c o n t e n t o f the leachates also lasted for the d u r a t i o n o f the e x p e r i m e n t a l t h o u g h it t o o gradually decreased in effectiveness with time. CONCLUSIONS These results, a l t h o u g h t h e y d i f f e r s o m e w h a t f r o m t h o s e r e p o r t e d in the earlier paper, nevertheless indicate t h a t considerable changes m a y o c c u r in the n u t r i e n t d y n a m i c s o f a Sitka spruce f o r e s t f l o o r following the a d d i t i o n of fertilizer materials and lime. B o t h papers clearly illustrate the p r o b l e m s t h a t arise in r e l a t i o n t o t h e i n t e r p r e t a t i o n o f results f r o m i n c u b a t i o n experim e n t s and, in particular, their e x t r a p o l a t i o n to what might h a p p e n u n d e r the c o n s i d e r a b l y d i f f e r e n t c o n d i t i o n s pertaining in the forest. In general, the results s h o w t h a t n i t r o g e n o u s fertilizer materials are easily leached f r o m Sitka spruce f o r e s t floors and t h a t in t h e i r m o v e m e n t t h r o u g h t h e y m a y bring a b o u t a small, b u t significant, release o f native p h o s p h o r u s and potassium. Phosphorus and lime application, a l t h o u g h n o t leached o u t as easily, result in a significant increase in t h e release o f n i t r o g e n and p o t a s s i u m f r o m the forest floor. A l t h o u g h the a d d i t i o n o f lime and fertilizers bring a b o u t significant changes in the n u t r i e n t d y n a m i c s o f the f o r e s t floor, the quantities of n u t r i e n t s included a p p e a r small relative to the overall n u t r i e n t budget. ACKNOWLEDGEMENTS G r a t e f u l a c k n o w l e d g e m e n t is e x t e n d e d t o the F o r e s t and Wildlife Service for financial aid and t o Miss Rachel Reid for assistance in the chemical analyses. This s t u d y is based o n part o f a larger s t u d y carried o u t b y M.L. Carey at University College, Dublin. REFERENCES Agarwal, A.S., Singh, B.R. and Kanehiro, Y., 1971. Ionic effects of salts on mineral nitrogen release in an allophanic soil. Soil Sci. Soc. Am. Proc., 35: 454--457. Beaton, J.D., Harapiak, J.T., Speer, R.C. and Gardiner, R.T., 1969. Release of plant nutrients from forest soils humus treated with nitrogen and sulphur fertilizers. Can. Soc. Soil Sci. Annu. Meeting, pp. 1--15. Carey, M.L., Farrell, E.P. and McAleese, D.M., 1981. Mobilisation of nutrients in a Sitka spruce (t~'cea sitchensis (Bong.) Carr.) forest floor. I. Influence of lime and fertilizers. Forest Ecol. Manage., 3: 209--227. Cole. D.W. and Gessel, S.P., 1963. Movement of elements through a forest floor as influenced by tree removal and fertilizer additions. In: C.T. Youngberg (Editor), Forest Soil Relationships in North America. Proc. 2nd. N. Am. For. Soil Conf. Oregon State Univ. Press, Corvallis, pp. 95--104.
236 Laura, R.D., 1976. The effects of alkali salts on carbon and nitrogen mineralisation of organic m a t t e r in soil. Plant Soil, 44: 587--596. McColl, J.C., 1973. E n v i r o n m e n t a l factors influencing ion transport in a Douglas fir forest soil in western Washington. J. Ecol., 61: 71--83. N ~ m m i k , H., 1968. Nitrogen mineralisation and t u r n o v e r in Norway spruce (Picea abies (L) Karst) raw h u m u s as influenced by liming. 9th Int. Cong. Soil Sci., Adelaide, 2: 533--545. Overrein, L.N., 1967. I m m o b i l i s a t i o n and mineralisation of tracer nitrogen in forest raw humus. I. Effects of t e m p e r a t u r e on the interchange of nitrogen after addition of ureaa m m o n i u m - and nitrate-N L5. Plant Soil, 27: 1--19. Overrein, L.N., 1970. Tracer studies on nitrogen immobilisation--mineralisation relationships in forest raw humus. Plant Soil, 32: 478--500. Riekerk, H., 1971. The m o b i l i t y of phosphorus, potassium and calcium in a forest soil. Soil Sci. Soc. Am. Proc. 35: 350--356. Viro, P.J., 1963. Factorial e x p e r i m e n t s on forest humus decomposition. Soil Sci., 95: 2 4 30. Williams, B.L., 1972. Nitrogen mineralisation and organic m a t t e r d e c o m p o s i t i o n in Scots pine humus. Forestry, 45: 177--188.