What is the purpose of adjusting soil pH with lime or sulfur?

• A. To optimize nutrient availability for most plants by moving unavailable nutrients into available ranges.
• B. To increase soil salinity for better water uptake.
• C. To change soil color for aesthetic reasons.
• D. To kill beneficial microbes.

Answer: (A)

The main idea is that soil pH controls how available nutrients are to plant roots. When soil pH is outside the range where a nutrient stays soluble, it can become unavailable even if it’s present, or it can become toxic in some cases. Adjusting pH with lime or sulfur moves the nutrient solubility into favorable ranges. Lime raises soil pH and adds calcium, helping a broad set of nutrients remain soluble for many plants. Sulfur lowers soil pH (through microbial oxidation to sulfuric acid) and can increase the availability of nutrients that prefer slightly acidic conditions, while also supplying sulfur as a nutrient. For most plants, a pH around 6.0 to 7.0 optimizes nutrient uptake, though some species have different preferences. So the purpose is to optimize nutrient availability rather than to affect salinity, change color, or kill microbes.