Effects of limited irrigation and herbicide on yield, yield components and water consumption of beans (Phaseolus vulgaris L.)

The effectiveness of productivity and sustainable agricultural development depends on the availability of natural resources as well as the efficiency of management measures in agricultural lands. Increasing water use efficiency is a promising way to manage agricultural production in arid and semi-arid regions where there is little or no prospect of expanding water resources (Boutraa, 2010). According to Malik et al. (1993) bean yield may be reduced up to 70% when faced in competition with weeds. Extending the irrigation cycle (limited irrigation) in beans is expected to diminish not only the water consumption but also to influence the weed density along with dry matter too.

This project was conducted at Khair-abad research station in Zanjan, Iran, over a period of two years starting from the 2017 growing season. The experimental design utilized a randomized complete block design (RCBD) with 24 treatments and three replications. The treatments were arranged in a strip plot layout. The vertical factor of the experiment consisted of three levels of irrigation intervals: efficient irrigation (every 4 days), limited irrigation (every 9 days), and more limited irrigation (every 12 days). The horizontal factor involved eight sub-factors of herbicides: Trifloraline, Imazethapyr, Trifloraline + Bentazone, Imazethapyr + Bentazone, Imazethapyr + Sitogate, Bentazon + Gallant Super, traditional hand mowing, and a test sub-factor with no control. Several traits were evaluated in this study, including the number of pods, number of seeds per pod, 100-seed weight, bean grain yield, biological yield, harvest index, and productivity index. Data analysis and mean comparisons were performed using the SAS statistical software, employing Duncan's multiple range tests.

The Results indicated that both the herbicides and irrigation periods were effective on density and dry matter of weeds. Reducing irrigation intervals will allow for greater control of weed density and dry matter. Imazethapyr and Trifloraline herbicides as pre-emergence and pre-plant followed by post emergence application of Bentazone leads to about 85 and 82 % reduction at in weeds density at bean 3rd three leaflet appearance stage, 85 and 82 % reduction at 50% flowering stage bean in tow year of the study recorded the most reduction on weeds density. Moreover, these herbicides inducing about 88 and 81% decrease at bean 3rd three leaflets and 91 and 87% decrease at bean 50% flowering stage. These treatments after weeding had the highest control on weed density and dry matter. Trifloraline, when applied as a pre-plant treatment, showed the lowest effectiveness in controlling weeds among all the treatments. It resulted in an average reduction of 49% at the appearance of the bean's third three leaflets and approximately 70% reduction at the 50% flowering stage of the bean plant. This treatment consistently ranked the lowest in terms of weed control throughout the study period. The treatments of Imazethapyr, whether applied solely as a pre-emergence treatment or in combination with Situgate as a post-emergence treatment, were found to be ineffective in controlling weeds. Therefore, these treatments are not recommended for weed management in beans, particularly under limited irrigation regimes. The maximum number of sheaths, grains per sheath, and weight of 100 grains were observed in the irrigation regime of every 4 days when integrated with the application of Trifloraline, traditional hand mowing, Imazethapyr + Situgate, and Imazethapyr alone. In terms of bean harvest, the highest yields of 5175 kg/ha, 4707 kg/ha, and 4624 kg/ha were obtained from the irrigation regime of every 4 days when integrated with traditional hand mowing, the application of Imazethapyr + Bentazone, and Imazethapyr + Situgate, respectively. On the other hand the best biological performance as 9950, 9783, and 9733 kg/ha were related to 4 days interval when integrated with application of Imazethapyr + Bentazone, hand mowing, and Imazethapyr + Situgate. The maximum bean harvest index at 52.82 and 50.80 percent were related to 4 and 9 days intervals integrated with hand mowing, followed by 50.54 percent related to 4 days round integrated with Imazethapyr and 9 days round integrated with Trifloraline+ Bentazone. The highest water efficiency as 0.83 was related to 9 days interval whereas the lowest one as 0.48 was related to 4 days round. Regarding the horizontal factors, during the two years study the maximum water efficiency as 0.86, 0.77, and 0.76 were registered at treatments of hand mowing, application of combined Imazethapyr + Bentazone, and combined Imazethapyr + Situgate, respectively.

Based on the overall results and considering water shortage as well as water usage efficiency and decreasing the amount of both performance and traits of performance reduction in Chiti bean "Kosha" leading to desirable weeds control and bean yield, nine days round irrigation could be recommended provided with application of Imazethapyr or trifloraline herbicides with Bentazone.