Response of yield and yield compounds of rain-fed chickpea cultivars (Cicer arietinum L.) to plant density and weed interference

The most important principle in the rain-fed cropping system is to maintain and optimal use of soil moisture. In this regard, selecting the appropriate cultivar and planting density is one of the most important management decisions. The open canopy structure, short stature, limited leaf area, and the slow growth rate of chickpea is responsible for its poor competitive ability against weeds. In rain-fed cropping systems, weeds can also play an important role in soil moisture depletion and can aggravate drought stress on crop at the end of the growing season. Among the weed control cropping methods, it is possible to select a competitive cultivar and/or increased planting density. After introducing a new cultivar from rain-fed chickpea, researchers have always compared it with older cultivars in terms of competitive ability against weeds. So far, there has been no comparative study of competitive ability or tolerance of a new rain-fed chickpea cultivar, Adel, against weeds with older cultivars. Consequently, the effect of planting density of this new rain-fed chickpea cultivar on the response of weeds was not investigated. Therefore, the aim of this study was to investigate the interaction of this new and old cultivars and planting density on weeds damage under rain-fed conditions in Kermanshah. 

This research was carried out at the research farm of the faculty of agriculture and natural resources of Razi University, Kermanshah, during 2013-2014 growing season. Wheat was planted in the same farm during the previous growing season. During the experiment, the total rainfall was 85.51 mm. After preparing the land to plots of 6 × 2 m2, the chickpea cultivars were manually planted with the distance of 40 cm on each row on 5 February 2013. The experiment was a factorial (3 crop densities × 4 chickpea cultivars × 2 weed interferences) in a completely randomized block design with three replications. Planting densities were 31.3, 38.5, and 50.0 plants m-2. Chickpea cultivars were Arman (FLIP90-96C), Azad (FLIP93-93C), Adel (FLIP99-66C), and Hashem (FLIP84-48C). The factor of weed interference was at two levels of weeding and unweeding. The crop was harvested on 28 June 2014 to evaluate yield and yield components. The samplings of weeds were performed to determine the total biomass using a 1 m2 quadrate on 20 May and 12 June 2014, which were coincident with the flowering time and physiological maturity of chickpea, respectively.  

In general, the economic yield was decreased by increasing the plant density in all chickpea cultivars. The planting densities of 38.5 and 50.0 plants m-2 reduced the economic yield up to 8.9 and 42.6% in Azad cultivar, 30.5 and 37.2% in Arman cultivar, 23.7 and 40.2% in Hashem cultivar and 32.9 and 36.3% in Adel cultivar compared to planting densities of 31.3 plants m-2, respectively. Azad cultivar produced the highest economic yield (146.4 g m-2) under weeded condition, while the lowest economic yield (45.2 g m-2) belonged to Arman cultivar under un-weeded condition. The presence of weeds resulted in a reduction of 59.1, 51.9, 61.2, and 46.3%, in the economic yield of Azad, Arman, Hashem, and Adel cultivars, respectively. During the first weeds sampling, the highest (25.7 g m-2) and the lowest (17.7 g m-2) weed biomass were observed at planting density of 31.3 and 38.5 plants m-2, respectively- whereas during the second weeds sampling, the highest (60.0 g.m-2) and the lowest (42.8 g. m-2) weed biomass were observed at 31.3 and 50.0 plants m-2, respectively. Moreover, during the second sampling of weeds, the highest (54.7 g m-2) and the lowest (40.8 g m-2) weed biomass were observed at the plots of Hashem and Adel cultivars, respectively. 

In this research, the planting density of 31.3 plants m-2 was optimal planting density for all four chickpea cultivars. It seems that the increase of planting density to control weeds in rain-fed chickpea cropping system is an unsuitable technique. Therefore, it is necessary to consider other techniques to control weeds in rain-fed chickpea cropping systems. An interesting observation in this study was that, although the economic yield of Adel cultivar was lower, the lower biomass of weeds in the plots of this cultivar was observed compared to other cultivars. This observation can be related to allelopathic compounds produced by Adel cultivar which is costly for the crop itself and has reduced its yield.