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Leaf litter decomposition and nutrient release patterns of six multipurpose tree species of central Himalaya, India
Biomass and Bioenergy 24 (2003) 3 – 11
Leaf litter decomposition and nutrient release patterns of six multipurpose tree species of central Himalaya, India R.L. Semwala , R.K. Maikhuria;∗ , K.S. Raob , K.K. Senb , K.G. Saxenac a G.B.
Pant Institute of Himalayan Environment and Development, Garhwal Unit, P.B. 92, Srinagar, Garhwal 246174, India Development and Rural Ecosystems Programme, G.B. Pant Institute of Himalayan Environment and Development, Kosi-Katarmal, Almora 263643, India c School of Environmental Sciences, Jawaharlal Nehru University, New Delhi 110067, India
b Sustainable
Received 5 October 2001; received in revised form 6 June 2002; accepted 28 June 2002
Abstract Chemical characteristics and decomposition patterns of six multipurpose tree species, viz., Alnus nepalensis, Albizzia lebbek, Boehmeria rugulosa, Dalbergia sissoo, Ficus glomerata and F. roxburghii were analysed in a mixed plantation established on an abandoned agricultural land site in a village at 1200 m altitude in Central Himalaya, India. Di4erences in chemical quality of litter species were most marked in polyphenol and N concentrations. A. lebbek, A. nepalensis and D. sissoo showed higher N (2.2–2.6%) but lower polyphenol concentrations (3.2– 4.7%) than B. rugulosa, F. glomerata and F. roxburghii (0.96 –1.97% N and 5.68–11.64% polyphenol). Signi:cant e4ects of species, incubation time and species × incubation time interaction on monthly mass, N, P and K release rates were observed. A linear combination of rainfall and temperature explained the variation in monthly mass loss better than rainfall and temperature independently. Percentage mass remaining after 1 year of incubation varied from 30 to 50, N remaining from 40 to 86, P remaining from 33 to 56 and K remaining from 1 to 3. Annual decomposition constants of mass and N were positively correlated with C and N concentrations and negatively correlated with C/N, lignin/N, polyphenol/N and lignin+polyphenol/N ratios of fresh litter. As all the species studied showed the highest rates of N and P release during the rainy season, rainy season crops are not likely to be as much nutrient stressed as winter season crops if leaf litter of these species is assumed to be the sole source of nutrients to crops in tree-crop mixed agroforestry. A. lebbek, A. nepalensis, D. sissoo and F. glomerata seem to be more appropriate for rapid recovery in degraded lands as their litter decomposed faster than B. rugulosa and F. roxburghii. A diverse multipurpose tree community provides not only diverse products but may also render stable nutrient cycling. ? 2002 Elsevier Science Ltd. All rights reserved. Keywords: Agroforestry; Decomposition constant; Lignin; Polyphenol; Soil fertility in degraded lands
1. Introduction Land degradation is a major problem all through the Himalayan mountain system covering eight ∗
Corresponding author. Tel.: +91-138852424. E-mail address: [email protected] (R.K. Maikhuri).
developing countries of South Asia including Afghanistan, Bangladesh, Bhutan, China, India, Myanmar, Nepal and Pakistan. Plantations of multipurpose trees alone or combined with agricultural crops could be an e4ective land rehabilitation strategy [1–3]. Litter production, decomposition and nutrient release patterns determine the potential of tree
0961-9534/03/$ - see front matter ? 2002 Elsevier Science Ltd. All rights reserved. PII: S 0 9 6 1 - 9 5 3 4 ( 0 2 ) 0 0 0 8 7 - 9
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R.L. Semwal et al. / Biomass and Bioenergy 24 (2003) 3 – 11
species to improve soil fertility and productivity in degraded lands. Though many studies on decomposition and nutrient release from agroforestry species are available [4–10], e4orts in the Himalayan region are limited [11–13]. The aim of this study was to compare decomposition and nutrient release patterns of six multipurpose tree species in Indian Central Himalaya. 2. Materials and methods 2.1. Study area The study was carried out in village Banswara (1200 m above mean sea level) in District Rudraprayag, Garhwal (latitude 30◦ 27 N and longitude 79◦ 5 E). This area experiences a typical monsoon climate. Monthly mean minimum and maximum temperatures vary in the range of 6 –21◦ C and 18–35◦ C, respectively. The average annual rainfall is 1700 mm. The soil is derived from felspathic quartz schist, quartz muscovite schist and quartz chlorite schist [14] and 30 –80 cm deep. 2.2. Multipurpose tree species The traditional multipurpose tree species selected for this study could be categorized by their products, litter fall patterns, nitrogen :xing ability and habitat. Local people value Boehmeria rugulosa, Ficus glomerata and Ficus roxburghii as the best quality fodder species, Albizzia lebbek and Dalbergia sissoo as the best quality timber species, and Alnus nepalensis as a medium quality fuelwood and timber species. Alnus nepalensis and Dalbergia sissoo are more frequent in forests and the remaining four on farms. B. rugulosa and F. roxburghii are evergreen species exhibiting peak leaf litter fall during April–June (summer season). F. glomerata and all the three nitrogen :xing species A. nepalensis, A. lebbek and D. sissoo are deciduous species showing peak litter fall during December–January (winter season). 2.3. Plantation Five rectangular plots (10 m×7 m) were laid out on an abandoned agricultural land site. Two individuals
of each of six species were planted at 3 m distance in July 1991 such that neighbouring individuals did not belong to the same species. After 3.5 years of growth, A. lebbek, A. nepalensis, B. rugulosa, D. sissoo, F. glomerata and F. roxburghii showed mean circumference and breast height as 19.9, 26.5, 20.5, 24.0, 32.0 and 21:5 cm, respectively, and height 4.9, 7.2, 3.9, 5.1, 6.0 and 3:9 m, respectively. The soil is sandy loam (17% clay, 36% silt and 47% sand) and mildly acidic (pH 6.25) with 1.4% organic carbon, 0.22% nitrogen, 0.08% total phosphorus and 0:05 g kg−1 exchangeable potassium. 2.4. Methods of study Decomposition was studied using the litter bag technique [15]. Leaf litter was collected in traps set up at 15 cm above ground level during the peak fall period of each species. Air dried leaf material (5 g) of a species was kept in 15 cm × 15 cm nylon bags (mesh size 1 mm permitting movement of micro-arthropods). Fifteen bags of each species were randomly placed in direct contact with soil in each plot within 2 weeks after litter collection. Thus, litter of A. nepalensis, D. sissoo and F. glomerata was incubated on December 31, 1994, A. lebbek on January 31, 1995 and B. rugulosa and F. roxburghii on April 30, 1995. One bag of each species from each plot was recovered at monthly intervals over a period of 1 year. Litter was removed from each sampled bag, brushed gently to remove soil and oven dried at 70+5◦ C. Three bulk samples of fresh litter and decomposed litter recovered from three randomly selected litter bags out of :ve sampled for mass loss estimation for each species were chemically analysed. The oven dried material was ground and passed through a 1 mm sieve. Lignin and cellulose concentrations were determined following Clancy and Wilson [16], carbon following Schlesinger [17] and Taylor et al. [18], and polyphenols extracted in hot 50% aqueous methanol [19] using tannic acid as a standard only in fresh litter. In all samples, nitrogen was estimated by the micro-kjeldahl method, phosphorus by the molybdenum blue method and potassium by an atomic absorption spectrophotometer [20]. Maximum and minimum temperatures and rainfall were recorded daily during the period of study (January 1995 –April 1996) and aggregated to obtain monthly means.
R.L. Semwal et al. / Biomass and Bioenergy 24 (2003) 3 – 11
The annual decomposition constant (k) [21] for the exponential relationship was calculated using the equation: ln(x0 =xt ) = kt, where x0 is the original biomass or nutrient content of litter, xt is the mass or nutrient content remaining after time t (in years). Analysis of variance and regressions were performed following Sokal and Rohlf [22].
season (mid June–September) and cold-dry winter season (October–February). Minor variations in monthly means between years are evident from January–April data recorded in 2 years (Fig. 1). 3.2. Litter quality
3.1. Climate The year could be di4erentiated into a warmdry summer season (March–May), warm-wet rainy
Rainfall (mm)
Rainfall
Max. temp.
Min. temp.
600 500 400 300 200 100 0
J F M A M J 1995
J
A S O N D J F M A 1996 Months
40 35 30 25 20 15 10 5 0
Temperature (°C)
Di4erences between species were most marked in polyphenol and N concentrations (Table 1). A. lebbek, A. nepalensis and D. sissoo showed higher N (2.62%, 2.51% and 2.19%, respectively) but lower polyphenol concentrations (3.2%, 4.7% and 4.5%, respectively) than B. rugulosa, F. glomerata and F. roxburghii (1.16%, 1.97%, 0.96% N and 5.68%,
3. Results
700
5
Fig. 1. Monthly rainfall and maximum and minimum temperatures during the study period (January 1995 –April 1996).
Table 1 Characteristics (mean ± standard deviation) of leaf litter of multipurpose tree species planted in degraded land at Banswara, Central Himalaya, India Characteristics
Moisturea (%) Lignin Cellulose C (%) N (%) P (%) K (%) Polyphenol (%) C/N ratio Lignin/N ratio Polyphenol/N ratio Lignin + polyphenol/ N ratio a%
Tree species Albizzia lebbek
Alnus nepalensis
Boehmeria rugulosa
Dalbergia sissoo
Ficus glomerata
Ficus roxburghii
4:40 ± 0:20 9:78 ± 0:70 20:23 ± 0:40 43:00 ± 0:50 2:62 ± 0:06 0:15 ± 0:01 0:60 ± 0:06 3:20 ± 0:44 16:41 ± 0:53 3:73 ± 0:25 1:22 ± 0:14 4:95 ± 0:37
5:90 ± 0:25 15:11 ± 0:20 31:79 ± 2:42 44:17 ± 0:28 2:51 ± 0:08 0:13 ± 0:01 0:60 ± 0:04 4:70 ± 0:77 17:59 ± 0:57 6:02 ± 0:13 1:87 ± 0:30 7:89 ± 0:36
8:00 ± 0:30 13:78 ± 0:70 23:19 ± 0:34 35:83 ± 0:28 1:16 ± 0:06 0:18 ± 0:01 0:92 ± 0:08 5:68 ± 0:46 30:88 ± 1:87 11:88 ± 0:77 4:90 ± 0:14 16:77 ± 0:67
5:02 ± 0:20 9:42 ± 0:52 21:43 ± 0:51 43:00 ± 0:50 2:19 ± 0:08 0:18 ± 0:01 1:12 ± 0:10 4:50 ± 0:53 19:63 ± 0:48 4:30 ± 0:37 2:05 ± 0:17 6:35 ± 0:30
7:71 ± 0:37 13:82 ± 2:45 25:92 ± 1:00 39:16 ± 0:76 1:97 ± 0:07 0:17 ± 0:01 1:10 ± 0:07 7:10 ± 1:06 19:88 ± 0:50 7:01 ± 1:25 3:60 ± 0:66 10:62 ± 1:49
8:70 ± 0:46 12:14 ± 0:24 23:20 ± 1:44 38:00 ± 0:50 0:96 ± 0:06 0:13 ± 0:01 0:98 ± 0:09 11:64 ± 2:56 39:58 ± 2:26 12:64 ± 0:58 12:12 ± 3:20 24:77 ± 3:70
Moisture in air dried litter kept for incubation.
Least signi:cant di4erence (P = 0:05) 0.55 1.97 2.23 0.88 0.12 0.01 0.14 2.17 2.26 1.20 1.39 1.97
R.L. Semwal et al. / Biomass and Bioenergy 24 (2003) 3 – 11
120
120
100
100 % total N remaining
% mass remaining
6
80 60 Albizzia lebbek Alnus nepalensis Boehmeria rugulosa Dalbergia sissoo Ficus glomerata Ficus roxburghii
40 20 1
2
3
4
5
6
7
8
Albizzia lebbek Alnus nepalensis Boehmeria rugulosa Dalbergia sissoo
40 20
9 10 11 12
Months after incubation
(a)
Ficus glomerata Ficus roxburghii
1
2
3
4
5
6
7
8
9 10 11 12
Months after incubation
(b) 120
120
% total K remaining
% total P remaining
60
0
0
100 80 60
Albizzia lebbek Alnus nepalensis Boehmeria rugulosa Dalbergia sissoo Ficus glomerata Ficus roxburghii
40 20
100 80
Albizzia lebbek Alnus nepalensis Boehmeria rugulosa Dalbergia sissoo Ficus glomerata Ficus roxburghii
60 40 20 0
0 1 (c)
80
2
3
4
5
6
7
8
9 10 11 12
Months after incubation
1 (d)
2
3
4
5
6
7
8
9 10 11 12
Months after incubation
Fig. 2. (a) – (d) Percent biomass and nutrient (N,P,K) mass remaining in di4erent months during one year of incubation of six multipurpose trees. The vertical lines represent least signi:cant di4erence (P = 0:05).
7.1% and 11.64% polyphenol concentration, respectively). B. rugulosa and F. roxburghii had the highest C/N, lignin/N, polyphenol/N and lignin+polyphenol/N ratios. A. lebbek and A. nepalensis, and D. sissoo and F. glomerata had similar C/N and polyphenol/N ratios but di4ered in respect of lignin and lignin+polyphenol/N ratios. 3.3. Monthly mass loss and nutrient release patterns Analysis of variance revealed signi:cant (P ¡ 0:01) di4erences in decomposition rates due to species, incubation time and species × incubation time interaction. A. nepalensis, A. lebbek, D. sissoo and F. glomerata showed three phases in mass loss and N and P release (Fig. 2a–c): a slow loss in the initial period of incubation, rapid loss during intermediate phase and again a slow loss during the end of the year. B. rugulosa and F. roxburghii showed two phases in mass loss and P release: a rapid loss during the :rst
5 months followed by a slow loss phase. Such phases were not marked in N release pattern of these two species. F. roxburghii showed a prolonged immobilization and started mineralizing N after 10 months of incubation. All species showed fast release of K (Fig. 2d) soon after incubation. Di4erences between species were more marked after 7 months onwards in mass, N and P remaining and during initial 6 months in K remaining. Percentage mass remaining after 1 year of incubation varied from 30.32 to 50.38, N remaining from 40.05 to 86.04, P remaining from 33.39 to 55.71 and K remaining from 1.01 to 3.08. F. roxburghii and B. rugulosa showed signi:cantly (P ¡ 0:05) higher mass, N and P remaining than other species after 8 months of incubation. 3.4. Mass loss in relation to rainfall and temperature Monthly mass loss was positively related with rainfall and temperature but these linear relationships
P ¡ 0:01) P ¡ 0:05) P ¡ 0:01) P ¡ 0:01) P ¡ 0:01) P ¿ 0:05) (R2 = 0:87; (R2 = 0:33; (R2 = 0:75; (R2 = 0:73; (R2 = 0:83; (R2 = 0:28; y = 0:016x1 + 0:29x2 − 2:50 y = 0:009x1 + 0:22x2 + 0:34 y = 0:009x1 + 0:12x2 + 0:71 y = 0:010x1 + 0:18x2 + 0:49 y = 0:015x1 + 0:05x2 + 2:34 y = 0:004x1 + 0:08x2 + 2:02 y = 0:50x − 4:39 (R2 = 0:51; P ¡ 0:01) y = 0:344x − 0:90 (R2 = 0:40; P ¡ 0:05) y = 0:231x − 0:13 (R2 = 0:38; P ¡ 0:05) y = 0:313x − 0:82 (R2 = 0:46; P ¡ 0:05) y = 0:239x + 0:53 (R2 = 0:24; P ¿ 0:05) y = 0:126x + 1:68 (R2 = 0:17; P ¿ 0:05) Albizia lebbek Alnus nepalensis Boehmeria rugulosa Dalbergia sissoo Ficus glomerata Ficus roxburghii
y = 0:021x + 2:63 y = 0:012x + 4:23 y = 0:011x + 2:99 y = 0:013x + 3:65 y = 0:015x + 3:19 y = 0:005x + 3:52
(R2 = 0:73; (R2 = 0:40; (R2 = 0:65; (R2 = 0:61; (R2 = 0:82; (R2 = 0:20;
P ¡ 0:01) P ¡ 0:05) P ¡ 0:01) P ¡ 0:01) P ¡ 0:01) P ¿ 0:05)
Rainfall+air temperature Air temperature Rainfall
Regression Species
Table 2 Regression between monthly rainfall (mm), mean temperature (◦ C) and monthly mass loss (y) for di4erent multipurpose tree species planted in degraded land at Banswara, Central Himalaya, India
R.L. Semwal et al. / Biomass and Bioenergy 24 (2003) 3 – 11
7
were not signi:cant (P ¿ 0:05) for temperature in all species and for both temperature and rainfall in F. roxburghii (P ¿ 0:05). A linear combination of rainfall and temperature explained the variation in monthly mass loss better than rainfall and temperature independently, but the degree of improvement due to multiple regression varied between species (Table 2). 3.5. Annual decomposition constants A single exponential decay model showed a fairly good :t in all species (R2 = 0:79– 0.98) except for N release from F. roxburghii (R2 = 0:25) (Table 3). All species showed the highest decomposition constant for K. B. rugulosa and F. roxburghii showed decomposition constant of P higher and other species lower than that of N. A. nepalensis showed the highest and F. roxburghii the lowest constants for mass, N and P. The highest constant for K was observed in A. lebbek and the lowest in B. rugulosa, F. glomerata and F. roxburghii with no signi:cant di4erence (P ¿ 0:05) between them. 3.6. Decomposition and nutrient release rates in relation to litter quality Annual decomposition constants of mass and N were positively correlated with C and N concentrations and negatively correlated with C/N, lignin/N, polyphenol/N and lignin+polyphenol/N ratios of fresh litter. The decomposition constant for N showed stronger correlations with N%, C/N, lignin/N and lignin+polyphenol/N (P ¡ 0:01) as compared to other litter quality parameters. However, non-signi:cant (P ¿ 0:05) relationships were noted between these chemical attributes and P and K decomposition constants (Table 4). 4. Discussion 4.1. Litter quality The key litter quality characteristics, viz., C, N, lignin and polyphenol concentrations and ratios integrating two characteristics observed in this study are within the reported range of values [5,7,8,23–25]. Litter quality may vary within a species growing in
8
R.L. Semwal et al. / Biomass and Bioenergy 24 (2003) 3 – 11
Table 3 Annual decomposition constants (k) of mass and nutrients for leaf litter of multipurpose tree species planted in degraded land at Banswara, Central Himalaya, India
Attributes
Species
Least signi:cant di4erence (P = 0:05)
Albizzia lebbek
Alnus nepalensis
Boehmeria rugulosa
Dalbergia sissoo
Ficus glomerata
Ficus roxburghii
Mass k R2
1.02 0.89
1.16 0.92
0.74 0.98
0.99 0.93
0.99 0.93
0.63 0.97
0.03
Nitrogen k R2
0.83 0.87
0.91 0.89
0.22 0.80
0.71 0.91
0.66 0.91
0.05 0.25
0.03
Phosphorus k R2
0.73 0.79
1.09 0.92
0.63 0.98
0.83 0.93
0.78 0.85
0.53 0.98
0.04
Potassium k R2
4.66 0.96
4.04 0.95
3.84 0.97
4.28 0.98
3.70 0.97
3.64 0.96
1.30
(k) is calculated using the equation ln x0 =xt = kt. R2 expresses the variance explained by the exponential model.
Table 4 Correlation coeKcients from linear regression of leaf litter quality parameters and annual decomposition constants (k) for litter mass and nutrients of multipurpose trees planted in degraded land at Banswara, Central Himalaya, India
Litter quality
Correlation coeKcients Mass
N (%) Lignin (%) Polyphenol (%) C/N Lignin/N Polyphenol/N Lignin+polyphenol/N
0.959∗∗
−0:001 −0:777 −0:936∗∗ −0:877∗ −0:867∗ −0:906∗
Nitrogen 0.985∗∗
−0:093 −0:783 −0:975∗∗ −0:932∗∗ −0:887∗ −0:945∗∗
Phosphorous
Potassium
0.769 0.255 −0:589 −0:761 −0:662 −0:707 −0:713
−0:664 −0:799 −0:667 −0:792 −0:692 −0:770
0.752
∗ P ¡ 0:05.
∗∗ P ¡ 0:01.
di4erent environments [26,27]. Nitrogen and phosphorus concentrations of A. nepalensis were comparable, but polyphenol concentration was 1.4 times lower than the values reported by Sharma et al. [13] for this species in more humid and cooler climate of Eastern Himalaya. Mineral and lignin concentration of D. sissoo are comparable and polyphenol concentration about two times higher than the values reported in a more arid and warm climate [28]. N concentration
in leaf litter of nitrogen :xing tree species was higher than non-nitrogen :xing species [5,25,28]. 4.2. Litter quality, litter fall period and decomposition patterns In strongly seasonal climates, as in this study, contribution of leaf litter of agroforestry trees to soil fertility through decomposition would be determined
R.L. Semwal et al. / Biomass and Bioenergy 24 (2003) 3 – 11
by litter quality as well as the timing of litterfall. A. nepalensis, A. lebbek, D. sissoo and F. glomerata showing a high-quality litter shed leaves in winter and thus face relatively higher moisture and temperature stresses for a period of about 6 months after litterfall, while low-quality litter of B. rugulosa and F. roxburghii is not exposed to these abiotic stresses as leaves are shed in the beginning of rainy season. In all species, rapid mass loss occurred during warm-wet rainy season evident from a positive correlation of monthly mass loss with a linear combination of rainfall and temperature. The more important role of rainfall as compared to temperature deduced from regression analysis is supported from other studies [11,29]. However, the e4ect of these abiotic factors was not as pronounced in very low-quality material, like F. roxburghii, as in the better quality ones [8,11]. Interaction of litter quality and peak litter fall period (incubation timing) was such that species e4ects were less marked in monthly mass, N and P release rates during the initial phase of decomposition. K did show marked species e4ects during early period suggesting that this element could be easily leached [30] by even low sporadic rainfall events occurring during summer and winter months. Three-phase decomposition pattern (initial slow phase, intermediate fast phase and terminal slow phase of decomposition) in A. lebbek, A. nepalensis, D. sissoo and F. glomerata incubated long before rainy season and two-phase pattern (initial fast followed by a slow phase) in B. rugulosa and F. roxburghii incubated in the beginning of rainy season are observed in other studies in a monsoon climate [11,29,31]. Available studies suggest that plant materials with N ¿ 1:7%, lignin ¡ 15%, polyphenol ¡ 3% and C/N ratio ¡ 20 generally mineralize while those exceeding these limits immobilize N [7,25,32,33]. This generalization is supported from this study except that species like A. nepalensis, A. lebbek, D. sissoo, F. glomerata having ¿ 3% polyphenol and B. rugulosa having C/N ratio ¿ 20 did not immobilize N and F. roxburghii with ¡ 15% lignin concentration showed prolonged immobilization. 4.3. Annual decomposition constants While monthly decomposition and nutrient release rates from litter incubated at the time of litter fall in-
9
dicates contribution from trees to nutrients demanded by crops, annual decomposition constants would reLect species potential in long-term soil fertility management. Annual decay constants or mass and nutrient release in 1 year reported in this study are lower than the values reported for other agroforestry tree leaf litter in relatively more humid regions in the Himalaya [11–13] and elsewhere in the tropics [4,9,34]. Sharma et al. [13] found decomposition constant of P about 1.5 times higher than that of N in A. nepalensis, while there was no signi:cant di4erence between the two in this study. These variations could be attributed to variation in decomposer community, environmental conditions, litter quality and bag mesh size [27,35,36]. A strong correlation of annual decomposition constant of N with litter quality parameters indicates the importance of litter quality in determining N release on an annual time scale. The data show that absolute lignin and polyphenol concentration were not as strongly correlated with annual N release as their concentrations in relation to N, as also observed by Constantinides and Fownes [25] in their laboratory based studies. Di4erences among studies in best predictor of N mineralization/immobilization arise partly from variation in methods used to measure these processes and partly from variation in ranges of chemical composition of the litter materials used [25]. Relationships between decomposition constants of P and K with litter quality parameters analysed were not signi:cant (P ¿ 0:05) suggesting that processes determining P and K release may not be correlated with N release. 4.4. Synchrony between nutrient release from tree leaf litter and crop demand In Central Himalayan agroforestry systems, traditionally two crops are grown in a year, one during the rainy season (sowing in May and harvesting in September/October) and the other during the winter season (sowing in October/November and harvesting in April/May) [37]). As all species studied showed the highest rates of N and P release during the rainy season, rainy season crops are not likely to be nutrient stressed as much as winter season crops if tree leaf litter is assumed to be the sole source of nutrients to crops. F. roxburghii litter immobilizes and B. rugulosa litter releases N at slow rates but this effect is likely to be minimized due to their low litter
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R.L. Semwal et al. / Biomass and Bioenergy 24 (2003) 3 – 11
production as they are lopped for fodder. A. lebbek, A. nepalensis, D. sissoo and F. glomerata litter on account of their fast decomposition seem to be more appropriate for rapid recovery in soil fertility in degraded lands. A diverse multipurpose tree community provides not only diverse products but may also render stable nutrient cycling. Further studies are needed to evaluate the potential of multipurpose trees in pure and various combinations of mixed plantations in respect of soil fertility management. Acknowledgements We are grateful to the Director, G.B. Pant Institute of Himalayan Environment and Development for the facilities and to the Tropical Soil Biology and Fertility (TSBF) Programme, Nairobi for partial :nancial support. References [1] Gilmour DA, King GC, Applegate GB, Mohns B. Silviculture of plantation forests in central Nepal to maximize community bene:ts. Forest Ecology and Management 1990;32:173–86. [2] Rao KS, Maikhuri RK, Saxena KG. Participatory approach to rehabilitation of degraded forest land: a case study in high altitude village of Indian Himalaya. International Tree Crops Journal 1999;10:1–17. [3] Maikhuri RK, Semwal RL, Rao KS, Singh K, Saxena KG. Growth and ecological impacts of traditional agroforestry tree species in central Himalaya, India. Agroforestry Systems 2000;48:257–72. [4] Okeke AI, Omaliko CPE. Leaf litter decomposition and carbon dioxide evolution of some agroforestry fallow species in southern Nigeria. Forest Ecology and Management 1992;50:103–16. [5] Montagnini F, Ramstad K, Sancho F. Litter fall, litter decomposition and the use of mulch of four indigenous tree species in the Atlantic lowlands of Costa Rica. Agroforestry Systems 1993;23:39–61. [6] Lehmann J, Schroth G, Zech W. Decomposition and nutrient release from leaves, twigs and roots of three alley-crop tree legumes in central Togo. Agroforestry Systems 1995;29: 21–36. [7] Palm CA. Contribution of agroforestry trees to nutrient requirements of intercropped plants. Agroforestry Systems 1995;30:105–24. [8] Vanlauwe B, Vanlangenhove G, Merckx R, Vlassak K. Impact of rainfall regime on the decomposition of leaf litter with contrasting quality under subhumid tropical conditions. Biology and Fertility of Soils 1995;20:8–16.
[9] Byard R, Lewis KC, Montagnini F. Leaf litter decomposition and mulch performance from mixed and monospeci:c plantations of native tree species in Costa Rica. Agriculture, Ecosystems and Environment 1996;58:145–55. [10] Mugundi DN, Nair PKR. Predicting the decomposition patterns of tree biomass in tropical highland micro regions of Kenya. Agroforestry Systems 1997;35:187–201. [11] Pandey U, Singh JS. Leaf litter decomposition in an oak-conifer forest in Himalaya: the e4ects of climate and chemical composition. Forestry 1982;47–59. [12] Upadhyay VP. Pattern of immobilization and release of nitrogen in decomposing leaf litter in Himalayan forests. Proceedings Indian Academy of Sciences (Plant Sciences) 1988;98:215–26. [13] Sharma R, Sharma E, Purohit AN. Cardamom, mandarin and nitrogen-:xing trees in agroforestry systems in India’s Himalayan region. I. Litterfall and decomposition. Agroforestry Systems 1997;35:239–53. [14] Rao PN, Pati UC. Geology and tectonics of Bhilangana valley and its adjoining parts, Garhwal Himalaya, with special reference to main central thrust. Himalayan Geology 1980; 220 –37. [15] Gilbert DJ, Bocock KL. Some methods of studying the disappearance and decomposition of leaf litter. In: Murphy PW, editor. Progress in soil zoology. London: Butterworth, 1962. p. 348–52. [16] Clancy MJ, Wilson RK. Development and application of a new chemical method for predicting the digestibility and intake of herbage samples. Proceedings of the 10th International Grassland Congress, 1966. p. 445 –53. [17] Schlesinger WH. Carbon balance in terrestrial detritus. Annual Review of Ecology and Systematics 1977;8:51–81. [18] Taylor BR, Parkinson D, Partons WFJ. Nitrogen and lignin content as predictors of litter decay rates: microcosm test. Ecology 1989;70:97–104. [19] Palm CA, Sanchez PA. Nitrogen release from some tropical legume as a4ected by lignin and polyphenol contents. Soil Biology and Biochemistry 1991;23:83–8. [20] Allen SE. Chemical analysis of ecological materials. London: Blackwell Scienti:c Publications, 1989. [21] Olson JS. Energy storage and balance of producers and decomposers in ecological systems. Ecology 1963;44: 320–31. [22] Sokal RR, Rohlf FJ. Biometry. New York: W.H. Freeman and Company, 1981. [23] Lekha A, Gupta SR. Decomposition of Populus and Leucaena leaf litter in an agroforestry system. International Journal of Ecology and Environmental Sciences 1989;15:97–108. [24] Toky OP, Singh V. Litter dynamics in short rotation high density tree plantations in an arid region of India. Agriculture, Ecosystems and Environment 1993;45:129–45. [25] Constantinides M, Fownes JH. Nitrogen mineralization from leaves and litter of tropical plants: relationship to nitrogen, lignin and soluble polyphenol concentrations. Soil Biology and Biochemistry 1994;26:49–55. [26] Berg B, Tamm CO. Decomposition and nutrient dynamics of litter in long term optimum nutrition experiments. Scandinavian Journal of Forest Research 1991;6:305–21.
R.L. Semwal et al. / Biomass and Bioenergy 24 (2003) 3 – 11 [27] Heal OW, Anderson JM, Swift MJ. Plant litter quality and decomposition: an historical overview. In: Cadisch G, Giller KE, editors. Driven by nature: plant litter quality and decomposition. Willingford: CAB International, 1997. p. 3–30. [28] Gupta S, Kaur B. The soil decomposer system: processes, control and management. In: Gopal B, Pathak PS, Saxena KG, editors. Ecology today: an anthology of contemporary ecological research. New Delhi: International Scienti:c Publications, 1998. p. 217–61. [29] Tripathi SK, Singh KP. Abiotic and litter quality control during the decomposition of di4erent plant parts in dry tropical bamboo savanna in India. Pedobiologia 1992; 36:241–56. [30] Swift MJ, Russell-Smith A, Perfect TJ. Decomposition and mineral-nutrient dynamics of plant litter in regenerating bush-fallow in sub-humid tropical Nigeria. Journal of Ecology 1981;69:981–95. [31] Bargali SS, Singh SP, Singh RP. Patterns of weight loss and nutrient release from decomposing leaf litter in an age series of Eucalypt plantations. Soil Biology and Biochemistry 1993;25:1731–8.
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[32] Oglesby KA, Fownes JH. E4ects of chemical composition on nitrogen mineralization of green manures of seven tropical leguminous trees. Plant and Soil 1992;143:127–32. [33] Myers RJK, Palm CA, Cuevas E, Gunatilleke IUN, Brossard M. The synchronization of nutrient mineralization and plant nutrient demand. In: Woomer PL, Swift MJ, editors. The biological management of tropical soil fertility. Sussex: Wiley, 1994. p. 81–116. [34] Palma RM, Prause J, Fontanive AV, Jimenez MP. Litter fall and litter decomposition in a forest of the Parque Chaqueno Argentino. Forest Ecology and Management 1998;106:205–10. [35] Swift MJ, Heal OW, Anderson JM. Decomposition in terrestrial ecosystems. Oxford: Blackwell Scienti:c Publications, 1979. [36] Vitousek PM, Turner DR, Parton WJ, Sanford RL. Litter decomposition on the Mauna-Loa environmental matrix, Hawaii: patterns, mechanisms and models. Ecology 1994;75:418–29. [37] Nautiyal S, Maikhuri RK, Semwal RL, Rao KS, Saxena KG. Agroforestry systems in the rural landscape—a case study in Garhwal Himalaya, India. Agroforestry Systems 1998;41: 151–65.
Leaf litter decomposition and nutrient release patterns of six multipurpose tree species of central Himalaya, India R.L. Semwala , R.K. Maikhuria;∗ , K.S. Raob , K.K. Senb , K.G. Saxenac a G.B.
Pant Institute of Himalayan Environment and Development, Garhwal Unit, P.B. 92, Srinagar, Garhwal 246174, India Development and Rural Ecosystems Programme, G.B. Pant Institute of Himalayan Environment and Development, Kosi-Katarmal, Almora 263643, India c School of Environmental Sciences, Jawaharlal Nehru University, New Delhi 110067, India
b Sustainable
Received 5 October 2001; received in revised form 6 June 2002; accepted 28 June 2002
Abstract Chemical characteristics and decomposition patterns of six multipurpose tree species, viz., Alnus nepalensis, Albizzia lebbek, Boehmeria rugulosa, Dalbergia sissoo, Ficus glomerata and F. roxburghii were analysed in a mixed plantation established on an abandoned agricultural land site in a village at 1200 m altitude in Central Himalaya, India. Di4erences in chemical quality of litter species were most marked in polyphenol and N concentrations. A. lebbek, A. nepalensis and D. sissoo showed higher N (2.2–2.6%) but lower polyphenol concentrations (3.2– 4.7%) than B. rugulosa, F. glomerata and F. roxburghii (0.96 –1.97% N and 5.68–11.64% polyphenol). Signi:cant e4ects of species, incubation time and species × incubation time interaction on monthly mass, N, P and K release rates were observed. A linear combination of rainfall and temperature explained the variation in monthly mass loss better than rainfall and temperature independently. Percentage mass remaining after 1 year of incubation varied from 30 to 50, N remaining from 40 to 86, P remaining from 33 to 56 and K remaining from 1 to 3. Annual decomposition constants of mass and N were positively correlated with C and N concentrations and negatively correlated with C/N, lignin/N, polyphenol/N and lignin+polyphenol/N ratios of fresh litter. As all the species studied showed the highest rates of N and P release during the rainy season, rainy season crops are not likely to be as much nutrient stressed as winter season crops if leaf litter of these species is assumed to be the sole source of nutrients to crops in tree-crop mixed agroforestry. A. lebbek, A. nepalensis, D. sissoo and F. glomerata seem to be more appropriate for rapid recovery in degraded lands as their litter decomposed faster than B. rugulosa and F. roxburghii. A diverse multipurpose tree community provides not only diverse products but may also render stable nutrient cycling. ? 2002 Elsevier Science Ltd. All rights reserved. Keywords: Agroforestry; Decomposition constant; Lignin; Polyphenol; Soil fertility in degraded lands
1. Introduction Land degradation is a major problem all through the Himalayan mountain system covering eight ∗
Corresponding author. Tel.: +91-138852424. E-mail address: [email protected] (R.K. Maikhuri).
developing countries of South Asia including Afghanistan, Bangladesh, Bhutan, China, India, Myanmar, Nepal and Pakistan. Plantations of multipurpose trees alone or combined with agricultural crops could be an e4ective land rehabilitation strategy [1–3]. Litter production, decomposition and nutrient release patterns determine the potential of tree
0961-9534/03/$ - see front matter ? 2002 Elsevier Science Ltd. All rights reserved. PII: S 0 9 6 1 - 9 5 3 4 ( 0 2 ) 0 0 0 8 7 - 9
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R.L. Semwal et al. / Biomass and Bioenergy 24 (2003) 3 – 11
species to improve soil fertility and productivity in degraded lands. Though many studies on decomposition and nutrient release from agroforestry species are available [4–10], e4orts in the Himalayan region are limited [11–13]. The aim of this study was to compare decomposition and nutrient release patterns of six multipurpose tree species in Indian Central Himalaya. 2. Materials and methods 2.1. Study area The study was carried out in village Banswara (1200 m above mean sea level) in District Rudraprayag, Garhwal (latitude 30◦ 27 N and longitude 79◦ 5 E). This area experiences a typical monsoon climate. Monthly mean minimum and maximum temperatures vary in the range of 6 –21◦ C and 18–35◦ C, respectively. The average annual rainfall is 1700 mm. The soil is derived from felspathic quartz schist, quartz muscovite schist and quartz chlorite schist [14] and 30 –80 cm deep. 2.2. Multipurpose tree species The traditional multipurpose tree species selected for this study could be categorized by their products, litter fall patterns, nitrogen :xing ability and habitat. Local people value Boehmeria rugulosa, Ficus glomerata and Ficus roxburghii as the best quality fodder species, Albizzia lebbek and Dalbergia sissoo as the best quality timber species, and Alnus nepalensis as a medium quality fuelwood and timber species. Alnus nepalensis and Dalbergia sissoo are more frequent in forests and the remaining four on farms. B. rugulosa and F. roxburghii are evergreen species exhibiting peak leaf litter fall during April–June (summer season). F. glomerata and all the three nitrogen :xing species A. nepalensis, A. lebbek and D. sissoo are deciduous species showing peak litter fall during December–January (winter season). 2.3. Plantation Five rectangular plots (10 m×7 m) were laid out on an abandoned agricultural land site. Two individuals
of each of six species were planted at 3 m distance in July 1991 such that neighbouring individuals did not belong to the same species. After 3.5 years of growth, A. lebbek, A. nepalensis, B. rugulosa, D. sissoo, F. glomerata and F. roxburghii showed mean circumference and breast height as 19.9, 26.5, 20.5, 24.0, 32.0 and 21:5 cm, respectively, and height 4.9, 7.2, 3.9, 5.1, 6.0 and 3:9 m, respectively. The soil is sandy loam (17% clay, 36% silt and 47% sand) and mildly acidic (pH 6.25) with 1.4% organic carbon, 0.22% nitrogen, 0.08% total phosphorus and 0:05 g kg−1 exchangeable potassium. 2.4. Methods of study Decomposition was studied using the litter bag technique [15]. Leaf litter was collected in traps set up at 15 cm above ground level during the peak fall period of each species. Air dried leaf material (5 g) of a species was kept in 15 cm × 15 cm nylon bags (mesh size 1 mm permitting movement of micro-arthropods). Fifteen bags of each species were randomly placed in direct contact with soil in each plot within 2 weeks after litter collection. Thus, litter of A. nepalensis, D. sissoo and F. glomerata was incubated on December 31, 1994, A. lebbek on January 31, 1995 and B. rugulosa and F. roxburghii on April 30, 1995. One bag of each species from each plot was recovered at monthly intervals over a period of 1 year. Litter was removed from each sampled bag, brushed gently to remove soil and oven dried at 70+5◦ C. Three bulk samples of fresh litter and decomposed litter recovered from three randomly selected litter bags out of :ve sampled for mass loss estimation for each species were chemically analysed. The oven dried material was ground and passed through a 1 mm sieve. Lignin and cellulose concentrations were determined following Clancy and Wilson [16], carbon following Schlesinger [17] and Taylor et al. [18], and polyphenols extracted in hot 50% aqueous methanol [19] using tannic acid as a standard only in fresh litter. In all samples, nitrogen was estimated by the micro-kjeldahl method, phosphorus by the molybdenum blue method and potassium by an atomic absorption spectrophotometer [20]. Maximum and minimum temperatures and rainfall were recorded daily during the period of study (January 1995 –April 1996) and aggregated to obtain monthly means.
R.L. Semwal et al. / Biomass and Bioenergy 24 (2003) 3 – 11
The annual decomposition constant (k) [21] for the exponential relationship was calculated using the equation: ln(x0 =xt ) = kt, where x0 is the original biomass or nutrient content of litter, xt is the mass or nutrient content remaining after time t (in years). Analysis of variance and regressions were performed following Sokal and Rohlf [22].
season (mid June–September) and cold-dry winter season (October–February). Minor variations in monthly means between years are evident from January–April data recorded in 2 years (Fig. 1). 3.2. Litter quality
3.1. Climate The year could be di4erentiated into a warmdry summer season (March–May), warm-wet rainy
Rainfall (mm)
Rainfall
Max. temp.
Min. temp.
600 500 400 300 200 100 0
J F M A M J 1995
J
A S O N D J F M A 1996 Months
40 35 30 25 20 15 10 5 0
Temperature (°C)
Di4erences between species were most marked in polyphenol and N concentrations (Table 1). A. lebbek, A. nepalensis and D. sissoo showed higher N (2.62%, 2.51% and 2.19%, respectively) but lower polyphenol concentrations (3.2%, 4.7% and 4.5%, respectively) than B. rugulosa, F. glomerata and F. roxburghii (1.16%, 1.97%, 0.96% N and 5.68%,
3. Results
700
5
Fig. 1. Monthly rainfall and maximum and minimum temperatures during the study period (January 1995 –April 1996).
Table 1 Characteristics (mean ± standard deviation) of leaf litter of multipurpose tree species planted in degraded land at Banswara, Central Himalaya, India Characteristics
Moisturea (%) Lignin Cellulose C (%) N (%) P (%) K (%) Polyphenol (%) C/N ratio Lignin/N ratio Polyphenol/N ratio Lignin + polyphenol/ N ratio a%
Tree species Albizzia lebbek
Alnus nepalensis
Boehmeria rugulosa
Dalbergia sissoo
Ficus glomerata
Ficus roxburghii
4:40 ± 0:20 9:78 ± 0:70 20:23 ± 0:40 43:00 ± 0:50 2:62 ± 0:06 0:15 ± 0:01 0:60 ± 0:06 3:20 ± 0:44 16:41 ± 0:53 3:73 ± 0:25 1:22 ± 0:14 4:95 ± 0:37
5:90 ± 0:25 15:11 ± 0:20 31:79 ± 2:42 44:17 ± 0:28 2:51 ± 0:08 0:13 ± 0:01 0:60 ± 0:04 4:70 ± 0:77 17:59 ± 0:57 6:02 ± 0:13 1:87 ± 0:30 7:89 ± 0:36
8:00 ± 0:30 13:78 ± 0:70 23:19 ± 0:34 35:83 ± 0:28 1:16 ± 0:06 0:18 ± 0:01 0:92 ± 0:08 5:68 ± 0:46 30:88 ± 1:87 11:88 ± 0:77 4:90 ± 0:14 16:77 ± 0:67
5:02 ± 0:20 9:42 ± 0:52 21:43 ± 0:51 43:00 ± 0:50 2:19 ± 0:08 0:18 ± 0:01 1:12 ± 0:10 4:50 ± 0:53 19:63 ± 0:48 4:30 ± 0:37 2:05 ± 0:17 6:35 ± 0:30
7:71 ± 0:37 13:82 ± 2:45 25:92 ± 1:00 39:16 ± 0:76 1:97 ± 0:07 0:17 ± 0:01 1:10 ± 0:07 7:10 ± 1:06 19:88 ± 0:50 7:01 ± 1:25 3:60 ± 0:66 10:62 ± 1:49
8:70 ± 0:46 12:14 ± 0:24 23:20 ± 1:44 38:00 ± 0:50 0:96 ± 0:06 0:13 ± 0:01 0:98 ± 0:09 11:64 ± 2:56 39:58 ± 2:26 12:64 ± 0:58 12:12 ± 3:20 24:77 ± 3:70
Moisture in air dried litter kept for incubation.
Least signi:cant di4erence (P = 0:05) 0.55 1.97 2.23 0.88 0.12 0.01 0.14 2.17 2.26 1.20 1.39 1.97
R.L. Semwal et al. / Biomass and Bioenergy 24 (2003) 3 – 11
120
120
100
100 % total N remaining
% mass remaining
6
80 60 Albizzia lebbek Alnus nepalensis Boehmeria rugulosa Dalbergia sissoo Ficus glomerata Ficus roxburghii
40 20 1
2
3
4
5
6
7
8
Albizzia lebbek Alnus nepalensis Boehmeria rugulosa Dalbergia sissoo
40 20
9 10 11 12
Months after incubation
(a)
Ficus glomerata Ficus roxburghii
1
2
3
4
5
6
7
8
9 10 11 12
Months after incubation
(b) 120
120
% total K remaining
% total P remaining
60
0
0
100 80 60
Albizzia lebbek Alnus nepalensis Boehmeria rugulosa Dalbergia sissoo Ficus glomerata Ficus roxburghii
40 20
100 80
Albizzia lebbek Alnus nepalensis Boehmeria rugulosa Dalbergia sissoo Ficus glomerata Ficus roxburghii
60 40 20 0
0 1 (c)
80
2
3
4
5
6
7
8
9 10 11 12
Months after incubation
1 (d)
2
3
4
5
6
7
8
9 10 11 12
Months after incubation
Fig. 2. (a) – (d) Percent biomass and nutrient (N,P,K) mass remaining in di4erent months during one year of incubation of six multipurpose trees. The vertical lines represent least signi:cant di4erence (P = 0:05).
7.1% and 11.64% polyphenol concentration, respectively). B. rugulosa and F. roxburghii had the highest C/N, lignin/N, polyphenol/N and lignin+polyphenol/N ratios. A. lebbek and A. nepalensis, and D. sissoo and F. glomerata had similar C/N and polyphenol/N ratios but di4ered in respect of lignin and lignin+polyphenol/N ratios. 3.3. Monthly mass loss and nutrient release patterns Analysis of variance revealed signi:cant (P ¡ 0:01) di4erences in decomposition rates due to species, incubation time and species × incubation time interaction. A. nepalensis, A. lebbek, D. sissoo and F. glomerata showed three phases in mass loss and N and P release (Fig. 2a–c): a slow loss in the initial period of incubation, rapid loss during intermediate phase and again a slow loss during the end of the year. B. rugulosa and F. roxburghii showed two phases in mass loss and P release: a rapid loss during the :rst
5 months followed by a slow loss phase. Such phases were not marked in N release pattern of these two species. F. roxburghii showed a prolonged immobilization and started mineralizing N after 10 months of incubation. All species showed fast release of K (Fig. 2d) soon after incubation. Di4erences between species were more marked after 7 months onwards in mass, N and P remaining and during initial 6 months in K remaining. Percentage mass remaining after 1 year of incubation varied from 30.32 to 50.38, N remaining from 40.05 to 86.04, P remaining from 33.39 to 55.71 and K remaining from 1.01 to 3.08. F. roxburghii and B. rugulosa showed signi:cantly (P ¡ 0:05) higher mass, N and P remaining than other species after 8 months of incubation. 3.4. Mass loss in relation to rainfall and temperature Monthly mass loss was positively related with rainfall and temperature but these linear relationships
P ¡ 0:01) P ¡ 0:05) P ¡ 0:01) P ¡ 0:01) P ¡ 0:01) P ¿ 0:05) (R2 = 0:87; (R2 = 0:33; (R2 = 0:75; (R2 = 0:73; (R2 = 0:83; (R2 = 0:28; y = 0:016x1 + 0:29x2 − 2:50 y = 0:009x1 + 0:22x2 + 0:34 y = 0:009x1 + 0:12x2 + 0:71 y = 0:010x1 + 0:18x2 + 0:49 y = 0:015x1 + 0:05x2 + 2:34 y = 0:004x1 + 0:08x2 + 2:02 y = 0:50x − 4:39 (R2 = 0:51; P ¡ 0:01) y = 0:344x − 0:90 (R2 = 0:40; P ¡ 0:05) y = 0:231x − 0:13 (R2 = 0:38; P ¡ 0:05) y = 0:313x − 0:82 (R2 = 0:46; P ¡ 0:05) y = 0:239x + 0:53 (R2 = 0:24; P ¿ 0:05) y = 0:126x + 1:68 (R2 = 0:17; P ¿ 0:05) Albizia lebbek Alnus nepalensis Boehmeria rugulosa Dalbergia sissoo Ficus glomerata Ficus roxburghii
y = 0:021x + 2:63 y = 0:012x + 4:23 y = 0:011x + 2:99 y = 0:013x + 3:65 y = 0:015x + 3:19 y = 0:005x + 3:52
(R2 = 0:73; (R2 = 0:40; (R2 = 0:65; (R2 = 0:61; (R2 = 0:82; (R2 = 0:20;
P ¡ 0:01) P ¡ 0:05) P ¡ 0:01) P ¡ 0:01) P ¡ 0:01) P ¿ 0:05)
Rainfall+air temperature Air temperature Rainfall
Regression Species
Table 2 Regression between monthly rainfall (mm), mean temperature (◦ C) and monthly mass loss (y) for di4erent multipurpose tree species planted in degraded land at Banswara, Central Himalaya, India
R.L. Semwal et al. / Biomass and Bioenergy 24 (2003) 3 – 11
7
were not signi:cant (P ¿ 0:05) for temperature in all species and for both temperature and rainfall in F. roxburghii (P ¿ 0:05). A linear combination of rainfall and temperature explained the variation in monthly mass loss better than rainfall and temperature independently, but the degree of improvement due to multiple regression varied between species (Table 2). 3.5. Annual decomposition constants A single exponential decay model showed a fairly good :t in all species (R2 = 0:79– 0.98) except for N release from F. roxburghii (R2 = 0:25) (Table 3). All species showed the highest decomposition constant for K. B. rugulosa and F. roxburghii showed decomposition constant of P higher and other species lower than that of N. A. nepalensis showed the highest and F. roxburghii the lowest constants for mass, N and P. The highest constant for K was observed in A. lebbek and the lowest in B. rugulosa, F. glomerata and F. roxburghii with no signi:cant di4erence (P ¿ 0:05) between them. 3.6. Decomposition and nutrient release rates in relation to litter quality Annual decomposition constants of mass and N were positively correlated with C and N concentrations and negatively correlated with C/N, lignin/N, polyphenol/N and lignin+polyphenol/N ratios of fresh litter. The decomposition constant for N showed stronger correlations with N%, C/N, lignin/N and lignin+polyphenol/N (P ¡ 0:01) as compared to other litter quality parameters. However, non-signi:cant (P ¿ 0:05) relationships were noted between these chemical attributes and P and K decomposition constants (Table 4). 4. Discussion 4.1. Litter quality The key litter quality characteristics, viz., C, N, lignin and polyphenol concentrations and ratios integrating two characteristics observed in this study are within the reported range of values [5,7,8,23–25]. Litter quality may vary within a species growing in
8
R.L. Semwal et al. / Biomass and Bioenergy 24 (2003) 3 – 11
Table 3 Annual decomposition constants (k) of mass and nutrients for leaf litter of multipurpose tree species planted in degraded land at Banswara, Central Himalaya, India
Attributes
Species
Least signi:cant di4erence (P = 0:05)
Albizzia lebbek
Alnus nepalensis
Boehmeria rugulosa
Dalbergia sissoo
Ficus glomerata
Ficus roxburghii
Mass k R2
1.02 0.89
1.16 0.92
0.74 0.98
0.99 0.93
0.99 0.93
0.63 0.97
0.03
Nitrogen k R2
0.83 0.87
0.91 0.89
0.22 0.80
0.71 0.91
0.66 0.91
0.05 0.25
0.03
Phosphorus k R2
0.73 0.79
1.09 0.92
0.63 0.98
0.83 0.93
0.78 0.85
0.53 0.98
0.04
Potassium k R2
4.66 0.96
4.04 0.95
3.84 0.97
4.28 0.98
3.70 0.97
3.64 0.96
1.30
(k) is calculated using the equation ln x0 =xt = kt. R2 expresses the variance explained by the exponential model.
Table 4 Correlation coeKcients from linear regression of leaf litter quality parameters and annual decomposition constants (k) for litter mass and nutrients of multipurpose trees planted in degraded land at Banswara, Central Himalaya, India
Litter quality
Correlation coeKcients Mass
N (%) Lignin (%) Polyphenol (%) C/N Lignin/N Polyphenol/N Lignin+polyphenol/N
0.959∗∗
−0:001 −0:777 −0:936∗∗ −0:877∗ −0:867∗ −0:906∗
Nitrogen 0.985∗∗
−0:093 −0:783 −0:975∗∗ −0:932∗∗ −0:887∗ −0:945∗∗
Phosphorous
Potassium
0.769 0.255 −0:589 −0:761 −0:662 −0:707 −0:713
−0:664 −0:799 −0:667 −0:792 −0:692 −0:770
0.752
∗ P ¡ 0:05.
∗∗ P ¡ 0:01.
di4erent environments [26,27]. Nitrogen and phosphorus concentrations of A. nepalensis were comparable, but polyphenol concentration was 1.4 times lower than the values reported by Sharma et al. [13] for this species in more humid and cooler climate of Eastern Himalaya. Mineral and lignin concentration of D. sissoo are comparable and polyphenol concentration about two times higher than the values reported in a more arid and warm climate [28]. N concentration
in leaf litter of nitrogen :xing tree species was higher than non-nitrogen :xing species [5,25,28]. 4.2. Litter quality, litter fall period and decomposition patterns In strongly seasonal climates, as in this study, contribution of leaf litter of agroforestry trees to soil fertility through decomposition would be determined
R.L. Semwal et al. / Biomass and Bioenergy 24 (2003) 3 – 11
by litter quality as well as the timing of litterfall. A. nepalensis, A. lebbek, D. sissoo and F. glomerata showing a high-quality litter shed leaves in winter and thus face relatively higher moisture and temperature stresses for a period of about 6 months after litterfall, while low-quality litter of B. rugulosa and F. roxburghii is not exposed to these abiotic stresses as leaves are shed in the beginning of rainy season. In all species, rapid mass loss occurred during warm-wet rainy season evident from a positive correlation of monthly mass loss with a linear combination of rainfall and temperature. The more important role of rainfall as compared to temperature deduced from regression analysis is supported from other studies [11,29]. However, the e4ect of these abiotic factors was not as pronounced in very low-quality material, like F. roxburghii, as in the better quality ones [8,11]. Interaction of litter quality and peak litter fall period (incubation timing) was such that species e4ects were less marked in monthly mass, N and P release rates during the initial phase of decomposition. K did show marked species e4ects during early period suggesting that this element could be easily leached [30] by even low sporadic rainfall events occurring during summer and winter months. Three-phase decomposition pattern (initial slow phase, intermediate fast phase and terminal slow phase of decomposition) in A. lebbek, A. nepalensis, D. sissoo and F. glomerata incubated long before rainy season and two-phase pattern (initial fast followed by a slow phase) in B. rugulosa and F. roxburghii incubated in the beginning of rainy season are observed in other studies in a monsoon climate [11,29,31]. Available studies suggest that plant materials with N ¿ 1:7%, lignin ¡ 15%, polyphenol ¡ 3% and C/N ratio ¡ 20 generally mineralize while those exceeding these limits immobilize N [7,25,32,33]. This generalization is supported from this study except that species like A. nepalensis, A. lebbek, D. sissoo, F. glomerata having ¿ 3% polyphenol and B. rugulosa having C/N ratio ¿ 20 did not immobilize N and F. roxburghii with ¡ 15% lignin concentration showed prolonged immobilization. 4.3. Annual decomposition constants While monthly decomposition and nutrient release rates from litter incubated at the time of litter fall in-
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dicates contribution from trees to nutrients demanded by crops, annual decomposition constants would reLect species potential in long-term soil fertility management. Annual decay constants or mass and nutrient release in 1 year reported in this study are lower than the values reported for other agroforestry tree leaf litter in relatively more humid regions in the Himalaya [11–13] and elsewhere in the tropics [4,9,34]. Sharma et al. [13] found decomposition constant of P about 1.5 times higher than that of N in A. nepalensis, while there was no signi:cant di4erence between the two in this study. These variations could be attributed to variation in decomposer community, environmental conditions, litter quality and bag mesh size [27,35,36]. A strong correlation of annual decomposition constant of N with litter quality parameters indicates the importance of litter quality in determining N release on an annual time scale. The data show that absolute lignin and polyphenol concentration were not as strongly correlated with annual N release as their concentrations in relation to N, as also observed by Constantinides and Fownes [25] in their laboratory based studies. Di4erences among studies in best predictor of N mineralization/immobilization arise partly from variation in methods used to measure these processes and partly from variation in ranges of chemical composition of the litter materials used [25]. Relationships between decomposition constants of P and K with litter quality parameters analysed were not signi:cant (P ¿ 0:05) suggesting that processes determining P and K release may not be correlated with N release. 4.4. Synchrony between nutrient release from tree leaf litter and crop demand In Central Himalayan agroforestry systems, traditionally two crops are grown in a year, one during the rainy season (sowing in May and harvesting in September/October) and the other during the winter season (sowing in October/November and harvesting in April/May) [37]). As all species studied showed the highest rates of N and P release during the rainy season, rainy season crops are not likely to be nutrient stressed as much as winter season crops if tree leaf litter is assumed to be the sole source of nutrients to crops. F. roxburghii litter immobilizes and B. rugulosa litter releases N at slow rates but this effect is likely to be minimized due to their low litter
10
R.L. Semwal et al. / Biomass and Bioenergy 24 (2003) 3 – 11
production as they are lopped for fodder. A. lebbek, A. nepalensis, D. sissoo and F. glomerata litter on account of their fast decomposition seem to be more appropriate for rapid recovery in soil fertility in degraded lands. A diverse multipurpose tree community provides not only diverse products but may also render stable nutrient cycling. Further studies are needed to evaluate the potential of multipurpose trees in pure and various combinations of mixed plantations in respect of soil fertility management. Acknowledgements We are grateful to the Director, G.B. Pant Institute of Himalayan Environment and Development for the facilities and to the Tropical Soil Biology and Fertility (TSBF) Programme, Nairobi for partial :nancial support. References [1] Gilmour DA, King GC, Applegate GB, Mohns B. Silviculture of plantation forests in central Nepal to maximize community bene:ts. Forest Ecology and Management 1990;32:173–86. [2] Rao KS, Maikhuri RK, Saxena KG. Participatory approach to rehabilitation of degraded forest land: a case study in high altitude village of Indian Himalaya. International Tree Crops Journal 1999;10:1–17. [3] Maikhuri RK, Semwal RL, Rao KS, Singh K, Saxena KG. Growth and ecological impacts of traditional agroforestry tree species in central Himalaya, India. Agroforestry Systems 2000;48:257–72. [4] Okeke AI, Omaliko CPE. Leaf litter decomposition and carbon dioxide evolution of some agroforestry fallow species in southern Nigeria. Forest Ecology and Management 1992;50:103–16. [5] Montagnini F, Ramstad K, Sancho F. Litter fall, litter decomposition and the use of mulch of four indigenous tree species in the Atlantic lowlands of Costa Rica. Agroforestry Systems 1993;23:39–61. [6] Lehmann J, Schroth G, Zech W. Decomposition and nutrient release from leaves, twigs and roots of three alley-crop tree legumes in central Togo. Agroforestry Systems 1995;29: 21–36. [7] Palm CA. Contribution of agroforestry trees to nutrient requirements of intercropped plants. Agroforestry Systems 1995;30:105–24. [8] Vanlauwe B, Vanlangenhove G, Merckx R, Vlassak K. Impact of rainfall regime on the decomposition of leaf litter with contrasting quality under subhumid tropical conditions. Biology and Fertility of Soils 1995;20:8–16.
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