Reducing consumption or increasing the efficiency of chemical inputs in the agriculture sector has been among the most important issues which are in line with sustainable use strategies. Despite some environmental impacts, chemical herbicides are widely used to control the weed population of crops due to advantages such as saving application costs, time, and labor force. Groundwater is the most common type of solvent for applying herbicides in farming systems. Hence, this research was conducted to investigate the effect of groundwater quality parameters (acidity and water hardness) on the suitability of herbicides registered in wheat fields of Khorasan-Razavi province in Iran. For this purpose, threshold-based water hardness and acidity classified maps were produced through the geographical information system (GIS)-based techniques, and the groundwater suitability of the study area was investigated for the application of various herbicides (narrow-leaf, broad-leaf, and dual-purpose). The results showed that most of the groundwater in the study area was alkaline (with an average value of pH 7.82) and hard (water hardness >200 PPM). It is shown that in the areas where the groundwater is alkaline and hard, the chemical weed management of wheat fields is extremely restricted. In this regard, it is shown that by simultaneously considering the two qualitative properties of groundwater (pH and water hardness), only two herbicides (Puma super and Atlantis) can be recommended without worrying about the decrease in their efficiency, while the rest of the herbicides, maybe are not applicable (in a strict mode) or can be used more conservatively through strongly advised suggestions. The study also revealed that water hardness compared to acidity has generally a more negative impact on the efficacy of wheat herbicides. In this research, a map of the amount of ammonium sulfate (AMS) needed to overcome the adverse effects of water hardness on the effectiveness of herbicides is produced. Overall, the present study suggests that by providing the raster map of groundwater quality parameters we can precisely locate the suitable areas where proper herbicides should be taken into account to, in turn, avoid any serious risks of leaving a huge amount of chemicals in the environment. From a practical point of view, such kind of information can also be uploaded into the Web-Based GIS Platforms or be implemented in software applications.

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