The effect of light quantity at different growth stages on agronomic traits of chickpea (Cicer arietinum L.)

Introduction
The growth of chickpea (Cicer arietinum L.), similar to that of other crops, is influenced by various environmental factors, particularly light intensity. Light plays a fundamental role in plant growth and development, serving as the primary energy source for photosynthesis, the synthesis of organic compounds, and the formation of plant tissues. Light intensity influences plant morphology by regulating leaf size, stem branching, root formation, and other structural traits, thereby ensuring a balanced allocation of resources and promoting coordinated growth among all plant organs. The objective of this study is to examine the effects of light intensity at different growth stages of chickpea and to elucidate how different light levels influence its growth and developmental processes.
 
Materials and methods
The experiment was carried out at the Research Farm of the Campus of Agriculture and Natural Resources, Razi University, Kermanshah, during the 2012–2013 growing season. A factorial experiment was arranged in a randomized complete block design (RCBD) with three replications. The experimental factors consisted of light intensity (100%, 75%, 50%, 25%, and no direct light) applied at different growth stages (vegetative, reproductive, and the entire growth period) of the chickpea cultivar ILC482. Rows were spaced 25 cm apart with a planting density of 40 plants per square meter. The planting date, early vegetative growth, early flowering, and ripening (harvest) stages occurred on November 3, March 13, April 28, and June 12, respectively. Plant height, total dry weight, grain yield, number of seeds per plant, number of pods per plant, and 1000-seed weight were measured at harvest. Data were analyzed using SAS statistical software, and treatment means were compared using Duncan's multiple range test at the 5% probability level.
 
Results and discussion
In general, the reduction of light intensity during the entire growth period had a pronounced adverse effect on yield and yield component traits. The impact of reduced light intensity was greater during the reproductive stage than the vegetative stage. Overall, decreasing light intensity led to a decline in yield traits and their components. Compared with 100% full light, under 75% light intensity during the vegetative stage, biological yield, grain yield, number of pods per plant, number of seeds per plant, and 1000-seed weight decreased by 24%, 30%, 28%, 27%, and 3.5%, respectively. During the reproductive stage, these reductions were even more severe (30%, 35%, 40%, 40%, and 4.5%, respectively). Reduced light intensity at the vegetative and reproductive stages primarily affected grain yield through changes in the number of seeds per plant, while the 1000-seed weight exerted the least influence. Leaf dry weight and leaf area index also declined with decreasing light intensity. Under full shading, leaf area decreased by 50%, 45%, and 55% during the vegetative, reproductive, and total growth stages, respectively, compared with the control. During the flowering stage, chlorophyll a content varied across light intensities, whereas chlorophyll b consistently decreased with decreasing light intensity. In general, the total chlorophyll content (a + b) was highest under full light conditions, and gradually decreased as light intensity diminished. Light intensity significantly affected the concentration of water‑soluble carbohydrates in leaves and stems. The higher levels of soluble sugars in stems and leaves during the vegetative stage compared to the reproductive stage may be attributed to a more extended compensation period under light stress during vegetative growth. In contrast, shading during the reproductive stage allowed only a limited compensation period, resulting in lower soluble sugar contents.
 
Conclusion
Even a 25% reduction in light intensity significantly decreased biological and grain yields, number of seeds per plant, 1000-seed weight, leaf dry weight and area, chlorophyll a, b, and total (a + b), as well as water-soluble carbohydrates in leaves and stems. Overall, chickpea growth is highly dependent on light intensity. A reduction in available light due to cloudy conditions (short- or long-term), mixed cropping with taller companion plants, or competition with weeds significantly reduces growth and yield, as chickpea is weak in competing for light resources.