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1
2FULL LENGTH ARTICLE
4Rice straw amendment ameliorates harmful effect
5of salinity and increases nitrogen availability in a
6saline paddy soil
7Toufiq Iqbal
8Department of Agronomy and Agricultural Extension, University of Rajshahi, Rajshshi 6205, Bangladesh
9Received 31 July 2016; accepted 9 November 2016
10
12 KEYWORDS
13
14 Soil pH;
15 Bio-availability;
16 Nutrient dynamics;
17 Mineralization;
18 Osmotic stress
Abstract High concentrations of salt (NaCl) in soils reduce plant growth and have enormous
influence on nitrogen dynamics in the soil solution. However, addition of rice straw is expected
to mitigate the effect of salinity on nitrogen cycling, therefore positively influencing plant growth.
This study describes how rice seedling emergence and early growth in a saline paddy soil can be
improved by adding rice straw to the soil and incubating the soil/straw mixtures for two months.
I conducted a short-term laboratory incubation and a plant growth experiment to evaluate the
benefit of rice straw addition to a saline paddy soil with respect to nitrogen availability and the
associated growth response of saline tolerant (BRRI Dhan47) and saline sensitive (BRRI Dhan28)
rice seedlings. A naturally saline paddy soil was collected from the coastal area of Bangladesh. The
soil was then incubated with rice straw (0%, 25%, 50%, 100%, and 200% of the straw yield) for
two months. After that, BRRI Dhan47 and BRRI Dhan28 rice varieties were sown in these incu-
bated soils. Rice seedlings were harvested after 14 days of sowing. My results indicated that raw rice
straw addition to saline paddy soil decreased the bio-availability of salt. Furthermore, BRRI
Dhan28 responded better than the BRRI Dhan47 to increased addition of rice straw to soil. Bulk
soil pH declined and nitrogen availability increased with increasing rice straw in addition to saline
paddy soil. This study concluded that rice straw can be a meaningful soil amendment to decrease
harmful effect of salt and increase nitrogen availability in a saline paddy soil.
Ó2016 The Author. Production and hosting by Elsevier B.V. on behalf of King Saud University. This isan
open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
19
20
1. Introduction
21Salinity is becoming an increasing problem in the world.
22
About 25% of the world’s croplands are affected by salinity
23
(Miller and Curtin, 2008). Salt affected soils are generally scat-
24
tered throughout the world, with around 20% of the world’s
25
cultivated land (Summer, 2000) and 50% of cropland being
26
affected by various degrees of salinity (Flowers and Yeo,
E-mail address: toufiq_iqbal@yahoo.com
Peer review under responsibility of King Saud University.
Production and hosting by Elsevier
Journal of the Saudi Society of Agricultural Sciences (2016) xxx, xxx–xxx
King Saud University
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www.ksu.edu.sa
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http://dx.doi.org/10.1016/j.jssas.2016.11.002
1658-077X Ó2016 The Author. Production and hosting by Elsevier B.V. on behalf of King Saud University.
This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
JSSAS 245 No. of Pages 9
21 November 2016
Please cite this article in press as: Iqbal, T. Rice straw amendment ameliorates harmful effect of salinity and increases nitrogen availability in a saline paddy soil.
Journal of the Saudi Society of Agricultural Sciences (2016), http://dx.doi.org/10.1016/j.jssas.2016.11.002
27 1995). Likewise, in Bangladesh, 20% of the country is coastal
28 area of which about 53% are affected by different degrees of
29 salinity (Haque, 2006). This salinity is the consequence of sea
30 level rise that causes intrusion of salt water into the rivers
31 and estuaries in the coastal area of Bangladesh (Uddin et al.,
32 2011).
33 Rice straw is an organic material available in significant
34 quantities for most rice farmers. Rice straw contains numerous
35 elements essential for plant growth, including nitrogen (N),
36 phosphorus (P), potassium (K) sulfur (S), and calcium (Ca).
37 (Gaihre et al., 2013). Approximately 40% of N, 30 to 35%
38 of P, 80–85% of K, and 40–45% of S taken up by rice remain
39 in the straw at crop maturity (Dobermann and Fairhurst,
40 2002). It also contains different biopolymers such as cellulose
41 (32–37%), hemicelluloses (29–37%), and lignin (5–15%)
42 (Conrad, 2002). These nutrients are released to soil through
43 mineralization processes and are, therefore, available for sub-
44 sequent crop growth (Byous et al., 2004). In many studies,
45 recycling of rice straw is reported to increase the organic car-
46 bon and nutrient contents in soil (Misra et al. 1996; Eagle
47 et al. 2000). Keeping all these factors in mind, an incubation
48 study was designed to investigate the effect of rice straw addi-
49 tion on change in nutrient status in a naturally salt-affected
50 saline paddy soil.
51 A previous study showed that how salinity influences the
52 decomposition of maize straw on the response of soil proper-
53 ties and nutrient dynamics (Wichern et al. 2006). Likewise,
54 another study showed that addition of rice straw only slightly
55 affected microbial properties and resulted in nitrogen mineral-
56 ization (Iqbal et al. 2016). However, there is only little infor-
57 mation available on how Bangladeshi saline paddy soil
58 influences the decomposition of rice straw addition on the
59 changes of soil properties and growth response of saline toler-
60 ant and saline sensitive varieties. In this perspective, Bangla-
61 desh Rice Research Institute (BRRI) developed an improved
62 rice variety, which is more salt tolerant than others. In this pre-
63 sent investigation the two varieties released by BRRI, the
64 BRRI Dhan28 (saline sensitive variety) and BRRI Dhan47
65 (saline tolerant variety) were used. Therefore, the present study
66 aims to do the following: (i) To investigate the effect of rice
67 straw addition to Bangladeshi saline paddy soils on changes
68 in selected soil properties, and (ii) to determine growth
69 response of saline tolerant (BRRI Dhan47) and saline sensitive
70 (BRRI Dhan28) rice varieties for the rice straw amendment in
71 saline paddy soil. It will be hypothesized that the BRRI
72 Dhan28 will be responded better than BRRI Dhan47 under
73 high rice straw added treatment. It will also be hypothesized
74 that rice straw amendment will increase nitrogen availability
75 in saline paddy soil.
76 2. Materials and methods
77 2.1. Collection and preparation of initial soil samples
78 The initial soil sample was collected from the naturally saline
79 paddy field at plough depth level (0–15 cm) immediately before
80 paddy rice transplanting stage. The samples were taken by
81 means of a spade from different locations covering the same
82 farmer’s field and mixed thoroughly to make composite sam-
83 ples. The composite sample was air-dried as well as ground
84 and sieved through a 2 mm mesh sieve and stored in a plastic
85
bag for physical and chemical analyses. The soil basic physical
86
and chemical properties are shown in Table 1.
87
2.2. Collected soil site conditions
88Dumuria is situated in the tidal floodplain of the Ganges Delta
89
in Bangladesh which is influenced by tidal cycles. The climate
90
is tropical monsoonal with moderately high temperature and
91
heavy rainfall during the Kharif season (April–September)
92
and scanty rainfall with a moderately low temperate during
93
the Rabi season (November–March). Average annual rainfall
94
is 1710 mm peaking in July and August. The average minimum
95
temperature is 12.5 °C in January and the average maximum
96
mean temperature is 36.5 °C in Dumuria Upazila of Khulna
97
district in Bangladesh (Bangladesh Meteorological
98
Department).
99
2.3. Background information about the naturally saline paddy
100
soil
101Naturally saline paddy soil resulted from sea-level rise and
102
saltwater intrusion in Bangladesh. The naturally saline paddy
103
soils in Bangladesh were characterized by high concentration
104
of soluble salts and low organic matter content. The naturally
105
saline paddy soil was less than 4 dS m
1
being within the tol-
106
erance of transplanted aman rice in the saline areas of
107
Bangladesh.
108
2.4. Collection and preparation of rice straw
109Rice straw was collected from agronomy farm of the Depart-
110
ment of Agronomy and Agricultural Extension, University
111
of Rajshahi, Rajshahi 6205, Bangladesh. Collected rice straw
112
was BRRI Dhan28 variety. After collection it was placed in
113
an oven. Before cutting it was taken from oven and then it
114
was cut into tiny sized pieces. This was also placed in a desica-
115
tor before mixing with collected saline paddy soil.
116
2.5. Rice straw mixing procedure within soil
117Coffee cup was used for this experiment. Size of coffee cup was
118
diameter 23 cm at top and diameter 11.2 cm at bottom and
119
height was 9.8 cm. Collected air-dried soil was placed in sepa-
120
rate coffee cup. A 300 g of soil was added in each cup. The
121
amount of rice straw was 0%, 25%, 50%, 100%, and 200%
122
dry weight of soil.
123
2.6. Incubation experimental procedure
124After mixing of rice straw within soil, each cup was placed in a
125
growth chamber with a constant temperature of 25 °C. Water
126
was maintained to field capacity. Each pot was placed within
127
growth chamber to decompose rice straw as well as release
128
nutrient from rice to the natural saline paddy soil under con-
129
stant temperature condition.
130
2.7. Plant material and seed germination technique
131Two saline tolerant (BRRI Dhan47) and saline sensitive
132
(BRRI Dhan28) varieties were used as a testing plant. Seeds
2 T. Iqbal
JSSAS 245 No. of Pages 9
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Please cite this article in press as: Iqbal, T. Rice straw amendment ameliorates harmful effect of salinity and increases nitrogen availability in a saline paddy soil.
Journal of the Saudi Society of Agricultural Sciences (2016), http://dx.doi.org/10.1016/j.jssas.2016.11.002
133 were soaked for 30 h in de-ionized water. After that it was cov-
134 ered with cloth for sprouting that helps to maintain optimum
135 temperature. Seed was sprouted after 48 h.
136 2.8. Sowing
137 Pre-germinated seed were placed within the soil in each cup.
138 Each cup contained 8 pre-germinated seed. After that pre-
139 germinated seed were covered with the naturally saline paddy
140 soil.
141 2.9. Seedling growth condition
142 Seedlings were grown in open air in a temperature range from
143 24 to 35 °C. Seedling growth period was 14 days. It was
144 expected that rice seedling can able to survive up to 14 days
145 of sowing without any additional nutrients or fertilization.
146 The soil was kept at field capacity (29% w/w) by weighing pots
147 during incubation and the growing period of rice seedlings.
148 Water was added to field capacity during seedling growth con-
149 dition. No basal nutrients and fertilizers were added in each
150 cup to avoid interaction between nutrients and rice straw. Seed
151 reserve nutrients were relied for seedling growth.
152 2.10. Seedling harvest
153 Seedlings were harvested at 14 days after sowing (DAS). Fresh
154 shoot weights were undertaken immediately after harvest.
155 After that shoots were stored in an oven at 70 °C for 3 days
156 for determination of shoot dry weight.
157 2.11. Measurements of soil physical and chemical properties
158 Bulk soil/straw mixture was analyzed for nutrients and soil pH
159 after final harvest. The pH of the bulk soil was determined in
160 deionized water using a soil-to-solution ratio of 1:5. Organic
161 carbon of the bulk soil samples was determined by wet oxida-
162 tion method (Walkley and Black, 1934). Bulk soil organic mat-
163 ter content was determined by multiplying the percent value of
164 organic carbon with the conventional Van-Bemmelen’s factor
165 of 1.724 (Piper, 1950). The nitrogen content of the bulk soil
166 sample was determined by distilling soil with alkaline potas-
167 sium permanganate solution (Subbiah and Asija, 1956). The
168 distillate was collected in 20 ml of 2% boric acid solution with
169 methylred and bromocresol green indicator and titrated with
170 0.02 N sulfuric acid (H
2
SO
4
)(Podder et al., 2012). Bulk soil
171 available S (ppm) was determined by calcium phosphate
172 extraction method with a spectrophotometer at 535 nm
173 (Petersen, 1996). The soil available K was extracted with 1 N
174
NH
4
OAC and determined by an atomic absorption spectrom-
175
eter (Biswas et al., 2012). The available P of the bulk soil was
176
determined by spectrophotometer at a wavelength of 890 nm.
177
The bulk soil sample was extracted by Olsen method with
178
0.5 M NaHCO
3
as outlined by Huq and Alam (2005). The
179
Zn in the bulk soil sample was measured by an atomic absorp-
180
tion spectrophotometer (AAS) after extracting with DTPA
181
(Soltanpour and Schwab, 1997).
182
2.12. Statistical analysis
183Results were analyzed by a one-way or two-way analysis of
184
variance (ANOVA) using Genstat 12th edn for Windows
185
(Lawes Agricultural Trust, UK).
186
3. Results
187
3.1. Impact of rice straw addition on growth response to saline
188
tolerant and sensitive rice seedlings
189
3.1.1. Number of seedlings emerged
190Result showed that the key effect of soil salinity has been
191
delayed for the reduction in seedling emergence. The rice straw
192
additions remarkably affect the emergence of paddy rice seed-
193
lings (Fig. 1). The emergence of rice seedlings increased due to
194
addition of rice straw. The number of paddy rice seedlings
Table 1 Properties of soils used in this study.
Soil
type
Site Location Electrical
conductivity (1:5
soil-water) (dS m
1
)
Water
holding
capacity
(%, w/w)
Soil pH
in H
2
O
(1:5)
Soil
organic
matter
(%)
N
(%)
P
(ppm)
K
(Cmol Kg
1
)
S
(ppm)
Zn
(ppm)
Alkaline Dumuria
Upazila
22.741°N
89.5167°E
3.7 71% 7.614 1.38 0.065 9.25 0.67 73.3 0.87
Rice straw
0% 25% 50% 100% 200%
Number of seedlings emergence
0
2
4
6
8
10
BRRI Dhan 28
BRRI Dhan 47
Figure 1 Number of paddy rice seedling emergence of BRRI
Dhan28 and BRRI Dhan47 due to addition of rice straw in a
saline paddy soil. Vertical bar represents LSD (p < 0.05) for rice
straw rice variety interaction.
Rice straw amendment 3
JSSAS 245 No. of Pages 9
21 November 2016
Please cite this article in press as: Iqbal, T. Rice straw amendment ameliorates harmful effect of salinity and increases nitrogen availability in a saline paddy soil.
Journal of the Saudi Society of Agricultural Sciences (2016), http://dx.doi.org/10.1016/j.jssas.2016.11.002
195 emergence was highest at 200% rice straw addition followed
196 by 100%, 50%, 25% and 0% respectively. Interestingly, seed-
197 ling emergence for the BRRI Dhan28 did not significantly dif-
198 fer with BRRI Dhan47 at 100% and 200% rice straw added
199 treatment. However, the number of emergence of rice seedlings
200 was significantly higher in BRRI Dhan47 than BRRI Dhan28
201 in the 0%, 25% and 50% rice straw added treatment.
202 3.1.2. Plant height at 7 DAS
203 The plant height was largely affected by the rice straw (Fig. 2).
204 The height of rice plant of BRRI Dhan47 was highest at 200%
205 rice straw addition followed by 100%, 50%, 25% and 0%
206 respectively. On the other hand height of rice plant of BRRI
207 Dhan28 was able to be measured only in 200% rice straw
208 added pot and in case 100%, 50% 25%, and 0% rice straw
209 added treatment plant height was enabled to be measured at
210 7 DAS. So, height of rice seedlings was tended to be differed
211 in between BRRI Dhan47 and BRRI Dhan28 in the 0%,
212 25%, 50%, 100% and 200% rice straw added treatment.
213 3.1.3. Plant height at harvest
214 The plant height was largely affected by the rice straw percent-
215 age (Fig. 3). The height of rice seedlings of BRRI Dhan47 sig-
216 nificantly differs at 200%, 100%, 25% and 0% rice straw
217 added treatment. Interestingly, the BRRI Dhan28 did not sig-
218 nificantly differ with BRRI dhan47 at 50% rice straw addition.
219 3.1.4. Fresh shoot weight
220 The rice straw additions remarkably affect the shoot fresh
221 weight of rice plant (Fig. 4). The fresh shoot weight of rice
222 plant increased due to addition of rice straw within saline
223 paddy soil. The weight of rice plant was highest at 200% rice
224 straw addition followed by 100%, 50%, 25% and 0% respec-
225 tively. It is noticeable that in 0% rice straw treatment shoot
226 weight of BRRI Dhan28 is zero.
227 3.1.5. Shoot dry weight
228 The shoot dry weight of rice seedling increased due to rice
229 straw addition in both BRRI Dhan28 and BRRI Dhan47
230
(Fig. 5). The shoot dry weight of BRRI Dhan47 tended to
231
be higher than BRRI Dhan28 at 200%, 100%, 50%, 25%
232
and 0% rice straw added treatment. It is noticeable that in
233
0% rice straw treatment shoot weight of BRRI Dhan28 was
234
zero.
235
3.2. Impact of rice straw addition on nutrient availability status
236
and changes in bulk soil properties
237
3.2.1. Bulk soil organic matter
238Bulk soil organic matter increases with the increase in rice
239
straw addition to soil (Fig. 6). The soil organic matter was
240
0.53%, 0.72%, 0.83%, 0.87% and 0.91% for the 0%, 25%,
241
50%, 100% and 200% rice straw addition to the soil.
Rice straw
0% 25% 50% 100% 200%
Plant height at 7 DAS (cm)
0
2
4
6
8
10
BRRI Dhan 28
BRRI Dhan 47
Figure 2 Plant height at 7 days after sowing (DAS) of BRRI
Dhan28 and BRRI Dhan47 due to addition of rice straw in a
saline paddy soil. Vertical bar represents LSD (p < 0.05) for rice
straw rice variety interaction.
Rice straw
0% 25% 50% 100% 200%
Plant height at harvest (cm)
0
2
4
6
8
10
12
14
BRRI Dhan 28
BRRI Dhan 47
Figure 3 Plant height at 7 days after sowing (DAS) of BRRI
Dhan28 and BRRI Dhan47 due to addition of rice straw in a
saline paddy soil. Vertical bar represents LSD (p < 0.05) for rice
straw rice variety interaction.
Rice straw
0% 25% 50% 100% 200%
Fresh shoot weight (g)
0.00
0.05
0.10
0.15
0.20
0.25
BRRI Dhan 28
BRRI Dhan 47
Figure 4 Fresh shoot weight of BRRI Dhan28 and BRRI
Dhan47 due to addition of rice straw in a saline paddy soil. Plant
was harvested after 14 days of sowing. Vertical bar represents LSD
(p < 0.05) for rice straw rice variety interaction.
4 T. Iqbal
JSSAS 245 No. of Pages 9
21 November 2016
Please cite this article in press as: Iqbal, T. Rice straw amendment ameliorates harmful effect of salinity and increases nitrogen availability in a saline paddy soil.
Journal of the Saudi Society of Agricultural Sciences (2016), http://dx.doi.org/10.1016/j.jssas.2016.11.002
242 3.2.2. Bulk soil pH
243 Bulk soil pH decreases with the increase in rice straw addition
244 to soil (Fig. 7). The bulk soil pH was 8.17, 8.13, 8.1, 8.03 and
245 8.03 for 0%, 25%, 50%, 100% and 200% rice straw addition
246 to the soil.
247 3.2.3. Bulk soil nitrogen
248 Bulk soil nitrogen increases with the increase in rice straw
249 addition to soil (Fig. 8). The soil nitrogen was 0.03, 0.0.04,
250 0.043, 0.047 and 0.053% for 0%, 25%, 50%, 100% and
251 200% rice straw addition to the soil.
252 3.2.4. Bulk soil phosphorus
253 In general, bulk soil available phosphorus was higher in less
254 rice straw added treatment and lower in high rice straw added
255 treatment (Fig. 9). Interestingly, soil available phosphorus was
Rice straw
0% 25% 50% 100% 200%
Shoot dry weight (g/pot)
0.00
0.01
0.02
0.03
0.04
0.05
BRRI Dhan 28
BRRI Dhan 47
Figure 5 Shoot dry weight of BRRI Dhan28 and BRRI Dhan47
due to addition of rice straw in a saline paddy soil. Plant was
harvested after 14 days of sowing. Vertical bar represents LSD
(p < 0.05) for rice straw rice variety interaction.
Rice straw
0% 25% 50% 100% 200%
Soil organic matter (%)
0.0
0.2
0.4
0.6
0.8
1.0
Figure 6 Changes in soil organic matter status due to addition of
rice straw in a saline paddy soil. Data were means of eight
replicates. Vertical bar represents LSD (p < 0.05) for rice straw
treatment.
Rice Straw
0% 25% 50% 100% 200%
Bulk soil pH
0
2
4
6
8
10
Figure 7 Changes in bulk soil pH due to addition of rice straw in
saline paddy soil. Data were means of eight replicates. Vertical bar
represents LSD (p < 0.05) for rice straw treatment.
Rice straw
0% 25% 50% 100% 200%
Soil nitrogen (%)
0.00
0.01
0.02
0.03
0.04
0.05
0.06
Figure 8 Changes in bulk soil nitrogen due to addition of rice
straw in a saline paddy soil. Data were means of eight replicates.
Vertical bar represents LSD (p < 0.05) for rice straw treatment.
Rice straw
0% 25% 50% 100% 200%
Bulk soil a va ilable P (ppm)
0
5
10
15
20
25
30
Figure 9 Changes in bulk soil phosphorus due to addition of rice
straw in a saline paddy soil. Data were means of eight replicates.
Vertical bar represents LSD (p < 0.05) for rice straw treatment.
Rice straw amendment 5
JSSAS 245 No. of Pages 9
21 November 2016
Please cite this article in press as: Iqbal, T. Rice straw amendment ameliorates harmful effect of salinity and increases nitrogen availability in a saline paddy soil.
Journal of the Saudi Society of Agricultural Sciences (2016), http://dx.doi.org/10.1016/j.jssas.2016.11.002
256 highest at 25% rice straw added treatment and tended to be
257 declined with the addition of rice straw.
258 3.2.5. Bulk soil potassium
259 Bulk soil potassium decreases with the increase in rice straw
260 addition to soil (Fig. 10). The bulk soil potassium was 0.62,
261 0.60, 0.51, 0.42 and 0.43 me/100 g for 0%, 25%, 50%, 100%
262 and 200% rice straw addition to the soil, respectively.
263 3.2.6. Bulk soil Zn
264 The bulk soil Zn tended to be declined with the addition of rice
265 straw to the saline paddy soil (Fig. 11). The bulk soil Zn was
266 highest in 0% rice straw followed by 25%, 50%, 100% and
267 200% rice straw added treatment.
268
4. Discussion
269
4.1. Rice straw reduces bio-availability of salinity from saline
270
paddy soil
271Additions of rice straw alleviate salt effect from the saline
272
paddy soil. This finding confirmed from the increased growth
273
response of saline sensitive variety of BRRI Dhan28 with the
274
addition of rice straw. My results showed that the addition
275
of rice straw increases the growth response of BRRI Dhan28
276
seedlings which was saline sensitive variety. The number of
277
plant emergence did not differ significantly (PP0.05) between
278
saline sensitive (BRRI Dhan28) and saline tolerant (BRRI
279
Dhan47) rice varieties for the 100% and 200% rice straw
280
added treatment (Fig. 1). It indicates that rice straw amelio-
281
rates harmful effect of salt in this saline paddy soil. A similar
282
observation was found from another study conducted in other
283
coastal areas of Bangladesh (Kaniz and Khan, 2013). They col-
284
lected soil sample from Amtali upazila in Barguna district
285
which was located between 20.15080 N latitude and 90.12640
286
E longitude. Their soil was silty clay loam affected by various
287
degrees of salinity, EC 3.36 dS/m, pH 5.35, Turbidity 940 mg/
288
kg, Organic Carbon 1.53%, total N 0.082%, available ammo-
289
nium N 14.55 mg/kg, available nitrate N 33.95 mg/kg. They
290
found that application of rice hull increased growth and yield
291
contributing characters of BRRI Dhan47. They also suggested
292
that the application of rice hull is effective in improving the
293
adverse effect of salinity and yield performance of BRRI
294
Dhan47.
295
The saline sensitive rice variety (BRRI Dhan28) prolifer-
296
ated in its roots and shoots due to addition of rice straw in this
297
saline paddy soil. The rice seedling height for both 7 days after
298
sowing (DAS) and harvest reached double for the maxim rice
299
straw treatment. Similarly, shoot dry weight and fresh shoot
300
reach 0–0.03 g and 0–0.15 g at maximum rice straw added
301
treatment. These finding indicates that addition of rice straw
302
to saline paddy soil reduces the bio-availability of salinity in
303
this saline paddy rice soil. Likewise, other study found that
304
addition of 1 g kg
1
of soil wheat straw lowers EC value 6%
305
in a naturally salt-effected soil (Mahmood et al., 2013).
306
Another study showed that the EC values reduced 2.87 dS m
1
307
to 1.95 dS m
1
is a naturally saline soil due to application of
308
rice straw (Mahmood et al., 2009). Similarly, Iqbal et al.
309
(2016) found that addition of rice straw reduced the salinity
310
within Bangladeshi saline paddy soil. They speculated that rice
311
straw amendments mitigated the negative effect of salinity
312
probably of its low availability to soil microorganisms and
313
the low amounts added (25 and 50% of straw yield). They also
314
found that soil fungi which might better cope with rice straw as
315
a substrate are generally very low level in this saline paddy soil.
316
This may be caused the decrease in the harmful effect of salt
317
with rice straw amendment.
318
These finding also confirmed that rice straw addition to this
319
naturally saline paddy soil decreased the bio-availability of
320
salinity proved from the growth response of BRRI Dhan28
321
seedlings. Also, there may be possibility that the extent of
322
the decomposition of the rice straw was increased when added
323
at the different rates due to incubation at field capacity at
324
25 °C. This may well have a bearing mechanisms involved in
325
the amelioration of the impact of soil salinity on the sensitive
326
seedlings.
Rice straw
0% 25% 50% 100% 200%
Bulk soil potassium (me/100 g)
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
Figure 10 Changes in bulk soil potassium due to addition of rice
straw in a saline paddy soil. Data were means of eight replicates.
Vertical bar represents LSD (p < 0.05) for rice straw treatment.
Rice straw
0% 25% 50% 100% 200%
Bulk soil available Zn (ppm)
0.0
0.2
0.4
0.6
0.8
1.0
1.2
Figure 11 Changes in bulk soil potassium due to addition of rice
straw in a saline paddy soil. Data were means of eight replicates.
Vertical bar represents LSD (p < 0.05) for rice straw treatment.
6 T. Iqbal
JSSAS 245 No. of Pages 9
21 November 2016
Please cite this article in press as: Iqbal, T. Rice straw amendment ameliorates harmful effect of salinity and increases nitrogen availability in a saline paddy soil.
Journal of the Saudi Society of Agricultural Sciences (2016), http://dx.doi.org/10.1016/j.jssas.2016.11.002
327 4.2. Seedling is a tool and its effect on age for the critical salinity
328 level
329 Seedling growth and age indicates the critical level of salinity.
330 The number of seedling emergence significantly differed
331 between BRRI Dhan28 and BRRI Dhan47 up to 50% rice
332 straw added treatment. However, seedling emergence did not
333 differ between BRRI Dhan28 and BRRI Dhan47 for 100%
334 and 200% rice straw added treatment (Fig. 1;Table 2). This
335 indicated that the seedling has the ability to grow in this crit-
336 ical salinity level. This also indicated that both BRRI Dhan28
337 and BRRI Dhan47 rice seedlings were also able to sustain in
338 the same soil condition that resulted from nitrogen availability
339 and reduction in bio-availability of salinity in this saline paddy
340 soil. Regardless of that both BRRI Dhan28 and BRRI
341 Dhan47 may very sensitive to salinity during seedling stage
342 and it impairs seedling growth and establishment. Reduced
343 seedling growth is a common phenomenon when grown under
344 increased salinity condition. For example, the deleterious effect
345 of salinity on the growth of rice was noticeable only in the
346 seedling stage. At the seedling stage, rice is sensitive to salinity,
347 but loses some of this sensitivity during more advanced stages
348 of growth (Thawornwong and Diest, 1974). Therefore, seed-
349 lings are the most sensitive stage of growth of plants to salinity.
350 4.3. Seedling survival and growth
351 Plant height at 7 days after sowing (DAS) data indicated that
352 both BRRI Dhan28 and BRRI Dhan47 seedlings were not
353 measurable up to 50% rice straw added treatment (Fig. 2).
354 The impact of salinity was great for the BRRI Dhan28. This
355 finding confirmed that the BRRI Dhan28 seedlings were very
356 sensitive to salinity during early seedling growth stage. My
357 speculation is that rice seedling growth depends on both salt
358 concentration and time of exposure. At low salt concentration,
359 longer exposure times were needed to produce measurable
360 effects. Likewise, there may be possibility that it was due to
366366366366366366
the extra water that could be held in the soil/straw matrix
367
which effectively diluted the salt in the soil, reducing the osmo-
368
tic stress on the sensitive germinating seed and growing seed-
369
lings. Other study also speculated that salinity dramatically
370
reduced seedling survival (Zhang et al., 2013). They have
371
found that rice seedling survival was reduced about 30% at
372
3.0 dS/m level of salinity and 20% at 1.9 dS/m level of salinity.
373
Both their study confirmed that rice is very sensitive to salinity
374
during early seedling growth and that EC levels in standing
375
water as low as 1.9 dS/m may affect growth and development.
376
These findings indicated that there is no critical point of salin-
377
ity where plants fail to grow. As the salinity increases growth
378
decreases until plants become chlorotic and die. This is because
379
the osmotic pressure of the soil solution increases as the salt
380
concentration increases. Apart from the osmotic effect of salts
381
in the soil solution, excessive concentration and absorption of
382
individual ions may prove toxic to the plants and/or may
383
retard the absorption of other essential plant nutrients.
384
4.4. Rice straw reduces bulk soil pH and increases nitrogen
385
availability
386Rice straw amendments to soil reduces soil pH and nitrogen
387
availability within the bulk soil. Initially, soil pH was 8.17.
388
But, due to 200% raw rice straw addition it was down to
389
8.03. Thus bulk soil pH reduces 0.14 units for the maximum
390
amount of rice straw addition to the saline paddy soil. The
391
reduction of bulk soil pH was started when 25% raw rice straw
392
was added to saline paddy soil. The bulk soil pH becomes
393
decline with the addition of rice straw (Fig. 7;Table 3). Since
394
the application of rice straw decreases soil pH, partly due to
395
the decomposition of organic matter. In contrast, nitrogen
396
availability in bulk soil increased due to addition of raw rice
397
straw. Similarly, a study showed that the total soil N concen-
398
tration increased by 10.4% due to incorporation rice straw in a
399
paddy soil (Wang et al., 2015). My findings showed that soil
400
nitrogen percentage reached 0.033–0.053% due to additions
401
of 200% rice straw (Fig. 8). Likewise, other study showed that
Table 2 Significance levels from the analysis of variance for the main effects on growth response of BRRI Dhan28 and BRRI Dhan47
wheat seedlings.
Source of variation Seedling emergence Plant height at 7 DAS Plant height at harvest Shoot fresh weight Shoot dry weight
Variety n.s. *** * ** *
Straw * *** *** *** ***
Straw Variety n.s. *** n.s. n.s. n.s.
Where n.s.,*,** and *** represent probability of >0.05, 60.05, 60.01 and 60.001. Values were means of three replicates.
Table 3 Significance levels from the analysis of variance for the effect of various rice straw addition to bulk saline paddy soil.
Source of variation Bulk soil pH Soil nitrogen Soil phosphorus Soil potassium Soil organic matter Soil available Zn
Rice straw ***
n.s. *** *** *
Where n.s.,*,** and *** represent probability of > 0.05, 60.05, 60.01 and 60.001. Values were means of three replicates.
Rice straw amendment 7
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Please cite this article in press as: Iqbal, T. Rice straw amendment ameliorates harmful effect of salinity and increases nitrogen availability in a saline paddy soil.
Journal of the Saudi Society of Agricultural Sciences (2016), http://dx.doi.org/10.1016/j.jssas.2016.11.002
402 initial soil pH 8.27 reached to 7.36 due to 5% raw rice straw
403 amendment [weight/weight (w/w)] (Li et al., 2013). This exper-
404 imental soil was Ansai (36°510N, 109°190E) collected from
405 Shaanxi Province, China. Based on pedogenesis and soil tax-
406 onomy, this soil was also classified Loessi-Orthic Primosols.
407 They also found that ammonium nitrogen (NH
4
+
-N) increased
408 0.38–1.47 mg/kg and nitrate nitrogen (NO
3
-N) increases 17.9–
409 31 mg/kg due to addition of same raw rice straw in the same
410 soil. This could be due to reason that rice straw addition
411 increases N availability to this saline paddy soil that resulted
412 in decrease in soil pH.
413 Long-term incubation effects on rice straw application
414 improved N availability. The improved N availability was
415 attributed to N mineralized from the added rice straw. Other
416 researchers speculated that improved N availability upon rice
417 straw application was due to reduced nitrification-
418 denitrification losses (Asten et al., 2005). Likewise, Rath and
419 Rousk (2015) argued that the slight increase in inorganic N
420 might rather have been caused by the release of NH
4
+
from
421 clay minerals from Na
+
available in saline soil. Our specula-
422 tion is that rice straw decomposed due to long-term incubation
423 that resulted in increase N availability in the saline paddy soil.
424 4.5. Nutrient dynamics
425 Soil extractable P increases at 25% rice straw added treatment.
426 After that it tended to be declined with the addition of rice
427 straw (Fig. 9). This could be due to the reason that rice seed-
428 ling takes up more P from soil for its growth and development,
429 as rice seedlings become prominent in the high straw added
430 treatment that resulted in more P uptake from the saline paddy
431 soil. A study speculated that the incorporation of rice straw
432 within saline soil increase the activity of phosphatase (Liang
433 et al., 2003). Similarly, bulk soil K also declined with the addi-
434 tion of rice straw added treatment. In contrast, bulk soil N
435 increased with the addition of rice straw addition to soil. Like-
436 wise, bulk soil organic matter increased due to addition of rice
437 straw. Although bulk soil available P and K were declined N
438 was not declined. This could be due to the reason that during
439 mineralization process rice straw releases more N from this sal-
440 ine paddy soil. This may result in excess N was available in this
441 saline paddy soil and even N was also taken up by rice seed-
442 lings. Regardless of that rice straw contains numerous ele-
443 ments essential for plant growth including N (Zhang et al.,
444 2013). Following the decomposition of rice straw, many of
445 these cation nutrients may release back into the soil solution
446 which in turn increases the N availability in this saline paddy
447 soil.
448 Rice straw amendment increases growth response of both
449 BRRI Dhan28 and BRRI Dhan47 (Fig. 3). This could be
450 due to reason that rice straw release nutrients from the saline
451 paddy soil that resulted in improved growth of both BRRI
452 Dhan28 and BRRI Dhan47, regardless of that P and K uptake
453 by rice seedlings which cause less availability of P and K in the
454 saline paddy bulk soil.
455 5. Conclusions
456 This study demonstrated that rice straw addition to saline
457 paddy soil reduces bio-availability of salinity. This proved
458 from the seedling growth performance of saline sensitive rice
459
variety BRRI Dhan28 on the rice straw added treatment.
460
Our findings also demonstrated that the growth response of
461
BRRI Dhan28 and BRRI Dhan47 did not significantly differ
462
at highest rice straw added treatment. This happened due to
463
reduction in harmful effect of salinity within the saline paddy
464
soil for rice straw amendment.
465
This study also demonstrated that raw rice straw amend-
466
ment to the saline paddy soil reduces bulk soil pH and
467
increases N availability in this saline paddy soil. The addition
468
of raw rice straw to soil also increased bulk soil organic matter
469
in this saline paddy soil. Thus, this study concluded that rice
470
straw amendment can reduce harmful effect of salinity and
471
increase N availability in saline paddy soil.
472
6. Uncited reference
473Iqbal and Anwar-ul-Hassan (2011).
474
Acknowledgments
475
The author would like to thank the personnel of Soil
476
Resources Development Institute (SRDI), Bangladesh for
477
their constructive suggestion regarding soil samples collection.
478
The author also thankful to Bangladesh Rice Research Insti-
479
tute to provide BRRI Dhan47 and BRRI Dhan28 seed for this
480
experiment.
481
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Rice straw amendment 9
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Journal of the Saudi Society of Agricultural Sciences (2016), http://dx.doi.org/10.1016/j.jssas.2016.11.002
