Alkalinity refers to the capacity of the water to neutralize acid or to resist a lowering of the water pH. The major 
contributors to alkalinity in natural waters are bicarbonates. Alkalinity influences plant growth by causing the pH of 
the growing medium to increase. At high pH, some nutrients become less available, resulting in nutrient deficiencies. 
High alkalinity can also contribute to the accumulation of ammonia in the growing medium, causing poor plant growth.

At low alkalinity levels, less than 50 ppm, the water has very little capacity to buffer against a pH decrease so a 
non-acid fertilizer is recommended. If the alkalinity is between 50 and 100 ppm no corrective action is needed. 
For alkalinity levels between 100 and 200 ppm the recommended action will depend on the calcium level of the 
water (Table 2). Calcium in the water acts as a natural control on the activity of bicarbonate, so more alkalinity 
can be tolerated in the presence of a higher level of calcium.

When the alkalinity is greater than 200 ppm, it is recommended that the bicarbonate be neutralized to a level of 100 
ppm.  The addition of mineral acids will be necessary to reduce the alkalinity to an acceptable level. The amount of 
acid needed will depend on the type and concentration of the acid used.  For more details go to pub listed below.

AGR-164 Water Quality Guidelines for Tobacco Float Systems
Bob Pearce and Gary Palmer