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Supplemental irrigation of wheat with saline water
agricultural water management 95 (2008) 253–258
available at www.sciencedirect.com
journal homepage: www.elsevier.com/locate/agwat
Supplemental irrigation of wheat with saline water C.P.S. Chauhan a, R.B. Singh a, S.K. Gupta b,* a b
Raja Balwant Singh College, Bichpuri, Agra 283105, India Central Soil Salinity Research Institute, Karnal 132001, India
article info
abstract
Article history:
In arid and semi-arid regions, both rainfall and surface irrigation water supplies are
Received 28 December 2006
unreliable and inadequate to meet crop water requirement. Groundwater in these regions
Accepted 9 October 2007
is mainly marginally saline (2–6 dS/m) to saline (>6 dS/m) and could be exploited to meet
Published on line 19 December 2007
crop water requirement if no adverse effects on crops and land resource occur. The fear of adverse effects has often restricted the exploitation of naturally occurring saline water. The
Keywords:
results reveal that substituting a part or all except pre-sowing irrigation with saline water
Groundwater
having an electrical conductivity (ECiw) of 8 dS/m is possible for cultivation of wheat.
Soil salinity
Similarly, saline water with ECiw ranging between 8 and 12 dS/m could be used to supple-
Wheat
ment at least two irrigations to obtain 90% or more of the optimum yield. In low rainfall
Supplementary irrigation
years, the use of such waters for all irrigations, except pre-sowing, produced more yield than
Saline irrigation water
skipping irrigations. Apparently, even at this level of osmotic salt stress, matric stress is more harmful. Thus, it would be interesting to use such waters for wheat production in monsoon climatic regions. # 2007 Elsevier B.V. All rights reserved.
1.
Introduction
Weather fluctuations are a bane for crop production in arid and semi-arid regions. To ensure high productivity, concerted efforts have been made to introduce irrigation through interbasin transfer of water. To prevent widespread crop failure, the concept of protective irrigation implying a limited water supply to agricultural lands, has been introduced. Consequently, crops suffer from moisture stress (Tyagi et al., 2003) and to this fact overall low productivity has been traced in many irrigation projects. Yet, spectacular results have been obtained when canal water is supplemented with groundwater (Dhawan, 1989). Since groundwater in many parts of arid and semi-arid regions is saline/sodic, groundwater has not been exploited for fear of adverse effects on crops and/or soils. Consequently, farmers switched over to less water requiring crops or crops that are more tolerant to salts. Earlier works related to the use of saline water in agriculture, however, proved the potential of these waters as a source of
irrigation in conjunction with fresh water (Vyas et al., 1986; Singh et al., 1992; Minhas, 1998; Oster and Grattan, 2002). The objectives of this paper are (i) to quantify the adverse effect of moisture stress in low rainfall years on wheat productivity in semi-arid regions and (ii) to prove that saline water can be beneficially used to supplement the canal water. Besides substantial increase in production, this strategy would lend sustainability to the agricultural production.
2.
Materials and methods
A field experiment was conducted during November 2000 to April 2003 at the experimental farm of the Raja Balwant Singh College, Agra, located at 27.98E longitude and 27.28N latitude, and 163 m above mean sea level. Agra is located in a semi-arid region with monsoon climate. The average annual rainfall in this region was 665 mm for the period 1973–2002. Around 80% of the total rainfall occurs during June–October while the
* Corresponding author. Tel.: +91 184 2292730/2294730; fax: +91 184 2290480. E-mail address: [email protected] (S.K. Gupta). 0378-3774/$ – see front matter # 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.agwat.2007.10.007
254
agricultural water management 95 (2008) 253–258
Table 1 – Physico-chemical properties of the soil before starting the experiment Horizon A1 A3 B2-1t B2-2t B3-Ca C
Depth (m)
pH2
ECse (dS/m)
CEC (cmol/kg)
Textural class
K (mm/h)
0.00–0.20 0.20–0.45 0.45–0.72 0.72–1.15 1.15–1.40 1.40–1.80
8.5 8.5 8.6 8.5 8.6 8.6
8.5 2.6 3.2 2.0 2.5 4.5
12.8 12.6 14.4 14.8 14.8 14.7
Sandy loam Loam Clay loam Clay loam Sandy loam Loam
11.5 6.5 6.0 6.0 8.1 18.2
Bulk density (Mg/m3) 1.45 1.52 1.52 1.51 1.44 1.42
ECse = EC of saturation extract, CEC = cation exchange capacity, K = saturated hydraulic conductivity.
remaining 20% occurs during the rest of the year. The rainfall fluctuated during the wheat growing seasons and was the lowest in 2000–2001 (27.6 mm) while it was relatively high and well distributed in 2001–2002 (67 mm) and 2002–2003 (48.7 mm). The soil of the site is of alluvial origin, and neither saline nor alkaline (Table 1). The permeability is fair and the vertical movement of water is not noticeably impeded. During the study period (April 2000 to June 2003), the water table fluctuated between 5.6 m (October) and 7.7 m (April) below the soil surface. Owing to the relatively large depth of the water table, groundwater contribution to crop water use was almost negligible. Micro-plots of (2.5 m 2.5 m), separated by polythene sheets to a depth of 90 cm on all four sides of each plot to prevent horizontal movement of water, were used for the study. Wheat (cv. Raj. 3077) was sown in November each year and was harvested during March of the next year. The saline water, which was used to supplement the best available water (BAW) was prepared artificially by dissolving CaCl2, MgCl2, MgSO4, NaCl and Na2SO4 in BAW such that the Ca:Mg ratio was 1:1.6 and the Cl:SO4 ratio 3:1 with SARiw = 10 mmol0.5/l0.5. The electrical conductivity (ECiw) of BAW was 3.2 0.6 dS/m. Wheat is sensitive to moisture deficit at the crown root initiation (CRI) and as such, irrigation is considered essential at this stage (Anonymous, 1975; Gajri and Prihar, 1988). Further, wheat is also sensitive to salt stress at the germination and establishment stage (Minhas and Gupta, 1992; Naresh et al.,
1993). Tyagi et al. (2003) observed that on an average, only 7–8 cm of water or the equivalent of one irrigation was available at the tail end of the Bhakra canal system. Considering these findings, it was decided to apply pre-sowing irrigation with BAW in all the treatments and apply at least one irrigation at CRI with BAW in nine treatments. In all, 12 treatment combinations were set up (Table 2) to test the effect of saline water as supplement to the fresh water application on wheat growth. The experiment was laid out in a randomized block design (RBD) with four replications. A pre-sowing irrigation of 7 cm with BAW was common to all the treatments. Depending upon the rainfall and climatic conditions the number of post-sown irrigations varied from 1 year to another. A total of five irrigations during 2000–2001 and four irrigations during 2001–2002 and 2002–2003, each of 7 cm depth, were applied in all the treatments except T2 to T4 (Table 2). Nitrogen (N) as urea, phosphorus (P) as single superphosphate and potassium (K) as muriate of potash were applied at the recommended rate of 120, 60 and 60 kg/ha. Plant parameters, viz. germination percentage, plant height and number of ears per plant were studied. Counted seeds were sown in each row of each plot. Three rows of each plot were selected and germinated seeds were counted at 8, 10 and 12 days. Since there was no change in germination at 10 and 12 days, the germination count at 10 days was used to calculate the average germination percentage in each treatment by dividing the germinated seeds by the total number of
Table 2 – Detail description of the treatments Number of irrigationsa
Treatment 2000–2001 T1 (All BAW) T2 (BAW at CRI) T3 (BAW at CRI and milking) T4 (BAW at CRI, jointing and milking) T5 = T2 + saline water ECiw = 6/8 dS/m T6 = T2 + saline water ECiw = 12 dS/m T7 = T3 + saline water ECiw = 6/8 dS/m T8 = T3 + saline water ECiw = 6/8 dS/m T9 = T4 + Saline water ECiw = 6/8 dS/m T10 = T4 + saline water ECiw = 12 dS/m T11 = All irrigations with saline water ECiw = 6/8 dS/m T12 = All irrigations with saline water ECiw = 12 dS/m
5 1 2 3 5 5 5 5 5 5 5 5
(4) (4) (3) (3) (2) (2)
2001–2002 4 1 2 3 4 4 4 4 4 4 4 4
(3) (3) (2) (2) (1) (1)
2002–2003 4 1 2 3 4 4 4 4 4 4 4 4
BAW: best available water; water salinity was 6 and 12 dS/m during 2000–2001 and 8 and 12 dS/m during 2001–2002 and 2002–2003. Values in parentheses indicate number of saline water irrigations. The number of irrigations was the same except in T2, T3 and T4.
a
(3) (3) (2) (2) (1) (1)
255
NS 2.2 2.4 NS 0.5 0.7 NS Some variation in values is due to different DAS during the 3 years; SD = significant difference.
1.6 6.7 3.6 2.5 4.5 NS NS SD ( p = 0.05)
NS
37.3 35.9 37.1 37.9 36.9 36.6 37.2 35.5 37.2 35.3 36.3 34.7 38.1 33.8 34.1 34.6 35.6 35.3 37.1 35.9 37.8 37.7 35.6 34.9 33.4 16.5 22.1 25.6 30.8 28.3 30.5 28.0 31.7 31.7 32.8 29.8 8.0 7.4 7.6 7.7 7.7 7.5 7.7 7.6 7.9 7.7 7.9 7.5 8.1 7.4 7.5 7.5 7.7 7.7 7.8 7.5 7.9 7.9 7.8 7.5 7.6 6.4 7.0 7.6 7.3 7.0 7.3 7.1 7.6 7.5 7.2 7.1 91.0 89.1 86.3 89.2 93.3 86.6 88.4 92.6 90.8 93.2 89.6 86.5 88.6 84.1 87.0 87.2 88.2 84.5 88.5 85.8 88.0 86.1 85.8 82.8 109.3 78.2 93.7 96.0 106.6 112.0 107.2 106.6 107.9 107.2 106.6 104.5 44.2 40.3 41.9 42.2 40.4 41.7 43.8 41.1 39.8 41.0 39.7 39.6 57.2 52.3 55.6 56.0 56.6 54.5 56.9 56.1 57.2 56.5 56.9 54.4
Ear length (cm)
2000–2001 2001–2002 2002–2003 2000–2001 2001–2002 2002–2003 Harvest (128–141 days) Mid-stage (60–70 days)
56.4 44.7 45.0 53.7 54.2 53.7 55.9 54.6 55.1 53.8 54.0 48.4 91 89 86 89 93 86 88 92 90 93 89 85 91 75 76 82 84 84 80 84 84 84 78 75 97 95 92 93 98 98 95 97 91 87 97 97 T1 T2 T3 T4 T5 T6 T7 T8 T9 T10 T11 T12
The yield attributing characteristics such as ear length in 2001–2002 and numbers of grain per ear head at harvest in 2000–2001 and 2001–2002 in T2 differed significantly over T1 and were significantly higher in T5 over T2 in 2000–2001. In the year 2001–2002, the differences in the ear length were significant in T12 over T1 although no differences were observed in the year 2002–2003 (Table 3). These differences could be attributed either to moisture or salt stress. Almost similar results were obtained for the number of grains per ear. Besides, there was significant improvement in the numbers of ears with supplemental irrigation over the respective
2000–2001 2001–2002 2002––2003 2000–2001 2001–2002 2002–2003
Yield attributing characteristics
2002
3.2.
2001
The germination did not vary between treatments over the years (Table 3). Although, soil salinity was enhanced wherever saline water was applied, i.e. from T5 onwards, it was not high enough to affect germination during the next season. Presowing irrigation with BAW in all the treatments had played an important role in reducing the salt level in these cases. As such, the difference in yield could be attributed only to moisture or salt stress after initial crop rooting. The plant height recorded at mid-stage (60–70 days) as well as at harvest (128–141 days) differed significantly amongst treatments in 2000–2001 and 2001–2002. It was significantly lower at mid-stage in T2 and T3 in 2000–2001 and in T2 in 2001–2002 than in T1 resulting from moisture stress. Similarly, at mid-stage it was significantly lower in T12 where all irrigations were given with water having ECiw of 12 dS/m than in T1 in all the years. In 2001–2002 even at harvest, the height in T12 was significantly less than in T1. It could mainly be attributed to salt stress since the number of irrigations was equal in both treatments. Apparently, both moisture stress and salt stress gave an initial setback to the crop.
2000
Germination and growth characteristics
Plant height (cm)
3.1.
Germination (%)
Results and discussion
Table 3 – Germination count, plant height, ear length and number of grains per ear of wheat under different treatments
3.
Treatments
seeds in 12 rows, 3 rows each of four replications. Plant height, ear length and number of grains per ear were studied by selecting five plants in each plot. The average values of 20 plants per treatment were worked out and reported. Grain and straw yields of the plots were recorded. On the basis of average yield of the four replications, relative yields of all the treatments were computed as a percentage of the four replications of treatment T1. Four soil samples from one location at the center of each replication were collected at sowing and harvest at 15 cm interval down to 30 cm and 30 cm interval down to 90 cm soil depth, air-dried, ground, passed through a 2 mm sieve and the electrical conductivity of a saturation paste extract (ECse) measured. Soil moisture was determined gravimetrically at sowing, before and after each irrigation and at harvest. Statistical analysis was carried out according to the standard procedure reported in Gomez and Gomez (1984). Pairs of treatments were compared for significant difference using the t-test. They are significantly different when their difference exceeds the computed significant difference SD.
Number of grains/ear
agricultural water management 95 (2008) 253–258
256
agricultural water management 95 (2008) 253–258
Table 4 – Grain and straw yield (t haS1) of wheat under different treatments Treatments
2000–2001
2001–2002
2002–2003
Mean yield
Grain
Straw
Grain
Straw
Grain
Straw
Grain
T1 T2 T3 T4 T5 T6 T7 T8 T9 T10 T11 T12
5.47 1.37 2.88 3.74 5.32 5.06 5.38 5.26 5.52 5.44 5.45 4.64
8.33 4.28 5.38 6.57 8.12 7.77 8.20 8.16 8.32 8.20 8.04 7.03
5.72 4.54 4.53 4.84 4.95 4.83 4.92 4.91 5.37 4.66 5.05 4.72
9.75 8.48 8.85 9.04 9.21 8.80 9.27 8.54 9.53 8.87 9.05 8.23
5.19 4.50 4.83 4.95 4.96 4.77 4.93 4.78 5.14 4.94 5.10 4.69
8.32 7.30 7.62 7.78 8.18 7.89 8.15 7.87 8.12 7.86 8.21 7.62
5.46 3.47 4.08 4.51 5.08 4.89 5.08 4.98 5.34 5.01 5.20 4.68
8.80 6.69 7.28 7.80 8.50 8.15 8.54 8.19 8.66 8.31 8.43 7.63
SD ( p = 0.05)
0.33
0.45
0.57
0.63
0.27
0.52
–
–
treatments. For example, the increase was significant in treatments T5 and T6 over T2 and T7, T8 over T3 and T9 and T10 over T4 in the year 2000–2001.
3.3.
Grain and straw yield
The grain and straw yield data of all the 3 years are reported in Table 4. The highest yield was recorded for T1 where only BAW was applied for all irrigations. The limitation of the fresh water supply in one irrigation at CRI stage only (T2), two irrigations at CRI and milking stages (T3) and three irrigations at CRI, Jointing and milking stages (T4) resulted in moisture stress and yield reduction, at least in low rainfall years as in 2000– 2001. The yield in this year increased with increasing number of fresh water irrigations and the order of yield was T2 < T3 < T4 < T1. The adverse effect of moisture stress was minimised in 2001–2002 with a rainfall of about 67 mm and in 2002–2003 with a rainfall of about 49 mm together with cloudy weather for quite a long period. As a result, treatments T2, T3 and T4 showed small variations. However, the average yield reduction over 3 years compared with T1 was 36, 25 and 17% for T2, T3 and T4, respectively. Almost similar results were obtained for the straw yield. These results are in conformity with the results obtained by Mishra et al. (1995). Since fresh water is limited in arid and semi-arid regions, it is not possible to apply the optimum number of irrigations. In such instances, saline groundwater can be used to provide the optimum number of irrigations after a limited number of irrigations with fresh water to obtain a higher yield than without supplemental irrigations with saline water. The data for treatments T5, T7 and T9 where saline waters with an ECiw of 6 dS/m (2000–2001) and 8 dS/m (2001–2002 and 2002–2003) were used clearly substantiates this. The yield in all these treatments was on a par with treatment T1. It seems that an ECiw of 8 dS/m is within the tolerable limit for wheat. Similarly, when using water with ECiw of 12 dS/m in treatments T6, T8 and T10, the mean yields of grain and straw ranged between 89 and 94% of the yield in treatment T1. The supplemental irrigations with ECiw of 12 dS/m enhanced the mean grain yield in T6 over T2 by 41%, in T8 over T3 by 22% and in T10 over T4 by 11%. Although the yield of T6 was significantly different from the yield of T1 in each of the 3 years, there were almost no
Straw
differences in the mean yield of T8 and T10 over the 3 years. Apparently, it justifies supplemental irrigations with water with ECiw of 12 dS/m at one or two stages following irrigations with fresh water. Another observation from this study is that the yield of T12 where all irrigations were given with a water salinity of 12 dS/m was on a par with T2, T3 and T4 in 2001–2002 and 2002–2003 and substantially greater in the abnormal dry year 2000–2001. The average yield of T12 over 3 years was slightly higher than that of T4 where three irrigations with BAW were applied. Moisture stress seems more harmful than salt stress. Consequently, even water of a relative high salinity can be used for supplemental irrigations when fresh water is limited.
3.4.
Soil salinity
The average soil salinity over 3 years at harvest for some selected treatments is presented in Fig. 1. The salt build-up was minimal in treatments T2 followed by T3, T4 and T1. The salinity increased wherever saline water was applied (T5 to T12) although the magnitude varied with water salinity and
Fig. 1 – Soil salinity build-up as a result of supplemental irrigations with saline water.
257
agricultural water management 95 (2008) 253–258
Table 5 – Rainfall pattern in winter months (December–March) at Agra during the last 30 years Rainfall range (mm) Number of years for rainfall range % of total number of years of record
<10 3 10
10–20 4 13
the number of irrigations with saline water. Similar results were reported by Gupta (1985). On an average basis, the highest salinity (14.5 dS/m) occurred in T12 where all irrigations were applied with water having an ECiw of 12 dS/m. For all other treatments, soil salinity was within the range determined by the curves of treatments T2 and T12. In general, the ECse values decreased with soil depth and were lowest at a depth of 60–90 cm. The data on soil salinity confirm the observation that moisture stress caused a yield decline in treatments without supplemental irrigation with saline water. When applying supplemental irrigation with saline water, the yield decline should be attributed to osmotic stress. At the onset of the monsoon following wheat harvesting, the salts accumulated in the root zone get leached. Within the month of July, the salt status of the soil profile is such that, in most cases, a kharif (monsoon season) crop can be grown when rainfall is supplemented with best available water. During the study period, the monsoon rainfall did not leach all accumulated salts and a slightly higher salinity prevailed in treatments T5 to T12, yet it did not affect the germination (Table 3). On the basis of long-term studies conducted (Sharma et al., 1994, 2001), it has been observed that, in monsoon climatic regions with an average annual rainfall exceeding 500 mm, more than 80% of the salts accumulated during wheat cultivation gets leached without any long-term increase in the soil salinity.
4.
Rainfall and production sustainability
Analysis of rainfall data for the last 30 years at Agra gauging station revealed that in 23% of the years, wheat production is likely to be adversely affected in the absence of supplemental irrigations, as the rainfall could be less than 20 mm during the growth period of wheat (Table 5). In 47% of the years, it might be slightly affected depending upon the amount and distribution of the rainfall during the crop growth period. In 30% of the years, it is likely that the crop might not be affected, even if limited fresh water is applied to the crop. As a result, sustainability of crop production is always uncertain because at least once in 4 years crop would be adversely affected. With such a scenario, saline groundwater, which is an assured source of water, offers an opportunity to supplement the canal water. The results reveal that if the salinity of groundwater is less than 8 dS/m, it could be applied as supplemental post-plant irrigations. If the groundwater salinity ranges between 8 and 12 dS/m, the water can be used for at least two post-plant irrigations and crop yield would still be more than or equal to 90% of the crop yield obtained with irrigations with low salinity water. The yield would certainly be more than when irrigations were skipped. Besides, this strategy would lend sustainability to the crop
20–30 6 20
30–40 8 27
40–50 1 3
>50 8 27
production programme, even in the absence of adequate fresh water supplies.
5.
Conclusion
From this study, it can be concluded that saline groundwater is a good source to exploit for irrigation. In wheat cultivation, saline groundwater with an ECiw of 6–8 dS/m can be used to supplement all irrigations except the pre-sowing irrigation (T5, T7, T9 and T11). Saline water with an ECiw of 12 dS/m can be used for at least two supplemental irrigations (T8) without any adverse effect on crop yield. The limited amount of available fresh water should be applied during the initial growth stage and supplemented with saline water at later growth stages. This strategy enables wheat production with saline water with an ECiw up to 12 dS/m giving a yield as high as 90% of the optimum crop yield obtained with low salinity water (T1).
references
Anonymous, 1975. Coordinator’s Report of AICRP on Research on Water Management. Central Soil Salinity Research Institute, Karnal, India, 178 pp. Dhawan, B.D., 1989. Studies on Irrigation and Water Management. Commonwealth Publishers, New Delhi, India, 255 pp. Gajri, P.R., Prihar, S.S., 1988. Effect of small irrigation amounts on the yield of wheat. Agric. Water Manage. 6, 31–41. Gomez, K.A., Gomez, A.A., 1984. Statistical Procedures for Agricultural Research. John Wiley and Sons, New York, USA, 680 pp. Gupta, S.K., 1985. Dynamics of salts in saline water irrigated soils. J. Instit. Eng. (India) 66 (AGI), 17–22. Minhas, P.S., 1998. Use of poor-quality waters. In: Singh, Sharma, (Eds.), 50 Years of Natural Resource Management Research. Indian Council of Agricultural Research, New Delhi, India, pp. 327–346. Minhas, P.S., Gupta, R.K., 1992. Quality of Irrigation Water— Assessment and Management. Indian Council of Agricultural Research, New Delhi, India, 123 pp. Mishra, H.S., Rathore, T.R., Tomar, V.S., 1995. Water use efficiency of irrigated wheat in Tarai region of India. Irrig. Sci. 16, 75–80. Naresh, R.K., Minhas, P.S., Goyal, A.K., Chauhan, C.P.S., Gupta, R.K., 1993. Conjunctive use of saline and non-saline waters. II. Field comparison of cyclic use and mixing for wheat. Agric. Water Manage. 23, 139–148. Oster, J.D., Grattan, S.R., 2002. Drainage water reuse. Irrig. Drainage Syst. 16, 297–310. Sharma, D.P., Rao, K.V.G.K., Singh, K.N., Kumbhare, P.S., Oosterbaan, R.J., 1994. Conjunctive use of saline and nonsaline irrigation waters in semi-arid regions. Irrig. Sci. 15, 25–33.
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Sharma, D.P., Singh, K.N., Kumbhare, P.S., 2001. Reuse of agricultural drainage water for crop production. J. Indian Soc. Soil Sci. 49, 483–488. Singh, R.B., Minhas, P.S., Chauhan, C.P.S., Gupta, R.K., 1992. Effect of high salinity and SAR waters on salinization, sodication and yield of pearl millet and wheat. Agric. Water Manage. 21, 93–105. Tyagi, N.K., Sakthivadivel, R., Sharma, D.K., Ambast, S.K., Agrawal, A., 2003. Farmers decision making in irrigation
commands: the need and scope for improvement. CSSRI Synthesis Paper 1. Central Soil salinity Research Institute, Karnal, 11 pp. Vyas, K.K., Singh, G.D., Yadav, B.L., 1986. Study on growth and yield of wheat as affected by irrigation levels with saline water and different levels of fertility, vol. 2. In: Proceedings of the International Symposium on Water Management in Arid and Semi-arid Zones, UNESCO-HAU, Hisar, pp. 65–73.
available at www.sciencedirect.com
journal homepage: www.elsevier.com/locate/agwat
Supplemental irrigation of wheat with saline water C.P.S. Chauhan a, R.B. Singh a, S.K. Gupta b,* a b
Raja Balwant Singh College, Bichpuri, Agra 283105, India Central Soil Salinity Research Institute, Karnal 132001, India
article info
abstract
Article history:
In arid and semi-arid regions, both rainfall and surface irrigation water supplies are
Received 28 December 2006
unreliable and inadequate to meet crop water requirement. Groundwater in these regions
Accepted 9 October 2007
is mainly marginally saline (2–6 dS/m) to saline (>6 dS/m) and could be exploited to meet
Published on line 19 December 2007
crop water requirement if no adverse effects on crops and land resource occur. The fear of adverse effects has often restricted the exploitation of naturally occurring saline water. The
Keywords:
results reveal that substituting a part or all except pre-sowing irrigation with saline water
Groundwater
having an electrical conductivity (ECiw) of 8 dS/m is possible for cultivation of wheat.
Soil salinity
Similarly, saline water with ECiw ranging between 8 and 12 dS/m could be used to supple-
Wheat
ment at least two irrigations to obtain 90% or more of the optimum yield. In low rainfall
Supplementary irrigation
years, the use of such waters for all irrigations, except pre-sowing, produced more yield than
Saline irrigation water
skipping irrigations. Apparently, even at this level of osmotic salt stress, matric stress is more harmful. Thus, it would be interesting to use such waters for wheat production in monsoon climatic regions. # 2007 Elsevier B.V. All rights reserved.
1.
Introduction
Weather fluctuations are a bane for crop production in arid and semi-arid regions. To ensure high productivity, concerted efforts have been made to introduce irrigation through interbasin transfer of water. To prevent widespread crop failure, the concept of protective irrigation implying a limited water supply to agricultural lands, has been introduced. Consequently, crops suffer from moisture stress (Tyagi et al., 2003) and to this fact overall low productivity has been traced in many irrigation projects. Yet, spectacular results have been obtained when canal water is supplemented with groundwater (Dhawan, 1989). Since groundwater in many parts of arid and semi-arid regions is saline/sodic, groundwater has not been exploited for fear of adverse effects on crops and/or soils. Consequently, farmers switched over to less water requiring crops or crops that are more tolerant to salts. Earlier works related to the use of saline water in agriculture, however, proved the potential of these waters as a source of
irrigation in conjunction with fresh water (Vyas et al., 1986; Singh et al., 1992; Minhas, 1998; Oster and Grattan, 2002). The objectives of this paper are (i) to quantify the adverse effect of moisture stress in low rainfall years on wheat productivity in semi-arid regions and (ii) to prove that saline water can be beneficially used to supplement the canal water. Besides substantial increase in production, this strategy would lend sustainability to the agricultural production.
2.
Materials and methods
A field experiment was conducted during November 2000 to April 2003 at the experimental farm of the Raja Balwant Singh College, Agra, located at 27.98E longitude and 27.28N latitude, and 163 m above mean sea level. Agra is located in a semi-arid region with monsoon climate. The average annual rainfall in this region was 665 mm for the period 1973–2002. Around 80% of the total rainfall occurs during June–October while the
* Corresponding author. Tel.: +91 184 2292730/2294730; fax: +91 184 2290480. E-mail address: [email protected] (S.K. Gupta). 0378-3774/$ – see front matter # 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.agwat.2007.10.007
254
agricultural water management 95 (2008) 253–258
Table 1 – Physico-chemical properties of the soil before starting the experiment Horizon A1 A3 B2-1t B2-2t B3-Ca C
Depth (m)
pH2
ECse (dS/m)
CEC (cmol/kg)
Textural class
K (mm/h)
0.00–0.20 0.20–0.45 0.45–0.72 0.72–1.15 1.15–1.40 1.40–1.80
8.5 8.5 8.6 8.5 8.6 8.6
8.5 2.6 3.2 2.0 2.5 4.5
12.8 12.6 14.4 14.8 14.8 14.7
Sandy loam Loam Clay loam Clay loam Sandy loam Loam
11.5 6.5 6.0 6.0 8.1 18.2
Bulk density (Mg/m3) 1.45 1.52 1.52 1.51 1.44 1.42
ECse = EC of saturation extract, CEC = cation exchange capacity, K = saturated hydraulic conductivity.
remaining 20% occurs during the rest of the year. The rainfall fluctuated during the wheat growing seasons and was the lowest in 2000–2001 (27.6 mm) while it was relatively high and well distributed in 2001–2002 (67 mm) and 2002–2003 (48.7 mm). The soil of the site is of alluvial origin, and neither saline nor alkaline (Table 1). The permeability is fair and the vertical movement of water is not noticeably impeded. During the study period (April 2000 to June 2003), the water table fluctuated between 5.6 m (October) and 7.7 m (April) below the soil surface. Owing to the relatively large depth of the water table, groundwater contribution to crop water use was almost negligible. Micro-plots of (2.5 m 2.5 m), separated by polythene sheets to a depth of 90 cm on all four sides of each plot to prevent horizontal movement of water, were used for the study. Wheat (cv. Raj. 3077) was sown in November each year and was harvested during March of the next year. The saline water, which was used to supplement the best available water (BAW) was prepared artificially by dissolving CaCl2, MgCl2, MgSO4, NaCl and Na2SO4 in BAW such that the Ca:Mg ratio was 1:1.6 and the Cl:SO4 ratio 3:1 with SARiw = 10 mmol0.5/l0.5. The electrical conductivity (ECiw) of BAW was 3.2 0.6 dS/m. Wheat is sensitive to moisture deficit at the crown root initiation (CRI) and as such, irrigation is considered essential at this stage (Anonymous, 1975; Gajri and Prihar, 1988). Further, wheat is also sensitive to salt stress at the germination and establishment stage (Minhas and Gupta, 1992; Naresh et al.,
1993). Tyagi et al. (2003) observed that on an average, only 7–8 cm of water or the equivalent of one irrigation was available at the tail end of the Bhakra canal system. Considering these findings, it was decided to apply pre-sowing irrigation with BAW in all the treatments and apply at least one irrigation at CRI with BAW in nine treatments. In all, 12 treatment combinations were set up (Table 2) to test the effect of saline water as supplement to the fresh water application on wheat growth. The experiment was laid out in a randomized block design (RBD) with four replications. A pre-sowing irrigation of 7 cm with BAW was common to all the treatments. Depending upon the rainfall and climatic conditions the number of post-sown irrigations varied from 1 year to another. A total of five irrigations during 2000–2001 and four irrigations during 2001–2002 and 2002–2003, each of 7 cm depth, were applied in all the treatments except T2 to T4 (Table 2). Nitrogen (N) as urea, phosphorus (P) as single superphosphate and potassium (K) as muriate of potash were applied at the recommended rate of 120, 60 and 60 kg/ha. Plant parameters, viz. germination percentage, plant height and number of ears per plant were studied. Counted seeds were sown in each row of each plot. Three rows of each plot were selected and germinated seeds were counted at 8, 10 and 12 days. Since there was no change in germination at 10 and 12 days, the germination count at 10 days was used to calculate the average germination percentage in each treatment by dividing the germinated seeds by the total number of
Table 2 – Detail description of the treatments Number of irrigationsa
Treatment 2000–2001 T1 (All BAW) T2 (BAW at CRI) T3 (BAW at CRI and milking) T4 (BAW at CRI, jointing and milking) T5 = T2 + saline water ECiw = 6/8 dS/m T6 = T2 + saline water ECiw = 12 dS/m T7 = T3 + saline water ECiw = 6/8 dS/m T8 = T3 + saline water ECiw = 6/8 dS/m T9 = T4 + Saline water ECiw = 6/8 dS/m T10 = T4 + saline water ECiw = 12 dS/m T11 = All irrigations with saline water ECiw = 6/8 dS/m T12 = All irrigations with saline water ECiw = 12 dS/m
5 1 2 3 5 5 5 5 5 5 5 5
(4) (4) (3) (3) (2) (2)
2001–2002 4 1 2 3 4 4 4 4 4 4 4 4
(3) (3) (2) (2) (1) (1)
2002–2003 4 1 2 3 4 4 4 4 4 4 4 4
BAW: best available water; water salinity was 6 and 12 dS/m during 2000–2001 and 8 and 12 dS/m during 2001–2002 and 2002–2003. Values in parentheses indicate number of saline water irrigations. The number of irrigations was the same except in T2, T3 and T4.
a
(3) (3) (2) (2) (1) (1)
255
NS 2.2 2.4 NS 0.5 0.7 NS Some variation in values is due to different DAS during the 3 years; SD = significant difference.
1.6 6.7 3.6 2.5 4.5 NS NS SD ( p = 0.05)
NS
37.3 35.9 37.1 37.9 36.9 36.6 37.2 35.5 37.2 35.3 36.3 34.7 38.1 33.8 34.1 34.6 35.6 35.3 37.1 35.9 37.8 37.7 35.6 34.9 33.4 16.5 22.1 25.6 30.8 28.3 30.5 28.0 31.7 31.7 32.8 29.8 8.0 7.4 7.6 7.7 7.7 7.5 7.7 7.6 7.9 7.7 7.9 7.5 8.1 7.4 7.5 7.5 7.7 7.7 7.8 7.5 7.9 7.9 7.8 7.5 7.6 6.4 7.0 7.6 7.3 7.0 7.3 7.1 7.6 7.5 7.2 7.1 91.0 89.1 86.3 89.2 93.3 86.6 88.4 92.6 90.8 93.2 89.6 86.5 88.6 84.1 87.0 87.2 88.2 84.5 88.5 85.8 88.0 86.1 85.8 82.8 109.3 78.2 93.7 96.0 106.6 112.0 107.2 106.6 107.9 107.2 106.6 104.5 44.2 40.3 41.9 42.2 40.4 41.7 43.8 41.1 39.8 41.0 39.7 39.6 57.2 52.3 55.6 56.0 56.6 54.5 56.9 56.1 57.2 56.5 56.9 54.4
Ear length (cm)
2000–2001 2001–2002 2002–2003 2000–2001 2001–2002 2002–2003 Harvest (128–141 days) Mid-stage (60–70 days)
56.4 44.7 45.0 53.7 54.2 53.7 55.9 54.6 55.1 53.8 54.0 48.4 91 89 86 89 93 86 88 92 90 93 89 85 91 75 76 82 84 84 80 84 84 84 78 75 97 95 92 93 98 98 95 97 91 87 97 97 T1 T2 T3 T4 T5 T6 T7 T8 T9 T10 T11 T12
The yield attributing characteristics such as ear length in 2001–2002 and numbers of grain per ear head at harvest in 2000–2001 and 2001–2002 in T2 differed significantly over T1 and were significantly higher in T5 over T2 in 2000–2001. In the year 2001–2002, the differences in the ear length were significant in T12 over T1 although no differences were observed in the year 2002–2003 (Table 3). These differences could be attributed either to moisture or salt stress. Almost similar results were obtained for the number of grains per ear. Besides, there was significant improvement in the numbers of ears with supplemental irrigation over the respective
2000–2001 2001–2002 2002––2003 2000–2001 2001–2002 2002–2003
Yield attributing characteristics
2002
3.2.
2001
The germination did not vary between treatments over the years (Table 3). Although, soil salinity was enhanced wherever saline water was applied, i.e. from T5 onwards, it was not high enough to affect germination during the next season. Presowing irrigation with BAW in all the treatments had played an important role in reducing the salt level in these cases. As such, the difference in yield could be attributed only to moisture or salt stress after initial crop rooting. The plant height recorded at mid-stage (60–70 days) as well as at harvest (128–141 days) differed significantly amongst treatments in 2000–2001 and 2001–2002. It was significantly lower at mid-stage in T2 and T3 in 2000–2001 and in T2 in 2001–2002 than in T1 resulting from moisture stress. Similarly, at mid-stage it was significantly lower in T12 where all irrigations were given with water having ECiw of 12 dS/m than in T1 in all the years. In 2001–2002 even at harvest, the height in T12 was significantly less than in T1. It could mainly be attributed to salt stress since the number of irrigations was equal in both treatments. Apparently, both moisture stress and salt stress gave an initial setback to the crop.
2000
Germination and growth characteristics
Plant height (cm)
3.1.
Germination (%)
Results and discussion
Table 3 – Germination count, plant height, ear length and number of grains per ear of wheat under different treatments
3.
Treatments
seeds in 12 rows, 3 rows each of four replications. Plant height, ear length and number of grains per ear were studied by selecting five plants in each plot. The average values of 20 plants per treatment were worked out and reported. Grain and straw yields of the plots were recorded. On the basis of average yield of the four replications, relative yields of all the treatments were computed as a percentage of the four replications of treatment T1. Four soil samples from one location at the center of each replication were collected at sowing and harvest at 15 cm interval down to 30 cm and 30 cm interval down to 90 cm soil depth, air-dried, ground, passed through a 2 mm sieve and the electrical conductivity of a saturation paste extract (ECse) measured. Soil moisture was determined gravimetrically at sowing, before and after each irrigation and at harvest. Statistical analysis was carried out according to the standard procedure reported in Gomez and Gomez (1984). Pairs of treatments were compared for significant difference using the t-test. They are significantly different when their difference exceeds the computed significant difference SD.
Number of grains/ear
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Table 4 – Grain and straw yield (t haS1) of wheat under different treatments Treatments
2000–2001
2001–2002
2002–2003
Mean yield
Grain
Straw
Grain
Straw
Grain
Straw
Grain
T1 T2 T3 T4 T5 T6 T7 T8 T9 T10 T11 T12
5.47 1.37 2.88 3.74 5.32 5.06 5.38 5.26 5.52 5.44 5.45 4.64
8.33 4.28 5.38 6.57 8.12 7.77 8.20 8.16 8.32 8.20 8.04 7.03
5.72 4.54 4.53 4.84 4.95 4.83 4.92 4.91 5.37 4.66 5.05 4.72
9.75 8.48 8.85 9.04 9.21 8.80 9.27 8.54 9.53 8.87 9.05 8.23
5.19 4.50 4.83 4.95 4.96 4.77 4.93 4.78 5.14 4.94 5.10 4.69
8.32 7.30 7.62 7.78 8.18 7.89 8.15 7.87 8.12 7.86 8.21 7.62
5.46 3.47 4.08 4.51 5.08 4.89 5.08 4.98 5.34 5.01 5.20 4.68
8.80 6.69 7.28 7.80 8.50 8.15 8.54 8.19 8.66 8.31 8.43 7.63
SD ( p = 0.05)
0.33
0.45
0.57
0.63
0.27
0.52
–
–
treatments. For example, the increase was significant in treatments T5 and T6 over T2 and T7, T8 over T3 and T9 and T10 over T4 in the year 2000–2001.
3.3.
Grain and straw yield
The grain and straw yield data of all the 3 years are reported in Table 4. The highest yield was recorded for T1 where only BAW was applied for all irrigations. The limitation of the fresh water supply in one irrigation at CRI stage only (T2), two irrigations at CRI and milking stages (T3) and three irrigations at CRI, Jointing and milking stages (T4) resulted in moisture stress and yield reduction, at least in low rainfall years as in 2000– 2001. The yield in this year increased with increasing number of fresh water irrigations and the order of yield was T2 < T3 < T4 < T1. The adverse effect of moisture stress was minimised in 2001–2002 with a rainfall of about 67 mm and in 2002–2003 with a rainfall of about 49 mm together with cloudy weather for quite a long period. As a result, treatments T2, T3 and T4 showed small variations. However, the average yield reduction over 3 years compared with T1 was 36, 25 and 17% for T2, T3 and T4, respectively. Almost similar results were obtained for the straw yield. These results are in conformity with the results obtained by Mishra et al. (1995). Since fresh water is limited in arid and semi-arid regions, it is not possible to apply the optimum number of irrigations. In such instances, saline groundwater can be used to provide the optimum number of irrigations after a limited number of irrigations with fresh water to obtain a higher yield than without supplemental irrigations with saline water. The data for treatments T5, T7 and T9 where saline waters with an ECiw of 6 dS/m (2000–2001) and 8 dS/m (2001–2002 and 2002–2003) were used clearly substantiates this. The yield in all these treatments was on a par with treatment T1. It seems that an ECiw of 8 dS/m is within the tolerable limit for wheat. Similarly, when using water with ECiw of 12 dS/m in treatments T6, T8 and T10, the mean yields of grain and straw ranged between 89 and 94% of the yield in treatment T1. The supplemental irrigations with ECiw of 12 dS/m enhanced the mean grain yield in T6 over T2 by 41%, in T8 over T3 by 22% and in T10 over T4 by 11%. Although the yield of T6 was significantly different from the yield of T1 in each of the 3 years, there were almost no
Straw
differences in the mean yield of T8 and T10 over the 3 years. Apparently, it justifies supplemental irrigations with water with ECiw of 12 dS/m at one or two stages following irrigations with fresh water. Another observation from this study is that the yield of T12 where all irrigations were given with a water salinity of 12 dS/m was on a par with T2, T3 and T4 in 2001–2002 and 2002–2003 and substantially greater in the abnormal dry year 2000–2001. The average yield of T12 over 3 years was slightly higher than that of T4 where three irrigations with BAW were applied. Moisture stress seems more harmful than salt stress. Consequently, even water of a relative high salinity can be used for supplemental irrigations when fresh water is limited.
3.4.
Soil salinity
The average soil salinity over 3 years at harvest for some selected treatments is presented in Fig. 1. The salt build-up was minimal in treatments T2 followed by T3, T4 and T1. The salinity increased wherever saline water was applied (T5 to T12) although the magnitude varied with water salinity and
Fig. 1 – Soil salinity build-up as a result of supplemental irrigations with saline water.
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Table 5 – Rainfall pattern in winter months (December–March) at Agra during the last 30 years Rainfall range (mm) Number of years for rainfall range % of total number of years of record
<10 3 10
10–20 4 13
the number of irrigations with saline water. Similar results were reported by Gupta (1985). On an average basis, the highest salinity (14.5 dS/m) occurred in T12 where all irrigations were applied with water having an ECiw of 12 dS/m. For all other treatments, soil salinity was within the range determined by the curves of treatments T2 and T12. In general, the ECse values decreased with soil depth and were lowest at a depth of 60–90 cm. The data on soil salinity confirm the observation that moisture stress caused a yield decline in treatments without supplemental irrigation with saline water. When applying supplemental irrigation with saline water, the yield decline should be attributed to osmotic stress. At the onset of the monsoon following wheat harvesting, the salts accumulated in the root zone get leached. Within the month of July, the salt status of the soil profile is such that, in most cases, a kharif (monsoon season) crop can be grown when rainfall is supplemented with best available water. During the study period, the monsoon rainfall did not leach all accumulated salts and a slightly higher salinity prevailed in treatments T5 to T12, yet it did not affect the germination (Table 3). On the basis of long-term studies conducted (Sharma et al., 1994, 2001), it has been observed that, in monsoon climatic regions with an average annual rainfall exceeding 500 mm, more than 80% of the salts accumulated during wheat cultivation gets leached without any long-term increase in the soil salinity.
4.
Rainfall and production sustainability
Analysis of rainfall data for the last 30 years at Agra gauging station revealed that in 23% of the years, wheat production is likely to be adversely affected in the absence of supplemental irrigations, as the rainfall could be less than 20 mm during the growth period of wheat (Table 5). In 47% of the years, it might be slightly affected depending upon the amount and distribution of the rainfall during the crop growth period. In 30% of the years, it is likely that the crop might not be affected, even if limited fresh water is applied to the crop. As a result, sustainability of crop production is always uncertain because at least once in 4 years crop would be adversely affected. With such a scenario, saline groundwater, which is an assured source of water, offers an opportunity to supplement the canal water. The results reveal that if the salinity of groundwater is less than 8 dS/m, it could be applied as supplemental post-plant irrigations. If the groundwater salinity ranges between 8 and 12 dS/m, the water can be used for at least two post-plant irrigations and crop yield would still be more than or equal to 90% of the crop yield obtained with irrigations with low salinity water. The yield would certainly be more than when irrigations were skipped. Besides, this strategy would lend sustainability to the crop
20–30 6 20
30–40 8 27
40–50 1 3
>50 8 27
production programme, even in the absence of adequate fresh water supplies.
5.
Conclusion
From this study, it can be concluded that saline groundwater is a good source to exploit for irrigation. In wheat cultivation, saline groundwater with an ECiw of 6–8 dS/m can be used to supplement all irrigations except the pre-sowing irrigation (T5, T7, T9 and T11). Saline water with an ECiw of 12 dS/m can be used for at least two supplemental irrigations (T8) without any adverse effect on crop yield. The limited amount of available fresh water should be applied during the initial growth stage and supplemented with saline water at later growth stages. This strategy enables wheat production with saline water with an ECiw up to 12 dS/m giving a yield as high as 90% of the optimum crop yield obtained with low salinity water (T1).
references
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Sharma, D.P., Singh, K.N., Kumbhare, P.S., 2001. Reuse of agricultural drainage water for crop production. J. Indian Soc. Soil Sci. 49, 483–488. Singh, R.B., Minhas, P.S., Chauhan, C.P.S., Gupta, R.K., 1992. Effect of high salinity and SAR waters on salinization, sodication and yield of pearl millet and wheat. Agric. Water Manage. 21, 93–105. Tyagi, N.K., Sakthivadivel, R., Sharma, D.K., Ambast, S.K., Agrawal, A., 2003. Farmers decision making in irrigation
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