‘Without bamboo, the land dies’: nutrient cycling and biogeochemistry of a Javanese bamboo talun-kebun system

Fores;fdogy Management ForestEcologyandManagement91 (1997) 155-173

‘Without bamboo, the land dies’ : nutrient cycling and biogeochemistry of a Javanesebamboo tahn-kebun system D. Mailly a?* , L. Christanty ‘, J.P. Kinunins a a Faculty

of Forestry,

Department of Forest Sciences, University of British ’ Gelong Baru Barat VI/& Tomang, Jakarta

Columbia, Vancouver, 11440, Indonesia

B.C. V6T lZ4,

Canada

Accepted17 July 1996

Abstract The accumulation and removal of biomass, and the inventory of five major nutrients (N, P, K, Ca, and Mg) in plants, litterfall, forest floor, and in the mineral soil were quantified at various stagesof a bamboo ru~u~-~&ur agroforestry system (West Java, Indonesia). Data were collected in order to explain the biogeochemistry of the system over an entire rotation cycle. This cycle consistedof 1 year of mixed speciesvegetable cropping (~!xuz) after the removal of bamboo, followed by a year of cassavacropping, and 4 years of bamboo fallow (&HZ): a total cycle length of 6 years. The accumulation of five major nutrients in live plant biomassduring a complete &urr-ke&n rotation cycle was 787, 134,692, 218, and 248 kg ha-’ for N, P, K, Ca, and Mg, respectively. The overall nutrient removals accounted for approximately 51%, 48%, 55%, 52%, and 56% of N, P, K, Ca, and Mg accumlated in the live plant biomass, respectively. Accumulation of N, P, K, Ca, and Mg in the forest floor peaked at the end of the mature r&n stage, i.e. when the forest floor mass accumulation reached its maximum. Fertilization was an important input during the fist year of cropping: it accountedfor 63%. 145%, 100%. 188%, and 225% of N, P, K, Ca, and Mg output, respectively, during this period. Cassava cultivation decreasedthe content of exchangeable K in the mineral soil during the second year of cropping. Available P in the surface 5 cm of mineral soil increasedslightly after clearing and hoeing, but decreasedto 92% and 75% of its original value in the fast and secondyear cropping stages,respectively,About 220 kg N ha-’ was lost from the systemover the 6-year rotation, a difference between input and output to and from the system which reflected changesin the soil N compartment. Soil data on P, Ca, and Mg did not suggest a current problem of declining availability of these elements on the site, although the use of an NPK fertilizer does suggest concern over the availability of K. Finally, soil leaching losses were very small in comparison to losses in harvest removals. 0 1997 Elsevier ScienceB.V. Keywords:

Agroforestry;Indonesia;Shiftingcultivation

1. Introduction Because of the high and growing population density in many areas of Java, farmers are forced to

* Correspondingauthor.E-mail:[email protected]

obtain their subsistence from a very limited and diminishing area of land. Consequently, they have had to develop food production methods that have a higher productivity and a greater sustainability of production than traditional shifting cultivation methods (Christanty, 1989; Christanty et al., 1997). Barnboo talun-kebun is one of the systems that has been

0378-1127/97/$17.00 Copyright0 1997ElsevierScienceB.V. All rightsreserved. PI1 SO378-1127(96)03893-5

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developed from the lower productivity and less sustainable conventional shifting cultivation methods (Soemarwoto et al., 1985). It requires much less land, it has a shorter rotation cycle and has proven to be sustainable even when it is practised on poor sites. Although it bears a resemblance to the shifting cultivation system, the talun-kebun is practised not in the natural forest but in a man-made one. Because of the sirnilarity of this system to shifting cultivation, the literature on the latter provides a useful background for understanding the biogeochemical processes involved in the bamboo tahn-kebun agroforestry system. There were relatively few detailed studies of nutrient cycling aspects of shifting cultivation in tropical ecosystems until the 196Os, but since then there has been increasing interest in this topic (Nye and Greenland, 1960; Sanchez, 1976; Norman, 1979; Jordan, 1987). However, there have been no detailed studies of nutrient cycling and biogeochemistry aspects of the bamboo t&n-kebun system of shifting cultivation. Also, little is known about the ecology, biomass accumulation, primary productivity, and nutrient cycling aspects of bamboos (Rae and Ramakrishnan, 1989; Tripathi and Singh, 19941. The objective of this study, of which the research reported here was a part, was to examine the production and nutrient cycling aspects of the bamboo tulun-kebun in West Java, Indonesia, and to investigate some of the long-teim consequences of altered land-use practices in the study area. The present paper: (1) describes and quantifies the distribution and dynamics of macronutrients in the bamboo tulun-kebun crop production system, and (2) develops conceptual models of biogeochemical cycles in each stage of a complete rotation cycle. The data presented in this paper also provide a useful basis with which one can evaluate the sustainability of this system under altered cropping practice.

2. Methods

The study area, vegetation structure, biomass, litter-fall and soil organic matter have been described previously (Christanty et al,, 1996).

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2.1. Study plots

Study plots were established in August 1983 in six adjacent fields, all of which had generally similar soil and topographic conditions. The chronosequence approach was used, with five study piots representing the different stages of development of the bamboo talun-kebun system. Site 1 (30 m X 140 ml, which had a slope gradient of 15Oand a southeasterly aspect, was a mature t&n field (i.e. it carried a closed-canopy crop of 4-year-old bamboo culm regrowth and was 6 years since the previous bamboo harvest). Part of site 1, which was subsequently known as site 2, was cleared in early September 1983 and used for the first year cropping studies. Four subplots (12 m X 10.5 m) were established for the first year cropping period. Site 3 (20 m X 35 ml. which was used for the study of second year cropping with cassava (Munihot esculentu), had a northwesterly aspect and also had a slope gradient of lSO: its soil condition was similar to that of sites 1 and 2, but there was no litter layer on the soil surface and no clear boundary between the A and B horizons because of soil hoeing (for details of the cultural treatments, see Christanty et al., 19%). Site 4 (20 m X 50 m) was located next to site 2 and was representative of an early bamboo fallow. Site 5 (7 m X 7 ml was located next to site 3 and was used to study the effect of a second year successive cropping of cassava (i.e. a third successive year of food plant cropping). 2.2. Plant tissue analyses

Samples for chemical analysis were the same as those used for biomass measurement (Christanty et al., 1996). Samples were weighed fresh and subsamples dried at 80°C to constant mass. Weed biomass was not separated for above- and below-ground components: instead, a ratio of below-ground to aboveground of 0.26 was used (Uhl, 1980). Plant tissues (leaves, stems, roots, rhizomes, tubers, flowers, fruits, and pods) were ground in a Wiley mill and sieved ( 1 mm mesh). N was determined by the semi-micro Kjeldahl digestion method. P was determined colorimetrically after digestion with nitric-perchIoric acid (Yoshida et al., 1976). Ca and Mg were determined

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by atomic absorption spectrophotometry following dry ashing, and K was determined by flame photometry (Yoshida et al., 1976). Three replicate analyses were run for each sample (four replicates for bamboo). Analyses were conducted at the National Institute of Chemistry, 3andung Indonesia.

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The sampling method for litterfall and forest floor/ectorganic material has been described previously (Christanty et al., 1996). The samples were analyzed using the same methods as for plant tissues. The mineral soil was sampled on sites l-4 at the beginning and at the end of the first year cropping, cassava cropping and the bamboo talun-kebun. Soil was sampled at various depths (O-5 cm, 5-25 cm, and 45-75 cm) at three locations in each site. The samples from each location consisted of a composite of five cores. Each composite sample was well mixed, oven-dried at 10X ground using a mortar and pestle, and sieved (2 mm mesh). Determination of soil texture was done by evaluating particle size distribution using the pipette method (Hidayat, 1978). Four volumetric cores were taken at each depth and each location for bulk density determinations. The cores were 5.4 cm in diameter, coated with saran-resin, and dried at 1OS’C to constant mass. Bulk density was determined by dividing each soil mass by its volume (Brasher et al., 1966). Soil pH was determined in water and in a 1.0 M KC1 solution using a soil:liquid volume ratio of 1:2 (Hidayat, 1978). Total N was determined by a semi-micro Kjeldahl technique (Bremmer, 1965; Hidayat, 1978). Available soil P was extracted using Bray-Kurtz II extractant solution, followed by calorimetric determination (Hidayat, 1978). Exchangeable cations in the soil were extracted using ammonium acetate at pH 7.0. Ca and Mg were determined using an atomic spectrophotometer, and K by using a flame spectrophotometer (Hidayat, 1978).

plastic containers (Wiersum, 1979). Throughfall and precipitation for chemical analysis were collected using polyethylene funnels containing a plug of glass wool, and polyethylene containers. Three collectors for throughfall were installed at three randomly chosen locations in each of sites l-4, 1 m above the soil surface to avoid soil splash. Collectors for precipitation were placed in an open tield. In addition to the existing precipitation collectors, a standard weather bureau rain gauge was installed to calibrate results of the trough-type rain gauge against the standard rain gauge. Throughfall and precipitation water in each collector were measured after each major rain storm from December 1983 until April 1984 (during the wet season), and samples were taken every second week. Precipitation data for May-November 1984 (during the dry season) were obtained from the local weather station, and throughfall data for this period were estimated using regression equations developed based on the relationship between precipitation and throughfall data for the December-April period at various stages of the talun-kebun rotation (Christanty, 1989). This method probably overestimates dry season throughfall, but we do not know by how much. Water samples collected in the field were brought to the laboratory after each collection. Analyses for Ca, Mg, and K were performed using a Varian Techtron atomic absorption spectrophotometer (Model 1200) with an air-acetylene flame. Ammonium ions and phosphate were measured on a Technicon Autoanalyzer IIR system using standard methods. Nutrient contents in precipitation and throughfall for the months of May-November 1984 were calculated using average concentrations from the months of December-April. Considering that nutrient concentrations in precipitation and throughfall during the dry period are usually higher than those of the wet period (Bruijnzeel, 1982), the results will underestimate the actual values for May-November.

2.4. Nutrients in precipitation and throughfall

2.5. Nutrient in fertilizers

Collectors for throughfall and bulk precipitation volume measurements consisted of V-shaped through-type rain gauges 140 cm long and 10 cm wide, which were connected by plastic tubing to

Nutrient content in the ash and manure mixture was measured using the same methods as for the mineral soil nutrients. Nutrient content in the fertilizer was measured by multiplying the known concen-

2.3. Litte$all, forest floor and mineral soil analyses

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trations of N, P, and K in the fertilizer by the mass of each type of fertilizer used (Christanty, 1989). The ash and manure mixture contributed 95.5, 10.4, 89.5, 28.9, and 51.1 kg haa’ of N, P, K, Ca, and Mg, respectively. Approximately 83, 12, and 12 kg ha-’ of N, P, and K were added to the soil by the application of commercial NPK and urea fertilizers during the first year of cropping. 2.6. Nitrogen fiation NZ fixation is considered an important input to the talun-kebun system because of the use of leguminous species in the system: hyacinth bean (Dolichos labZab1, and some Albiziu trees. NZ fixation rates were not measured in this study, but were estimated from the available literature. Dennis (1977) measured hyacinth bean NZ fixation rates of 31-33 kg ha-’ per year on limed soil in Ghana: therefore, a value of 32 kg ha- ’ per year was used as an estimate for hyacinth beans in the taiun-kebun. NZ fixation rates by Albizia trees, which are commonly found scattered between the bamboo clumps, has been estimated based on values of approximately 150 kg ha- ’ per year for Albizia trees grown in pure stands (D. Binkley, personal communication, 1995). Since the number of Albiziu trees per hectare in the t&n-kebun system is rather low ( < 100 trees ha-’ 1, an estimate of 10% of the above value (i.e. 15 kg ha- ’ per year) was used as a reasonable estimate of NZ fixation rate for that species. 2.7. Nutrient losses in leaching and sutiace runo# and from the slash burned in piZes Six ceramic suction cup soil solution samplers of 4.8 cm diameter (Model 1900, 2 bars; Soil Moisture mpment Corp.) were installed at each of sites 1 and 2 at depths of 25 and 75 cm (three replicates for each depth). Because of the limited number that were available, only four samplers were installed at each of 25 and 75 cm depths at each of sites 3 and 4. The samplers were inserted into holes excavated using a 5 cm diameter insertion tool (Soil Moisture Equipment Corp.) near the location for throughfall collection. Water samples were collected every 15 days over the 5-month period (December 1993 to April 1984). The samples were analysed usmg the same

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methods as those for precipitation and throughfall. To estimate the volume of soil water flux, a water balance was calculated as follows: D=P-(R+E+S) where D is drainage, P is precipnation, R is runoff, E is evapotranspiration, and s is change in soil moisture content between the sampling dates. Conservative assumptions were made such that there was no change in soil moisture content between December and April, runoff equals zero, and evapotranspiration can be estimated as 50% of the total precipitation in all stages, because both crops and bamboo achieved canopy development during the measurement periods (Chang, 1968; Wiersum, 19791. The quantities of nutrients lost in the burnpiles were calculated by subtracting the nutrient content of weighed quantities of slash (litter and bamboo foliage) placed in a burnpile and the content in the ash after the bum. Approximately 84.5, 1,O, 4.5, 3.4, and 1.9 kg ha- ’ of N, P, K, Ca, and Mg, respectively, were lost during the bum. 2.8. Nutrient uptake by plants and internal cycling The gross uptake of nutrients was calculated as the product of the net annual production of different plant components and their respective nutrient concentrations. The internal conservation of nutrients in bamboo was estimated at the end of both the early fallow and mature t&n stages, respectively. The nutrient retranslocation in the leaves during senescence was estimated by using nutient:Ca ratios as. suming that Ca is relatively immobile or practically immobile (Vitousek and Sanford, 1986): Retranslocation(%)

= 11 - ( x/y)]

x

100

where X is (nutrient concentration in leaf htter)/(.Ca concentration in leaf litter), and Y is &nrient concentration in green leaf)/(Ca concentration in green leaf).

3.1. Nutrient accumulation and remowl in biomass Knowledge of the inventory and dynamics of nutrients in plant components and soil sub&rates is

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important for assessing changes in site nutrient reserves and future productivity under alternative cropping strategies. In shifting cultivation systems, the rapid mineralization of organic matter and the addition of ash after clearing and burning provide a significant increase in soil pH and in available nutrients to the first crops planted on most tropical soils (Sanchez, 1976). In a bamboo r&&&un system, the use of fertilizers provides an additional input of nutrients which favors nutrient accumulation during the first year cropping stage. Table 1 presents the accumulation and removal of nutrients (N, P, K, Ca, and Mg) in the above- and below-ground components of live plant biomass during the first year of cropping. The majority of nutrients were accumulated in the above-ground components of crop biomass: 346.1, 17.1, 121.4, 49.3, and 39.3 kg ha- ’ for N, P, K, Ca, and Mg, respectively, representing 77%, 54%, 56%, 66%, and 49% of the nutrients accumulated in the total biomass. Most nutrients accumulated in plant biomass in the first year cropping were removed in harvested products: 398.6, 21.8, 154.1, 54.8, and 52.6 kg ha-’ for N, P, K, Ca, and Mg, respectively, representing 89%, 69%, 71%, 73%, and 65% of the total nutrients accumulated. Cassava accumulated 47% of the total biomass N during the second year cropping, of which 19% was in the above-ground materials and 28% was in tubers (Table 2). Although the below-ground biomass of cassava was much higher than the above-ground biomass, the P and Ca content of the below-ground cassava (3.8 and 5.9 kg ha-‘, respectively) was lower than that of the above-ground (6.1 and 12.3 kg ha- ‘, respectively) due to the low concentration of these nutrients in the tubers. In contrast, more K and Mg was stored in the below-ground component (47.7 and 10.1 kg ha- ’ , respectively) than in above-ground (36.1 and 5.2 kg ha-‘, respectively). Considering a tuber production of 4.6 Mg ha- ‘, cassava extracted an average of 10.4 kg K ha- ’ per tonne of harvested roots, a value slightly higher than the 1.5-9.9 kg ha-’ range as reported by Howeler (1980). Nutrients accumulated in weeds and bamboo biomass during the second year cropping amounted to 89.5, 18.3, 96.7, 29.3, and 41.4 kg ha-’ for N, P, K, Ca, and Mg, respectively, representing 53%, 65%, 54%, 62%, and 73%. Since no weeding occurred during the

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second year cropping, nutrients accumulated in weeds and bamboo were not removed from the site. The accumulation of nutrients in the plant components was rapid after the cropping ceased at the end of the second year. Bamboo accumulated 123.2, 42.5, 170.5, 59.5, and 72.2 kg ha-’ of N, P, K, Ca, and Mg, respectively, during the early fallow stage (Table 3). In contrast, weeds accumulated only 21.1, 1.4, 12.3, 1.5, and 3.9 kg ha-‘, respectively, representing 15%, 3%, 7%, 2%, and 5% of the total accumulation of these nutrients in this stage. The weed values became negligible at the end of the rotation cycle as the weeds were shaded out. Kalpage (1974, p. 142) reported that the rate of accumulation of nutrients in forest vegetation in a shifting cultivation system was high in the early years of fallow, reflecting the period of maximum biomass accumulation. By the end of the talun stage, nutrient contents in bamboo biomass were 420.3, 252.1, 167.3, 140.2, and 89.3 kg ha-’ for K, N, Mg, Ca, and P, respectively (Table 3). Nutrients removed in the bamboo were 276.3, 130.9, 120.9, 104.8, and 54.4 kg haa1 for K, N, Mg, Ca, and P, respectively, representing 66%, 52%, 72%, 75%, and 61%. Table 4 summarizes accumulation and removal of biomass and nutrients over a complete talun-kebun rotation cycle. Total biomass accumulation over the 6-year cycle was 97.4 Mg ha-‘, consisting of 59.9 Mg ha-’ of above-ground biomass and 37.5 Mg ha- ’ of below-ground biomass. Biomass removal in the form of harvested products amounted to 50.7 Mg ha-‘, i.e. approximately 52% of total biomass. Harvest residues that were later returned to the soil as composted materials amounted to 11.6 Mg ha- ’ or 12% of total biomass. N and K constituted the major part of the nutrient accumulation (786.6 and 692.3 kg ha- ‘, respectively) and removal (607.5 and 5 12.9 kg ha- ‘, respectively). Approximately 186.0, 177.0, and 85.9 kg ha-’ of Mg, Ca, and P were removed during the 6-year rotation cycle. 3.2. Nutrients in litte$all, forest floor and mineral soil The contents of the five macronutrients in litterfall for the Iirst year and second year cropping stages were in the order N > Ca > K > Mg > P, while for bamboo (early fallow and mature talun stages) these

* Above’ Above-

of live plant biomass

(7.25) (0.10) (7.35)

(1.32) (0.46) (1.78)

(0.51) ~0.00~ (0.51)

(9.99) (0.64) (10.63)

7.25 0.10 7.35

I .32 0.46 1.78

0.5 I 9.50 10.51

10.57 IO.15 20.72

17.0 0.7 17.7

13.7 0.1 13.8

385.0 64.8 449.8

5.2 49.4 54.6

33.7 11.9 45.6

315.4 2.1 318.1

N

Nutrient

(Mg

of all components that was removed

(0.61) (0.08) (0.69)

0.62 0.08 0.70

biomass biomass

(0.30) ~0.00~ (0.30)

0.37 0.01 0.38

Biomass

and below-ground and below-ground

Cucumber a Above-ground Below-ground Total Bitter solarium a Above-ground Below-ground Total Hyacinth bean a Above-ground Below-ground Total Weeds ’ Above-ground Below-ground Total Bamboo ’ Above-ground Below-ground Total Total Above-ground Below-ground Total

Component

Table 1 Accumulation (and removal) Java, Indonesia

I.3 0.0 1.3

2.3 0.0 2.3

20.9 10,s 31.4

1.3 9.5 10.8

2.5 0.9 3.4

13.5 0.1 13.6

P

(kg ha-’

(20.8) (1.0) (21.8)

(1.3) (0.0) (1.3)

co.91 (3.4)

(2.5)

(13.5) (0.1) (13.6)

(1.3) co.01 (1.3)

(2.2) co.01 (2.2)

) in different

(145.4) (8.7) (154.1)

(4.8) co.01 (4.8)

(20.2) (7.1) (27.3)

(90.0) (0.8) (90.8)

(17.2) (0.8) (18.0)

(13.2) (0.0) (13.2)

during

the first

53.4 21.2 74.6

1.6 19.0 20.6

2.5 0.9 3.4

43.8 1.2 45.0

3.1 0.1 3.2

2.4 0.0 2.4

Ca

in parentheses)

(52.6) (2.2) (54.8)

cl.61 co.01 (1.6)

CO.91 (3.4)

49.0 31.6 80.6

1.8 27.6 29.4

7.9 2.8 10.7

34.8 0.6 35.4

2.4 0.6 3.0

2.1 0.0 2.1

%

stage of a bamboo

Cl.5)

(43.8) (1.2) (45.0)

(3.0) (0.1) (3.1)

(1.7) (0.0) (1.7)

year cropping

fruit harvest (removals (removals in parentheses).

146.4 71.6 218.0

4.8 62.7 67.5

20.2 7.1 27.3

90.0 0.8 90.8

17.3 0.8 18.1

14.1 0.2 14.3

K

components

at the end of the cropping period plus cumulative by weeding/pruning during the cropping period

(383.3) (15.3) (398.6)

(5.2) ~0.0~ (5.2)

(33.7) (11.9) (45.6)

(318.1)

(2.7)

(315.4)

(16.7) (0.7) (17.4)

(12.3) (0.0) (12.3)

ha- ’ ) and nutrients

(48.6) (4.0) (52.6)

(I.81 to.01 (1.8)

(7.9) (2.8) (10.7)

(35.4)

(0.6)

(34.8)

(2.4) (0.6) (3.0)

(1.7) co.01 (1.7)

talus

kebun,

5 L 2

3 L!

L

5

ii i?

2

:

2 -T 2 2 2 P s t! 8

,y

a Above-

and below-ground

Cassava ’ Above-ground Below-ground Total Weeds Above-ground Below-ground Total Bamboo Culm Branch Foliage Rhizome Root Total Total Above-ground Below-ground Total

Component

co.01 (0.0) co.01

co.01 co.01 (0.0) co.01 (0.0) co.01

(2.1) (4.6) (6.7)

1.1 0.4 1.5

2.7 0.7 0.7 6.5 1.0 11.6

7.3 12.5 19.8

biomass

(6.7)

79.5 89.2 168.7

4.9 3.1 14.1 28.5 5.1 55.7

25.0 8.8 33.8

32.4 46.8 79.2

N

Nutrient

14.5 13.7 28.2

3.5 1.4 1.7 7.8 1.4 15.8

1.8 0.7 2.5

6.1 3.8 9.9

P

(kg ha-’

at the end of the cropping

(32.4) (46.8) (79.2)

co.01 (0.0) (0.0) (0.0) co.01 co.01

co.01 (0.0) (0.0)

(32.4) (46.8) (79.2)

(Mg ha - ’ ) and nutrients

of all components

(4.6)

2.1 4.6 6.7

0.1)

of live plant biomass

Biomass

Table 2 Accumulation (and removal) Java, Indonesia

period

(removals

(36.1) (47.7) (83.8)

(0.0) co.01 (0.0) co.01 co.01 (0.0)

(0.0) co.01 co.01

(36.1) (47.7) (83.8)

during

in parentheses).

81.6 98.8 180.5

(6.1) (3.8) (9.9)

17.6 5.6 7.1 40.3 5.5 76.1

15.2 5.4 20.6

36.1 41.7 83.8

K

components

co.01 co.01 (0.0) co.01 co.01 (0.0)

co.01 co.01 (0.0)

(9.9)

(3.8)

(6.1)

) in different

27.8 19.7 47.5

8.9 1.4 3.4 11.7 1.5 26.9

1.8 0.6 2.4

12.3 5.9 18.2

Ca

the second

(12.31 (5.9) (18.2)

(12.3) (5.9) (18.2)

year cropping

26.4 30.3 56.7

9.7 1.6 3.8 16.3 1.8 33.2

6.1 2.1 8.2

5.2 10.1 15.3

Ws

stage of a bamboo

(5.2) (10.1) (15.3)

co.01 co.01 (0.0) co.01 co.01 co.01

co.01 co.01 (0.0)

(10.1) (15.3)

6.2)

t&n-

kebun,

a Above-

of live plant biomass

of all components

132.7 119.4 252.1

45.3 31.6 76.9

biomass

55.0 18.6 57.3 32.6 86.8 250.3

34.4 6.0 4.7 IO.5 21.0 76.6

75.0 69.3 144.3

15.00 13.78 28.78

1.8 0.0 1.8

15.6 10.3 33.5 24.9 38.9 123.2

9.20 2.40 2.60 5.80 1.10 21.70

0.16 0.06 0.22

15.6 5.5 21.1

N

c 130.9) c-j (130.9)

(55.0) (18.6) (57.3) c-j c-1 030.91

c-1 c-1 c-1

c-1 c-1 c-1

c-1 t--j c-1 c--j C-1 c-1

c-1 c-1

c-1

ha- ’ ) and nutrients

1.0 0.4 1.4

54.5 34.8 89.3

37.8 7.2 9.4 11.6 23.1 89.1

0.1 0.1 0.2

24.9 19.0 43.9

12.9 4.8 6.2 8.7 9.9 42.5

P

period

(removals

(kg ha- ’ ) in different

at the end of the cropping

Nutrient

(Mg

0.28 1.08

Biomass

(and removal) Java, Indonesia

and below-ground

Mufure talun waCdSe &ove-ground $&low-ground Te4al Bamboo CMm Branch We IWwme hot Total TotaJ Above-ground B&w-ground Tc&il

hot Total Total Above-ground Below-ground Total

RhiWtIE

weedsa Above-ground Below-ground Total Bamboo culm Branch FfAiige

Early fallow

Component

Table 3 Accumulation talun- kebun,

in parentheses)

277.8 142.5 420.3

192.6 39.0 44.7 52.5 89.5 418.3

1.5 0.5 2,o

(276.3) c-j (276.3)

(192.6) (39.0) (44.7) c-j c-1 (276.3)

c-1 c-j C-J

C-J c-j c-j

c-j c-1 c-1 C--J c-1 c-1

55.2 16.8 26.0 33.6 38.9 170.5 107.1 75.7 182.8

c-j t-1

c-j

during

9.1 3.2 12.3

K

components

fallow

105.0 35.2 140.2

86.0 6.6 12.2 13.7 2J.4 139.9

0.2 0.1 0.3

43.1 17.9 61.0

26.7 4.1 Il.2 8.1 9.4 59.5

1.1 0.4 I.5

Ca

the early

(104.8) c-j (104.8)

(86.0) (6.6) (12.2) c-j t-j (104.8)

C-j c-j C-J

c-1 c-1 c-1

t-j c-1 c-j c-1 t-1 c-j

c-j c-1

c-1

and mature

121.5 45.8 167.3

96.3 9.6 15.0 20.0 25.6 166.5

0.6 0.2 0.8

50.1 26.0 76.1

29.4 4.8 13.0 13.3 11.7 72,2

2.9 1.0 3.9

h%!

f&u

stages of a bamboo

D. Mailly Table 4 Accumulation

and mmovai

Component

of biomass Accumulation

(Mg

et al. /Forest

ha-’

Ecology

1 and nutrients

’

Removal Market

and Management

(kg ha-’

91 (1997)

) over a complete

155-173

163

talun-kebun

rotation,

West

Java, Indonesia

’ products

Residues

Total

Above-ground Below-ground Total

59.9 37.5 97.4

46.1 4.6 50.7

(47.3) (4.7) (52.0)

IO.9 0.7 11.6

(11.2) co.71 (11.9)

57.0 5.3 62.3

(58.5) (5.4) (63.9)

Above-ground Below-ground Total

590.7 195.9 786.6

355.6 46.8 402.4

(45.2) (5.9) (51.1)

189.8 15.3 205.1

(24.1) (1.9) (26.0)

545.4 62.1 607.5

(69.3) (7.8) (77.i)

Above-ground Below-ground Total

84.3 49.7 134.0

60.4 3.8 64.2

(45.1) (2.8) (47.9)

20.7 1.0 21.7

(15.5) (0.8) (16.3)

81.1 4.8 85.9

(60.6) (4.0) (64.2)

Above-ground Below-ground Total

484.6 207.7 692.3

333.6 47.7 381.3

(48.2) (6.9) (55.1)

122.9 8.6 131.6

(17.8) (1.2) (19.0)

456,6 56.3 512.9

(66.0) (8.1) (74.1)

Above-ground Below-ground Total

173.6 44.3 217.9

108.0 5.9 113.9

(49.6) (2.7) (52.3)

61.4 1.7 63.1

(28.2) ~0.8~ (29.0)

169.4 7.6 177.0

(77.8) (3.5) (81.3)

Above-ground Below-ground Totai

184.7 63.0 247.7

128.6 10.1 138.7

(51.9) (4.1) (56.0)

45.6 1.7 47.3

(18.4) (0.7) (19.1)

174.2 11.8 186.0

(70.3)

N

P

K

Ca

W

a Represents biomass of bamboo and wezds (mature talun) + crop, weeds, and above-ground bamboo (frst weeds (second year cropping) + weeds (early fallow). ’ Number within pare.ntheses represents proportion of harvest (%) over total accumulation during the whole

Table 5 Biomass (Mg ha-’ ), and nutrient system, Java, Indonesia Component

Biomass

First year cropping Litterfall Forest floor Second year cropping Litterfall Forest floor Early fallow Litterfall Forest floor Mature talun Litterfall Forest floor a Number

content

within

(kg ha-’ Nutrient

1 in above-ground

leaf litterfall

and in forest

floor

(4.8) (75.1)

year cropping) rotation

at various

+ cassava

cycle.

stages of a talun-kebun

’

N

P

K

Ca

ME

1.8 0.8

42.0 (1.4) 21.3 (4.9)

1.5 (0.2) I .o (0.2)

4.8 (0.8) 2.6 (0.9)

34.1 (7.4) 14.9 (2.3)

4.5 (1.4) 4.2 (2.5)

2.4 1.3

48.5 (1.8) 25.3 (2.1)

1.1 (0.4) 0.9 (0.3)

10.4 (0.1) 4.9 (1.5)

10.8 (1.7) 6.8 (0.5)

6.1 (1.6) 4.4 (1.4)

3.0 2.2

28.2 (4.2) 36.2 (7.3)

5.3 (1.1) 3.3 (1.0)

19.4 (6.0) 18.3 (5.0)

9.5 (2.2) 7.0 (1.8)

6.6 (1.8) 7.5 (1.3)

4.7 13.5

45.2 (8.5) 105.6 (11.9)

7.6 (2.2) 11.5 (3.6)

31.9 (6.2) 69.3 (15.2)

9.9 (2.3) 27.5 (6.2)

7.2 (1.6) 24.6 (2.4)

parentheses

represents

standard

deviation.

and

164

D. Mailly

et al. /Forest

Ecology

nutrients accumulated in the order of N > K > Mg > Ca > P (Table 5). The N content of above-ground litterfall in the mature t&n was 1.6 times that of the early fallow. Nitrogen concentration in bamboo leaf litterfall did not show any significant decrease in comparison to its live foliage N concentration, for both the early fallow and mature tub stages. Accumulation of N, P, K, Ca, and Mg in the forest floor peaked at the end of the mature t&n, i.e. when forest floor mass accumulation reached its maximum (13.5 Mg ha-’ ). Forest floor nutrients at the end of the mature tulun were approximately 3-4 times higher than those during the early fallow stage (36 months after the previous harvesting of bamboo). Total N in the upper 25 cm of mineral soil varied between 6000 and 7000 kg ha-’ throughout the 6-year tab-kebun rotation cycle (Table 6). Sanchez (1976) stressed that, in moist tropical forest ecosystems, the bulk of nitrogen (70-80%) is in the soil and not the live biomass. Therefore, changes in available N are more important than changes in total N for assessing changes in soil fertility in relation to the decline in crop productivity when cultivation is

Table 6 Total N, available Indonesia

P, and exchangeable

Soil depth (cm)

AjIer clearing and hoeing O-5 5-25 25-45 End offirst year cropping o-5 5-25 25-45 End of second year cropping o-5 5-25 25-45 End ofjirst year offallow o-5 5-25 25-45 Mature talun o-5 5-25 25-45

K, Ca, and Mg

(kg

ha-‘)

and Management

91 (1997)

1.55-I

73

prolonged. Unfortunately, due to time and labour limitations, the availability of N in the soil was not measured in this study. There was a reduction in the content of the available P in the 5-25 and 25-45 cm mineral soil depths during the cassava cropping. Quantities of exchangeable nutrients in the mineral soil were present in the order Ca > Mg > K. The exchangeable K content in the O-25 cm soil depth increased by 54.5 kg ha- ’ after the first year of cropping. This increase, which may be due to the input of fertilizers, was followed by a decrease of 160.2 kg ha-’ after cassava cropping, Similarly, exchangeable Ca and Mg in the O-25 cm soil depth increased after the first year of cropping, but this was followed by a gradual decrease at the end of the cassava cropping stage. 3.3. Soil texture, pH, and bulk densi&

There was no significant difference in soil texture under various stages of the tuhn-kebun cycle. The soils have a high clay content (71-84%), 14-24% silt, and 2-7% sand (Christamy, 1989). Soil pH

in various

soil

layers

and stages of a bamboo

t&n--k&~,

Java, -

Nutrient N

P

K

Ca

1610 5206 -

1.4 12.0 6.1

87.6 307.6 229.9

321.1 1683.5 1461.6

198.1 748.6 532.9

1495 5126 -

4.7 9.5 5.8

74.3 375.4 131.4

364.8 1664.0 1377.6

187.8 780.8 532.9

1380 4987

3.8 6.4 3.4

66.9 222.6 132.4

372,4 1610.4 1371.6

201.7 714.4 537. I

1438 4961

3.8 6.3 4.1

60.0 159.0 131.4

356.5 1594.1 1360.8

184.7 694.6 s22.1

1955 4687 -

5.1 10.5 4.9

100.0 254.4 131.4

334.3 1447.1 1377.6

196.8 754. I 532.9

D. Mailly

et al. / Forest

Ecology

measurements ranged from 5.0 to 5.6 when measured in HZO, and 3.8 to 4.2 when measured in KCI. Soil pH in the top O-25 cm depth increased after clearing and burning but decreased gradually with time (Christanty, 1989). Soil bulk density increased with soil depth. The mean bulk density over a tulun-kebun rotation cycle ranged from 1.12 to 1.18 g cme3 and from 1.18 to 1.22 Mg mm3, at O-5 cm and 5-25 cm depths, respectively (Christamy, 1989). 3.4. Nutrients in precipitation and throughfall

Total rainfall for the 12-month period (1 December 1983 until 30 November 1984) was estimated to be 2096 mm. Throughfall under various stages of the talun-kebun system accounted for 62-95% of the precipitation. The chemical content of precipitation reported here represents bulk precipitation (mixture of rain and dry fallout), because the collectors were continuously open to the atmosphere. Precipitation during the l-year period was estimated to contain 1.6, 2.0, and 0.6 kg ha- ’ of K, Ca, and Mg, respectively (Table 7). N and P were not detectable in the precipitation water. Throughfall contained higher nutrient quantities than rainwater for all stages of the talun-kebun rotation cycle, the difference between precipitation and throughfall being attributed to leaf wash. This transferred 0.5-l .l kg ha-’ per year of

Table I Nutrient content in precipitation and throughfall (kg ha-’ ; December at various stages of a talun-kebun system, Java, Indonesia Stage

Precipitation All stages Throughfall ’ First year cropping Second year cropping Early fallow Mature talun Soil leaching losses First year cropping Second year cropping Early fallow Mature talun

and Management

91 (1997)

155-173

165

N03-N from foliage to the soil during the various stages of the taiun-kebun rotation cycle. Approximately 0.8-0.9 kg ha-r of P was returned to the forest floor layer in net canopy wash over a l-year period. Most of these transfers are believed to have occurred during the period of heavy rain (December-April). Approximately 2.2 kg haa’ of K was added to the rainwater after hitting the cassava leaves, and 7.1-7.7 kg haa’ of K was contributed to throughfall by the bamboo canopy during the fallow stage. Mg content in throughfall under bamboo was nearly 7 times the value in precipitation during the early fallow and mature t&n stages (Table 7). There was negligeable foliar leaching of Ca throughout the cycle, except during the cassava stage. 3.5. Soil leaching losses

Studies of nutrient leaching in various shifting cultivation systems have shown that there is an increase in soil leaching losses following clearcutting (Toky and Ramakrishnan, 1981; Mishra and Ramakrishnan, 1984; Jordan, 1987). Since shifting cultivation is usually practised on steep slopes, clearcutting followed by burning and cropping also increases nutrient losses in run-off water. The amounts of nutrient losses in leaching under various t&n-kebun stages are summarized in Table 7. Toky and Ramakr-

1983 to November

19841, and soil leaching

losses (kg ha-’

per year)

Nutrient N

P

K

Ca

Ms

-

-

1.6

2.0

0.6

1.1 1.0 0.6 0.5 0.30 0.20 0.04 0.04

(1.1) (1.0) (0.6) (0.5)

0.8 0.9 0.8 0.8 0.30 0.20 0.20 0.04

(0.8) (0.9) (0.8) CO.81

2.5 3.8 9.3 8.7 2.80 3.70 1.80 0.40

(0.9) (2.2) (7.7) (7.1)

2.1 3.1 1.5 1.5 1.10 6.80 3.90 2.00

(0.1) (1.1) C-0.5) (-0.5)

0.7 1.4 4.1 3.9

(0.1) (0.8) (3.5) (3.3)

6.10 5.90 2.70 1.20

’ Number within parentheses represents net leaching/leaf wash, Note that the dry season component of annual throughfall overestimated. The degree of visible error will vary between the different stages and for different nutrients. See Figs. l-5.

may have been

166

D. Mailly

et al. /Forest

Ecology

ishnan (1981) estimated leaching losses of 1.1, 0.02, 0.5, 2.7, and 0.9 kg ha-’ per year during the early fallow, and of 0.5, 0.01, 0.2, 1.6, and 0.5 kg haa’ per year in a mature fallow for N, P, K, Ca, and Mg, respectively. These relatively low values support our findings that soil leaching was considered an unimportant mechanism, particularly in the fallow stages. Leaching losses reported by Toky and Ramakrishnan (1981) for the cropping stage were 9.2, 0.07, 13.7, 4.6, and 2.3 kg ha-’ per year for N, P, K, Ca, and Mg, respectively, in comparison to 0.3, 0.3, 2.8, 7.7, and 6.1 kg ha-’ per year as measured in our study. 3.6. Nutrient uptake and internal cycling Table 8 shows gross nutrient uptake by crops, bamboo, and weeds at various stages of the talunkehn system. The first year crops have a much higher N, P, and K uptake in comparison to cassava and bamboo. EIyacinth beans dominate nutrient uptake of the first year crops: the value for N (361.4 kg ha- ’ ) excludes the estimated Nz fixation by the Table Gross

8 annual

uptake

Species

of nutrients

(kg ha-’

) at various

and Management

91 (1997)

155- 173

hyacinth beans. The uptake of nutrients by weeds is highest during the first year cropping stage, but decreases toward the mature talm &age as weed biomass becomes negligible. Bamboo shows a low nutrient uptake during the early fallow stage, but uptake of nutrients increases with increasing age. K uptake in bamboo was relatively high compared to other macronutrients. This finding is in agreement with Toky and Ramakrishnan (19821 who reported that bamboo (genus Dendrocalanm~ is an accumulator of K. The internal conservation of nutrients was estimated only for bamboo during the early fallow and mature talun stages. The concentration of N in leaf litterfall did not show any significant decrease in comparison to live foliage N. This result is in agreement with Seth et al. (19631, who reported that the concentration of N in the litter-fall of Demfrucabmm strictus was the same as the N concentration of its foliage. N retranslocation rates of up to 58-62% have been reported for dry-poor bamboo savannas on the Vindhyan plateau in India; these high rates have

stages of a talun-kebzuz

system,

Java, Indonesia

Nutrient N

P

K

Ca

W

First year cropping Cucumber Bitter solanum Hyacinth bean weeds Bamboo Total

15.3 22. I 361.4 45.6 5.2 449.6

2.5 1.6 15.6 3.4 1.3 24.4

15.5 205 96.1 21.3 4.8 164.2

2.9 4.6 79.3 3.4 1.6 91.8

2.5 3.x 40.0 10.7 1.8 5n.x

Second year cropping Cassava Weeds Bamboo Total

123.7 33.8 37.3 194.8

10.5 2.5 10.2 23.2

92.2 20.6 46.5 159.3

28.0 2.4 19.1 49.5

20.3 x2 21.6 50.1

Early fallow Weeds Bamboo Total

21.1 115.0 136.1

1.4 34.5 35.9

12.3 136.4 148.7

1.5 50.8 52.3

3.Y 55.7 59.6

Mature tahm Weeds Bamboo Total

1.8 101.3 103.1

0.2 27.5 27.7

2.1 125.3 127.4

0.3 41.1 41.4

0.8 44.4 45.2

D. Mailly

et al. /Forest

Ecology

and Management

167

Data presented above are combined into an overall model of the biogeochemical characteristics of the talun-kebun agroforestry system in Figs. l-5. These figures present calibrated flowcharts of the biogeochemistry of N, P, K, Ca, and Mg in five different stages that make up a complete rotation cycle of a bamboo talon-kebun: the mature bamboo

1.6

45.2 7.6 31.9 9.9 7.2

N P

1.2 0.0 K 4.2 Ca 0.0 big 5.0 K

Q Runotv Erosion

155-173

3.7. Overall biogeochemical characteristics of the bamboo talun-kebun

been attributed to the accumulation of N in belowground parts and immobilization in the decomposing leaf mass due to oligotrophic conditions on the site (Tripathi and Singh, 1994). P and Ca concentrations in leaf litterfall did not show any significant decrease in comparison to their respective foliage concentration, but there was a 12% and 40% decrease in concentration of K and Mg, respectively, which reflects internal cycling and foliar leaching of these nutrients.

K

91(1997)

6.4

N 105.6

o

b

UPPER MtNERAL SOIL (O-25 cm) N 6642 P 16 K 354

Ca 1782 I&g 951

Fig. 1, Flowchart summary of the biogeochemistry of the mature bamboo faluh of a bamboo talun-kebun system, West Java, Indonesia. The system is shown as a series of major compartments (boxes), transfer pathways (lines and diamonds joining the boxes), and inputs/outputs (circles). Nutrient contents in kg ha- ’ .

D. Mailly

168

CLEARING

et al. /Forest

Ecology

and Management

91 (1997)

15% 17?

AND HOEING

N P

0.0 0.0

N

130.9 54.4

K Ca Mg

1.6 2.0 0.6

K Ca Ng

276.3 104.8 120.9

K

73. 45. K 231. 92. ca Mg 105.

N P

9.5

Ca

19.0

62.7

Ng

27.6

60 6 6 9

N r-

----

P

1-c

\/t ,-F&:S~FLOiii3

7

I

I

I

I

I ------

l

RUllOfU

Eroshm

?

’

rnL

1

SOIL (Q-25efn) N

Fig. 2, Flowchart Indonesia. Lktails

summary of the biogeochemistry as in Fig. 1.

6816 19

Ca

2005

of the clearing

~UZWI(Fig. I), the clearing of bamboo and burning (Fig. 21, the f ns t year cropping (Fig. 3), the second year cropping (Fig. 41, and. the early fallow stage (Fig. 5). The system is shown as a series of major compartments (boxes), transfer pathways (lines and diamonds joining the boxes), and inputs/outputs (circles). In this conceptual model, uptake of nutrients from the different soil layers was assumed to be in proportion to the vertical distribution of fine roots. Therefore, the quantity of fine roots in the forest

of bamboo

and burning.

in a bamboo

t&u-kehn

system,

West

Java,

floor (root mats) and in mineral soil, as compared to total fine roots, was used to apportion uptake between forest floor and mineral soil in the mature bamboo stages. Uptake during the early fallow and the cropping stages was assumed to be directly from the O-25 cm depth of mineral soil. The contribution of fine root production and turnover was not included in the estimates for lack of data. The biogeochemical cycle during the mature bamboo talzm (Fig. 1) is comparable to that of the #ate

D. Mailly

et al. / Forest

Ecology

and Management

YM

N

155-l

169

73

kebun system confms

the important role played by bamboo in nutrient conservation following slash and bum (Ramakrishnan, 1989): the system soon recovers through a quick succession, and the elements highly susceptible to leaching and runoff are conserved in the living biomass.

stage of the fallow in a shifting cultivation cycle. The processes that occur during the clearing of bamboo and the burning of litter and harvest residue (Fig. 2) are also basically similar to the clearing and burning stage of shifting cultivation. The system differs from traditional shifting cultivation in that chemical fertilizers are used as additional inputs during the cropping stage (Fig. 3). The recovery stage of fallow vegetation in shifting cultivation is similar to the processes that take place during the early fallow stage of the talun-kebun. The taZun-

1st

91 (1997)

3.8. Overall input-output balance of macronutrients in the talun-kebun system

Table 9 summarizes the overall input-output balante of five major nutrients (N, P, K, Ca, and Mg)

CROPPING

0.0

N 398.6 P 21.8 K 154.1 Ca 54.8 Mg 52.6

N 281.9p 15.4 K 102.0 Ca 15.5 tdg 22.7

VEGETATIQN N 449.8 P 31.4 K 218.0 N P K Ca

2,

-

x7 ,c

N

42.0

Ca 74. Mg 80.6 Ca big

1.1 0.8 0.9 0.1

178.5 22.4 K 101.5 Ca 28.9 bfg 51.1

-

-rN

P

P

K

weethep 0 K

ring

Fig. 3. Flowchart summary Details as in Fig. 1.

450

t4g

1.0 2.6

2029 969 2.8 Ca 7.7 Ma 6.1

K

.

of the biogeochernistry

of the first

Ca 14.9 Mg 4.2

year cropping

in a bamboo

talun-kebun

system,

West

Java,

Indonesia.

170

D. Mailly

et al. / Forest

Ecology

and Management

over a 6-year bamboo tahn-kebun rotation cycle. Harvest removals were clearly the major pathway of nutrient loss, accounting for 82%, 92%. 93%, 80%, and 87% of the total N, P, K, Ca, and Mg output from the 6-year cycle, respectively. Soil leaching losses were small for N, P, and K (0.1 %, 1.l%, and 2.2% of the total loss, respectively), but significant for Ca (155%) and Mg (10.4%). Although lysimeter-based estimates of quantitative leaching losses are subject to considerable error, the data suggest that leaching losses were only important for the two

2nd YEAR

N P K

91 C1997)

IS-

173

divalent cations. Losses in the burning of litter and slash were only important for N (14% of total losses). About 219.6 kg ha-’ of N, or an average uf 36.6 kg ha-’ per year, was lost from the sys&emover the 6-year rotation. The difference between input and output to and from the system reflected changes in the soil N compartment. Soil mineral tutroger? to a 25 cm depth declined by 243 kg haa’ over the 3-year period after clearcutting (2 years of cropping and 1 year of fallow). However, the negative baIance for the nitrogen budget may have been partly caused

CROPPING

0.0 0.0 1.6

N P K

c%

Mg

P

28.2

K

180.5

79.2 9-9 83.8

&J P K

18.2 15.3

ca

5.9

ng

10.1

Ca

46.8 3.8 47.7

48-S 1.1 10.4 10.8 6.1

47.5

l&g 56.7

P 0.9 K 2.2 Ca 1.1

G

Oil

Fig. 4. Flowchart summary Details as in Fig. 1.

of the biogexhemistry

In

of the second

year cropping

N

25.3

P K

0.9

Ca

6.8

4.9

ng

4.4

in a bamboo

r&n-kebun

I

system,

West

Java, Indonesia.

D. Mailly

et al. / Forest

Ecology

and Management

91 (1997)

155-l

Ill

73

should be conducted. There may also have been some losses to denitrification, but this was not measured. The net differences in the input-output balance of P, K, Ca, and Mg were presumed to be compensated for by the release from soil minerals by weathering, but this was not measured or estimated because of the lack of data. The net loss of K > Mg > Ca > P could presumably lead to a depletion of these elements in the surface soil. However, there are no data to suggest a current problem of declining availability

by an underestimate of the rate of Nz fixation by Afbizia and hyacinth bean, for which literature values were used. If the rate of N2 tixation by Albizia is changed to 50 kg haa’ per year instead of 15 kg ha- i per year, the net difference shifts from - 219.6 to -9.6 kg ha-’ over the 6-year rotation, or an average annual input-output balance of only - 1.6 kg ha-’ per year. Considering the importance of inputs from biological Nz fixation to the input-output balance of the system, a detailed study on the role of Nz fixing species and the rate of Nz fixation

O-l Precipitation

N

0.0

P 0.0 K 1.6 Ca 2.0

N

0.2

P

0.0

K 2.6 Ca 0.0 Mg 4.4

vFtunotU EWeion

I I

P

K

o

I

lea

24.1 99.6 35.0

\

6

K Ca Ma

Fig. 5. Flowchart Details as in Fig.

summary 1.

of the biogeochemistry

of the the early

fallow

stage in a bamboo

1.8 3.9 2.1

ralun-kebun

system,

West

Java, Jndonesia.

172 Table 9 Input-output

D. h4aill.y et aL. / Forest

balance

of N, P, K, (2,

Ecology

and Management

and Mg (kg haa’ J over a 6-year

9f (1997)

talun-kebun

rotation

155-l

cycle,

73

West Java, Indonesia

Nutrient N Inputs Precipitation (6 years) BiologicaJ Na fiiation ’ First year cropping Second year cropping 4 years of fallow Fertilization Total input

’ Estimated

input-output

values

K

-.

outputs Losses in the bum Soil leaching losses First year cropping Second year cropping 4 years of faBow Harvest removals First year cropping Second year cropping Mature talun Removal of dead branches Total output Net difference Average annual

P

balance

CCI 9.6

Mg 12.0

-

3.6

-

47.0 15.0 60.0 178.5 310.5

22.4 22.4

101.5 Ill.1

28.9 40.9

84.5

1.0

45

3.4

1.9

0.3 0.2 0.2

0.3 0.2 0.3

2.8 3.7 3.0

I.7 6.8 9.9

6. I 5.9 5.3

281.9 79.2 73.6 10.2 530.1

15.4 9.9 45.0 4.3 76.4

101.9 83.8 231.6 16.5 447.8

1s.4 18.2 92.6 3.8 157.8

22.7 15.3 105.9 3.0 166. I

-219.6 - 36.6

- 54.0 -9.0

- 336.7 -56.1

- 116.9 - 19.5

st.1 54.7

ill.4 - 18.6

based on literature.

of these elements on this site? although the use of an NPK fertilizer does suggest concern over the availability of P and K, and the estimated net loss of 56.1 kg ha-’ per year of K is certainly noteworthy. It is possible that the periodic deposition of volcanic ash in this region may replenish the supply of weatherable minerals containing these elements sufficiently that this rate of loss may not be of significance for long-term productivity on these sites.

bamboo, the land dies’. Although some farmers have already changed from this traditional system to monoculture cropping, and have replaced bamboo with cash crops, the majority are still practising the traditional cropping pattern. It is recommended that the long-term implications of the nutrient budgets presented in this study, and how they might change if economic pressures result in an abandonment of this traditional subsistence agroforestry system in favour of a cash-crop system, should be explored using a simulation modeliing approach.

4. Conclusion The results of this study indicate the important role of bamboo in the ~uZMZ-M.W~ agroforestry system. Data on nutrient’ accumulation in the forest floor during the fallow stage’ show a build-up of soil humus and an increase in site nutrient reserves released after the clearing and hoeing of the mature tab, giving support to the farmers’ saying ‘without

Ackmw

ts

This study was partly funded by the Ford Foundation, the University of British Columbia, the institute of Ecology (Padjadjaran University, Indonesial, and by an EMDI-CIDA scholarship awarded to L.C. The authors wish to thank the following Persons for their

D. Mailly

et al. / Forest

Ecology

valuable help: Dr. 0. Soemarwoto at the Ecological Institute in Bandung, Indonesia; Drs. MC. Feller, L.M. Lavkulich, and H.E. Schreier for their useful comments; Dr. D. Binkley for the estimate of N2 fixation rates for AZbizia trees. Help and encouragement from J. Iskandar, H.Y. Hadikusumah, Y. Yuhana, M.R. Noerdin, D. Hermanto, H. Sukandar, M.A. Laturiuw, N. Price, and two anonymous reviewers are gratefully acknowledged.

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