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Organic matter status and organic recycling in Bangladesh soils
Resources and Conservation, 13 (1987) 117-124 Elsevier Science Publishers B.V., Amsterdam - Printed
117 in The Netherlands
ORGANIC MATTER STATUS AND ORGANIC RECYCLING IN BANGLADESH SOILS*
Z.H. BHUIYA Department of Soil Science, Bangladesh Agricultural University, Mymensingh (Bangladesh) (Received
May 31,1986;
accepted
June 19,1986)
ABSTRACT Bangladesh has a tropical monsoon climate. The major climatic differences within the region concern the total rainfall. About 500 soil series have been recognized and in the local Bangladesh classification these are grouped into 17 general soil types. Organic matter is an important constituent of mineral and peat soils. Organic-matter content in soil is dependent on agro-climatic conditions and is difficult to conserve at a high level in tropical and subtropical conditions. Soils of Bangladesh are low in organic matter, and conserving and maintaining it at moderate levels is one of the serious problems in soil management. This may be accomplished through: maximum return of crop and animal residues to soil; balanced use of chemical fertilizers such as urea, triple superphosphate and muriate of potash; use of biofertilizers; green manuring in crop rotation; and proper utilization of farm manure, night soil, composts and nitrogenous organic materials, such as crushed bones, fish wastes, mustard, sesame, castor cakes, etc. INTRODUCTION
Bangladesh is a delta of 144,000 km’, formed principally by the rivers Ganges and Brahmaputra. The climate is characterized by high temperature, heavy rainfall, often high relative humidity and fairly marked seasonal changes (it has a tropical monsoon climate). The average annual rainfall ranges from 1250 to 5500 mm. However, the distribution of rainfall varies from season to season as well as from region to region. In winter (November--February) the amount of rainfall received ranges from 125 to 250 mm. During the Nor’wester (land-based cyclonic storms) season (March-May), rainfall ranges from 250 to 750 mm. The combined rainfalls of the S.W. Monsoon (June-August) and the retreating S.W. Monsoon (SeptemberOctober) periods range from 1000 to 4550 mm. Thus heavy rainfall and high humidity, coupled with high temperatures, make the prevailing climate highly congenial for rapid vegetative growth and biomass production. An excellent general account of the geography of the region is provided by Johnson [ 11. *Paper presented at the International Symposium on Recycling Fertilizer, Food, Feed and Fuel, Hong Kong, August 28-30,1985.
of Organic
Wastes for
118 GENERAL SOIL CHARACTERISTICS
Bangladesh has three major physiographic units: floodplains, terraces and hills which cover about 80, 8 and 12% of the area, respectively. Floodplains underlain by loose recent alluvial deposits occur in the meanders of the Brahmaputra, Ganges, Meghna and Tista rivers. There are also Piedmont aprons, low-lying basins and tidal estuarine flats. The Barind and Madhupur tracts include the uplifted and locally dissected terrace areas of Tertiary “Madhupur-Clays”. The hills comprise the folded and dissected Tertiary sandstones and shales. About 500 soil series are recognized and in the local Bangladesh classification the soils are grouped into 17 general soil types [ 21. All soils differ in their general fertility status as well as in physical properties. Calcareous soils found in Gangetic alluvium are generally rich in Ca and Mg while most recent floodplain soils have high reserves of potassium. The soil pH ranges from a minimum of around 4.0 in the tea soil to 8.0 in the Ganges floodplain. In most soils pH ranges between 5.0 and 7.0. SOIL ORGANIC-MATTER
CONTENT
Organic matter is an important constituent of mineral and peat soils. In the former soil, it varies from 0.1 to 5% while in the composition of the latter type of soil it ranges from 20 to 95%. The role of soil organic matter in soil fertility and productivity needs no emphasis. Besides improving the physical and microbiological properties of soil, it plays an important role in replenishing some macro- and micronutrients to plants [ 31. In a tropical monsoon climate like that of Bangladesh, vegetation and crop plants in general grow luxuriantly due to the favourable temperature and rainfall. Moreover, two-thirds of the country remain under water for 3 to 6 months during the rainy season and aquatic vegetation grows abundantly. As the flood water recedes, this aquatic vegetation dies and adds organic matter to soil. Due to the same seasons of high temperature and rainfall the organic matter that is added to soil in the form of biomass is decomposed rapidly (except in perennially waterlogged areas) by microbes and little is left in the soil. Due to intensive cultivation, the agricultural soils are being disturbed vigorously through tillage operations like ploughing, puddling, laddering, etc., which enhance decomposition of organic matter. There is an acute shortage of fuel in rural areas and, therefore, farmers nowadays leave very little crop residues (stump, stubble, roots) in their fields. The current greater use of inorganic fertilizer than in the past, to raise agricultural production, also enhances decomposition of organic matter. Nutrients present in the fertilizer act as food for decomposing soil microbes. The tropical monsoon climate and centuries of cultivation have, therefore, caused low organic-matter contents of most Bangladesh soils (Table 1). Organic-matter content is very much dependent on agro-climatic conditions and it is difficult to conserve it at a high level in tropical and sub
119 TABLE
1
General
soil types and organic-matter
General soil type
Non-calcareous
Calcareous
contents
of Bangladesh
Soil series alluvium
alluvium
Grey floodplain
Ramgati
soils
soils
Depth (cm)
Soil organic-matter content (a)
O-l 2.1 12.7-20.3 20.3-55.3 O-12.7 12.7-17.8 17.8-45.7
0.99
0.54 0.79 1.68 0.99 0.42
Sabhar Bazar
O-12.7 12.7-33.0 33.0-53.3
2.40 1.12 0.92
Pritimpasa
O-10.2 10.2-17.8 17.8-35.6
Acid basin clays
Chakla
O-7.6 7.6-l 5.2 15.2-33.0
1.11 0.55 0.55 5.20 4.07 2.46
Non-cafcareous dark grey floodplain soils
Lokdeo
O-10.2 10.2-15.2 15.2-38.1
2.18 0.97 0.97
Calcareous soils
dark grey floodplain
Ghior
Calcareous soils
brown floodplain
O-10.2 10.2-15.2 15.2-35.6 o-15.2 15.2-40.6 40.6-55.9 O-12.7 12.7-33.0 33.0-61.0 O-10.2 10.2-12.7 12.7-35.6 O-10.2 10.2-33.0 33.0-66.0 O-2.5 2.5-10.2 10.2-22.9 O-3.8 3.8-7.6 7.6-15.2
Grey piedment
soils
Non-calcareous soils
Gopalpur
brown floodplain
Pirgachha
Black terai soils
Lakhipur
Brown hill soils
Kulaura
Shallow
red-brown
Deep red-brown
Brown mottled
Grey terrace
terrace
terrace
soils
Peat
Acid sulphate
terrace
soils
soils
soils
soils
Gerua
-
7.89
2.28 1.26 0.50 0.36 1.16 1.68 0.31 2.80 _ 0.22 1.44 2.62 1.86
Noadda
O-l 0.2 10.2-30.5 30.5-53.03
1.85 1.38 0.95 2.44 1.90 1.18 1.82 1.17 0.71
Chhiata
O-7.6 7.6-12.7 12.7-17.8
1.47 0.87 0.69
Satla
O-20.3 20.3-63.5 63.5-78.7 O-7.6 7.6-12.7 12.7-33.0
35.37 62.1 87.1 3.46 3.17 1.89
Tejgaon
Bhadar Khali
120
tropical conditions [4]. However, many authors have gathered evidence to show that farmyard manure and organic residues are effective in increasing the level of organic matter even under tropical conditions [ 51. It is believed that unsatisfactory crop performance in many places of Bangladesh, even with adequate NPK fertilization, is associated with low soil organic-matter contents [ 61. At Bangladesh Agricultural University [ 71 a laboratory incubation experiment with Jamuna and Tista Floodplain, Saline Tidal Zone and Madhupur Red Soils indicated that the organic matter content of these soils decreased gradually with increase in incubation period up to 42 days [8]. It was further noted that increase in the application rate of urea-N (0, 56, 112, 168 kg/ha of N) resulted in increased losses of organic matter in soil. Such losses might be due to the increased activity of microorganisms in the urea-treated samples. ORGANIC RECYCLING IN BANGLADESH SOILS
The various practices of recycling or cycling organic materials in soil have become intensified and more widespread in Asia during the past few years as the countries recognize the need to supplement mineral fertilizers to improve physical and microbiological conditions in soils, to conserve soil and reduce environmental pollution. Biomass of different sources which can be utilized as agents of organic recycling in Bangladesh soils [ 91 are: (1) Animal wastes (cattle dung and urine); (2) Crop wastes (straw, husks, stalks, stubble, weeds, grasses, leaves, sugarcane trash, etc.); (3) Human-habitation wastes (night soil, urine, sewage sludge, garbage); (4) Green manures (leguminous pulses, oilseed producing crops, forage/ fodder crops and other leguminous plants); (5) Biofertilizers (rhizobia inoculants, blue-green algae, Azolk); (6) Organo-mineral manures; (7) Tank, pond and river silt; and (8) Other sources (fish wastes, slaughter-house refuse, animal bones, municipal and urban wastes, forest wastes, mustard, sesame and castor cakes, etc.). Animal and crop wastes
During the year 1981-82 there were 35.07 million heads of cattle, 1.6 million buffaloes, 12.9 million goats and sheep, 73 million poultry birds and 20.86 million ducks [lo]. Annually 36.67 million cattle and buffaloes produce about 32.27 Tg of farm manure (air dry); 12.9 million goats and sheep produce about 10.32 Tg of manure per year; 73 million poultry birds yield yearly about 2.43 Tg of droppings. Rice crops yield about 28 Tg
121
and wheat produces 1.6 Tg of straw [ 111. These quantities together are equivalent to a huge supply of urea, triple superphosphate and muriate of potash. With all these available organic wastes farmers are advised to prepare composts by mixing crop wastes with animal excreta and refuse. Preparation of organic manure from animal wastes and crop residues through biogas plants has been introduced in Bangladesh only on a limited scale because of the high cost of installation of the digester tank. At present, farmers misuse cow dung by burning (about 35%), due to shortage of fuel. They are also advised not to take away the crop residues that are left in the field after crop harvest but rather plough them in during land preparation. Human-habitation wastes In Bangladesh only three major cities (Dhaka, Chittagong and Khulna) have set up sewerage lines in limited locations, but these lack digestion plants. Night soil and urine through the sewerage pipes are collected in some low-lying areas away from the cities, and are left to decompose naturally. For want of digestion tanks, sludge and effluent cannot be separated. The sludge formed has a foul smell and the farmers would not like to use it as a manure. Green manures The potential amount of nitrogen that can be fixed by a green-manure crop is adequate for a maximum yield of most crops now grown in the tropics. In South Asia, fixation by legumes is commonly reported to be around 40 kg/ha-y N, but up to 600 kg/ha-y N has been reported, so there is a good potential for nitrogen fixation in this part of the world. Often a farmer must fit a green-manure crop into a relatively short time span between other crops. The amount of nitrogen fixed in a short time and then added to the soil, however, can be high, up to 150 kg/ha in eight weeks if the crop is grown as a green manure and then incorporated into the soil. This amount of nitrogen can be equivalent to a much greater fertilizer rate, because the slow decomposition of the added plant matter has the effect of a slow-release fertilizer. The nitrogen added this way is not easily leached or lost as nitrogenous fertilizer. The potential for green manuring is high in Bangladesh, but research must be done to fit its use in current cropping systems, and the benefits of its use must be understood by the farmers who will use it. Bio fertilizers Rising costs of energy and, in turn, chemical fertilizers have focused attention on biological sources of nitrogen, the element most commonly limiting crop production. Even though in many eastern countries (including Bangla-
122
desh) farmers do not fertilize their fields, it appears that biological nitrogen fixation often permits a moderate rice harvest in the case of native varieties. De [ 121 first attributed the natural fertility of flooded soils in (presentday) Bangladesh to blue-green algae. In Bangladesh, studies in this field, however, remained neglected for many years. Studies on symbiotic nitrogenfixing systems in laboratory and pot culture were first initiated at Dhaka University in 1968 [ 13,141. Substantial studies have been made since 1976 at Bangladesh Agricultural University in the field of biological nitrogen fixation and production of biofertilizers. Many pot and field experiments have been carried out with local isolated strains of rhizobia along with some recommended exotic strains in soybean, black gram, grasspea and chickpea with respect to nodulation, dry matter production, N uptake and grain yield [15-201. Some highly effective strains of soybean, grasspea and black gram rhizobia have been identified through many pot and field trials. Peat-based biofertilizer inoculum has been prepared successfully at Bangladesh Agricultural University and so far more than 2000 kg have been sold. Nitrogen-fixing blue-green algae have been isolated from soils of Bangladesh and their nitrogen-fixing abilities evaluated in different soil media [21,22]. Algal inoculation has been found to increase rice yield significantly [23,24]. Some studies on the growth and biomass production of different strains of Azolla are being carried out. Favourable effects of “Azotobacterin” on rice and jute have also been observed [ 25,261. Organo-mineral manures
These manures are prepared by mixing organic wastes (such as rice straw, wheat straw, goundnut husks, tobacco wastes, sugarcane trash, etc.) which have higher C/N ratios, with inorganic nitrogenous and phosphatic fertilizers. Tank, pond and river silt
In Bangladesh efforts are being made to excavate silted rivers, canals, tanks and ponds to store rain water in summer. The silt, which includes organic matter, can act as a manure for new banana plantations. Other sources
Other sources for organic manures are fish wastes, slaughterhouse refuse, animal bones, municipal and urban wastes, forest wastes, mustard, sesame and castor cakes, etc. These by-products are rich in plant nutrients and have not been fully utilized as organic manures in Bangladesh. The Fisheries Development Corporation has taken the initiative in organizing collection, processing and marketing of fish wastes through fishermen’s co-operative societies. Crushed animal bones are not available for manuring soil.
123 REFERENCES
2 3 4
5
9
10 11 12 13 14
15
16
17
18
19
20 21
22
Johnson, B.L.C., 1982. Bangladesh. Heineman, London, 2nd edn., 133 pp. FAO, 1971. Soil Survey Project, Bangladesh: Soil Resources. AGL: SF/PAK 6, Technical Report No. 3. Food and Agriculture Organization, Rome, 211 pp. Bremner, J.M., 1956. Some soil organic-matter problems. Soils Fert., 19: 115-123. Jenny, H. and Raychaudhuri, S.P., 1960. Effect of climate and cultivation on nitrogen and organic matter research in Indian soils. Indian Council of Agricultural Research, New Delhi, 126 pp. Gaur, A.C., Sadasivam, K.V., Vimal, D.P. and Mathur, R.S., 1971. A study on the decomposition of organic matter in an alluvial soil, CO, evolution, microbiological and chemical transformations. Plant Soil, 34: 17-28. Bhuiyan, N.I., 1983. Experiences on soil-related problems to crop production in Bangladesh. Bangladesh Rice Research Institute, Joydevpur, Bangladesh, 26 pp. Hoque, M.S., 1983. Experiences on soil-related problems to crop production in Bangladesh. Bangladesh Agricultural University, Mymensingh, Bangladesh, 20 pp. Bhuiya, Z.H., Sattar, M.A. and Islam, M.S., 1983. Effect of urea on the available phosphorus and organic matter in some Bangladesh soils. Indian J. Agric. Sci., 44: 466-469. Huq, Munirul, 1980. Importance of organic matter on soil fertility. Soil Resources and Development Institute, Dhaka, Bangladesh, 14 pp. FAO, 1983. Production Year Book. Vol. 36. 1982. Food and Agriculture Organization, Rome, 320 pp. FAO, 1982. Agricultural Year Book of Bangladesh 1982. Bangladesh Bureau of Statistics, Statistical Division, Ministry of Planning, Bangladesh, 806 pp. De, P.K., 1939. The role of blue-green algae in nitrogen fixation in rice fields. Proc. R. Sot. London, Ser. B., 127: 121-139. Chowdhury, M.S. and Khan, A.K.M.S.I., 1968. Cultural characteristics of certain native strains of root-nodule bacteria of East Pakistan. Pak. J. Soil Sci., 4: 21-29. Bhuiya, Z.H. and Khan, S.I., 1982. Role, needs and potential of the nodulated legume. In: J.M. Vincent (Ed.), Nitrogen Fixation in Legumes. Academic Press, New York, NY, pp. 263-284. Hoque, M.S., Ali, M. and Mannan, M., 1980. Response of Bragg soybean to inocuand dry matter lation with different strains of Rhizobium japonicum. I. Nodulation production. Thai J. Agric. Sci., 13: 303-314. Hoque, M.S., Ali, M. and Sikder, B.H., 1981. Response of Bragg soybean to inoculation with different strains of Rhizobium japonicum. II. Yield and yield contributing characters. Thai J. Agric. Sci., 14: 41-50. Hoque, M.S., Solaiman, A.R.M. and Bhuiya, Z.H., 1982. Effectiveness of some locally prepared and imported inoculants of soybean in Bangladesh. Thai J. Agric. Sci., 15: 127-134. Hoque, MS., Islam, A.B.M.S. and Ali, M.I., 1983. Effect of temperature and storage duration in the survival of some strains of soybean rhizobia. Thai J. Agric. Sci., 16: l-11. Bhuiya, Z.H., Islam, M.R., Alam, A.B.M.M. and Hoque, M.S., 1983. Effect of different locally isolated strains of Rhizobium leguminosarum on nodulation, N uptake and yield of Khesari (Lathyrus satiuus L.). Bangladesh J. Soil Sci., 19: 63-67. Bhuiya, Z.H., Hoque, M.S. and Miah, M.M., 1983. Final Report FAO/IAEA/SIDA Research Coordination Meeting. International Atomic Energy Agency, Vienna, 6 pp. Bhuiya, Z.H., Hashem, M.A. and Islam, A.K.M.N., 1980. Isolation and identification of dominant nitrogen-fixing blue-green algae from Bangladesh soils. In: Current Perspectives in Nitrogen Fixation. Australian Academy of Science, Canberra, p. 498. Bhuiya, Z.H., Hashem, M.A., Rahman, M.M. and Miah, M.H., 1983. Nitrogen fixing capacity of different species of blue-green algae of BAU Campus soils, Mymensingh. Bangladesh J. Soil Sci., 19: 35-38.
124 23
24
25 26
Sarker, N.I. and Bhuiya, Z.H. Effect of blue-green algae on the yield of rice (BR-4) in the presence of different levels of nitrogen fertilizer. Bangladesh J. Soil. Sci., 18: 12-16. Bhuiya, Z.H., Islam, A.K.M.N., Hashem, M.A., Tahmida Begum, Z.N. and Rahman, M.M., 1984. Effect of blue-green algae as bio-fertilizer on rice. Bangladesh J. Agric., 9( 2): 47-51. Mian, M.H. and Bhuiya, Z.H., 1977. Effect of Azotobacterin on the yield of rice. Bangladesh J. Agric., l(2): 119-112. Mian, M.H. and Bhuiya, Z.H. Effect of Azotobacterin on the dry matter yield and length of jute. Bangladesh J. Agril. Sci., 4: 45-52.
117 in The Netherlands
ORGANIC MATTER STATUS AND ORGANIC RECYCLING IN BANGLADESH SOILS*
Z.H. BHUIYA Department of Soil Science, Bangladesh Agricultural University, Mymensingh (Bangladesh) (Received
May 31,1986;
accepted
June 19,1986)
ABSTRACT Bangladesh has a tropical monsoon climate. The major climatic differences within the region concern the total rainfall. About 500 soil series have been recognized and in the local Bangladesh classification these are grouped into 17 general soil types. Organic matter is an important constituent of mineral and peat soils. Organic-matter content in soil is dependent on agro-climatic conditions and is difficult to conserve at a high level in tropical and subtropical conditions. Soils of Bangladesh are low in organic matter, and conserving and maintaining it at moderate levels is one of the serious problems in soil management. This may be accomplished through: maximum return of crop and animal residues to soil; balanced use of chemical fertilizers such as urea, triple superphosphate and muriate of potash; use of biofertilizers; green manuring in crop rotation; and proper utilization of farm manure, night soil, composts and nitrogenous organic materials, such as crushed bones, fish wastes, mustard, sesame, castor cakes, etc. INTRODUCTION
Bangladesh is a delta of 144,000 km’, formed principally by the rivers Ganges and Brahmaputra. The climate is characterized by high temperature, heavy rainfall, often high relative humidity and fairly marked seasonal changes (it has a tropical monsoon climate). The average annual rainfall ranges from 1250 to 5500 mm. However, the distribution of rainfall varies from season to season as well as from region to region. In winter (November--February) the amount of rainfall received ranges from 125 to 250 mm. During the Nor’wester (land-based cyclonic storms) season (March-May), rainfall ranges from 250 to 750 mm. The combined rainfalls of the S.W. Monsoon (June-August) and the retreating S.W. Monsoon (SeptemberOctober) periods range from 1000 to 4550 mm. Thus heavy rainfall and high humidity, coupled with high temperatures, make the prevailing climate highly congenial for rapid vegetative growth and biomass production. An excellent general account of the geography of the region is provided by Johnson [ 11. *Paper presented at the International Symposium on Recycling Fertilizer, Food, Feed and Fuel, Hong Kong, August 28-30,1985.
of Organic
Wastes for
118 GENERAL SOIL CHARACTERISTICS
Bangladesh has three major physiographic units: floodplains, terraces and hills which cover about 80, 8 and 12% of the area, respectively. Floodplains underlain by loose recent alluvial deposits occur in the meanders of the Brahmaputra, Ganges, Meghna and Tista rivers. There are also Piedmont aprons, low-lying basins and tidal estuarine flats. The Barind and Madhupur tracts include the uplifted and locally dissected terrace areas of Tertiary “Madhupur-Clays”. The hills comprise the folded and dissected Tertiary sandstones and shales. About 500 soil series are recognized and in the local Bangladesh classification the soils are grouped into 17 general soil types [ 21. All soils differ in their general fertility status as well as in physical properties. Calcareous soils found in Gangetic alluvium are generally rich in Ca and Mg while most recent floodplain soils have high reserves of potassium. The soil pH ranges from a minimum of around 4.0 in the tea soil to 8.0 in the Ganges floodplain. In most soils pH ranges between 5.0 and 7.0. SOIL ORGANIC-MATTER
CONTENT
Organic matter is an important constituent of mineral and peat soils. In the former soil, it varies from 0.1 to 5% while in the composition of the latter type of soil it ranges from 20 to 95%. The role of soil organic matter in soil fertility and productivity needs no emphasis. Besides improving the physical and microbiological properties of soil, it plays an important role in replenishing some macro- and micronutrients to plants [ 31. In a tropical monsoon climate like that of Bangladesh, vegetation and crop plants in general grow luxuriantly due to the favourable temperature and rainfall. Moreover, two-thirds of the country remain under water for 3 to 6 months during the rainy season and aquatic vegetation grows abundantly. As the flood water recedes, this aquatic vegetation dies and adds organic matter to soil. Due to the same seasons of high temperature and rainfall the organic matter that is added to soil in the form of biomass is decomposed rapidly (except in perennially waterlogged areas) by microbes and little is left in the soil. Due to intensive cultivation, the agricultural soils are being disturbed vigorously through tillage operations like ploughing, puddling, laddering, etc., which enhance decomposition of organic matter. There is an acute shortage of fuel in rural areas and, therefore, farmers nowadays leave very little crop residues (stump, stubble, roots) in their fields. The current greater use of inorganic fertilizer than in the past, to raise agricultural production, also enhances decomposition of organic matter. Nutrients present in the fertilizer act as food for decomposing soil microbes. The tropical monsoon climate and centuries of cultivation have, therefore, caused low organic-matter contents of most Bangladesh soils (Table 1). Organic-matter content is very much dependent on agro-climatic conditions and it is difficult to conserve it at a high level in tropical and sub
119 TABLE
1
General
soil types and organic-matter
General soil type
Non-calcareous
Calcareous
contents
of Bangladesh
Soil series alluvium
alluvium
Grey floodplain
Ramgati
soils
soils
Depth (cm)
Soil organic-matter content (a)
O-l 2.1 12.7-20.3 20.3-55.3 O-12.7 12.7-17.8 17.8-45.7
0.99
0.54 0.79 1.68 0.99 0.42
Sabhar Bazar
O-12.7 12.7-33.0 33.0-53.3
2.40 1.12 0.92
Pritimpasa
O-10.2 10.2-17.8 17.8-35.6
Acid basin clays
Chakla
O-7.6 7.6-l 5.2 15.2-33.0
1.11 0.55 0.55 5.20 4.07 2.46
Non-cafcareous dark grey floodplain soils
Lokdeo
O-10.2 10.2-15.2 15.2-38.1
2.18 0.97 0.97
Calcareous soils
dark grey floodplain
Ghior
Calcareous soils
brown floodplain
O-10.2 10.2-15.2 15.2-35.6 o-15.2 15.2-40.6 40.6-55.9 O-12.7 12.7-33.0 33.0-61.0 O-10.2 10.2-12.7 12.7-35.6 O-10.2 10.2-33.0 33.0-66.0 O-2.5 2.5-10.2 10.2-22.9 O-3.8 3.8-7.6 7.6-15.2
Grey piedment
soils
Non-calcareous soils
Gopalpur
brown floodplain
Pirgachha
Black terai soils
Lakhipur
Brown hill soils
Kulaura
Shallow
red-brown
Deep red-brown
Brown mottled
Grey terrace
terrace
terrace
soils
Peat
Acid sulphate
terrace
soils
soils
soils
soils
Gerua
-
7.89
2.28 1.26 0.50 0.36 1.16 1.68 0.31 2.80 _ 0.22 1.44 2.62 1.86
Noadda
O-l 0.2 10.2-30.5 30.5-53.03
1.85 1.38 0.95 2.44 1.90 1.18 1.82 1.17 0.71
Chhiata
O-7.6 7.6-12.7 12.7-17.8
1.47 0.87 0.69
Satla
O-20.3 20.3-63.5 63.5-78.7 O-7.6 7.6-12.7 12.7-33.0
35.37 62.1 87.1 3.46 3.17 1.89
Tejgaon
Bhadar Khali
120
tropical conditions [4]. However, many authors have gathered evidence to show that farmyard manure and organic residues are effective in increasing the level of organic matter even under tropical conditions [ 51. It is believed that unsatisfactory crop performance in many places of Bangladesh, even with adequate NPK fertilization, is associated with low soil organic-matter contents [ 61. At Bangladesh Agricultural University [ 71 a laboratory incubation experiment with Jamuna and Tista Floodplain, Saline Tidal Zone and Madhupur Red Soils indicated that the organic matter content of these soils decreased gradually with increase in incubation period up to 42 days [8]. It was further noted that increase in the application rate of urea-N (0, 56, 112, 168 kg/ha of N) resulted in increased losses of organic matter in soil. Such losses might be due to the increased activity of microorganisms in the urea-treated samples. ORGANIC RECYCLING IN BANGLADESH SOILS
The various practices of recycling or cycling organic materials in soil have become intensified and more widespread in Asia during the past few years as the countries recognize the need to supplement mineral fertilizers to improve physical and microbiological conditions in soils, to conserve soil and reduce environmental pollution. Biomass of different sources which can be utilized as agents of organic recycling in Bangladesh soils [ 91 are: (1) Animal wastes (cattle dung and urine); (2) Crop wastes (straw, husks, stalks, stubble, weeds, grasses, leaves, sugarcane trash, etc.); (3) Human-habitation wastes (night soil, urine, sewage sludge, garbage); (4) Green manures (leguminous pulses, oilseed producing crops, forage/ fodder crops and other leguminous plants); (5) Biofertilizers (rhizobia inoculants, blue-green algae, Azolk); (6) Organo-mineral manures; (7) Tank, pond and river silt; and (8) Other sources (fish wastes, slaughter-house refuse, animal bones, municipal and urban wastes, forest wastes, mustard, sesame and castor cakes, etc.). Animal and crop wastes
During the year 1981-82 there were 35.07 million heads of cattle, 1.6 million buffaloes, 12.9 million goats and sheep, 73 million poultry birds and 20.86 million ducks [lo]. Annually 36.67 million cattle and buffaloes produce about 32.27 Tg of farm manure (air dry); 12.9 million goats and sheep produce about 10.32 Tg of manure per year; 73 million poultry birds yield yearly about 2.43 Tg of droppings. Rice crops yield about 28 Tg
121
and wheat produces 1.6 Tg of straw [ 111. These quantities together are equivalent to a huge supply of urea, triple superphosphate and muriate of potash. With all these available organic wastes farmers are advised to prepare composts by mixing crop wastes with animal excreta and refuse. Preparation of organic manure from animal wastes and crop residues through biogas plants has been introduced in Bangladesh only on a limited scale because of the high cost of installation of the digester tank. At present, farmers misuse cow dung by burning (about 35%), due to shortage of fuel. They are also advised not to take away the crop residues that are left in the field after crop harvest but rather plough them in during land preparation. Human-habitation wastes In Bangladesh only three major cities (Dhaka, Chittagong and Khulna) have set up sewerage lines in limited locations, but these lack digestion plants. Night soil and urine through the sewerage pipes are collected in some low-lying areas away from the cities, and are left to decompose naturally. For want of digestion tanks, sludge and effluent cannot be separated. The sludge formed has a foul smell and the farmers would not like to use it as a manure. Green manures The potential amount of nitrogen that can be fixed by a green-manure crop is adequate for a maximum yield of most crops now grown in the tropics. In South Asia, fixation by legumes is commonly reported to be around 40 kg/ha-y N, but up to 600 kg/ha-y N has been reported, so there is a good potential for nitrogen fixation in this part of the world. Often a farmer must fit a green-manure crop into a relatively short time span between other crops. The amount of nitrogen fixed in a short time and then added to the soil, however, can be high, up to 150 kg/ha in eight weeks if the crop is grown as a green manure and then incorporated into the soil. This amount of nitrogen can be equivalent to a much greater fertilizer rate, because the slow decomposition of the added plant matter has the effect of a slow-release fertilizer. The nitrogen added this way is not easily leached or lost as nitrogenous fertilizer. The potential for green manuring is high in Bangladesh, but research must be done to fit its use in current cropping systems, and the benefits of its use must be understood by the farmers who will use it. Bio fertilizers Rising costs of energy and, in turn, chemical fertilizers have focused attention on biological sources of nitrogen, the element most commonly limiting crop production. Even though in many eastern countries (including Bangla-
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desh) farmers do not fertilize their fields, it appears that biological nitrogen fixation often permits a moderate rice harvest in the case of native varieties. De [ 121 first attributed the natural fertility of flooded soils in (presentday) Bangladesh to blue-green algae. In Bangladesh, studies in this field, however, remained neglected for many years. Studies on symbiotic nitrogenfixing systems in laboratory and pot culture were first initiated at Dhaka University in 1968 [ 13,141. Substantial studies have been made since 1976 at Bangladesh Agricultural University in the field of biological nitrogen fixation and production of biofertilizers. Many pot and field experiments have been carried out with local isolated strains of rhizobia along with some recommended exotic strains in soybean, black gram, grasspea and chickpea with respect to nodulation, dry matter production, N uptake and grain yield [15-201. Some highly effective strains of soybean, grasspea and black gram rhizobia have been identified through many pot and field trials. Peat-based biofertilizer inoculum has been prepared successfully at Bangladesh Agricultural University and so far more than 2000 kg have been sold. Nitrogen-fixing blue-green algae have been isolated from soils of Bangladesh and their nitrogen-fixing abilities evaluated in different soil media [21,22]. Algal inoculation has been found to increase rice yield significantly [23,24]. Some studies on the growth and biomass production of different strains of Azolla are being carried out. Favourable effects of “Azotobacterin” on rice and jute have also been observed [ 25,261. Organo-mineral manures
These manures are prepared by mixing organic wastes (such as rice straw, wheat straw, goundnut husks, tobacco wastes, sugarcane trash, etc.) which have higher C/N ratios, with inorganic nitrogenous and phosphatic fertilizers. Tank, pond and river silt
In Bangladesh efforts are being made to excavate silted rivers, canals, tanks and ponds to store rain water in summer. The silt, which includes organic matter, can act as a manure for new banana plantations. Other sources
Other sources for organic manures are fish wastes, slaughterhouse refuse, animal bones, municipal and urban wastes, forest wastes, mustard, sesame and castor cakes, etc. These by-products are rich in plant nutrients and have not been fully utilized as organic manures in Bangladesh. The Fisheries Development Corporation has taken the initiative in organizing collection, processing and marketing of fish wastes through fishermen’s co-operative societies. Crushed animal bones are not available for manuring soil.
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