مدیریت تلفیقی علف‌های‌هرز نخود (Cicer arietinum L.) در شرایط محیطی شوشتر

Introduction
Chickpea is a poor competitor to weeds because of slow growth rate and limited leaf area development at early stages of crop growth and establishment. Crop yield loss could be be in high extent due to increasing of weed biomass, weed density and weed species. Chickpea yield losses due to weed competition have been estimated to range between 40 and 87% depending on weed species and density. Herbicides play a key role in weed control and are used extensively today. The current tendency in chickpea weed control in the Mediterranean region is to shift from the costly manual mechanical energy to the chemical energy through more usage of effective herbicides particularly with the increased adoption of winter sowing. Several herbicides with different mode of action such as Trifloralin (Treflan) and Pendimetalin (Prowl) are used for weed control in chickpea farms. Nevertheless herbicide application may have several important environmental issues. These include unintended damage occurring both on the sprayed site, and offsite. Herbicide use also injures the human and animals. Integrated weed management (IWM) is the most important strategies to avoid herbicide environmental issue and increasing inputs productivity. Furthermore, integrated weed management strategies attempt to limit the deleterious effects of weed growing on crop plants. The present report describes the effect of integrated methods on weed density and grain yield of chickpea under Shoushtar conditions.

Materials & Methods
In order to study the effects of integrated weed management (chemical and mechanical) in chickpea (Cicer arietinum L.) a field experiment was conducted during 2009-2010 at IAU Shooshtar Branch. The experiment was designed as a randomized complete block with four replications. Treatments were consisted of eleven combinations of once and twice mechanical control (using cultivator) with Trifloralin and Pendimetalin herbicides (pre-plant) and two control treatments, consisted weedy and weed-free plots. Herbicides where mixed with soil one week before planting. Weed samples were taken by randomly throwing a quadrate of 0.25 m2 area. Analysis of variance was performed using the SAS Ver 9.1 software and treatment means were compared using LSD (Least significant difference) at 5% of probability.

Results & Discussion
Results showed that the highest weed controls was related to the treatments with twice cultivation+ Trifloralin+ Pendimetalin. Malcolmia behboudiana and Chenopodium album control in this treatment was 87.2 and 91.8%, respectively. The highest weed control with 75.6, 78.85 and 88.86% was in Trifloralin+ twice cultivation, Pendimetalin+ twice cultivation and twice cultivation+ Pendimetalin+ Trifloralin treatments, respectively.
The lowest grain yield was observed in weedy plots without weed control. Grain yield reduction under weedy treatment was 72% lower than weed free plots. There was no significant difference between control treatment without weed control and once cultivation treatment. Integrating weed control had higher controlling impact on weed growth compared with individual use of cultivation and herbicides. Twice cultivation+ Pendimetalin+ Trifloralin treatment had the highest grain yield. Higher grain yield in these treatments was due to increase in lateral branches, the number of pods per plant, and accordingly, the number of grains per plant. The effect of treatments on number of pods per main and lateral branches and also the number of pods per plant was significant. Integrated weed control treatment with twice cultivation plus both herbicides had the highest pod number per plant.
Chickpea biological yield in weedy control showed a significant reduction of 32.4% compared with weed free treatment. The highest chickpea biological yield was belonged to weed free and twice cultivation+ Pendimetalin+ Trifloralin treatments. The effect of weed control treatments on the number of pods per plant was significant.

Conclusion
In general, the results of this study showed that chickpea plants are not poor competitor to weeds only at its early stages, but at later stages of growth had a low ability to compete with weeds. Thereby, treatments such as pre-plant herbicides and once cultivation that control weeds only in the earlier stages of the crop growth are less effective than the combination of herbicide and twice cultivation.