INTRODUCTION
Chickpea (C. arietinum L.) is an important grain legume (pulse) crop, which in 2010 was grown globally on 12 million hectares with a total production of 11 million tonnes (FAOSTAT, 2012). India, Pakistan, Turkey, Australia, Myanmar, Ethiopia, Iran and Mexico are the major chickpea-producing countries. South Asia is not only an important producer (8 million tonnes in 2009), but also an important importer (0.7 million tonnes in 2009) of chickpea. It has considerable importance as food, feed and fodder. As a human food, chickpea is used as a green vegetable, as whole grain, split and dehulled to produce a stew (dahl or dal), hummus, and ground to produce flour with many items prepared from the flour.
Chickpea is primarily a rainfed crop grown on in-season rainfall in Mediterranean climatic regions such as southern Australia, west Asia and southern Europe, and on conserved soil moisture in south Asia and north-eastern Australia. Chickpea suffers from drought and high temperatures during reproductive development resulting in the production of fewer pods and seeds and reduced yields (Behboudian et al., Reference Behboudian, Ma, Turner and Palta2001; Fang et al., Reference Fang, Turner, Yan, Li and Siddique2010; Leport et al., Reference Leport, Turner, French, Tennant, Thomson and Siddique1998, Reference Leport, Turner, French, Barr, Duda, Davies, Tennant and Siddique1999, Reference Leport, Turner, Davies and Siddique2006; Turner, Reference Turner2003). In the north-western plain zone of India, chickpea was displaced to marginal soils and rainfall zones as the production of irrigated rice and wheat increased to meet the requirements of the Green Revolution. However, yields of rice and wheat are stagnating in many parts of the world (Brisson et al., Reference Brisson, Gate, Gouache, Charmet, Oury and Huard2010) including in north-west India and China, as a consequence of climate change, greater use of mildly-saline and deeper groundwater and lack of sufficient fertilizer input (Brisson et al., Reference Brisson, Gate, Gouache, Charmet, Oury and Huard2010; Tilman et al., Reference Tilman, Balzer, Hill and Befort2011). Moreover, there is over-exploitation of groundwater in many parts of the world (Jägerskog and Jønch Clausen, Reference Jägerskog and Jønch Clausen2012.), with the result groundwater resources are becoming scarcer (Deng et al., Reference Deng, Shan, Zhang and Turner2006; Hira, Reference Hira2009) and improved water productivity of water resources is required to meet the food requirements and the changing eating habits of the increasing world population.
To overcome the yield reductions from terminal drought, chickpea is grown with supplemental irrigation in some part of the world, particularly in west Asia and northern India (Anonymous, 2003), where it increases chickpea productivity (Erman et al., Reference Erman, Demir, Ocak, Tüfenkci, Oğuz and Akkőpru2011; Khamssi et al., Reference Khamssi, Golezani, Salmasi and Najaphy2010; Leport et al., Reference Leport, Turner, French, Tennant, Thomson and Siddique1998, Reference Leport, Turner, French, Barr, Duda, Davies, Tennant and Siddique1999; Yadav et al., Reference Yadav, Kumar, Yadav, Singh, Yadav, Turner and Redden2006). The application of one irrigation (Munirathnam and Sangita, Reference Munirathnam and Sangita2009), two irrigations (Abraham et al., Reference Abraham, Sharma, Thenua and Shivakumar2010; PAU, 2011) or three irrigations (Mansur et al., Reference Mansur, Palled, Halikatti, Chetti and Salimath2010) has been observed to increase chickpea grain yields substantially. However, the actual number of irrigations required depends upon many factors including the rainfall received, soil texture, weather conditions, and crop duration. Studies with chickpea in Mediterranean-climatic regions have shown that supplemental irrigation can significantly increase yields and water productivity (Oweis et al., Reference Oweis, Hachum and Pala2004; Zhang et al., Reference Zhang, Pala, Oweis and Harris2000). In a study in northern Syria, yields increased linearly with the amount of water applied, but water productivity did not always increase, depending on time of planting. Eighty millimetres of supplemental irrigation increased the water productivity of chickpea on an average over 4 years by 11% from 4.2 to 4.7 kg ha−1 mm−1 with a late November sowing and from 4.7 to 5.2 kg ha−1 mm−1 with a late February sowing, but did not increase the water productivity when sown in mid-January (Oweis et al., Reference Oweis, Hachum and Pala2004). Whether supplemental irrigation will increase water productivity where chickpea is grown on conserved soil moisture is unknown.
In the present study the effect of irrigation application to chickpea at the vegetative stage, flowering, podding or at a combination of different stages on its growth, yield and water productivity were conducted over two growing seasons in northern India. The hypotheses tested were (i) that supplemental irrigation would increase the yield and water productivity of the chickpea crop, and (ii) that supplemental irrigation during reproductive development would increase yields and water productivity to a greater extent than supplemental irrigation during vegetative growth.
MATERIALS AND METHODS
Site characterization
Field experiments were conducted during the winter season of 2007–08 and 2008–09 at the experimental farm of the Punjab Agricultural University, Ludhiana (30° 56′ N, 72° 52′ E, altitude 247 m), India. The soil at the experimental site was loamy sand, low in available nitrogen, but with a medium level of available phosphorus and potash. It had a water-holding capacity of 350 mm over the upper 1.8 m. Major properties of the experimental soil are presented in Table 1. Meteorological data were recorded at the Meteorological Observatory of the Punjab Agricultural University, Ludhiana, which is situated about 4 km from the experimental site.
Table 1. Mean soil properties in the surface 0.15 m at the experimental site.
Treatments and experimental design
In 2007–08, three treatments (i) no irrigation, (ii) irrigation at the late vegetative/early flowering stage (72 days after sowing, DAS), and (iii) irrigation at both the late vegetative/early flowering (72 DAS) and podding (118 DAS) stages, were imposed in a randomized block design with three replications. In 2008–09, the three treatments were (i) no irrigation, (ii) irrigation at flowering (108 DAS), and (iii) irrigation at podding (123 DAS), in a randomized complete block design with three replications. Each plot was 10 m × 3.3 m and the plots were separated with 0.70 m wide buffers to avoid movement of irrigation water from one plot to another. At each irrigation event 75 mm of water was applied as flood irrigation. In common with farmer practice, all treatments received a pre-sowing irrigation of 100 mm in both years of study.
Crop husbandry and observations recorded
After harvesting the preceding rice crop in October, the pre-sowing irrigation was applied and when the soil moisture level was suitable the seedbed was prepared by disk plough, followed by one cultivation and then levelled. Chickpea (C. arietinum L. cultivar PBG 1) was sown on 18 November 2007 and 13 November 2008 in rows 30 cm apart using a seed rate of 45 kg ha−1. Before sowing, 15.5 kg N and 40 kg P2O5 ha−1 was applied as diammonium phosphate (18% N and 46% P2O5). Weeds were controlled by hand weeding at 30 and 60 days after sowing (DAS). Two sprays of Thiodan 35 EC (endosulphan) @ 2.5 L ha−1 were applied at 120 and 134 DAS to control pod borer (Helicoverpa armigera Hub.). The crop was harvested on 20 April 2008 (154 DAS) and 25 April 2009 (163 DAS). At maturity, data on plant height, number of primary branches, number of secondary branches and number of pods were recorded on five randomly selected plants. Seeds of 10 randomly-chosen pods were used to record number of seeds pod−1. Biological yield (aboveground total dry matter of the crop at the time of harvest) and grain yield were recorded on a whole plot basis and converted into kg ha−1. Harvest index – the ratio of grain yield to aboveground dry matter – was calculated by multiplying grain yield by 100 and dividing by the biological yield. Data on 100-seed weight were also recorded by weighing 100 randomly-selected seeds after threshing.
Water productivity
Water productivity (based on irrigation (WPI) and irrigation + rainfall (WPI+R)) for grain yield and biomass was computed as:
\begin{equation*}
{\rm Grain}\,{\rm WP}_{\rm I} \,{\rm (kg}\,{\rm m}^{ - 3} ) = {\rm Grain}\,{\rm yield}\,({\rm kg}\,{\rm ha}^{ - 1} )/{\rm Total}\,{\rm irrigation}\,{\rm amount}\,({\rm m}^3)
\end{equation*}
\begin{equation*}
{\rm Biomass}\,{\rm WP}_{\rm I} \,({\rm kg}\,{\rm m}^{ - 3}) = {\rm Biomass}\,({\rm kg}\,{\rm ha}^{ - 1})/{\rm Total}\,{\rm irrigation}\,{\rm amount}\,({\rm m}^3)
\end{equation*}
\begin{eqnarray*}
{\rm Grain}\,{\rm WP}_{{\rm I} + {\rm R}} \,({\rm kg}\,{\rm m}^{ - 3}) &=& {\rm Grain}\,{\rm yield}\,({\rm kg}\,{\rm ha}^{ - 1})/{\rm Irrigation}\,{\rm water}\,{\rm applied}\nonumber\\
&& + \,{\rm Rainfall}\,({\rm m}^{\rm 3})
\end{eqnarray*}
\begin{equation*}
{\rm Biomass}\,{\rm WP}_{{\rm I} + {\rm R}} ({\rm kg}\,{\rm m}^{ - 3}) = {\rm Biomass}\,({\rm kg}\,{\rm ha}^{ - 1})/{\rm Irrigation}\,{\rm water}\,{\rm applied}\,{\rm + }\,{\rm Rainfall}\,({\rm m}^3)
\end{equation*}
Statistical analysis
All data were subjected to analysis of variance as one-way ANOVA (Cochran and Cox (Reference Cochran and Cox1959) using CPCS‒1 software (Cheema and Singh, Reference Cheema and Singh1991). Wherever the ‘F’ ratio was significant, the least significant difference (LSD) values were calculated at 5% level of significance for comparing the treatment means.
RESULTS
Weather
Figure 1 shows the mean weekly rainfall and maximum and minimum temperatures over the cropping season for the two years of the study. During 2007–08 and 2008–09, 88.7 mm and 81.2 mm rainfall was received during the crop season. The temperatures, especially the minimum temperatures, were lower in 2007–08 than in 2008–09. Furthermore, in 2007–08 there were 19 nights (on 31 December and 18 throughout January) when frost occurred (the temperature decreased below 0 °C), and only two nights in 2008–09 when the temperatures were this low.
Figure 1. Weekly rainfall (a) and mean weekly maximum and minimum temperatures (b) during the cropping seasons of 2007–08 and 2008–09.
Crop growth, yield attributes and yield
The yield of the unirrigated chickpeas in 2008–09 was more than double the yield in 2007–08. This was presumably the result of the colder temperatures and greater frequency of frosts in 2007–08 than in 2008–09. In 2007–08, irrigation at the vegetative stage significantly (p = 0.01) increased the aboveground biomass and grain yield by 59% and 36%, respectively, as compared to no irrigation (Figure 2). The additional irrigation at podding increased the aboveground biomass (p = 0.01) by a further 26%, but failed to increase the grain yield further. In 2008–09, irrigation at podding increased the aboveground biomass (p = 0.05) and grain yield (p = 0.05) as compared to the unirrigated control by about 30%, but irrigation at flowering did not significantly increase the biomass and only increased yields by 7%. So a single irrigation of 75 mm had a much greater effect on aboveground biomass and yield in 2007–08 than 2008–09. The single irrigation at the vegetative stage increased (p = 0.05) the harvest index from 47 to 54% in 2007–08, but the harvest indices did not differ in 2008–09.
Figure 2. Effect of three irrigation treatments on grain yield, biological yield (aboveground biomass) and harvest index of chickpeas in the growing seasons of 2007–08 and 2008–09. The mean values for each treatment (n = 3) are given along with the least significant difference (p = 0.05) where statistically significant.
The greater biomass in 2008–09 arose from a greater number of secondary, but not primary branches and was expressed as greater height than in 2007–08 (Figure 3). However, the application of irrigation did not influence plant height, primary branches plant−1 or secondary branches plant−1 in either year of study (Figure 3). The greater grain yield in 2008–09 was associated with a higher number of pods plant−1, but not a higher number of seeds pod−1 or a difference in seed size (100-seed weight) compared with 2007–08 (Figure 4). The number of seeds pod−1 was unaffected by irrigation, number of pods plant−1 was increased by the double irrigation in 2007–08 (p = 0.05) and by irrigation at flowering or podding in 2008–09 (p = 0.05) (Figure 4). The 100-seed weight increased significantly (p = 0.01) only in 2007–08 with irrigation in the vegetative/early flowering phase and was further increased by the additional irrigation at the podding stage (Figure 4).
Figure 3. Effect of three irrigation treatments on plant height, the number of primary branches and secondary branches in chickpea in the growing seasons of 2007–08 and 2008–09. The mean values for each treatment (n = 3) are given along with the least significant difference (p= 0.05) where statistically significant.
Figure 4. Effect of three irrigation treatments on the number of pods per plant, the number of seeds per pod and the 100-seed weight of chickpeas in the growing seasons of 2007–08 and 2008–09. The mean values for each treatment (n = 3) are given along with the least significant difference (p = 0.05) where statistically significant.
Water productivity
The higher grain yield in 2008–09 compared with 2007–08 resulted in quite higher grain and biomass water productivity (WPI as well as WPI+R) than in 2007–08 (Table 2). Irrigation in 2007–08 had little effect on grain and biomass water productivity (WPI as well as WPI+R) and actually reduced it in 2008–09. In 2007–08, the application of a total of 150 mm in the vegetative and podding stages reduced the grain and biomass water productivity (WPI as well as WPI+R) as compared with 75 mm irrigation water applied at vegetative stage only. In 2008–09, a single irrigation at podding provided the most efficient use of water and greatest boost to yield, resulting in higher grain and biomass water productivity (WPI as well as WPI+R).
Table 2. Effect of irrigation scheduling on grain and biomass water productivity (WPI and WPI+R) in chickpea.
DISCUSSION
Plant growth, yield attributes and grain yield
Adequate soil moisture is a requirement for obtaining an optimum plant stand, good growth and consequent high productivity of chickpea (Singh et al., Reference Singh, Sekhon and Sharma2011). Optimum moisture at podding is known to increase the transfer of assimilates to reproductive organs, thereby reducing flower and pod abortion and increasing yield (Leport et al., Reference Leport, Turner, French, Barr, Duda, Davies, Tennant and Siddique1999, Reference Leport, Turner, Davies and Siddique2006). In the present study, on a coarse-textured soil, one or two irrigations at different stages improved chickpea grain yield substantially (Figure 2) in both the years of study primarily due to an increase in the number of pods plant−1 (Figure 3), as shown previously (Ahlawat et al., Reference Ahlawat, Gangaiah and Singh2005; Shamsi et al., Reference Shamsi, Kobraee and Haghparast2010). This is in line with Turner et al. (Reference Turner, Abbo, Berger, Chaturvedi, French, Ludwig, Mannur, Singh and Yadava2006) who reported that water shortage, as the plant enters its reproductive phase, induces the end of reproductive development and ultimately yield is reduced. Irrigation during pod development delays the cessation of flowering and pod development leading to an increase in the number of pods per plant and yield (Leport et al., Reference Leport, Turner, French, Tennant, Thomson and Siddique1998, Reference Leport, Turner, French, Barr, Duda, Davies, Tennant and Siddique1999, Reference Leport, Turner, Davies and Siddique2006).
The study has also highlighted the large differences in yield from year to year at the same site with and without irrigation. We suggest that this was largely the result of the reduction in the number of frosts and warmer temperatures in 2008–09 than 2007–08. Cool temperatures below 12 °C are known to increase flower abortion and decrease yields (Crosier et al., Reference Crosier, Clarke, Siddique and Khan2003). The single irrigation in 2007–08 was applied when the cool temperatures and frosts were likely affecting flower and pod abortion (Crosier et al., Reference Crosier, Clarke, Siddique and Khan2003) and suggest that the irrigation may have alleviated the effects of the cool temperatures and frosts by the release of latent heat (Mavi, Reference Mavi1996).
Water productivity
In the favourable growing season of 2008–09, grain and biomass water productivity (WPI as well as WPI+R) was higher in all treatments than in 2007–08, indicating that the cool temperatures in the vegetative phase in 2007–08 had a much greater effect on yields and that irrigation could not completely alleviate the poor growing conditions. Chickpea genotypes may vary in water use (Zaman-Allah et al., Reference Zaman-Allah, Jenkinson and Vadez2011a, Reference Zaman-Allah, Jenkinson and Vadez2011b) and, therefore, screening the genotypes for potential utilization under limited moisture conditions may help in improving chickpea yields (Yadav et al., Reference Yadav, Kumar, Yadav, Singh, Yadav, Turner and Redden2006). However, this study has highlighted that other factors, such as cool temperatures, can markedly affect the water productivity and that these and other factors (Gan et al., Reference Gan, Warkentin, Bing, Stevenson and McDonald2010; Pramanik et al., Reference Pramanik, Singh and Singh2009) may override any cultivar differences.
There are challenges of considering water productivity as a sole indicator, as no-irrigation treatments (with low yield) exhibited higher WP while high yielding treatments showed lower WP. Thus WP should be interpreted carefully, considering other yield parameters. Further, linear yield increase does not necessarily mean higher WP.
Crop diversification with chickpea and optimum irrigation scheduling – a necessity for sustainable agriculture
In northern Indian states such as Punjab, Haryana and Uttar Pradesh, and in parts of northern China, the ground water level is decreasing at an alarming rate (Deng et al., Reference Deng, Shan, Zhang and Turner2006; Hira, Reference Hira2009). To sustain agriculture in these regions, irrigation water needs to be used judiciously. Chickpea requires little irrigation compared to other crops grown during the same season such as wheat and winter maize (Zea mays). For example, chickpea requires only one irrigation, whereas wheat and winter maize require four and six irrigations, respectively (PAU, 2011), though the number of irrigations may vary with rainfall. In the present study, one irrigation applied at podding increased grain yield by 27% in 2008–09 and the additional irrigation at podding increased grain yield by 9% in 2007–08. Thus, one irrigation during podding can increase chickpea grain yields substantially, with consequently higher net returns. Surprisingly in 2007–08, a single irrigation in the late vegetative phase increased yields by 59%, but this appears to be a result of the cool temperatures during early flowering increasing flower abortion and irrigation helping to counteract this increase in abortion. Thus the timing of the single irrigation may depend on the weather conditions at the site and in the particular season. Diversifying the cropping system with chickpea – a lesser water requiring crop – and timely irrigation during podding (or the early flowering if temperatures are low and frosts frequent) can help save underground water for the long-term sustainability of agriculture.
