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Nutrient Return Through Leaf Litter Decomposition of Common Cropland Agroforest Tree Species of Bangladesh

Md. Hasanuzzaman*
Forestry and Wood Technology Discipline, Khulna University, Khulna- 9208, BANGLADESH

Mahmood Hossain
Forestry and Wood Technology Discipline, Khulna University, Khulna- 9208, BANGLADESH

Abstract/ Executive Summary:

Cropland agroforestry is an important production system in Bangladesh. Melia azadirachta, Azadirachta indica, Eucalyptus camaldulensis, Swietenia macrophylla, Mangifera indica, Zizyphus jujuba, Litchi chinensis, Albizia saman, Artocarpus heterophyllus, Acacia auriculiformis, Dalbergia sissoo and Khaya anthotheca are common in the cropland agroforest of Bangladesh and have been selected for this study. This study focused on the mass loss of leaf litter and nutrient (N, P and K) addition in soil through the microbial decomposition of leaf litter of the selected cropland agroforest tree species of Bangladesh. Leaf litter decomposition experiment was conducted using litter bag technique both in dry and wet season in a controlled environment. The mass loss was found the highest (57% and 63%) for M. azadirachta followed by E, camaldulensis (50% and 56%), A. indica (53% and 58%) and the lowest (11% and 19%) was found for L. chinensis in dry and wet season respectively. The highest rate of decomposition (0.32 g/day and 0.35 g/day) was observed for M. azadirachta and the lowest (0.06 g/day and 0.10 g/day) was detected for L. chinensis. Significant (p=0.05) differences were observed among the mass loss of leaf litter and N, P and K concentration of decomposed soil of the studied species between dry and wet season. The decay constant (k) was found the highest for M. azadirachta (0.005 and 0.005) followed by E. camaldulensis (0.004 and 0.005), A. indica (0.004 and 0.005) and the lowest for L. chinensis (0.001 and 0.001) in dry and wet season respectively. A similar pattern of nutrient concentration (P> K> N) in the decomposed soil of the entire studied tree species were observed. Among the considered cropland agroforest tree species, M. azadirachta was found to be the best followed by, E. camaldulensis, L. chinensis and A. heterophyllus in terms of N, P and K return.

Keywords: Cropland agroforestry, Leaf litter decomposition, Decay constant, Organic matter, Nutrient return, Species selection.

Location: Khulna, Jessore and Satkhira districts

Start Date: 00-04-2013

End Date: 00-09-2013

Program Area: Crop-Soil-Water Management

Commodity: Manures, Agroforestry

Objectives:

This study aimed to prioritize the commonly planted cropland agroforest tree species of Bangladesh on the basis of nutrients (N, P and K) return to the soil through microbial decomposition of leaf litter.

Methodology:

Description of the study area: Bangladesh is located between 20°34'-26°3' N; and 88°01'-92°41' E, on the South bordered by the Bay of Bengal and on all the other sides India along with a small part of Myanmar. Khulna, Jessore and Satkhira districts are located at the southwestern Bangladesh that characterizes low, flat, and fertile deltaic plain predominated by calcareous to non calcareous alluvium soils 25. A tropical to subtropical monsoon climate characterizes with three distinct seasons i.e. summer, rainy and winter in this region 26. The average of monthly rainfall is 155 mm, the highest average rainfall (339 mm) occurs during the month of June to September and the lowest average rainfall (16 mm) occurs in the month of November to February in the study area. January is the coldest month and May is the warmest month of the years. The mean annual temperature is 26 °C with a range of 22–31 °C. The average relative humidity is the highest (86%-88%) during the month of July to August and the lowest (72%-74%) during February to April11 . Collection and processing of leaf samples: Bulk of yellowish senescence leaves of M. azadirachta, A. indica, E. camaldulensis, S. macrophylla, M. indica, Z. jujuba, L. chinensis, A. saman, A. heterophyllus, A. auriculiformis, D. sissoo and K. anthotheca were picked from trees of selected cropland agroforest. Leaves of individual species were thoroughly mixed and 100 grams of leaves were considered as individual sample. Experimental setup: The microbial decomposition of leaf litter of the selected tree species was conducted by using litter bag technique9 . The experiment was conducted at the glass house of Forestry and Wood Technology Discipline Nursery, Khulna University. The experiment was conducted during April, 2013 to September, 2013 for both dry and wet season but dry and wet season was manually controlled on the basis of the previous year’s daily rainfall data. Dry season was controlled following the rainfall of October to March, 2012 and wet season was controlled following the rainfall of April to September, 2012. A total of 12 species were tested and for each species 6 plastic bowls (3 replicate for dry season and 3 replicate for wet season) were prepared with 10 kg of air dried soil. At the same time 1 kg of air dried soil was brought to the laboratory for measuring the initial nutrient and organic matter status of soil. Individual leaf samples were placed in every litter bag (30 x 20 cm) with 1 mm2 mesh size. 6 litter bags of each species were prepared for dry and wet season study and 3 litter bags of each species was brought to the laboratory for calculating conversion ratio of fresh to oven-dry weight at 80 °C to constant weight. Each litter bag was placed in single bowl. Thus a total of 72 bowls with 72 litter bags was prepared (36 for dry and 36 for wet season) for the selected 12 species. Water was supplied to the bowls considering the previous year’s rainfall data discussed earlier. At the end of experiment (6 month) litter bags were removed from the bowls and the soils were thoroughly mixed. The soils were then air dried for further analysis. Sample Collection and processing: Litter bags were collected from the glass house at the end of six months experiment (dry and wet season). The collected leaf litter samples were washed gently and the sediments and dirt particles were removed using a soft brush with running tap water and final rinsing by distilled water. Each leaf litter sample was then oven-dried at 80 °C to constant weight. After the collection of leaf litter bags, the soil samples were mixed thoroughly and air dried. The air dried soil samples were then brought in the Nutrient Dynamics Laboratory for chemical analysis. The decomposed soil sample of each species was then oven-dried at 80 °C to constant weight. Mass loss and decay constant: The amount of mass loss of leaf litter of the studied tree species was calculated from the initial converted oven-dry mass and the remaining mass at the end of experiment. The decomposition rate of leaf litter was calculated from the mass loss (%) divided by duration of decomposition period (days). Decay constants were calculated using negative exponential decay model for leaf litter of the studied species. X / X0= exp (−kt) 27 where, X-final weight at time t, X0 -the initial weight, exp- the base of natural logarithm, k- the decay rate coefficient and t-is the time (days) in year. Organic matter and nutrients addition through leaf litter decomposition: Soil organic matter content addition through microbial decomposition of leaf litter of the studied species was determined by ignition method28. One gram soil sample of oven dried at 105ºC was taken in a porcelain cup and placed in a muffle furnace (Wise Therm, FH-05, DAIHAN Scientific co. ltd, Korea) and kept at 450 ºC for four hours. After cooling to room temperature, the weight of the ignited sample was taken. Percentage of loss on ignition was calculated from the calculation. Statistical analysis: The relationship among mass loss of leaf litter; organic matter, N, P and K concentrations of decomposed soil of the studied tree species between dry and wet season was evaluated by unpaired t test using SPSS (17) statistical software.

Source of Information: International Research Journal of Biological Sciences Vol. 3(8), 82-88, August (2014) ISSN 2278-3202

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Achievement/Findings:

A considerable amount of organic matter and nutrients can be added to the soil of different agroforestry practices through the process of leaf litter decomposition and a portion of these organic matter and nutrients are reused by the plants. The added nutrients can contribute sustainable soil fertility, an important issue for agroforestry practices. Among the considered tree species, M. azadirachta was found to be the best followed by, E. camaldulensis, L. chinensis and A. heterophyllus in terms of N, P and K return.

Knowledge Management: Journal