Influence of dust deposition and light intensity on yield and some agro-physiologic characteristics of chickpea (Cicer arietinum L.) in dry conditions

Dust creates fine particulate matter and industrial and urban pollutants including factories of cement, gypsum, stone crasher, flour, daily winnowing of grain storage silos, heavy and light machinery traffic on dirt roads, car smoke and burning oil derivatives, power plants, etc. The dust damages the plants in various forms. The first damage the photosynthetic system by entering through the pores, and then by deposition on the leaf surface, reducing the light reached to the leaf, reducing the amount of photosynthetic pigments, changing the leaf temperature, and reducing the quantum yield, reducing the assimilation and closing stomata, exacerbated fungal and bacterial activity, pests and diseases, and ultimately reduce growth and yield. The amount of damage to the plant depends on the type of plant, cultivar, leaf area characteristics, the growth stage of the dust on the leaf surface, the type of dust and wind speed, the amount of dust thickness on the leaf, and the irrigation regime. Accordingly, the simulation of the effect of dust deposition and the reduction of light intensity due to it and their interactions on the growth and yield of chickpea cultivar Bivanich was performed as the dominant cultivar in the region. 

This experiment was carried out to investigate the effect of dust and light intensity on yield and some physiological and agronomic characteristics of chickpea cv. Bivanich, at the Research Field, Campus of Agriculture and Natural Resources, Razi University, Kermanshah, Iran in 2016-2017. Experiment was Factorial based on randomized complete block design with three replications. Factors included light intensity (100, 75, 50, 25 and 0% light intensity) and dust deposition at flowering onset and no dust deposition. Sowing date was in late March 2016 in dryland with 25 cm line spacing and 13.5 cm inter-plant spacing in 6 lines with 3 m plots long. Shading was applied with plastic wrap fasteners that were 1 cm wide. The amount of chlorophylls a, b, total and carotenoides and soluble carbohydrates were investigated in mid grain filling. Yield traits and components of grain yield were studied at physiological maturity. The water requirement and water use efficiency were calculated for both total dry matter and grain yield. The data were analyzed by SAS software and the means were compared with LSD at 5% probability level. 

The results showed that from flowering stage, the interaction effects of dust deposition and different light intensities were significant on yield traits such as biomass yield, grain yield and number of seeds per plant. Both biomass and grain yields at 100 and 75% light intensities were not significantly different in non-dust treatments, but the number of seeds per plant decreased at 75% light intensity compared to 100%. In dust conditions, there was a significant difference between the light intensities of 75% and 100%, which was reduced significantly. This indicates that the deposition of the dust by increasing stress on the plant increased the sensitivity of chickpea to the amount of light intensity. In this experiment, the number of grains per plant was ranged between 13.6 to 16.9 for the light intensity levels and 9.3 and 14.3 between the dust conditions. The effects of dust deposition on the 100-grain weight were not significant but were significant due to light intensities and the light intensity of 0% decreased maximum of 8.4%. The effects of two treatments on photosynthetic pigments and soluble carbohydrates were significant. In general, the dust deposition reduced the amount of photosynthetic pigments and soluble carbohydrates. With decreasing light intensities decreased chlorophyll a and carotenoids, but increased chlorophyll b and total chlorophyll. Water requirement and water use efficiency were also affected by treatments. 

In general, the results showed that the deposition of dust from flowering stage caused damage to biomass yield, grain yield, grain number per plant, 100 seed weight, photosynthetic pigments and water use efficiency. Rate of this damage for biomass yield was 24.4%, grain yield 16.8%, grain number per plant 15.4%, chlorophyll a 13.5%, chlorophyll b 21.7%, carotenoids 10.7%, soluble carbohydrates 18.8% Water use efficiency was 24.6%. By reducing the light intensity up to 75% were not significantly decreased in no-dust conditions (control treatment), total dry matter yield, grain yield and grain number per plant. Effect of light intensity reduction from 50% (at no dust treatment) until 0% (without direct light) reduced the most important traits such as biomass yield, grain yield and grain number per plant, but in dust treatment with decrease in light intensity from 100% decreased significant. Both the deposition of dust and the reduction in light intensity had severe effects on the water use efficiency of chickpea. Accordingly, the ranges of changes were for water use efficiency between 0.61 and 1.23 (based on total dry matter).