Crop water requirement
The daily ETc values for the growing season are presented in the Fig 1. The seasonal ETc of chickpea for the growing season was 325 mm. The daily crop evapotranspiration increased with the advancement of the season reaching its peak in the second week of February. The decline in crop evapotranspiration at the end stage was mainly due to senescence and reduced evapotranspiration demand by the crops.
Plant biometric parameters
Application of plastic mulch significantly improved the plant height. At daily irrigation interval (1-day), treatment with plastic mulch (DM1) showed the highest plant height of 75.93 cm, while it was 65.70 cm under no-mulch treatment (DNM1). As compared to check basin method (CB7), the plant height under these treatments was 46 and 26% higher. Frequent irrigations resulted in better plant growth as compared to treatments having larger irrigation interval. When irrigation was applied at 1-day interval, the plant spread was maximum under DM1 and DNM1 (61.98 and 60.85 cm, respectively) and it was lowest in case of CB7 (25.65cm). At 1-day irrigation interval, application of plastic mulch did not show significant effect on plant spread during 2017 (Table 2). This implies that regular irrigation, with or without mulch, results in higher vegetative growth.
The number of branches was significantly affected by irrigation methods and scheduling. Application of irrigation at 1-day (DM1) and 2-day (DM2) irrigation with mulch resulted in more number of branches (18.33 and 17.19 branches/plant) as compared with irrigation on same intervals without mulch (DNM1 and DNM2). Better vegetative growth (plant height, plant spread and number of branches) achieved under treatments having 1-day and 2-day irrigation interval may lead to higher photosynthetic activity which manifests into increased crop yields
(Mafakheri et al., 2010).
Irrespective of irrigation method or application of mulch, the dry matter production under 7 days irrigation interval was lowest in both years. Comparing among irrigation intervals, treatments with 1 and 2 day irrigation interval showed significant difference in 2016 while during 2017 it was insignificant. Dry matter production under the treatments with 7 day interval (DM7 and DNM7) was 1.6 and 12.4% less than that obtained under farmers practice (CB7). It is obvious that under limited water supplies the dry matter production will be adversely affected
(Muniyappa et al., 2017).
Chickpea root characteristics were also significantly influenced by irrigation and mulch treatments. Higher root depth was observed in treatments with longer (7 day) irrigation intervals. For treatments with more frequent irrigation (DM1, DM2, DNM1 and DNM2), there was no significant difference between root length recorded under mulched and non-mulched plots. Length of tap roots was shortest when irrigation was applied at 1-day and 2-day intervals. Under longer irrigation intervals the root length was observed to be maximum under DM7 (14.38 cm), DNM7 (14.78 cm) and CB7 (14.07 cm) treatments (Table 3). Continuous availability of soil moisture in the root zone under DM1, DM2, DNM1 and DNM2 treatments led to reduced root length with treatment DNM2 showing the least root length of 8.57 cm.
At 1-day irrigation interval, the root spread under mulched condition was about 19% higher as compared to non-mulched condition. Previous researchers (Benjamin and Nielsen, 2006) have also demonstrated that root length increased with application of plastic mulch. Previous reports have showed that large root length improved yield under water-limited conditions but not under non-stressor one cycle of moisture stress (Mambani and Lal, 1983;
Kumar et al., 2010). The root spread exhibited an opposite trend as compared to root depth. More frequent scheduling of irrigation tended to increase the spread of roots and at the same time mulching resulted in higher spread of root as compared to non-mulch plots. Root spread recorded under the treatments with 7 days interval showed that CB7 had better root spread (10.03cm) over drip systems with and without mulch. The 1-day irrigation interval resulted in wider root spread as compared to 2-day irrigation interval. Mulching too, had a significant effect on root spread (Table 3). In a particular irrigation interval, drip irrigation with mulch resulted in higher root spread than that under drip irrigation without mulch. There is also evidence that the moisture stress resulting from higher irrigation intervals leads to elongation of roots (Benjamin and Nielsen, 2006).
Yield attributes
Highest number of pods per plants (387.0 in 2016 and 441.2 in 2017) were observed in drip irrigation treatments with use of plastic mulch at 1-day intervals (DM1) (Table 4). Under mulched plots, the number of pods per plant recorded under DM1 and DM2 were statistically at par while for non-mulched plots the number of pods differed significantly for DNM1 (223.5) and DNM2 (197.3). Comparing the results for same irrigation interval the number of pods was consistently higher under mulched conditions. It deserves a mention that CB7 resulted in higher number of pods (112.5 and 101.5) than DNM7 (130.0 and 128.0), respectively in 2016 and 2017.
Test weight was a trait which did not show significant difference under different irrigation methods or schedules in both the years. Irrigation methods as well as irrigation scheduling did not affect test weight significantly. For both the study seasons, the statistical analysis revealed higher P value (>0.05) for test weight implying no significant impact of these treatments (Table 4). Moisture availability or stress did not show any effect on seed test weight. It can be inferred that test weight is quite a resilient trait which remains unaffected by moisture regimes. It is apparent that once the grain filling sets in, all grains attain a weight close to a certain mean which remains constant for a season. These results finds support from Khodadadi (2013) who concluded that in chickpea 100 seed weight and number of days to pod filling were not affected by terminal drought stress. Purushottaman
et al.. (2016) observed that 100-seed weight was not generally correlated with yield and this trait has had minimum contribution or role in grain yield determination in chickpea.
Pasandi et al., (2014) observed that plant height, canopy spread, primary and secondary branches, chlorophyll content, days to maturity, grain yield and yield components of chickpea were significantly affected by irrigation regimes.
Harvest index, yield and water productivity
Harvest index was significantly affected by moisture regimes and treatments producing lower yield tended to exhibit higher harvest index and vice-versa. Treatments with 7 day irrigation interval resulted in higher harvest index of 57.4, 56.9 and 52.5 under DM7, DNM7 and CB7 treatments (Table 5). The highest value of harvest index (69.4) was observed under DM7 during the year 2017. These findings get support from
Kashiwagi et al., (2013) and
Purushottaman et al., (2016), who observed that treatments having moisture stress resulted in higher harvest index compared to treatments with optimum irrigation. Variation of harvest index is due to environmental factors which influence the partitioning of assimilates to harvestable product
(Wnuk et al., 2013).
Chickpea seed yield was significantly (P<0.01) influenced by irrigation methods as well as irrigation intervals. Highest yield of 19.38 and 17.2 q/ha was obtained from DM1during 2016 and 2017, respectively. However, the difference in yields obtained under DM1 and DM2 was statistically not different during 2016. In both the years of experimentation, DNM7 recorded the lowest chickpea yields. Under mulched conditions the chickpea seed yields in 1-day and 2-day irrigation intervals was 5.2 and 42.2% higher over 7 day interval, while for un-mulched conditions the yields increased by 2.5 and 17.2%, respectively. Compared to check basin method (CB7), the yields obtained under DM7 and DNM7 were 21.9 and 14.4% higher, respectively. Longer irrigation interval might have led to water stress in the crop root zone leading to reduced chickpea yields. Decrease in yield by water stress have been reported in lentil (
Singh and Saxena, 1990; Lal
et al.,1988), in chickpea
(Singh et al., 2015; Fang et al., 2011). Inhibition of photosynthesis and less translocation of assimilates towards reproductive parts due to soil water stress leads to reduced crop yield
(Razzak et al., 2017). Further, field observations revealed that the soil in the check basin plots was comparatively compact which may pose mechanical resistance and hinder exchange of air in the rhizosphere leading to reduced crop yields
(Fernandez-Garcia et al., 2013).
Marked variation was observed in the water productivity of chickpea across the treatments (Table 5). Drip irrigation with mulch recorded the water productivity in the range of 0.35 to 0.54 kg/m
3 (Fig 2). Compared to non-mulched drip, application of plastic mulch increased the water productivity by 32.9, 29.5 and 9.6% at 1-day, 2-day and 7-day irrigation intervals, respectively. It has been observed that the water productivity is genotype dependant and heritable
(Kaloki et al., 2019, Ucak et al., 2018). The farmers practice (CB7) recorded the lowest WP of 0.30 kg/m
3. Interestingly
Jabow et al., (2015) observed that in desert conditions of Sudan, chickpea crop exhibited higher water productivity when the interval of irrigation was 15 days as compared to 10 days.