Decomposition of leaves of six multipurpose tree species in Chipata, Zambia

Forest Ecok~y and

Management

ELSEVIER

Forest Ecologyand Management64 (1994) 209-216

Decomposition of leaves of six multipurpose tree species in Chipata, Zambia R o b s o n D. Mwiinga*,", F r e d d i e R. Kwesiga a, C h e r m o r S. K a m a r a b aZambia/ICRAFAgroforestryProject,MsekeraRegionalResearchStation, P.O. Box 510089, Chipata, Zambia bSADC/ICRAFAgroforestryProject. ChalimbanaExperimentalStation, c/o P.O. Box 50291, Lusaka, Zambia

Abstract

The objectives of the study were to investigate (1) whether decomposition rates of foliage differs among the multipurpose trees (MPTs) Leucaena leucocephala (LEL), Fiemingia congesta (FLC), Pericopsis angolensis (PEA), Cassia siamea (CAS), Sesbania sesban (SES) and Gliricidia sepium (GLS), and (2) whether nitrogen (N) concentrations and mineralization in the foliage differ among these MFrs. Litter bags containing foliage from each species were arranged in a randomized block design with three replicates and sampled at 0, 2, 4, 8 and 12 weeks in a repeated measures manner, after placement to determine decomposition and N release. Estimates were made of N mineralization and equations were developed for predicting rate of decomposition, N concentration, and N content for each species. Significant differences existed in decomposition rates ( GLS > LEL = SES > CAS > PEA = FLC) and N contents ( GLS = LEL > SES > PEA = FLC = CAS). No significant differences existed in N concentration between the species. Based on these results, GLS and LEL showed the greatest potential for use as green manures. Further ~udies are required to determine time, amounts and method of green manure application. Key words:Decomposition;Multipurposetree species;Nitrogenconcentration;Mineralization

1. Introduction Low crop production, largely attributable to low soil fertility status, is a critical problem in Zambia (Ngugi, 1988). To overcome this fertility problem, farmers apply various amendments including inorganic fertilizers, crop rotation, fallowing a n d / o r intercropping with grain legumes such as groundnuts and beans. Adoption of alternatives to chemical fertilizer *Correspondingauthor at: ForestryAssociationof Botswana, P.O. Box 2088, Gaborone,Botswana.

use such as organic manures has been low because of high labour demands. Also, with the advent of the 'green revolution' and the accompanying emphasis on high input technologies, green manuring has had a low research priority in Zambia and many other developing countries. One of the main constraints to the use of chemical fertilizers is cost. The price of inorganic fertilizers has continued to increase as fertilizer subsidies have been removed. It is unlikely that the majority of small-scale farmers will be able to afford the high cost of chemical fertilizers in the near future if the prices continue to

0378-1127/94/$07.00 © 1994ElsevierScienceB.V. All rightsreserved SSDI0378-1127(93)06052-7

210

R.D. Mwiingaet aL / ForestEcologyandManagement64 (1994.)209-216

rise. An alternative viable fertilization technology needs to be developed. Therefore, improved planted fallow and hedgerow intercropping (alley cropping) using leguminous trees and shrubs are possible alternatives. Periodic removal of the leaves provides organic materials which serve as mulch and nitrogen (N) sources. Simpson (1976) and I_add et al. ( 1981 ) reported that the main value of leaves from N-fixing trees was in the accumulation of soil organic N so that adequate N can be made available for future crops. However, data on the contribution of leaves from leguminous trees and shrubs to soil nutrients for crops are not currently available under conditions in Zambia. In assessing the role of green manures, litter decomposition is considered essential in assessing nutrient addition and improvement of soil conditions. This study was conducted to determine: ( 1 ) differences in decomposition rates of foliage of the multipurpose tree species (MPTs) Leucaena leucocephala (LEL), Flemingia congesta (FLC), Percopsis angolensis (PEA), Cassia siamea (CAS), Sesbahia sesban (SES) and Gliricidia sepium (GLS), and (2) whether N concentrations and mineralization of the green manure differs among the MPTs, LEL, PEA, CAS, SES and GLS.

2. Materials and methods 2.1. Study site

The study conducted at the Msekera Regional Research Station, Chipata, in Eastern Zambia (32 ° 34'E, longitude, 13 ° 39'S, latitude and 1024 m above sea level). The mean annual rainfall is 960 mm (range 887-1014 mm) with approximately g5% of the rain falling between December and March. The average air temperatures vary between 15 and 18°C in the cool months (June and July) and between 21 and 26°C during the hottest months (September and October). The soils are sandy loams on the surface (pH 4.5-5.6) and classified as ferric luvisols (FAO/UNESCO, 1974).

2.2. Field procedures

The experimental site was a maize field in the season prior to establishing this experiment. It was cleared by removing weeds with a hand hoe I week before establishing the plots. Plots were laid out in a randomized block design with three replicates. Sampling was done in a repeated measurement manner, with the three replicates sampled at 2, 4, 8 and 12 weeks after litter bag placement in the field. Leaves from the top third of 3-year-old trees (trees were 3-4 m tall) were randomly collected from each species, placed in paper bags and taken to the laboratory. Leaf samples were dried in a forced air oven to a constant weight at temperatures between 65 and 70°C. A roll of I mm nylon mesh was cut into 22 cm×22 cm pieces. The pieces were stitched into 90 20 cm × 20 cm litter bags. Immediately after drying, 20 g of leaves were placed into each of 72 litter bags ( 18 bags per species). The bags were then closed by folding over the open end and stitching, and placed in the field for determination of decomposition rate and N release. Eighteen samples (three per species) were retained in the laboratory for determination of the initial N concentrations and contents. 2.3. Laboratory procedures

Collected litter bags were transferred into paper bags and oven-dried at 65°C. All oven-dry foliage was ground in a Wiley mill to pass through a 1.0 mm sieve. Subsamples of ground foliage were dry ashed at 450°C in a muffle furnace and the ash was dissolved in dilute HCI. Nitrogen concentrations were determined by the microKjeldahl procedure (Wilde et al., 1979). 2.4. Statistical analysis

All statistical analyses were conducted using Statistical Analysis Systems (SAS) procedures (SAS, 1985). An exponential decomposition constant k was derived from the decomposition equation (Budelman, 1988):

211

R.D. Mwiinga et al. / Forest Ecology and Management 64 (1994) 209-.216 Y ( t ) = Y ( O ) e -kt

( 1)

where Y(0) is original amount of material applied (leaf weight, g), N concentration and element content (N, g per bag); Y ( t ) is amount of green manure left after a period of time t (if time t is given in weeks k is expressed in week- i ) and; e is base of the natural logarithm (e=2.718). This decomposition equation was determined, a priori, to be the appropriate model to describe decomposition and changes in nutrient concentration and content. Other studies (Jenny et al., 1949; Olson, 1963; Aber and Melillo, 1980; Woods and Raison, 1982; Janssen, 1984; Jordan, 1985; Berg and McClaugherty, 1987; Budelman, 1988) have also used this, or similar models, in quantifying leaf litter decomposition rates. Leaf weight, Y(0) was kept constant for the decomposition rate equation; Y ( 0 ) = 2.995737 (In 20) since all litter bags initially contained 20 gm of leaves. Equation ( 1 ) was also inverted to obtain the nutrient release function developed by Bodelman, 1988 as follows:

and Olson, 1973; Wiant and Ham©r, ! 979) were made, The fertilizer (N) values of foliage were calculated.

3. Results and discussion 3. I. Decomposition rates

Fitting the data on the nutrient losses from the samples to eqn. (1) gives excellent "goodness of fit' (Table I ). Decomposition rates were significantly different among the six MPT species (Table 2, Fig. 1 ). The order of magnitude of the rate of decomposition among the six MPT species were GLS> LEL=SES> CAS> PEA --FLC. GLS weight decreased 21% more rapidly, over time, than LEL and SES (Table 2, Fig. 1 ) and 75.2% faster than PEA and FLC. Table 1 Regression coefficientsfor estimatIngN concentrationsof foliagefromsix multipurposetrees/shrubs SpeciesI

-kt R ( t ) = ( D P ) ( l - e -k*) R ( t ) = ( D P ) ( 1 - e -k*)

(2)

in which R ( t ) is amount of a specific nutrient released in kg h a - t after a certain period oftime (t in weeks); D is the foliage dry matter quantity initially applied in kg h a - t and assumed to be 5000 kg; Pis initial nutrient concentration of the foliage; e=2.718 and (content slope); k is release constant (content slope). Since the litter bag sizes and weight of foliage used were 20X20 cm and 20 g per bag, respectively, the value of D was 5000 kg h a - ' (from 250 000X20 g per 1000). P was the mean nutrient concentration (corrected intercept) in the foliage of each species. Slope coefficients (k) from regression equations of each species were tested using analysis of variance and Duncan's Multiple Range test at P=0.05 (Meredith and Stehman, 1991 ). Correction factors for the bias owing to logarithmic transformation (Baskerville, 1972; Beauchamp

FLC CAS

N concentration Replicate

/7o

bt

R2

Sy'x

1 2 3 1 2

1.20 1.20 1.20 0.95 0.75 0.74 1.00 1.20 1.10 1.20 1.20 1.20 1.50 1.50 1.40 1.40 1.50 1.50

-0.07 --0.06 -0.06 -0.09 -0.07 -0.09 -0.07 -0.09 -0.08 -0.06 -0.07 -0.07 -0.06 -0.08 -0.09 -0.08 -0.08 -0.09

0.99 0.97 0.96 0.76 0.98 0.95 0.99 0.95 0.98 0.86 0.87 0.94 0.80 0.93 0.95 0.86 0.89 0.74

0.001 0.002 0.004 0.059 0.002 0.010 0.001 0.009 0.003 0.014 0.015 0.006 0.020 0.012 0.008 0.026 0.017 0.059

3

PEA

1 2 3

SES LEL GLS

1 2 3 1 2 3 1 2 3

RegressionmodelIn Y=ln bo+b~Xwhere Yis N concentration, bo and v~ are interceptand slope parameters, respectively,X is time in weeks. aFlemingia congesta (FLC), Cassia siamea ( CAS ), Pericopsis angolensis (PEA), Sesbania sesbania ( SES ), Leucaena leucophala ( LEL), Gliricidia sepium ( GLS ).

212

R.D. Mwiingaet al. / ForestEcologyand Management 64 (1994)209-216

Table 2 Regressionequation parameters for estimating dry weight loss, N concentration and N content of foliagefrom six multipurpose trees Speciesa

Weight loss

N concentration

N content

Interceptb

Slope

Intercepte

Slope

Intercept

Slope

FLC

2.99

I. 17

PEA

2.99 2.99

- 0.065f (0.0053) - 0.079 ( 0.0047 ) - 0.084 (0.0072) -0.065 (0.0021 ) - 0.076 (0.0081 ) - 0.083 (0.0028) 0.10

- 0.44

CAS

-0.029a c (0.0020) d - 0.031a (0.0009) - 0.048b (0.0024) -0.091c (0.0015 ) - 0.099c (0.0042) - 0.121d (0.0038) <0.01

-0.095a (0.0018) - 0.112ba ( 0.0048 ) - 0.118b (0.0074) -0.144c (0.0048) - 0.173d ( 0.0091 ) - 0.189d (0.0043) <0.01

SES

2.99

LEL

2.99

GLS

2.99

Plevels

I. 14 0.81 1.21 1.45 1.45

- 0.47 - 0.92 -0.55 - 0.19 - 0.32

aAbbreviationsas in text and Table 1. ball intercepts are natural logarithms. The intercepts for weight loss are the same because all the species had 20 g as their initial weight. CMeanswithin a column with the same letter are not significantlydifferent (alpha = 0.05; Duncan's Multiple Range Test ). dStandard errors are in parentheses below each mean. eIntercept corrected for bias (Baskerviile, 1972). fMeans not followedby letters were not separated because the slope effect was non-significant. sObserved significancelevels are below each comparison group. 3.2. Nitrogen concentration

Nitrogen concentrations in decaying foliage were not significantly different between species, over t i m e (Table 2, Fig. 2). 3.3. Nitrogen content

Nitrogen content loss rates (g p e r b a g ) were sif~nificantly different a m o n g the six M P T species (Table 2, Fig. 3). The o r d e r o f m a g n i t u d e o f N content in decaying foliage, a m o n g the six M P T species, over time, was G L S - - L E L > SES > P E A = F L C = CAS. G L S a n d LEL N content decreased at a 20% faster rate t h a n SES (Table 2, Fig. 3). SES decreased at a 25% faster rate than PEA, CAS a n d FLC. G L S decreased at a 41% faster rate t h a n PEA. The lack o f significant differences in rate o f decrease o f N concentration a m o n g the species and a significant difference in N content loss rates is the result o f GLS, LEL a n d SES losing m o r e

dry m a t t e r per unit t i m e than PEA, F L C or CAS. Plant nutrients are gradually released during the d e c o m p o s i t i o n process a n d become available for crop production. Foliage decomposition can be considered to function analogously to a socalled 'slow release fertilizer' (Budelman, 1988). The total a m o u n t o f N needed for the entire hybrid m a i z e crop rotation is 112 kg h a - ~. During the first 4 weeks the plants require 20 kg h a a n d after 4 weeks until the end o f the rotation they require an additional 92 kg ha -~ (MePhillips, 1987). T h e c o m m o n practice a m o n g farmers in Eastern Z a m b i a is to apply 200 kg h a -~ o f 10-10-10 fertilizer at planting (during sowing) which a m o u n t s to 20 kg N h a - ~. In addition, after 4 weeks, 200 kg urea fertilizer (460-0) ha-~ are applied which supplies an additional 92 kg N h a - ~. Using eqn. ( 2 ) , the release patterns o f N h a were d e t e r m i n e d (Table 3). During the first week, the a m o u n t o f N released from G L S and LEL foliage was 35%, 50%, 64% a n d 59%, higher

R.D. Mwiinga et al. / Forest E:'ology and Management 64 (1994) 209-216 Weight

(g)l

213 I

,~.o~

,

.

~

~

10.0-

.

"~

-~.

.

"'~.

.

~

~, "-~. ~.

"~,.~.

Fk2m~gio conggsta 5-0.

.

~-~ .......

Cossio siamga P~icopsis ongo~ns~

------

S~bon~ sQsbon

"~"",,~ "~" "~..~

...... Leucaena ~uCoc~phala ~'~ 0

Gliric~dia sep~um

i

,

o

~

~

'

;

'

~

'

,;

'

Time,weeks Fig. 1. D e c o m p o s i t i o n rates for foliage o f six multipurpose trees/shrubs over a 12 week period at Chipata, Zambia.

Nitrogen,%

so I 4 0 " [ :-~' l J, 3 • v.n

"~"~-. •~, ..,

~. •,....

.~

.~

",~

..... ,

2.0- ""

Costa s , ~ , a

.~.

"~ ......

FlemingLa conggsta

.....

~ Sest:x3nlo s~,sban - - - - ~ L~Jcc~r,o I~.lCOc~pho~ - - . - - G h n c i d ~ a seplum

~"~. ~'-~. ".-,. . "'~ ~..~.

~,

~

~.

"......

~...~.. .~.

,..,.

"~ ~

1.0-

"~. ..

'~'"

"'"

_. . . . . . .

Time,weeks

Fig. 2. Curves showing percentage N changes o f foliage o f six multipurpose t r e e s / s h r u b s over a 12 week period at Chipata, Zambia.

214

R.D. Mwiingaet aL / ForestEcologyand Management 64 (1994)209-216

Nih'ogen

g/bag[

0.6

Fl~ingia cong~nsia . . . . . Cassia siam~a .......... P~icopsis angoIensis ~ Sosbania ~ b a n ~ " ~ LQucaena leucocephala ~'~ Gtiricidia s~pium

'.\\

" ' ~ ~ " \ . •. ~ ' \ ~ ~ 0-6- "" ~. . ....... ~ '\.. ~. .... '..

.... ~ . ~ . . _ . . . . . . . . . ~

0

0

,

~

,

~

,

~

t

~

,

i 10

,--

12

Time,weeks Fig. 3. Curves showing changes in N content (g per bag) of foliage of six multipurpose trees/shrubs over a 12 week period at Chipata, Zambia.

Table 3 Nitrogenfertilizervalue (kg ha- J per week) of foliagefrom six multipurposetrees Species=

FLC CAS PEA SES LEL GLS

Time(weeks) 0-1

1-2

2-3

3-4

4-5

5-6

6-7

7-8

8-9

9-10

10-11

1 1 - 1 2 Total

14 12 17 22 33 34

13 II 15 19 28 29

12 l0 13 17 23 24

II 9 12 14 20 20

10 8 II 12 17 17

9 7 l0 l0 14 14

8 6 8 9 12 11

7 6 7 8 10 9

7 5 7 7 8 8

6 4 6 6 7 6

6 4 5 5 6 5

6 3 5 5 5 4

103 85 ll6 134 183 181

aAbbreviationsas in text and Table 1. than SES, PEA, CAS and FLC foliage, respectively. In addition, after 4 weeks, GLS, LEL, SES, PEA, FLC and CAS had released 107, 104, 72, 57, 50, and 42 kg N ha -~, respectively. Based on these results, a farmer would require 5, 8, 40, 55, 62 and 70 kg ha-~ of chemical nitrogen fertilizers to supplement the N derived from the GLS, LEL, SES, PEA, FLC and CAS foliage, respectively. The high foliage N content of GLS and LEL as measured in this study has also been re-

ported by other workers (Wilson and Kang, 1981; Agboola et at., 1981; Wilson et al., 1986). The time required for a certain proportion of the foliage to decompose can be calculated from eqn. ( 1 ). For example, if it is desired to know the length of time for half the original stock of foliage to decompose, Y ( t ) is taken to be half of Y(0): Y ( t ) / Y ( O ) = 0 . 5 (Olson, 1963; Woods and Raison, 1983; Jordan, 1985; Budelman, 1988) and the equation is solved for t using the

R.D. Mwiinga et al. / Forest Ecology and Management 64 (1994) 209-216

Table 4 Comparisonof loss patterns of N from foliageof two multipurpose trees Speciesa

GLS LEL

Half-life(days)

215

age of leaves, form in which nutrients are reo leased by each species and n u t r i e n t budgets).

Decomposition constant k (per day)

Budelman (1988)

Present Budelman Present study (1988) studyb

21.7 38.5

25.7 27.7

0.032 0.018

0.027 0.025

Foliage was applied at a rate of 4000 kg ha-~ (Budelman, 1988) or 5000 kg ha- i (current study). aAbbreviationsas in Table I. bk valueswere convertedto per day from per weekby dividing by 7. relevant value for parameter k (Table 2). The 'half life' results for GLS a n d LEL from Budelman's (1988) a n d this study were compared (Table 4). I n B u d e l m a n ' s (1988) study, LEL took twice the a m o u n t of time: 39 days to release half o f the N compared with 22 days for GLS. I n the present study, the loss pattern for the two species was similar. It took 26 days to lose half of the N from GLS a n d 28 days to lose half o f the N from LEL. The differences between our results a n d those o f Budelman (1988) could result from the fact that ( 1 ) in the present study, oven-dried leaves confined in litter bags were used while Budelman (1988) used fresh unconfined leaves, (2) Budelman applied a rate o f 4000 kg fresh leaves h a - ~ while the current study applied 5000 kg oven-dried leaves h a - ~.

4, Conclusions Based on this study, GLS a n d LEL have the greatest potential to act as a green m a n u r e species because they have the highest N, P a n d K concentrations a n d total N, P a n d K inputs, decomposition rates a n d highest N contents. However, before r e c o m m e n d i n g GLS a n d LEL for selection as the 'best' green m a n u r e species, other studies are needed (e.g. nutrient availability, crop d e m a n d a n d uptake, timing of application, stor-

5, References

Abcr,,I.D.and Mclillo,J., 1980. Litter decomI~sition:m ~ uring relative contributions of organic rr~tter and nitrogen to forest soils. Can. J. Bot., 58: 416--421. Agboola,A.A.,Wilson,G.F., Getahum,A. and Yamo~, C.F., 1981. Gliricidia sepium: a possible means to sustained cropping.In: L.T. McDonald(Editor), Agroforestryin the lowland humid tropics. Proceedingsof a workshop held in Nigeria-Ibadan,27 April to I May 1981. p. 141. Baskervalle,G.L., 1972. Use of logarithmicregressionin the estimationof plant biomass.Can. J. For., 2: 49-53. Beanchamp,JJ. and Olson,J.S., 1973.Corre~ion for bias in regression estimates after logarithmic transformations. For. Sci., 31 (2): 358-366. Berg, B. and McClaugherty,C., 1987. Nitrogen releasefrom litter in relation to the disappearance of lignin. Biogeochemistry, 4: 219-224. Budeiman,A., 1988. The decompositionof leaf mulches of Leucaena leucocephala, Glir/cLdia sepium and F/emingia macrophflla under humid tropical conditions. Agrofor. Syst., 7 ( 1): 33-45. FAO/UNESCO, 1974. SoilMap of the World,Vol.6, Africa. Food and AgricultureOrganization,Paris. Janssen,B.H., 1984.A simplemethodfor calculatingdecompositionand accumulationof 'youngsoil"organicmatter. Plant Soil, 76: 297-304. Jenny, H., Gessel, S.P. and Bingham,ET., 1949. Comparative study of decomposition rates of organic matter in temperate and tropical regions.SoilSci., 68: 419--432. Jordan, C.F., 1985.Nutrient Cyclingin TropicalForest Ecosystems: Principles and Their Application in Management and Conservation.Wiley,New York, 190 pp. I.add, J.N., Oades,J.M. and Amato,J.M., 1981. Distribution and recovery of nitrogen from legume residues decomposing in soils sown to wheat in the field. Soil Biol. Biochem., 13: 151-256. McPhillips, K. (Editor), 1987. CommercialCrop Production Recommendations.Department of Agriculture,Lusaka, Zambia, 57 pp. Meredith, M.P. and Stehman, S.V., 1991. Repeated measures experimentsin forestryfocuson analysisof response curves. For. J. Res., 21: 957-965. Ngugi, D.N. (Editor), 1988. Agroforestry Research Project for the Maize-LivestockSystemin the UnimodalUpland Plateau (Chipata and Katete) in Eastern Province of Zambia. No. 10. Prepared by the Zambia Agroforestry Task Force, 80 pp. Olson, J.S., 1963. Energystorage and the balanceof the pro-

216

R.D. Mwiinga et al. / Forest Ecology and Management 64 (1994) 209-216

ducers and decomposers in ecological systems. Ecology, 44: 322-332. Simpson, J.R., 1976. Transfer ofnitrogen from three pasture legumes under periodic defoliation in a field environment. Aust. J. Exp. Agric. Anita. Hush., 16: 863-870. Statistical Analysis Systems Institute, 1985. SAS/STATISTICS. Guide for Personal Computers. Cary, NC, 378 pp. Wiant, H.V. Jr. and Harner, E.J., 1979. Percent bias and standard error in logarithmic regression. For. Sci., 25 ( 1): 167-168. Wilde, S.A., Corey, R.B., Iyer, J.G. and Voight, G.IC, 1979. Soil and Plant Analysis for Tree Culture, 5th revised edn. Oxford and IBH Publishing, New Delhi, 22 pp. Wilson, G.F. and Kang, B.T., 1981. Developing stable and

productive biological cropping systems for the humid tropics. In: B. Stonehou~ ~.Editor), Biological Husbandry: A Scientific Approach to Organic Farming. Butterworths, London, pp. 193-203. Wilson, G.F., Kang, B.J. and Mulongoy, IC, 1986. Alley cropping: trees as a source ofgreen manure and mulch in the tropics. Biol. Agric. Hortic., 3: 351-267. Woods, P.V. and Raison, RJ., 1982. An appraisal of techniques for the study of litter decomposition in eucalypt forests. Aust. J. Ecol., 7:215-225. Woods, P.V. and Raison, R.J., 1983. Decomposition of litter in sub-alpine forest of Eucalyptus delegatensis, Eucalyp. tuspauciflora and Eucalyptus dives. Aust. J. Ecol., 8: 289299.