Effect of sink removal on yield and yield components of chickpea (Cicer arietinum L.) under different nitrogen fertilizer levels and irrigation regimes

IntroductionChickpea (Cicer arietinum L.), an annual with indeterminate growth, is one of the most important food legumes. Loss of seeds due to pod borer (Heliothis armigera) attack is prevalent. Such loss of pods may affect the yield and yield components. The source-sink relationship changes during growth stages. Some factors influence this relationship including nitrogen fertilizer and water. This experiment was conducted in order to study the effects of nitrogen fertilizer, supplementary irrigation and depodding on yield and yield components of chickpea (var. ILC482).
Materials & MethodsThe experiment was conducted as split-split plot based on a randomized complete block design with three replications at Agricultural Research Station of Ferdowsi University of Mashhad, during growing season of 2012. Main plot was nitrogen fertilizer including 30, 75 and 150 kg N/ha and sup plot was irrigation regimes including full irrigation, supplementary irrigation at flowering and supplementary irrigation at flowering, seed podding and depodding including 0, 25%, 50% and 75% as sub subplot. Leaf and stem dry weight, seed weight per plant, shoot weight, pod number per plant, grain number per plant, 100-seed weight and harvest index of chickpea were all recorded.
Results & DiscussionThe results indicated that all traits excluded of harvest index were higher in 150 kg N/ha treatment than other treatments. Nitrogen rate of 150 kg/ha produced the highest seed weight (3.8 g/plant). The highest harvest index (36%) was obtained from 30 kg/ha N treatment. Supplementary irrigation at flowering and podding stages with grain yield 4.4 g/plant was higher than full and supplementary irrigation at flowering. Supplementary irrigation at flowering and podding stages produced the highest harvest index (39%). In irrigation regimes including full irrigation and supplementary irrigation at flowering stage, 75% depodding decreased seed weight to 60%, but this was 45% in Supplementary irrigation at flowering and podding stages. In this interaction, full irrigation and 0% depodding (control), produced the highest seed weight (195 g/m2). The lowest seed weight (40 g/m2) was obtained from supplementary irrigation at flowering stage and 75% depodding. Supplementary irrigation at flowering and podding stages with 25% depodding produced the highest harvest index (45%) too. Increase of harvest index mostly was related to improve photosynthesis and remobilization in mid drought stress and also low depodding (by devotion photosynthetic assimilates to un-removed pods). The highest shoot weight was obtained from 150 kg N/ha (12.8 g/plant) and full irrigation (14.3 g/plant). Depodding decreased the most of mentioned traits significantly. 75% depodding decreased seed weight and shoot dry weight to 56% and 30% respectively compared to control. The lowest harvest index (23%) was obtained from 75% depodding. In nitrogen rate of 75 kg/ha, the highest (177 g/m2) and lowest (46 g/m2) seed weight was obtained from 0% and 75% depodding, respectively. This result also was observed in traits of seed number and pod number in this interaction. High N application improved the ability of plant to compensate the pods that removed. All of traits including pod number, seed number, harvest index and shoot dry weight had positive and significantly correlation with seed weight. Pod number (75%) had highest correlation with yield.
ConclusionGenerally, increasing depodding intensity decreased grain yield. But nitrogen fertilizer application decreased the negative effects of depodding in low levels. Among irrigation regimes, supplementary irrigation at flowering and depodding stages was best treatment, therefore under water deficit condition, supplementary irrigation at flowering and podding stages recommend. Under severe stress condition (supplementary irrigation at flowering stage), high nitrogen application did not effect on seed weight. In this condition, favorite yield will obtain by 30 kg nitrogen fertilizer application as starter.