Boron is an essential micronutrient for plant growth, but excessive levels can be toxic. The optimal boron levels in irrigation water vary depending on the crop. For example, sensitive crops like citrus and avocado require boron levels below 0.5 mg/L, while tolerant crops like alfalfa and wheat can tolerate levels up to 2 mg/L. Understanding the specific boron requirements for each crop is critical to preventing boron toxicity and ensuring optimal crop growth.