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Nitrogen fertilizer management strategies for rice production in Bangladesh.

Rice is the major cereal crop in Bangladesh. With increase in population, the demand for rice is increasing over the years. With intensive research rice yield per unit area has increased gradually over the years (Table 1). Consequently fertilizer consumption especially N fertilizer has also been increased gradually (Table 2). Nitrogen (N) is a primary nutrient for all crops. Rice crop requires large amount of N for its growth, development and grain production (Sahrawat, 2000). Generally rice plant removes around 14-20 kg N to produce one tonne of rough rice including straw (Table 3). Most of the rice soils of the world are deficient in N, and biological nitrogen fixation by Cyanobacteria and diazotrophic bacteria can only meet a fraction of the N requirement (Sattar et al., 2008; Hashem, 2001; Baldani et al., 2000). Thus, fertilizer N application is essential to meet the crop requirement. But, the efficiency of added fertilizer N in rice culture depends on N sources, application method, rate of N as well as management practices as evidenced by the 15N tracer studies (Wang et al., 2011; Chen et al., 2010; Wang et al., 2008). Prilled urea (PU) is applied as N source for rice but the efficiency of added N from PU is very low, generally it is around 30-45% and in many cases even much lower as determined by the 15N tracer technique (Table 4).

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.

Conclusion

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.

References

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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: atmachoudhury@hotmail.com; (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
Article Type:Report
Geographic Code:9BANG
Date:Nov 1, 2013
Words:5059
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