Glyphosate is known to chelate or bind with magnesium ions and other divalent cations. 

Chelation: Glyphosate acts as a chelating agent, meaning it forms stable complexes with metal ions, including magnesium (Mg²⁺).

Reduced Availability: When glyphosate binds to magnesium, it reduces the availability of these essential minerals to plants. This can impact plant growth and health because magnesium plays a crucial role in processes like photosynthesis.

Impact on Herbicide Effectiveness: Hard water, which contains high concentrations of magnesium and calcium ions, can interfere with the effectiveness of glyphosate-based herbicides. 

The positively charged magnesium ions bind with the negatively charged glyphosate molecules, making the herbicide less readily absorbed by plants.