The effect of sowing date and deficit irrigation regimes on yield and yield components of chickpea (Cicer arietinum L.)

Chickpea (Cicer arietinum L.) is one of the most important legumes in the world (Keifer, 2018). After India, Australia, and Pakistan, Iran has taken the fourth rank in terms of chickpea cultivation area, and the decrease in rainfall and especially the plant's exposure to heat and drought stress at the end of the season is the reason for the decrease in crop yield (SabaghPour et al., 2010; FAO, 2018). In general, drought stress and its relationship with the reduction of yield and its components in crops plants can be primarily attributed to the closing of stomata in response to low soil water content, during which the entry of carbon dioxide into the leaf is reduced, and as a result, it causes a reduction in photosynthesis.

In order to investigate the effect of irrigation regimes on the yield and yield components of chickpea (Cicer arietinum L.), an experiment was conducted at the research farm of Shahed University during 2021–2022 as a split plot design in the form of random complete blocks. The first factor is irrigation systems at three levels: 1) supplementary irrigation (Irrigation at two sowing times and before flowering based on 20% available soil water, 2) complete or control irrigation (irrigation based on 20% available soil water), 3) Low irrigation regime (irrigation based on 40% available soil water) is the second factor of autumn (November 15) and spring (March 15) sowing dates. Irrigation was carried out in the form of streams and stacks, and the ends of the plots were completely closed to prevent water from escaping. Data analysis and calculations related to simple Pearson correlation coefficients between traits were performed with SAS (ver 9.4) and SPSS (ver 23) software, respectively, and the average of treatments was compared by LSD test at a statistical level of 5%. The graphs were drawn using Excel software.

The results of the variance analysis of the interaction between irrigation regime and planting date showed that there is a significant difference between the traits of number of branches per plant, number of pods per plant, plant height, number of seeds per plant, harvest index, biological yield and seed yield. The results of comparing the averages also showed the highest number of branches per plant (9.83), the number of pods per plant (30.5), plant height (51.08) cm, and the number of seeds per plant (26.66). The harvest index was 0.48 percent, the biological yield was 4670 kg ha-1, and the seed yield was 2384.17 kg ha-1 for the autumn planting date treatment under the autumn irrigation regime (irrigation based on draining 20% of crop capacity moisture). The highest correlations with grain yield were obtained by traits: plant height (r = 0.986**), number of branches per plant (r = 0.966**), harvest index (r = 0.962**), number of seeds per plant (r = 0.961*), biological yield (r = 0.956**), hundred seed weight (r = 0.933**) and number of empty pods per plant (r = 0.880*).

In general, the results of this experiment indicate that the Low irrigation regime is more efficient than Supplementary irrigation in all traits after the control irrigation regime in autumn sowing. Therefore, the Low irrigation regime is suggested as a low irrigation regime suitable for the conditions of the tested region for the sowing of chickpeas in autumn, and in addition, other autumn sowing dates of this variety should be studied.