Description of cropping systems, climate, and soils in Bangladesh                 (by Dr. J. Timsina, N.Guilpart)

Bangladesh has a primarily agrarian economy, although agriculture's contribution to total GDP has been decreasing in recent years. Despite this trend, agriculture remains the largest sector of the economy comprising about 19% (including livestock) while the crop sector is 13% of the country's GDP; in addition, the agricultural sector employs around 26% of the total labor force (AIS 2013, and BBS 2012). The performance of this sector has large impact on major macroeconomic objectives like employment generation, poverty alleviation, human resources development and food security.

The total land area is about 14.84 Mha of which 3.74 Mha (25% of total) is not available for agriculture due to use for urban areas, industrial buildings, rural homesteads, roads and other infrastructure. Although net cultivated area declined to 7.84 Mha in 2011 from 8.85 Mha in 1985, the total harvested crop area increased to 14.95 Mha due to increases in annual double-, triple- and even quadruple-cropping on the same piece of land. Average cropping intensity was 1.9 in 2010-11. Land utilization statistics for Bangladesh are provided in Table 1.

Table 1: Land utilization statistics in Bangladesh (2010-11)

Land utilization	Area (Mha)	% Total area	% Arable land
Area not available for cultivation	3.74	25.2
Forest area	2.58	17.4
Waste land area	0.23	1.6	2.7
Fallow area	0.47	3.2	5.5
Single-cropped area	2.24	15.1	26.3
Double-cropped area	4.11	27.7	48.2
Triple-cropped area	1.46	9.8	17.2
Quadruple-cropped area	0.01	0.06	0.1
Net crop area	7.84	52.8	100.0
Total harvested crop area	14.95	--

Source: BBS, 2012

Rice, wheat, maize, potato, pulses, and oil seeds are major food crops in Bangladesh. While rice is the primary staple food and the most important crop, wheat and maize are of second and third importance. Pulses and oilseeds are important crops in the context of supplying plant-based proteins for rural people. Jute and sugarcane are important cash crops. Average yields, cultivated area, and production of major food crops or the last six years (2006-2012) are shown in Table 2.

Table 2: Average (2006-2012) yield, harvested area and yield of major food crops in Bangladesh

Crop	Average yield (t ha-1)	Harvested  area (Mha)	Total production (Mt)
Aus rice	1.81	1.021	1.85
Aman rice	2.13	5.48	11.65
Boro rice	3.80	4.65	17.66
Total rice	2.80	11.14	31.16
wheat	2.32	0.38	0.88
Potato	16.68	0.42	6.94
Maize	4.97	0.17	0.82
Pulses	0.89	0.25	0.22
Oil seeds	1.69	0.35	0.60

Source: BBS(2012)

The geography of Bangladesh is dominated by flood plains of the Ganges, Brahmaputra, and Meghna rivers. Thirty agro-ecological regions and 88 sub-regions have been classified on the basis of physiography, soil characteristics, depth and duration of seasonal flooding, length of crop season and growing period, and seasonal temperature. Soil fertility status of these regions varies considerably. Individual farmers have fragmented the land into small parcels causing wide variation in the management of each piece of land. This leads to the large variation in the soil fertility level even between adjacent fields.

The Soil Resources Development Institute (SRDI) has identified about 500 soil series in Bangladesh. All have been mapped by the SRDI through a reconnaissance soil survey carried out during 1965 and 1975. The resulting soil series have been described to be consistent with the FAO-UNESCO soil units of Fluvisols, Gleysols, Histosols, Planosols, Luvisols, Cambisols and Arenosols. According to the USDA soil taxonomy, these soil series are Entisols, Inceptisols, Histosols, Mollisols, Ultisols and Alfisols.

A total of 21 general soil types are recognized in Bangladesh. These general soil types give a broad generalization of soil characteristics. Each general soil type includes several soil series, developed in more than one kind of parent material and may include a wide range of chemical and physical properties. The objective of this scheme is to classify soils with broadly similar characteristics so as to provide an overview of soil conditions for the country. Table 3 gives the area under various soil types.

Table 3 : General soil types of Bangladesh

General soil type	Area (ha)	(%)
Floodplain soils	9,718,722	78.96
Calcareous Alluvium	591,796	4.81
Non-calcareous Alluvium	562,242	4.57
Calcareous Brown Floodplain soils	478,518	3.89
Calcareous Grey Floodplain soils	170,767	1.39
Calcareous Dark Grey Floodplain soils	1,434,678	11.66
Non Calcareous  Grey Floodplain soils	3,387,153	27.52
Non Calcareous Brown Floodplain soils	383,312	3.11
Non Calcareous Dark Grey Floodplain soils	1,599,645	13.00
Black Terai soils	83,408	0.68
Acid Basin clays	348,994	2.84
Acid Sulphate soils	226,647	1.84
Peat	130,005	1.06
Grey Piedmont Soils	215,279	1.75
Made-land	106,278	0.86
Hill soils (Brown Hill Soils)	1,561,472	12.69
Terrace soils	1,028,030	8.35
Shallow Red-Brown Terrace soils	72,549	0.59
Deep Red-Brown Terrace soils	189,380	1.54
Brown Mottled Terrace soils	34,235	0.28
Shallow Grey Terrace soils	265,427	2.16
Deep Grey Terrace soils	352,152	2.86
Grey Valley soils	114,287	0.93
Total soil area	12,308,224	100.0
Source: FAO/UNDP, 1988 and H Brammer, 1996

 

The climate of Bangladesh is generally sub-tropical in north to hot humid in the south. Southwest monsoon influences the climate during June to October. In winter from November to March, the climate is controlled by the northwest monsoon. The summer is hot and humid and the winter is mild. Highest monthly average maximum temperature of 36.3°C is recorded in April and the lowest monthly average minimum temperature of 9.5° C is recorded in January. Ranges for maximum and minimum temperatures vary within the range of 1.6 to 9.5 °C   and 1.4 to 5.6°C over the country.  Annual rainfall ranges from <1500 mm in the dry northwest region to over 5000 mm in the wet northeast region. The country's average annual total rainfall is 2428 mm. The country is vulnerable to many environmental hazards, including frequent floods, droughts, cyclones and storm surges that damage life, property, and agricultural production.

Agriculture in Bangladesh is predominantly based on smallholders with about 80% of the farmers cultivating less than one hectare. Agriculture is characterized by traditional farming methods using draft animals for ploughing and hand hoe for land preparation and sowing. Small-scale mechanization is increasing through use of two-wheeled tractors for tillage and power threshers for paddy rice and wheat. Irrigated area has expanded in recent years. In 2010-11, total irrigated area for boro rice, aman rice and wheat were 4.58 Mha (95% of total boro rice), 0.69 Mha (12% of total aman rice), and 0.33Mha (91% of total wheat), respectively. Irrigation area increased by 10%, 3%, and 6% in 2010-11 in comparison to 2009-10 for boro rice, aman rice and wheat, respectively.

Boro rice and rabi (winter) maize crops in Bangladesh are either fully or partially irrigated, while aman and aus rice and kharif-1 (spring) maize are predominantly rainfed, with some crops applied with partial irrigation. Wheat is also predominantly grown with full irrigation (~80%), with remaining 20% under either partial irrigation or strictly rainfed. Despite this, the SPAM database reports a significant fraction of the harvested area for rice and maize to be under rainfed conditions. We suspect that most of the SPAM-reported rainfed area for rice and maize crops corresponds to partially-irrigated crops. Hence, we used the sum of SPAM-reported rainfed and irrigated harvested areas for selection of reference weather stations buffers and up-scaling of yield potential and yield gaps estimates for rice and maize.

Ground water is the primary source of irrigation, especially for boro rice cultivation (BBS, 2012). Intensive abstraction for irrigation (25–75 wells per km² of irrigated land) occurs in many areas of northwestern Bangladesh and began during the late 1960s to early 1970s with the installation of deep (depth >80 m) tubewells (DTWs) by the Bangladesh Water Development Board. Initially, irrigation from groundwater was provided by these DTWs in addition to surface water irrigation with low-lift pumps and other traditional methods. During the 1980s and 1990s the government, with support from international organizations, installed thousands of shallow (depth <80 m) irrigation tubewells (STWs) to utilize large quantities of groundwater at relatively shallow depths. Withdrawals exceed recharge rates, however, due to excessive irrigation such that groundwater is declining by 0.01-0.5 m/yr in many areas in the northeast, northwest and southwest where boro rice is intensively cultivated. Thus the current irrigation practices for agriculture, especially for rice farming, are not sustainable, and is a serious concern for future food security in Bangladesh.

Cropping systems are highly diverse, intensive and complex in Bangladesh. The predominant cropping patterns are annual double- or triple crops of rice-rice, rice-wheat, rice-maize, potato-rice-rice, wheat-rice–rice, wheat-mungbean–rice, mustard-rice-rice and rice-rice-rice. Rice is grown in annual single-, double-, and triple-cropping patterns in the boro, aus, and aman seasons depending on inundation and land topography.  In recent years, the area under rice-wheat and rice-rice cropping patterns is declining while that under rice-maize is increasing among farmers who have livestock or fish production enterprises. In the northern region, maize is also being introduced as an intercrop with one or more other crops such as vegetables (potato, red amaranth, sweat gourd). Groundwater decline and hence scarcity of irrigation water is also another factor for decline of boro rice area and increase of maize area due to reduced irrigation requirements for maize.

Data Sources and Assumptions (following GYGA protocols)

Harvested area

Harvested area of irrigated maize, irrigated wheat, irrigated and rainfed rice were retrieved from SPAM2000 (http://mapspam.info/).

Weather data and reference weather stations

A total of 11 reference weather stations (RWS) were selected in Bangladesh following the protocols described by Grassini et al. (2015) and van Bussel et al (2015), with 5 RWS for irrigated maize, 7 RWS for irrigated wheat, 9 RWS for irrigated rice and 9 RWS for rainfed rice. This led to a good coverage of these crops as 60 to 80 % of national harvested areas felt within RWS buffer zones and 70 to 90 % within the selected climate zones (Table 4). All RWS had measured data for 15+ years, except one for which weather data were propagated according to the method described in Van Wart et al. (2015) in order to fill important gaps (but still <10% of days) in daily Tmin and Tmax and missing solar radiation.

Table 4. Crop harvested area within selected climate zones and RWS buffer zones in Bangladesh with respect to national harvested area of irrigated maize, irrigated wheat, irrigated and rainfed rice.

	Harvested area
crop	national	within climate zones		within buffer zones
	x 1000 ha	x 1000 ha	% *	x 1000 ha	% *
Irrigated maize	155	140	91	124	80
Irrigated wheat	445	333	75	364	82
Irrigated rice	5055	3617	72	3131	62
Rainfed rice	7082	6127	87	4472	63
* of national harvested area for that crop

 

Actual yields

District-level data on actual yields from 2008 to 2012 (5 years) for maize, wheat and rice were retrieved from the 2012 Yearbook of agricultural statistics of Bangladesh from the Bangladesh Bureau of Statistics (http://bbs.gov.bd/). Data were available by season (i.e. aman, boro, aus). Actual yields from the boro season were used for irrigated rice actual yields, while average actual yields from the aman and aus season were used for rainfed rice actual yields after weighting by harvested area in each season (aman and aus) at each location.

Soil data

Major soil types (i.e. 3 to 5 dominant soil types) within rainfed rice RWS buffer zones were retrieved from the ISRIC-WISE soil database (http://www.isric.org/). The proportion of each major soil type was calculated and used to upscale the results.

 

Crop system and management information for crop simulations

Management practices for each crop and RWS buffer zone were retrieved from local agronomists^#. Simulations of rice were performed using the ORYZA(v3) model (Bouman et al., 2001), simulations of maize were performed with the Hybrid Maize model (Yang et al., 2004) and simulations of wheat were performed with the WOFOST model (Boogaard et al., 1998). Separate simulations were performed for potential (Yp, for irrigated crops) and water-limited conditions (Yw, for rainfed crops). All crop models were calibrated such as simulated dates of flowering and maturity matched the ones reported by local agronomists.

In order to reach a compromise between (i) best representing how a given crop is produced in terms of weather, soils and cropping systems, (ii) limit the number of simulations to be run, the following assumptions were made about rice-based cropping systems in Bangladesh:

• First, cropping systems involving local/traditional rice varieties were not taken into account for three reasons: (i) only about 15% of rice area is grown with local varieties and this value is decreasing every year, (ii) since farmers' actual yields are very low (0.5-1.5 t/ha) with these varieties their contribution to national food security is very low even if they can play a significant role for food security at the household level, (iii) phenology observations (sowing, transplanting, flowering and maturity dates) are sparse for these varieties which prevents from any reliable calibration of crop models.
• Second, direct-seeded rice systems were not taken into account in the rice yield gap analysis in Bangladesh. The reasons are: (i) farmers adoption of these systems is low: they represent about 5% or less of rice harvested area, so their contribution to national food security is low; (ii) in most cases these systems involve the use of local/traditional varieties that are broadcasted (farmers leave the seeds for a long time in fields before the floods start in flood-prone and deep water fields, and the planting patterns/systems vary a lot among farmers and regions), which makes these systems difficult to simulate with current crop models such as Oryza(v3) which has been used to simulate rice potential yield in this project. 

^#Local agronomists' names and affiliations: Mr. Saiful Islam (Cropping Systems Agronomist, CIMMYT, Dhaka, Bangladesh), Dr. Harun-ur-Rashid (Cropping Systems Agronomist, Bangladesh Rice Research Institute (BRRI), Gazipur, Bangladesh), Dr. Akbar Hossain (Senior Scientific Officer/Agronomist, Wheat Research Centre, Bangladesh Agriculture Research Institute (BARI), Dinajpur, Bangladesh).

References

Agricultural Information System (AIS), 2013. Ministry of Agriculture, Government of People's Republic of Bangladesh, Dhaka, Bangladesh

Batjes, N.H., 2012.  ISRIC WISE derived soil properties on a 5 by 5 arc-minutes global grid (ver. 1.2). Report 2012/01. ISRIC - World Soil Information, Wageningen, The Netherlands, 57 pp.

BBS, 2102.Yearbook of Agricultural Statistics of Bangladesh. Bangladesh Bureau of Statistics, Statistics Division, Ministry of Planning, Government of People's Republic of Bangladesh, Dhaka. 

Boogaard, H. L., Van Diepen, C. A., Rotter, R. P., Cabrera, J. M. C. A., Van Laar, H. H., 1998. WOFOST 7.1; user's guide for the WOFOST 7.1 crop growth simulation model and WOFOST Control Center 1.5 (No. 52). SC-DLO.

Bouman, B.A.M., Kropff, M.J., Tuong, T.P., Wopereis, M.C.S., Ten Berge, H.F.M.,  Van Laar, H.H., 2001. ORYZA2000: modeling lowland rice. International Rice Research Institute, Los Baños, Philippines, and Wageningen University and Research Centre, Wageningen, Netherlands, 235 pp.

Brammer, H., 1996. The Geography of the Soils of Bangladesh, University Press Limited, Red Crescent Building, 114 Motijheel C/A, P.O. Box 2611, Dhaka  1000, Bangladesh.

FAO/UNDP, 1988. Land resources appraisal of Bangladesh for agricultural development, Vol 2, Rome.

Grassini, P., Bussel, L. G. J. Van, Wart, J. Van, Wolf, J., Claessens, L., Yang, H., Cassman, K. G., 2015. How good is good enough? Data requirements for reliable crop yield simulations and yield-gap analysis. Field Crops Research, 177, 49–63.

Hussain, S.G., Chowdhury, M.K.A., Chowdhury, M.A.H., 2012. Land utilization assessment and Crop Zoning of Bangladesh, Bangladesh Agricultural Research Council, Farm gate, Dhaka.  110 p.

ISRIC-WISE soil database. http://www.isric.org/data/isric-wise-derived-soil-properties-5-5-arc-minutes-global-grid-version-12.

Van Bussel, L. G. J., Grassini, P., Van Wart, J., Wolf, J., Claessens, L., Yang, H., van Ittersum, M. K. (2015). From field to atlas: Upscaling of location-specific yield gap estimates. Field Crops Research, 177, 98–108.

Van Wart, J., Grassini, P., Yang, H., Claessens, L., Jarvis, A., Cassman, K. G., 2015. Creating long-term weather data from thin air for crop simulation modeling. Agricultural and Forest Meteorology, 209-210, 49–58.

Yang, H. S., Dobermann, A., Lindquist, J. L., Walters, D. T., Arkebauer, T. J., Cassman, K. G., 2004. Hybrid-maize—a maize simulation model that combines two crop modeling approaches. Field Crops Research, 87(2), 131-154.

You, L., Z. Guo, J. Koo, W. Ojo, K. Sebastian, M.T. Tenorio, S. Wood, U. Wood-Sichra. 2010. Spatial Production Allocation Model (SPAM) 2000 Version 3 Release 1. http://MapSPAM.info.