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Response of onion (Allium cepa L.) to different levels of irrigation water
agricultural water management 89 (2007) 161–166
available at www.sciencedirect.com
journal homepage: www.elsevier.com/locate/agwat
Response of onion (Allium cepa L.) to different levels of irrigation water Satyendra Kumar a,*, M. Imtiyaz b, Ashwani Kumar c, Rajbir Singh a a
Central Institute of Post Harvest Engineering and Technology, Abohar 152116, Punjab, India College of Agricultural Engineering, Allahabad Agricultural Institute (Deemed University), Allahabad 211007, India c Water Technology Center for Eastern Region, Bhubaneswar 751023, India b
article info
abstract
Article history:
The study analyses the response of onion to different irrigation levels with microsprinkler
Accepted 11 January 2007
irrigation system. The four treatments comprised different ratio of irrigation water (IW) to cumulative pan evaporation (CPE) namely 0.60 (T1), 0.80 (T2), 1.0 (T3) and 1.20 (T4). Irrigation
Keywords:
had significant effect on growth parameters of onion and subsequently influenced the crop
Irrigation
yield. The best yields were recorded from T3 and T4, associated with the higher percentage of
Water use efficiency
bulbs having diameter greater than 45 mm. Protein content in bulbs was highest when
Bulb yield
associated to T1, but the loss in marketable produce during the storage was also highest in
Yield characteristics
T1. Irrigation water use efficiency and water use efficiency both were highest in T2 and then declined with the increase in irrigation. Hence, in water constraint situation, T2 would be the
Onion
most appropriate irrigation level for onion production with microsprinkler irrigation system. Production functions of yield versus irrigation water applied and yield versus crop evapotranspiration were found to be polynomial. The developed functions can be used as a guide to yield potential allocation decision related to limited irrigation water. # 2007 Elsevier B.V. All rights reserved.
1.
Introduction
India is the second largest producer of onion (Allium cepa L.) after China, but the average yield (10.38 t/ha) is considerably lower than world’s productivity of 18.08 t/ha (www.fao.org//, 2005). Many reasons could be attributed to low productivity, but poor water and nutrient management practices contribute significantly (Palled et al., 1988). Being a shallow-rooted crop, onion is sensitive to water stress and requires frequent and light irrigation to avoid water deficiency and to adequately recharge the plant root zone (Koriem et al., 1994). Few research studies have been conducted to characterize an appropriate irrigation level for onion, but the irrigation water management varies with soil-agro-climatic condition and with irrigation systems. Few studies have been examined the irrigation
criteria for drip irrigated onions (Shock et al., 1998; Chopade et al., 1998; Martin de Santa Olalla et al., 2004) which indicated that the best yields occur when soil was constantly moist and irrigation should cease 2 weeks before harvest to prevent rotting and sprouting during storage. However, information is not available about microsprinkler irrigation scheduling of onion especially under semi-arid climate. Further, this study was planned with the assumption that microsprinkler with an appropriate irrigation schedule may protect the crop from adverse climate like frost during winter and desiccating wind during summer. With this background, the present study was undertaken to characterize the use of microsprinkler irrigation and to contrast the effects of different irrigation levels on yield and yield characteristics of onion, water use efficiency as well as growth response of onion.
* Corresponding author. Tel.: +91 1634 225313. E-mail address: [email protected] (S. Kumar). 0378-3774/$ – see front matter # 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.agwat.2007.01.003
162 2.
agricultural water management 89 (2007) 161–166
Materials and methods
The investigations were carried out during winter/summer crop growing season (January–May) of 2004 and 2005 at the research farm of Central Institute of Post Harvest Engineering & Technology, Abohar, Punjab, India (308090 N, 748130 E, 185.6 m above mean sea level). The region experiences semi-arid climate with extremely hot during summers and cold during winters. The average temperature, relative humidity, wind speed and pan evaporation rate during first year ranged from 10 to 37.8 8C, 29–91%, 0.3–2.0 m/s and 1.5–8.5 mm, respectively, and in second year, these parameters were varied, respectively, from 7.5 to 35.3 8C, 35–94%, 0.1–1.80 m/s and 1.3–7.6 mm during the crop growing season. Rainfall during crop growing season was recorded as 27 and 36 mm in first and second year, respectively. The percentage of sand, silt and clay in the experimental soil were 76.5, 15.4 and 8.1, respectively. Field capacity, wilting point and bulk density of top 30 cm of the soil were 11.5%, 3.9% and 1.5 g/cm3. The soil available water was 11.7 cm/m. The concentrations (kg/ha) of N, P2O5 and K2O were 51.1, 12.5 and 265.6, respectively. The soil had an organic matter concentration of 0.34%. The treatment consisted of four levels of irrigation on the basis of ratio of irrigation water (IW) to cumulative pan evaporation (CPE). These ratios were 0.60 (T1), 0.80 (T2), 1.00 (T3) and 1.20 (T4). CPE was computed as sum of daily evaporation of USWB class-A open pan. The pan was located adjacent to the experimental field with moderate grass cover. The total available water (TAW) to the plant was estimated as the difference between field capacity and permanent wilting point. In this investigation, root zone depth of onion was taken as 30 cm. Hence, total available water (rooting depth in m plant available water in mm/m) was estimated as 35.10 mm. The readily available water (RAW) was determined as RAW = TAW p, where permissible soil water depletion level ( p) was taken 30% as reported by Orta and Ener (2001) for higher yield of onion. As a result of the above, RAW was found to be 10.50 mm. This value was taken as the maximum irrigation dose (depth of water in each irrigation) to be applied during the experimental season. Water use assessed as crop evapotranspiration, was calculated using the water balance model (Eq. (1)) under variable irrigation (Simsek et al., 2005): ETc ¼ IW þ P D R DS ðETc ¼ kp E; kp : 0:60; 0:80; 1:0 and 1:20Þ
(1)
where ETc is the seasonal crop evapotranspiration, kp the crop pan coefficient (irrigation treatment; 0.60: T1, 0.80: T2, 1.0: T3 and 1.20: T4, respectively), E the evaporation, P the precipitation, D the drainage, R the runoff and DS is the variation in water content of the soil profile. All terms are expressed in mm of water in the onion root zone. Soil moisture content of different soil layer was estimated by gravimetric method. The change in soil water contents of 30–90 cm soil layer was considered to be deep percolation. Run-off was taken to be zero since it did not occur with the use of microsprinkler irrigation system. Observation for dry matter accumulation started after 45 days of transplanting and continued up to 105 days at 15
days interval. Destructive sampling was done, plants were divided into two parts, i.e. biomass (above ground part) and bulb (below ground part), and were cut into small pieces and dried at 70 8C to a constant weight for estimation of dry matter. Leaf water content was estimated from leaf fresh weight and leaf dry weight (Bonnet et al., 2000). Matured crop was harvested after 120–125 days of transplanting for estimation of onion yield. For estimation of mean bulb weight, 1.5 m 1.5 m area was earmarked in each plot and from total weight and number of harvested bulbs, mean bulb weight was determined. Similarly, 5 kg sample of onion bulbs was taken randomly from each treatment combination for measuring polar and equatorial diameter using vernier caliper. Mean size of bulb was presented as square root of polar and equatorial diameter. For grading, onion bulbs were classified into four categories on the basis of size of bulb: A, with size > 60 mm; B, with size 60–41 mm; C, with size 40–30 mm; D, with size < 30 mm under each irrigation treatment. Total soluble solids (TSS) was estimated using hand held refractometer (0–50 8B, ERMA, Japan). Percentage protein in the bulbs was estimated by using spectrophotometer (Spectron 20) by following standard procedure (AOAC, 2000). In order to estimate loss in marketable yield during storage, field cured onion bulbs with a sample size of 20 kg were stored on cemented floor in loose at room temperature. The average room temperature varied between 27–32 and 25–31 8C during the first and second year storage period, respectively. The observation on loss in marketable yield was recorded at 15 days interval till 90 days of storage. Loss in marketable yield included loss in weight as well as rotting. Rotted bulbs were considered unsuitable for consumption and were taken for loss in marketable yield count. Irrigation water use efficiency (IWUE) was estimated as the ratio of crop yield, Ya (kg/ha) and irrigation water applied (IW), in mm (Stanhill, 1986). IWUE ¼
Ya IW
(2)
WUE was obtained as crop yield per unit seasonal ET (ETc) WUE ¼
Ya ETc
(3)
Onion seedlings (Agrifound Light Red) were transplanted on 18th January in each year with plant and row spacing of 0.1 m 0.15 m. Prior to installation of the microsprinkler irrigation system, test runs were carried out to verify the rated design discharge of microsprinklers. The average discharge of microsprinkler was 63.10 lph at 1.20 kg/cm2 operating pressure. The microsprinklers were placed at 3 m. The area of each experimental plot was 36 m2 (6 m 6 m). A buffer zone with spacing of 1.0 m was provided between the plots. The experiment was laid out in randomized block design (RBD) with four replications. The data were analyzed statistically by standard analysis of variance (ANOVA). Least significant difference (LSD) test was used to determine whether differences existed between certain comparisons. The probability level for determination of significance was 0.05.
agricultural water management 89 (2007) 161–166
3.
Results and discussion
3.1.
Irrigation water applied and water use
The irrigation water applied to T1, T2, T3 and T4 were, respectively, 275, 343, 407 and 468 mm for first year and 257, 315, 389 and 451 mm in second year. Before the start of treatment, crop received equal amount of water, i.e. 61 and 52 mm, respectively, in first and second year, for proper establishment of seedlings. Thereafter, treatment commenced and stopped when 50% of the crop in a plot showed neck fall. The crop evapotranspiration (ETc) during the crop growing period (after establishment of crop) were determined to be 234, 292, 347 and 380 mm in first year and 217, 279, 323 and 349 mm in second year for T1, T2, T3 and T4, respectively. Hence, the values of IW for T4 were found to be higher than ETc values in both years. ETc < IW in T4 was due to the fact that the water applied to the plants in this regime was higher than the crop’s need and occurrence of deep percolation. The values of ETc and IW during the period of variable irrigation were almost similar (IW = 342; ETc = 335; average of 2 years) in T3. However, the IW values were found to be smaller than ETc in T1 and T2. Thus, it could be said that the water extracted by the crops from the soil in these treatments was higher than the water applied.
3.2.
163
Fig. 1 – Soil moisture content under different irrigation treatments in 0–0.30 m soil depth (second year).
weight per plant might be attributed to variation in size of bulb. Martin de Santa Olalla et al. (1994) indicated that bulb diameter and height are directly related to amount of water applied. Leaf water content (LWC) was measured at mid growth stage of plant in order to show the average LWC and minimize
Soil moisture
Fig. 1 indicates greater depletion in available soil moisture with treatment T1, which was probably due to insufficient irrigation. In treatment T4, soil moisture content remained closer to field capacity because of the highest irrigation. However, irrigation in T3 also seems to be sufficient as soil moisture depletion was often found in the range of 25 10% of available soil moisture.
3.3.
Growth dynamics
The trend of growth parameters with different levels of irrigation water was similar in both the years. Therefore, graphical presentation of data has been done with the mean values of two consecutive seasons to draw the inferences. The cumulative trends of the vegetative growth parameters (i.e. plant height, number of leaves, neck thickness, etc.) were similar to the biomass produced (Fig. 2a). Results indicated that biomass dry weight per plant influenced with the amount of water applied and varied between the treatments directly due to the variation in vegetative growth parameters. Fig. 2a shows that it increases through out the growing season up to 90 DAT for each treatment. After 90 DAT, biomass dry weight per plant decreased slightly in T3 and T4, while biomass reduced significantly in T1 due to the loss of dry leaves. Bulb dry weight per plant increased progressively up to 105 days in T3 and T4 while, a little difference in bulb dry weight was observed in T1 at 90 and 105 DAT (Fig. 2b). Bulb dry weight was almost similar which shows an early maturity in T1 than the other treatments. The analysis of variance for each sampling after 60 DAT showed significant differences between the treatments except T3 and T4, which were related to the soil moisture availability to the crop. The variation in bulb dry
Fig. 2 – Measured values of: (a) biomass dry weight and (b) bulb dry weight per plant at different growth stages under different irrigation treatments; vertical bars indicate WM.S.E.; values averaged over 2 years (2004–2005).
164
agricultural water management 89 (2007) 161–166
Table 1 – Onion yield, irrigation water use and water use efficiencies for different irrigation treatments Year
Treatment
Onion yield (t/ha)
IW (mm)
ETc (mm)
IWUE (kg/ha mm)
2004
T1 T2 T3 T4
19.20 26.40 30.88 33.63
275.32 342.87 407.40 467.75
233.62 291.50 346.50 379.93
69.74 76.99 75.80 71.90
82.18 90.56 89.12 88.52
2005
T1 T2 T3 T4
20.44 28.43 32.83 34.40
257.15 315.11 389.20 451.34
217.41 278.73 323.11 348.73
79.48 90.22 84.35 76.22
94.01 101.99 101.60 98.64
the age effects. Leaf water content (%) values for T1, T2, T3 and T4 for 2004 were 86.93, 88.46, 89.96 and 90.14, respectively. The corresponding values for 2005 were 87.52, 89.05, 90.41 and 91.34. It appears that LWC increased with increasing irrigation water in both years. The decline in LWC with decreasing irrigation was expected as soil matrix potential increases with water stress (Cha-un et al., 2006).
3.4.
Onion yield and yield characteristics
Slightly higher onion yield was obtained in second year with all treatments. The reason for the differences was attributed to variation in climate. However, statistical analysis of the results showed significant increase in onion yield with increasing irrigation from T1 to T3 in both years (Table 1). The variation in onion yield between the treatments was recorded due to the variation in bulb size and mean weight of bulbs. Chung (1989) reported that water stress during critical growth period causes reduction in onion size and weight of bulbs. The onion yield in T3 and T4 was found to be nonsignificant which was probably due to the fact that irrigation in T3 was adequate to provide sufficient soil moisture for optimum onion production. These results are in agreement with Orta and Ener (2001). The yield reduction in T1 and T2 from the optimum yield (T3) was 37.71 and 13.82%, respectively. Fig. 3 shows the percentage of bulbs according to size for each treatment. It was observed that the percentage of B grade (most preferred size) bulbs was high (above 50%) in T3 and T4.
The least percentage of B and the highest percentage of D (smallest sized bulbs) grade were produced in the most restrictive treatment (T1). However, the lowest percentage of D grade was produced in T4. Similar trend was observed in both years. In general, percentage of B grade bulb decreased and D grade bulbs increased with the decrease in irrigation water. This may be due to the variation in magnitude of water stress under variable irrigation. A similar effect of irrigation on size of onion bulb was also observed by Martin de Santa Olalla et al. (2004) under drip irrigation system. Similarly, mean bulb weight was also influenced positively by irrigation water (Table 2). Mean bulb weight varied significantly between the treatments except T3 and T4. Least irrigation (T1) produced the minimum mean bulb weight due to higher percentage of smaller sized (D-grade) bulbs for both the years. Protein content in onion bulb decreased with increasing irrigation level (Table 2). The highest protein content found in T1 was statistically at par with T2. The least protein content was recorded in T3 for 2004 and in T4 for 2005. El-Gizawy et al. (1993) have also observed similar results and reported that total protein content increased significantly with the decreasing soil moisture. The total soluble solids of onion bulb increased with the increase in irrigation from T1 to T3 in year 2004, while in year 2005, irrigation had no significant effect on TSS (Table 2). Change in TSS with irrigation may probably be due to fulfillment of crop water demand and better utilization of nutrient under optimum soil moisture availability. Though, results are in accordance with Chopade et al. (1998), who reported higher TSS in onion with optimum application of water. However, Orta and Ener (2001) observed different trend. Loss in marketable yield (MYL) was significantly higher in irrigation treatment T1 in both years (Table 2). The higher MYL in T1 was observed might be due to early rotting of onion bulb. Results revealed that crop grown under T1 had shown early maturity and resulted into development of either immature or partial matured bulbs, which started rotting during storage at an early date. Ali and Elshabrawy (1971) have observed increased incident of neck rot disease in early harvested onion bulbs during storage, which resulted in higher MYL.
3.5.
Fig. 3 – Percentage of different sized bulbs under different irrigation treatments.
WUE (kg/ha mm)
Water use efficiency
Irrigation water use efficiency and water use efficiency (WUE) of onion obtained for different treatments are presented in Table 1. Treatment T2 gave the maximum IWUE in both years, while the least IWUE was recorded in T1 in first year and in T4
165
agricultural water management 89 (2007) 161–166
Table 2 – Post-harvest attributes of onion under different irrigation treatments Treatment
Mean bulb weight (g) 2004
T1 T2 T3 T4
29.09a 39.40b 46.98c 51.05 c
2005 a
30.69 44.42 b 49.74 c 52.12 c
Protein (g/100 g) 2004 c
1.04 1.02b c 0.98 a 1.00 ab
TSS (8B)
2005
2004
bc
a
1.03 1.02 ab 1.01 a 1.00 ab
13.10 13.30 ab 13.50 b 13.10 a
Loss in marketable yield (%) 2005 a
13.20 12.90 a 13.30 a 13.00 a
2004 b
17.02 15.04 a 14.76 a 14.21 a
2005 15.62 b 13.31 a 12.81 a 13.59 a
Numbers followed by same letters under same heads in a column are statistically non-significant by LSD test at p 0.05.
in second year. Highest IWUE (76.99 and 90.22 kg/ha mm) reveals that water was used most effectively in T2. IWUE declined in T3 and T4 because, improvement in yield (16.04 and 24.03%) was less than the percentage increase in irrigation water (21.06 and 39.68%) as compared to T2. By and large, IWUE is the function of crop yield and water applied and decreased with increasing irrigation. Water use efficiency was also highest in T2 (90.56 and 101.99 kg/ha mm), but reduction in WUE with T3 was not significant (89.12 and 101.60 kg/ha mm). This result indicated that increase in yield was almost linear with ETc up to treatment T3. The overall results indicated that deficit and excess irrigation both did not show significant effect on yield and water use efficiencies. Chopade et al. (1998) and Imtiyaz et al. (2000) also reported similar findings. Relationships between yield (Y) and irrigation water applied (IW) and crop evapotranspiration (ETc) were
determined yield was against IW (Fig. 4a and
3.5.1.
through non-linear regression analysis. Onion taken as dependent variable and plotted and ETc to derive mathematical functions b).
Relationship between IW and Y
Year 2004 : Y ¼ 0:0002IW2 þ 0:2524IW 32:11
(4)
Year 2005 : Y ¼ 0:0004IW2 þ 0:3639IW 45:52
(5)
3.5.2.
Relationship between ETc and Y
Year 2004 : Y ¼ 0:0003ETc2 þ 0:2513ETc 25:73
(6)
Year 2005 : Y ¼ 0:0004ETc2 þ 0:3093ETc 29:93
(7)
Correlation coefficients were found to be 0.91, 0.89, 0.92 and 0.93, respectively, for Eqs. (4)–(7), which was statistically significant. Linear effects in the determined relationships were all positive, while the quadratic effects were all negative. These results indicated that the increase in onion yield was not proportional with the increment in amount of irrigation water. The developed relationship can successfully be used for predicting onion yield under similar agro-climatic condition without conducting tedious crop experiments. These equations can also be used as guide to yield potential allocation decision related to limited irrigation water.
4.
Fig. 4 – The relationship between: (a) onion yield (Y) and irrigation water and (b) onion yield (Y) and crop evapotranspiration (ETc) for 2004 and 2005, respectively.
Conclusions
Results of the study indicated that irrigation water had significant influence on response of microsprinkler irrigated onion. Irrigation water influenced the yield with different grades of onion bulbs. Percentage of bulbs (<30 mm in diameter) was found to be less than 5% when irrigation water was adequate (T3–T4). T3 and T4 gave the highest yield. Maximum protein content was recorded in the bulbs grown under most restrictive treatments, but weight loss during storage was also highest. Irrigation water use efficiency was highest in T2, which indicates most efficient utilization of water with microsprinkler irrigation system. Hence, if water becomes limiting factor, T2 would be most appropriate irrigation level for growing onion with microsprinkler irrigation system in a semi-arid climate.
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agricultural water management 89 (2007) 161–166
references
Ali, A.A., Elshabrawy, A.M., 1971. Effect of some cultural practices and some chemicals control of neck rot disease caused by Bortrytis alli during storage and in the field for seed onion production in A.R.E. Agric. Res. Rev. Plant Pathol. 57, 103. AOAC, 2000. Official Methods of Analysis, 17th ed. Association of Official Agricultural Chemists, Washington, DC. Bonnet, M., Camares, O., Veisseire, P., 2000. Effect of zinc and influence of Acremonium lolli on growth parameters, chlorophylla fluorescence and antioxidant enzyme activities of ryegrass (Lolium Perenne L.). J. Exp. Bot. 51, 945–953. Cha-un, S., Supaibulwatana, K., Kirdmanee, C., 2006. Water relation, photosynthetic ability and growth of Thai rice (Oryza sativa L.) to salt stress by application of exogenous glycinebetaine and chlorine. J. Agron. Crop Sci. 192, 25–36. Chopade, S.O., Bansode, P.N., Hiwase, S.S., 1998. Studies on fertilizer and water management to onion. PKV Res. J. 22, 44–47. Chung, B., 1989. Irrigation and bulb onion quality. Acta Hort. 247, 233–236. El-Gizawy, M., Abdallah, E.M.H., Mohamed, A.R.G., Abdalla, A.A.G., 1993. Effect of soil moisture and nitrogen levels on chemical composition of onion bulbs and on onion storability after treatment with gamma-radiation. Bull. Faculty Agric. Uni. Calro 44, 169–182.
Imtiyaz, M., Mgadla, N.P., Chepete, B., Manase, S.K., 2000. Response of six vegetable crops to irrigation schedules. Agric. Water Manage. 45, 331–342. Koriem, S.O., El-koliey, M.M.A., Wahba, M.F., 1994. Onion bulb production from ‘‘Shandwell’’ sets as affected by soil moisture stress. Assuit J. Agric. Sci. 25, 185–193. Martin de Santa Olalla, F., Dominguez-padilla, A., Lopez, R., 2004. Production and quality of onion crop (Allium capa L.) cultivated in semi-arid climate. Agric. Water Manage. 68, 77–89. Martin de Santa Olalla, F., Valero, J.A.J., Cortes, C.F., 1994. Growth and production of onion crop (Allium cepa L.) under different irrigation scheduling. Eur. J. Agron. 3 (1), 85–92. Orta, A.H., Ener, M., 2001. Irrigation scheduling of onion in Turkey. J. Biol. Sci. 1 (8), 735–736. Palled, Y.B., Kachapur, M.D., Chandrasekharan, A.M., Prabakar, A.S., 1988. Response of onion to irrigation and nitrogen. Ind. J. Agron. 33 (1), 22–25. Shock, C.C., Feibert, E.B.G., Saunders, L.D., 1998. Onion yield and quality affected by soil water potential as irrigation threshold. Hort. Sci. 33 (7), 1181–1191. Simsek, M., Tonkaz, T., Kacira, M., Comiekcioglu, N., Dogan, Z., 2005. The effects of different irrigation regimes on cucumber (Cucumbis salivus L) yield and yield characteristics under open field conditions. Agric. Water Manage. 73, 173– 191. Stanhill, G., 1986. Water use efficiency. Adv. Agron. 39, 53–85.
available at www.sciencedirect.com
journal homepage: www.elsevier.com/locate/agwat
Response of onion (Allium cepa L.) to different levels of irrigation water Satyendra Kumar a,*, M. Imtiyaz b, Ashwani Kumar c, Rajbir Singh a a
Central Institute of Post Harvest Engineering and Technology, Abohar 152116, Punjab, India College of Agricultural Engineering, Allahabad Agricultural Institute (Deemed University), Allahabad 211007, India c Water Technology Center for Eastern Region, Bhubaneswar 751023, India b
article info
abstract
Article history:
The study analyses the response of onion to different irrigation levels with microsprinkler
Accepted 11 January 2007
irrigation system. The four treatments comprised different ratio of irrigation water (IW) to cumulative pan evaporation (CPE) namely 0.60 (T1), 0.80 (T2), 1.0 (T3) and 1.20 (T4). Irrigation
Keywords:
had significant effect on growth parameters of onion and subsequently influenced the crop
Irrigation
yield. The best yields were recorded from T3 and T4, associated with the higher percentage of
Water use efficiency
bulbs having diameter greater than 45 mm. Protein content in bulbs was highest when
Bulb yield
associated to T1, but the loss in marketable produce during the storage was also highest in
Yield characteristics
T1. Irrigation water use efficiency and water use efficiency both were highest in T2 and then declined with the increase in irrigation. Hence, in water constraint situation, T2 would be the
Onion
most appropriate irrigation level for onion production with microsprinkler irrigation system. Production functions of yield versus irrigation water applied and yield versus crop evapotranspiration were found to be polynomial. The developed functions can be used as a guide to yield potential allocation decision related to limited irrigation water. # 2007 Elsevier B.V. All rights reserved.
1.
Introduction
India is the second largest producer of onion (Allium cepa L.) after China, but the average yield (10.38 t/ha) is considerably lower than world’s productivity of 18.08 t/ha (www.fao.org//, 2005). Many reasons could be attributed to low productivity, but poor water and nutrient management practices contribute significantly (Palled et al., 1988). Being a shallow-rooted crop, onion is sensitive to water stress and requires frequent and light irrigation to avoid water deficiency and to adequately recharge the plant root zone (Koriem et al., 1994). Few research studies have been conducted to characterize an appropriate irrigation level for onion, but the irrigation water management varies with soil-agro-climatic condition and with irrigation systems. Few studies have been examined the irrigation
criteria for drip irrigated onions (Shock et al., 1998; Chopade et al., 1998; Martin de Santa Olalla et al., 2004) which indicated that the best yields occur when soil was constantly moist and irrigation should cease 2 weeks before harvest to prevent rotting and sprouting during storage. However, information is not available about microsprinkler irrigation scheduling of onion especially under semi-arid climate. Further, this study was planned with the assumption that microsprinkler with an appropriate irrigation schedule may protect the crop from adverse climate like frost during winter and desiccating wind during summer. With this background, the present study was undertaken to characterize the use of microsprinkler irrigation and to contrast the effects of different irrigation levels on yield and yield characteristics of onion, water use efficiency as well as growth response of onion.
* Corresponding author. Tel.: +91 1634 225313. E-mail address: [email protected] (S. Kumar). 0378-3774/$ – see front matter # 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.agwat.2007.01.003
162 2.
agricultural water management 89 (2007) 161–166
Materials and methods
The investigations were carried out during winter/summer crop growing season (January–May) of 2004 and 2005 at the research farm of Central Institute of Post Harvest Engineering & Technology, Abohar, Punjab, India (308090 N, 748130 E, 185.6 m above mean sea level). The region experiences semi-arid climate with extremely hot during summers and cold during winters. The average temperature, relative humidity, wind speed and pan evaporation rate during first year ranged from 10 to 37.8 8C, 29–91%, 0.3–2.0 m/s and 1.5–8.5 mm, respectively, and in second year, these parameters were varied, respectively, from 7.5 to 35.3 8C, 35–94%, 0.1–1.80 m/s and 1.3–7.6 mm during the crop growing season. Rainfall during crop growing season was recorded as 27 and 36 mm in first and second year, respectively. The percentage of sand, silt and clay in the experimental soil were 76.5, 15.4 and 8.1, respectively. Field capacity, wilting point and bulk density of top 30 cm of the soil were 11.5%, 3.9% and 1.5 g/cm3. The soil available water was 11.7 cm/m. The concentrations (kg/ha) of N, P2O5 and K2O were 51.1, 12.5 and 265.6, respectively. The soil had an organic matter concentration of 0.34%. The treatment consisted of four levels of irrigation on the basis of ratio of irrigation water (IW) to cumulative pan evaporation (CPE). These ratios were 0.60 (T1), 0.80 (T2), 1.00 (T3) and 1.20 (T4). CPE was computed as sum of daily evaporation of USWB class-A open pan. The pan was located adjacent to the experimental field with moderate grass cover. The total available water (TAW) to the plant was estimated as the difference between field capacity and permanent wilting point. In this investigation, root zone depth of onion was taken as 30 cm. Hence, total available water (rooting depth in m plant available water in mm/m) was estimated as 35.10 mm. The readily available water (RAW) was determined as RAW = TAW p, where permissible soil water depletion level ( p) was taken 30% as reported by Orta and Ener (2001) for higher yield of onion. As a result of the above, RAW was found to be 10.50 mm. This value was taken as the maximum irrigation dose (depth of water in each irrigation) to be applied during the experimental season. Water use assessed as crop evapotranspiration, was calculated using the water balance model (Eq. (1)) under variable irrigation (Simsek et al., 2005): ETc ¼ IW þ P D R DS ðETc ¼ kp E; kp : 0:60; 0:80; 1:0 and 1:20Þ
(1)
where ETc is the seasonal crop evapotranspiration, kp the crop pan coefficient (irrigation treatment; 0.60: T1, 0.80: T2, 1.0: T3 and 1.20: T4, respectively), E the evaporation, P the precipitation, D the drainage, R the runoff and DS is the variation in water content of the soil profile. All terms are expressed in mm of water in the onion root zone. Soil moisture content of different soil layer was estimated by gravimetric method. The change in soil water contents of 30–90 cm soil layer was considered to be deep percolation. Run-off was taken to be zero since it did not occur with the use of microsprinkler irrigation system. Observation for dry matter accumulation started after 45 days of transplanting and continued up to 105 days at 15
days interval. Destructive sampling was done, plants were divided into two parts, i.e. biomass (above ground part) and bulb (below ground part), and were cut into small pieces and dried at 70 8C to a constant weight for estimation of dry matter. Leaf water content was estimated from leaf fresh weight and leaf dry weight (Bonnet et al., 2000). Matured crop was harvested after 120–125 days of transplanting for estimation of onion yield. For estimation of mean bulb weight, 1.5 m 1.5 m area was earmarked in each plot and from total weight and number of harvested bulbs, mean bulb weight was determined. Similarly, 5 kg sample of onion bulbs was taken randomly from each treatment combination for measuring polar and equatorial diameter using vernier caliper. Mean size of bulb was presented as square root of polar and equatorial diameter. For grading, onion bulbs were classified into four categories on the basis of size of bulb: A, with size > 60 mm; B, with size 60–41 mm; C, with size 40–30 mm; D, with size < 30 mm under each irrigation treatment. Total soluble solids (TSS) was estimated using hand held refractometer (0–50 8B, ERMA, Japan). Percentage protein in the bulbs was estimated by using spectrophotometer (Spectron 20) by following standard procedure (AOAC, 2000). In order to estimate loss in marketable yield during storage, field cured onion bulbs with a sample size of 20 kg were stored on cemented floor in loose at room temperature. The average room temperature varied between 27–32 and 25–31 8C during the first and second year storage period, respectively. The observation on loss in marketable yield was recorded at 15 days interval till 90 days of storage. Loss in marketable yield included loss in weight as well as rotting. Rotted bulbs were considered unsuitable for consumption and were taken for loss in marketable yield count. Irrigation water use efficiency (IWUE) was estimated as the ratio of crop yield, Ya (kg/ha) and irrigation water applied (IW), in mm (Stanhill, 1986). IWUE ¼
Ya IW
(2)
WUE was obtained as crop yield per unit seasonal ET (ETc) WUE ¼
Ya ETc
(3)
Onion seedlings (Agrifound Light Red) were transplanted on 18th January in each year with plant and row spacing of 0.1 m 0.15 m. Prior to installation of the microsprinkler irrigation system, test runs were carried out to verify the rated design discharge of microsprinklers. The average discharge of microsprinkler was 63.10 lph at 1.20 kg/cm2 operating pressure. The microsprinklers were placed at 3 m. The area of each experimental plot was 36 m2 (6 m 6 m). A buffer zone with spacing of 1.0 m was provided between the plots. The experiment was laid out in randomized block design (RBD) with four replications. The data were analyzed statistically by standard analysis of variance (ANOVA). Least significant difference (LSD) test was used to determine whether differences existed between certain comparisons. The probability level for determination of significance was 0.05.
agricultural water management 89 (2007) 161–166
3.
Results and discussion
3.1.
Irrigation water applied and water use
The irrigation water applied to T1, T2, T3 and T4 were, respectively, 275, 343, 407 and 468 mm for first year and 257, 315, 389 and 451 mm in second year. Before the start of treatment, crop received equal amount of water, i.e. 61 and 52 mm, respectively, in first and second year, for proper establishment of seedlings. Thereafter, treatment commenced and stopped when 50% of the crop in a plot showed neck fall. The crop evapotranspiration (ETc) during the crop growing period (after establishment of crop) were determined to be 234, 292, 347 and 380 mm in first year and 217, 279, 323 and 349 mm in second year for T1, T2, T3 and T4, respectively. Hence, the values of IW for T4 were found to be higher than ETc values in both years. ETc < IW in T4 was due to the fact that the water applied to the plants in this regime was higher than the crop’s need and occurrence of deep percolation. The values of ETc and IW during the period of variable irrigation were almost similar (IW = 342; ETc = 335; average of 2 years) in T3. However, the IW values were found to be smaller than ETc in T1 and T2. Thus, it could be said that the water extracted by the crops from the soil in these treatments was higher than the water applied.
3.2.
163
Fig. 1 – Soil moisture content under different irrigation treatments in 0–0.30 m soil depth (second year).
weight per plant might be attributed to variation in size of bulb. Martin de Santa Olalla et al. (1994) indicated that bulb diameter and height are directly related to amount of water applied. Leaf water content (LWC) was measured at mid growth stage of plant in order to show the average LWC and minimize
Soil moisture
Fig. 1 indicates greater depletion in available soil moisture with treatment T1, which was probably due to insufficient irrigation. In treatment T4, soil moisture content remained closer to field capacity because of the highest irrigation. However, irrigation in T3 also seems to be sufficient as soil moisture depletion was often found in the range of 25 10% of available soil moisture.
3.3.
Growth dynamics
The trend of growth parameters with different levels of irrigation water was similar in both the years. Therefore, graphical presentation of data has been done with the mean values of two consecutive seasons to draw the inferences. The cumulative trends of the vegetative growth parameters (i.e. plant height, number of leaves, neck thickness, etc.) were similar to the biomass produced (Fig. 2a). Results indicated that biomass dry weight per plant influenced with the amount of water applied and varied between the treatments directly due to the variation in vegetative growth parameters. Fig. 2a shows that it increases through out the growing season up to 90 DAT for each treatment. After 90 DAT, biomass dry weight per plant decreased slightly in T3 and T4, while biomass reduced significantly in T1 due to the loss of dry leaves. Bulb dry weight per plant increased progressively up to 105 days in T3 and T4 while, a little difference in bulb dry weight was observed in T1 at 90 and 105 DAT (Fig. 2b). Bulb dry weight was almost similar which shows an early maturity in T1 than the other treatments. The analysis of variance for each sampling after 60 DAT showed significant differences between the treatments except T3 and T4, which were related to the soil moisture availability to the crop. The variation in bulb dry
Fig. 2 – Measured values of: (a) biomass dry weight and (b) bulb dry weight per plant at different growth stages under different irrigation treatments; vertical bars indicate WM.S.E.; values averaged over 2 years (2004–2005).
164
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Table 1 – Onion yield, irrigation water use and water use efficiencies for different irrigation treatments Year
Treatment
Onion yield (t/ha)
IW (mm)
ETc (mm)
IWUE (kg/ha mm)
2004
T1 T2 T3 T4
19.20 26.40 30.88 33.63
275.32 342.87 407.40 467.75
233.62 291.50 346.50 379.93
69.74 76.99 75.80 71.90
82.18 90.56 89.12 88.52
2005
T1 T2 T3 T4
20.44 28.43 32.83 34.40
257.15 315.11 389.20 451.34
217.41 278.73 323.11 348.73
79.48 90.22 84.35 76.22
94.01 101.99 101.60 98.64
the age effects. Leaf water content (%) values for T1, T2, T3 and T4 for 2004 were 86.93, 88.46, 89.96 and 90.14, respectively. The corresponding values for 2005 were 87.52, 89.05, 90.41 and 91.34. It appears that LWC increased with increasing irrigation water in both years. The decline in LWC with decreasing irrigation was expected as soil matrix potential increases with water stress (Cha-un et al., 2006).
3.4.
Onion yield and yield characteristics
Slightly higher onion yield was obtained in second year with all treatments. The reason for the differences was attributed to variation in climate. However, statistical analysis of the results showed significant increase in onion yield with increasing irrigation from T1 to T3 in both years (Table 1). The variation in onion yield between the treatments was recorded due to the variation in bulb size and mean weight of bulbs. Chung (1989) reported that water stress during critical growth period causes reduction in onion size and weight of bulbs. The onion yield in T3 and T4 was found to be nonsignificant which was probably due to the fact that irrigation in T3 was adequate to provide sufficient soil moisture for optimum onion production. These results are in agreement with Orta and Ener (2001). The yield reduction in T1 and T2 from the optimum yield (T3) was 37.71 and 13.82%, respectively. Fig. 3 shows the percentage of bulbs according to size for each treatment. It was observed that the percentage of B grade (most preferred size) bulbs was high (above 50%) in T3 and T4.
The least percentage of B and the highest percentage of D (smallest sized bulbs) grade were produced in the most restrictive treatment (T1). However, the lowest percentage of D grade was produced in T4. Similar trend was observed in both years. In general, percentage of B grade bulb decreased and D grade bulbs increased with the decrease in irrigation water. This may be due to the variation in magnitude of water stress under variable irrigation. A similar effect of irrigation on size of onion bulb was also observed by Martin de Santa Olalla et al. (2004) under drip irrigation system. Similarly, mean bulb weight was also influenced positively by irrigation water (Table 2). Mean bulb weight varied significantly between the treatments except T3 and T4. Least irrigation (T1) produced the minimum mean bulb weight due to higher percentage of smaller sized (D-grade) bulbs for both the years. Protein content in onion bulb decreased with increasing irrigation level (Table 2). The highest protein content found in T1 was statistically at par with T2. The least protein content was recorded in T3 for 2004 and in T4 for 2005. El-Gizawy et al. (1993) have also observed similar results and reported that total protein content increased significantly with the decreasing soil moisture. The total soluble solids of onion bulb increased with the increase in irrigation from T1 to T3 in year 2004, while in year 2005, irrigation had no significant effect on TSS (Table 2). Change in TSS with irrigation may probably be due to fulfillment of crop water demand and better utilization of nutrient under optimum soil moisture availability. Though, results are in accordance with Chopade et al. (1998), who reported higher TSS in onion with optimum application of water. However, Orta and Ener (2001) observed different trend. Loss in marketable yield (MYL) was significantly higher in irrigation treatment T1 in both years (Table 2). The higher MYL in T1 was observed might be due to early rotting of onion bulb. Results revealed that crop grown under T1 had shown early maturity and resulted into development of either immature or partial matured bulbs, which started rotting during storage at an early date. Ali and Elshabrawy (1971) have observed increased incident of neck rot disease in early harvested onion bulbs during storage, which resulted in higher MYL.
3.5.
Fig. 3 – Percentage of different sized bulbs under different irrigation treatments.
WUE (kg/ha mm)
Water use efficiency
Irrigation water use efficiency and water use efficiency (WUE) of onion obtained for different treatments are presented in Table 1. Treatment T2 gave the maximum IWUE in both years, while the least IWUE was recorded in T1 in first year and in T4
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Table 2 – Post-harvest attributes of onion under different irrigation treatments Treatment
Mean bulb weight (g) 2004
T1 T2 T3 T4
29.09a 39.40b 46.98c 51.05 c
2005 a
30.69 44.42 b 49.74 c 52.12 c
Protein (g/100 g) 2004 c
1.04 1.02b c 0.98 a 1.00 ab
TSS (8B)
2005
2004
bc
a
1.03 1.02 ab 1.01 a 1.00 ab
13.10 13.30 ab 13.50 b 13.10 a
Loss in marketable yield (%) 2005 a
13.20 12.90 a 13.30 a 13.00 a
2004 b
17.02 15.04 a 14.76 a 14.21 a
2005 15.62 b 13.31 a 12.81 a 13.59 a
Numbers followed by same letters under same heads in a column are statistically non-significant by LSD test at p 0.05.
in second year. Highest IWUE (76.99 and 90.22 kg/ha mm) reveals that water was used most effectively in T2. IWUE declined in T3 and T4 because, improvement in yield (16.04 and 24.03%) was less than the percentage increase in irrigation water (21.06 and 39.68%) as compared to T2. By and large, IWUE is the function of crop yield and water applied and decreased with increasing irrigation. Water use efficiency was also highest in T2 (90.56 and 101.99 kg/ha mm), but reduction in WUE with T3 was not significant (89.12 and 101.60 kg/ha mm). This result indicated that increase in yield was almost linear with ETc up to treatment T3. The overall results indicated that deficit and excess irrigation both did not show significant effect on yield and water use efficiencies. Chopade et al. (1998) and Imtiyaz et al. (2000) also reported similar findings. Relationships between yield (Y) and irrigation water applied (IW) and crop evapotranspiration (ETc) were
determined yield was against IW (Fig. 4a and
3.5.1.
through non-linear regression analysis. Onion taken as dependent variable and plotted and ETc to derive mathematical functions b).
Relationship between IW and Y
Year 2004 : Y ¼ 0:0002IW2 þ 0:2524IW 32:11
(4)
Year 2005 : Y ¼ 0:0004IW2 þ 0:3639IW 45:52
(5)
3.5.2.
Relationship between ETc and Y
Year 2004 : Y ¼ 0:0003ETc2 þ 0:2513ETc 25:73
(6)
Year 2005 : Y ¼ 0:0004ETc2 þ 0:3093ETc 29:93
(7)
Correlation coefficients were found to be 0.91, 0.89, 0.92 and 0.93, respectively, for Eqs. (4)–(7), which was statistically significant. Linear effects in the determined relationships were all positive, while the quadratic effects were all negative. These results indicated that the increase in onion yield was not proportional with the increment in amount of irrigation water. The developed relationship can successfully be used for predicting onion yield under similar agro-climatic condition without conducting tedious crop experiments. These equations can also be used as guide to yield potential allocation decision related to limited irrigation water.
4.
Fig. 4 – The relationship between: (a) onion yield (Y) and irrigation water and (b) onion yield (Y) and crop evapotranspiration (ETc) for 2004 and 2005, respectively.
Conclusions
Results of the study indicated that irrigation water had significant influence on response of microsprinkler irrigated onion. Irrigation water influenced the yield with different grades of onion bulbs. Percentage of bulbs (<30 mm in diameter) was found to be less than 5% when irrigation water was adequate (T3–T4). T3 and T4 gave the highest yield. Maximum protein content was recorded in the bulbs grown under most restrictive treatments, but weight loss during storage was also highest. Irrigation water use efficiency was highest in T2, which indicates most efficient utilization of water with microsprinkler irrigation system. Hence, if water becomes limiting factor, T2 would be most appropriate irrigation level for growing onion with microsprinkler irrigation system in a semi-arid climate.
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