Nitrogen fertilizer management strategies for rice production in Bangladesh.
This low N use efficiency in rice culture is attributed mainly to denitrification, ammonia volatilisation and leaching losses (Hakeem et al, 2011; Mai et al., 2010; Zhao et al., 2010; Choudhury and Kennedy, 2005). Ammonia volatilisation and denitrification cause atmospheric pollution through the production of greenhouse gases like nitrous oxide, nitric oxide and ammonia (Choudhury and Kennedy, 2005; Reeves et al., 2002). Nitrous oxide absorbs infrared radiation and depletes the stratospheric ozone layer. Nitric oxide causes acid deposition by forming nitric acid. Leaching causes nitrate toxicity in the groundwater. High nitrate toxicity in the groundwater causes human health problems (Shrestha and Ladha, 1998). These problems are of great concern to the agronomists, soil and environmental scientists and policy makers around the world. Appropriate strategies should be taken to reduce N losses and thereby minimize these environmental problems. In this regard, research has been conducted around the world in several research organizations including Bangladesh Rice Research Institute (BRRI). This paper reviews some salient findings of BRRI already published in different journals to accumulate the information altogether indicating N fertilizer management strategies for sustainable rice production and control of environmental pollution problems.
Sources and forms of nitrogen fertilizer. Now-a-days different sources and forms of N fertilizer are available in the market for commercial use. The most commonly used N fertilizer for rice crop is prilled urea (PU). Urea super granule (USG) is a modified form of urea having an average diameter of 11.5 mm. It has been developed at the International Fertilizer Development Centre (IFDC), United States of America. The superiority of USG over PU in rice culture has been found in many investigations (Roy, 1988; Craswell et al., 1985). Urea large granule (ULG), another modified form of urea having an average diameter of 7 mm, has been developed in the Netherlands. This modified form of urea, because of its larger granule size than PU, may go deep into the mud simply by force throwing, and thus may be expected to be more efficient than PU. Azollon, a slow release nitrogen fertilizer, has been developed in Germany. It is a urea-formaldehyde condensation product containing 38% N. A field experiment was conducted on a clay loam soil at BRRI to evaluate the relative performances of PU, ULG, USG and azollon in wetland rice culture (Choudhury et al., 1994a). Considering grain yield, USG was significantly superior to PU and azollon; whereas, ULG had a slight edge over PU, but statistically not significantly different (Table 5). Total N uptake increased significantly in ULG and USG treated plots compared to the conventional PU treated plots. Agronomic efficiency and apparent recovery of added N were considerably higher with USG and ULG as compared to PU. Azollon was inferior to PU.
The increase in fertilizer N use efficiency due to the use of modified forms of urea will reduce environmental pollution problems like eutrophication (over enrichment in nutrients), production of greenhouse gases like nitrous oxide and nitrate toxicity in the ground water. However, these modified forms of urea are not commonly used by farmers. Farmers awareness of environmental benefits of these practices should be created at farm level in order to use USG and ULG for rice production.
Methods of nitrogen fertilizer application. Generally, urea is applied as surface broadcasting which causes losses of urea by different mechanisms, and thereby N use efficiency becomes low. Sub-surface placement of N fertilizer into the anaerobic soil zone has been proposed by many investigators as a possible mean of increasing N use efficiency (Reddy and Mitra, 1985). Pneumatic urea injector, an instrument for deep placement of prilled urea, has been developed in the Netherlands. Prilled urea (PU) can be placed through injection by this instrument with necessary calibration into a depth of 8-10 cm. A field experiment was conducted on a clay loam soil at BRRI to evaluate the relative performance of PU surface broadcasting and PU injection for N use efficiency in wetland rice culture (Choudhury and Bhuiyan, 1994). In the surface broadcasting method, PU was applied in three equal splits (1/3 immediately after seedling establishment + 1/3 at active tillering stage + 1/3 at 5-7 days before panicle initiation); while in the injection method, PU was applied at a time immediately after seedling establishment. Three rates ofN (29, 58 and 87 kg N/ha) were used in both methods of N application. A nitrogen control treatment was also used in the trial. The injection method gave higher grain yield over the surface broadcasting method at all the rates of applied N, however, the difference was significant only at 87 kg N/ha (Table 6). Straw yield and total N uptake were significantly higher with the injection method over the surface broadcasting method at all the rates of added N. Agronomic efficiency and apparent recovery of added N were considerably higher with the injection method.
Although deep place of PU is time consuming and laborious, this will reduce environmental problems by minimizing N fertilizer losses by volatilisation and denitrification in addition to increase in rice yield. Adoption of this technique at farm level by proper demonstration is necessary.
Nitrogen and sulphur interactions. Sulphur (S) is a secondary nutrient for all crops. The metabolism ofN and S in plants is closely interrelated. As a result plant cannot utilize N properly in S deficient soils and conversely S utilization of plant is being adversely affected by N deficiency in soils (Shah et al., 1996). A field experiment was conducted on a silty clay soil at BRRI to study the synergistic effects of N and S on growth and yield of wetland rice (Choudhury et al.,, 1994b). A strong synergistic effect between N and S was observed (Table 7). At 0 kg N/ha, S application at 20 kg/ha increased grain yield by only 0.3 t/ha, while the same S rate increased grain yield by 0.9 t/ha at 120 kg N/ha. Similarly at 0 kg S/ha, N application at 120 kg/ha increased grain yield by 1.2 t/ha, while the same N rate increased grain yield by 1.8 t/ha at 20 kg S/ha. Agronomic efficiency of added N increased gradually with increasing S rates up to 40 kg S/ha.
In S deficient soils, combined application ofN and S is necessary to optimize grain yield. Investigations in India showed that combined application of N and S increased N and S uptakes by rice significantly (Srivastava and Singh, 2007). This implies that interactions between N and S have large effects on N and S transfers to rice plants for increasing grain production. Generally farmers are not using S fertilizer for rice. Awareness should be grown at farm level for the benefit S fertilisation in S deficient soils for increasing N use efficiency in rice production.
Varietal difference in nitrogen response. The magnitude of N response may vary from variety to variety depending upon their agronomic traits like plant height and growth duration in addition to N fertility status of the soil. Therefore, variety and soil specific N fertilizer recommendation is necessary to get optimum yield (Saleque et al., 2004). Agronomic efficiency (kg grain/kg added N) varies among rice varieties (Table 8). Nitrogen fertilizer requirement for maximum grain yield varies among varieties (Choudhury et al., 2002). Nitrogen rate for the maximum yield of a rice variety can be estimated from the regression equation Y = a + bx - [cx.sup.2] as follows (Gomez and Gomez, 1984):
Ny = b/2c
where, Ny = N rate (kg/ha) for maximum yield. Determination ofN rates for maximum grain yields of different varieties is necessary to avoid indiscriminate application ofa single N rate for all the varieties. This information will help to reduce N fertilizer losses through indiscriminate application of N and thus reduces environmental pollution to some extent.
Nitrogen response of short and tall statured varieties.
Nitrogen response may vary among rice varieties based on their plant stature in addition to growth duration. A field experiment was conducted using four rice varieties (BR1, BR3, BR14 and BRRIdhan 29) having different agronomic parameters (Table 9) in a clay soil at BRRI farm in 1993 (BRRI, 1996). BR1 and BR14 are short duration varieties, while BR3 and BRRIdhan 29 are long duration ones. Again heights of BR1 and BR3 were relatively shorter than BR14 and BRRIdhan 29. Number of tiller as well as panicle production per unit area was the highest in BR1 followed by BRRIdhan 29, BR3 and the lowest in BR14. Six rates ofN (0, 40, 80, 120, 160 and 200 kg N/ha) were used in the experiment. Grain yield response to added N varied among the varieties (Table 10). The most interesting finding is that the tall statured varieties (BR14 and BRRIdhan 29) out yielded the short statured ones (BR1 and BR3) in N control plots by 0.4 to 0.6 t/ha. This indicates that the tall statured varieties can exploit more soil N for grain production. Root mass density was relatively higher in tall statures varieties (BR14 and BRRIdhan 29) compared to short statured ones (BR1 and BR3) at 10-20 cm depth in N control plots (Table 11). This implies that having deeper root system the tall varieties were able to utilize more soil N for grain production compared to the short ones in N control plots which enabled them to produce extra grain without fertilizer input. So, modern rice varieties having relatively taller plant stature will be economically advantageous for marginal farmers to produce extra grain without fertilizer input.
Nitrogen response of traditional and improved plant types. A field experiment was conducted on a clay soil at BRRI during 1994 to evaluate the N response behaviour of four rice varieties (NigerSail, BR22, Pajam and BR25) using six N rates (0, 30, 60, 90, 120 and 150 kg N/ha) in wetland culture (Choudhury et al., 1997b). The variety BR22 is the improved plant type of Niger-Sail while BR25 is the improved plant type of Pajam. Grain yield response to added N varied among the varieties (Table 12). While, NigerSail responded to added N up to 90 kg N/ha, its improved plant type BR22 responded up to 150 kg N/ha. Both Pajam and its improved plant type BR25 responded up to 120 kg N/ha. However, BR25 out yielded Pajam at all the rates of added N. Regression analysis indicated that the estimated response function between N rate and grain yield for all the varieties was quadratic in nature (Table 13).
However, the rate of response as evidenced from the response co-efficient (b value) was higher in the improved plant types (BR22 and BR25) compared to their respective traditional plant types (NigerSail and Pajam). While, the b value was only 0.018 for NigerSail, it was 0.023 for its improved plant type BR22. Again the b value for Pajam was 0.021 against the b value of 0.032 for its improved plant type BR25. The b value is the slope of regression line which measures the estimated rate of response (either increase or decrease). This implies that improved plant type can utilize fertilizer N more efficiently for grain production compared to their respective traditional plant type. Estimated N rate for maximum yield varies among the varieties. Estimated N rates for maximum grain yield were 160, 115, 105 and 90 kg/ha for BR25, BR22, Pajam and NigerSail, respectively. This information implies that there are differences among rice varieties for N requirement for maximum grain production.
Nitrogen use efficiency in rice culture can be increased considerably by using modified forms of urea like USG and ULG. The efficiency of the conventional prilled urea in rice culture can be increased to some extent by injecting it into the sub-surface by the instrument "Pneumatic Urea Injector". In sulphur deficient soils, N use efficiency in rice culture can be increased by combined application ofN and S. Modern rice varieties having relatively taller plant stature will be economically advantageous for marginal farmers to produce extra grain without fertilizer input. There are varietal differences for N requirement for maximum grain production. This information will be helpful to avoid indiscriminate application ofa single N rate for all the varieties. These ways of increasing N use efficiency will reduce environmental pollution problems due to eutrophication (over enrichment in nutrients), production of greenhouse gases like nitrous oxide, and nitrate toxicity in the ground water.
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Abu Turab Mohammad Ali Choudhury (ab)*, Mohammad Abu Saleque (a), Shafiuddin Kaisar Zaman (a), Nurul Islam Bhuiyan (a), Abdul Latif Shah (a) and Mohammad Shamsur Rahman (a)
(a) Soil Science Division, Bangladesh Rice Research Institute, Gazipur 1701, Bangladesh
(b) SUNFix Centre for Nitrogen Fixation; Faculty of Agriculture and Environment, Biomedical Building, 1 Central Avenue, Australian Technology Park, University of Sydney, Eveleigh, NSW 2015, Australia
(received November 22, 2012; revised December 31, 2012; accepted January 4, 2013)
* Author for correspondence;
E-mail: firstname.lastname@example.org; (b) Present address
Table 1. Population, rice cropped area, rice production and yield in Bangladesh over the years since 1960 Year Population Rice cropped Paddy Paddy yield (million) area (000 ha) production (000 tonnes) t/ha kg/person 1960 51.585 8857 14522 1.64 282 1970 66.671 9912 16731 1.69 251 1980 88.219 10309 20844 2.02 236 1990 109.820 10435 26781 2.57 244 2000 129.194 10887 37633 3.46 291 2010 153.437 11800 48455 4.11 316 Year Rice production Rice available (kg/person) excluding import (g/person/day) 1960 197 540 1970 176 481 1980 165 453 1990 171 468 2000 204 559 2010 221 606 The population data was collected from the website http://www. populstat-info/Asia/bangladesh-htm-The data on rice cropped area and paddy (un-milled rice) production have been collected from the USDA database available in the IRRI website (IRRI, 2011). Paddy yield per person was converted to rice (milled rice) yield considering 70% milling outturn which is average of varieties (BRRI, 2000). Table 2. Consumption of fertilizer N, P and K in Bangladesh over the years since 1961 Year Fertilizer consumption (000 tonnes) N P K 1961 20.0 DNA 1.5 1970 99.2 34.0 10.4 1980 266.2 118.4 28.7 1990 609.2 231.8 90.0 2000 995.8 250.3 143.0 2010 1275.0 420.0 220.3 Source: IFA, 2011; DNA = data not available. Table 3. N, P, K and S removal of four rice varieties Rice Grain Total amount of Reference variety yield nutrients (kg) removed (t/ha) by grain and straw per tonne of grain production N P K S Choudhury et al., 1992 BR1 4.2 19.76 3.10 21.43 1.90 Choudhury et al., 1994c BR3 5.6 13.93 3.39 20.89 2.14 Choudhury et al., 1994c BR11 5.2 17.69 3.08 22.31 1.92 Choudhury et al., 1992 BR22 4.6 15.65 2.83 19.13 1.96 Choudhury et al., 1992 Table 4. Fertilizer N uptake and recovery of MR185 rice in different soils as determined by the 15N tracer technique Soil series Fertilizer N uptake (kg/ha) Fertilizer N applied by whole plant N recovery (kg/ha) (grain and straw) Total N Fertilizer N uptake uptake Guar 40 96.53 6.40 16 80 133.21 18.49 23 120 151.68 28.50 24 Hutan 40 54.39 8.02 20 80 54.94 13.94 17 120 47.66 14.22 12 Idris 60 67.82 23.74 40 120 90.37 48.62 41 180 116.75 74.44 41 Tebengau 60 53.31 23.72 40 120 79.46 50.40 42 180 93.02 68.63 38 Source: Choudhury (2000). Table 5. Effects of forms and sources of nitrogen fertilizer on grain yield of BR3 rice, total N uptake, agronomic efficiency and apparent recovery of added N N rate N fertilizer Grain yield Total N uptake (kg/ha) form/source (tonnes/ha) (kg/ha) 0 -- 2.9 (d) 36.7 (e) 87 Prilled urea 4.0 (b) 62.6 (c) 87 Urea large granule 44a (b) 70.3 (b) 87 Urea super granule 4.6 (a) 91.0 (a) 87 Azollon 3.6 (c) 53.0 (d) N rate Agronomic Apparent (kg/ha) efficiency recovery of (kg grain/kg added N(%) added N) 0 -- -- 87 12.6 29.8 87 17.2 38.6 87 19.5 62.4 87 8.1 18.7 Values followed by different letters within a column are significantly different at 5% level by Duncan's Multiple Range Test (DMRT); source: Choudhury et al. (1994a). Table 6. Effects of rates and methods of nitrogen fertilizer application on grain and straw yields of BR3 rice, total N uptake, agronomic efficiency and apparent recovery of added N N rate Method of Grain yield Straw yield Total N (kg/ha) application * (t/ha) (t/ha) uptake (kg/ha) 0 -- 2.7 1.8 35.9 29 SB 3.3 2.0 44.3 58 SB 3.6 2.3 49.8 87 SB 4.0 2.6 55.9 29 I 3.7 2.5 51.4 58 I 4.0 2.8 59.2 87 I 4.6 3.4 69.9 LSD (0.05) 0.42 0.41 3.3 N rate Agronomic Apparent (kg/ha) efficiency recovery of (kg grain/kg added N(%) added N) 0 -- -- 29 20.7 29 58 15.5 24 87 14.9 23 29 34.5 53 58 22.4 40 87 21.8 39 LSD (0.05) -- -- * SB = surface broadcasting; I = injection; source: Choudhury and Bhuiyan (1994). Table 7. Effects of nitrogen and sulphur on grain yield of BR3 rice and agronomic efficiency of added N N rate Sulphur rate Mean (kg/ha) (kg/ha) 0 20 40 Grain yield (tonnes/ha) 0 2.9 3.2 3.2 3.1 c 60 4.0 4.1 4.2 4.1 b 120 4.1 5.0 5.2 4.8 a Mean 3.7 b 4.1 a 4.2 a Agronomic efficiency of [N.sup.1] 60 18.3 20.0 21.7 20.0 120 10.0 17.5 19.2 15.6 Mean 14.2 18.8 20.5 Kg grain per kg added N compared to the plots those received neither N nor S; in a row/column, values followed by different letters are significantly different at 5% level by DMRT; source: Choudhury et al. (1994b). Table 8. Grain yield of some modern rice varieties without and with fertilizer N Rice Grain yield (t/ha) variety Without With Difference * fertilizer fertilizer N N (120kg N/ha) BR1 2.60 4.70 2.10 BR3 2.60 4.80 2.20 BR14 3.00 5.20 2.20 BR22 2.50 4.30 1.80 BR25 3.10 5.10 2.00 BRRIdhan 29 3.60 5.90 2.30 Rice Agronomic Reference variety efficiency ** BR1 17.50 Choudhury et al., 1997a BR3 18.33 Choudhury et al., 1997a BR14 18.33 Choudhury et al., 1997a BR22 15.00 Choudhury et al., 1997b BR25 16.67 Choudhury et al., 1997b BRRIdhan 29 19.17 Choudhury et al., 1997a * = differences were statistically significant at 5% probability level; ** = kg grain per kg added N. Table 9. Some agronomic parameters of four modern rice varieties Variety Plant Growth Tiller Panicle height duration number/ number/ (cm) (days) * [m.sup.2] [m.sup.2] BR1 63 150 414 404 BR3 79 170 302 291 BR14 91 155 263 247 BRRIdhan 29 90 168 310 296 * = period started from date of nursery sowing; source: BRRI, (1996). Table 10. Effect of N fertilisation on grain yield of four modern rice varieties N rate Grain yield (t/ha) (kg/ha) BR1 BR3 BR14 BRRIdhan 29 0 2.6 (dB) 2.6 (dB) 3.0 (dAB) 3.2 (cA) 40 3.4 (cBC) 3.2 (cC) 3.7 (cB) 47 (bA) 80 3.7 (cC) 4.2 (bBC) 4.3 (bB) 5.3 (aA) 120 4.7 (bB) 4.8 (aB) 5.2 (aAB) 5.4 (aA) 160 5.3 (aAB) 5.0 (aB) 5.3 (aA) 5.6 (aA) 200 5 1 (abB) 5.2 (aAB) 5.2 (aAB) 5.7 (aA) Source: BRRI (1996); figures followed by a common letter within a column (small letter) or row (capital letter) are not significantly different at 5% level by Duncan's Multiple Range Test (DMRT). Table 11. Effect of N fertilization on root mass density of four modern rice varieties at flowering stage N rate Root mass density (mg/cm3) (kg/ha) BR1 BR3 BR14 BRRI N Mean dhan29 0-10 cm depth 0 1.10 2.50 1.98 2.15 1.93 (d) 40 1.35 3.22 2.47 2.44 2.37 (cd) 80 1.56 3.35 3.02 2.61 2.64 (bc) 120 1.86 3.43 3.50 2.88 2.92 (ab) 160 2.05 3.49 3.54 3.07 3.04 (ab) 200 2.12 4.13 3.84 3.57 3.42 (a) Variety 1.67 (B) 3.3 (A) 3.06 (A) 2.79 (A) -- mean 10-20 cm depth 0 0.06 0.08 0.10 0.16 0.10 (b) 40 0.07 0.15 0.17 0.18 0.14 (ab) 80 0.11 0.17 0.17 0.19 0.16 (a) 120 0.12 0.14 0.15 0.18 0.15 (ab) 160 0.04 0.13 0.13 0.15 0.11 (ab) 200 0.03 0.11 0.10 0.15 0.10 (b) Variety 0.07 (B) 0.13 (AB) 0.14 (A) 0.17 (A) -- mean Source: BRRI (1996); figures followed by a common letter within a column (small letter) or row (capital letter) are not significantly different at 5% level by DMRT. Table 12. Effects of N fertilization on grain yield of four rice varieties N rate Grain yield (t/ha) (kg/ha) NigerSail BR22 Pajam BR25 0 2.6 2.5 3.0 3.1 30 3.2 3.5 3.7 3.9 60 3.3 3.8 4.0 4.7 90 3.6 4.0 4.3 4.8 120 3.3 4.3 4.8 5.1 150 3.2 4.7 4.8 4.9 Source: Choudhury etal. (1997b). Table 13. Regression equation and [R.sup.2] value relating grain yield and N rate for four rice varieties Variety Regression equation NigerSail y = 2.681 + 0.018x - 0.0001[x.sup.2] BR22 y = 2.626 + 0.023x - 0.0001[x.sup.2] Pajam y = 3.002 + 0.021x - 0.0001[x.sup.2] BR25 y = 3.119 + 0.032x - 0.0001[x.sup.2] Variety [R.sup.2] Estimated N value rate (kg/ha) for maximum yield NigerSail 0.86 * 90 BR22 0.96 ** 115 Pajam 0.98 ** 105 BR25 0.98 ** 160 * = significant at 10% level of probability; ** = significant at 1% level of probability; source: Choudhury et al. (1997b).
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|Author:||Choudhury, Abu Turab Mohammad Ali; Saleque, Mohammad Abu; Zaman, Shafiuddin Kaisar; Bhuiyan, Nurul I|
|Publication:||Pakistan Journal of Scientific and Industrial Research Series B: Biological Sciences|
|Date:||Nov 1, 2013|
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