In some Georgia farm ponds a satisfactory phytoplankton growth is not produced following the application of normal amounts of fertilizer. Chemical investigations indicated a slightly acid condition and a low total hardness in these problem ponds. This condition was corrected by the addition of one ton per acre of agricultural lime or with varying amounts of hydrated lime added periodically. Phytoplankton production was definitely improved in over 100 Georgia farm ponds after the addition of lime. The average total hardness increase in these ponds, using agricultural lime at the rate of one ton per acre, was 15 ppm. Results lasted from 2-4 years. Hydrogen ion alone is not a satisfactory measure of the need for lime. Total hardness of the water was found to be the best and most reliable measure for lime supplements. For optimum fertilization results, the total hardness range should be 20 ppm or above. From 10-20 ppm results were varied, and below 10 ppm fertilization results were unsatisfactory. Ponds with a calcium oxide content in the bottom soils of 1500 Ibs. per acre or above produced good fertilization results. With calcium oxide in the range of 1000-1500 Ibs. per acre, results were varied, and below 1000 Ibs. per acre of calcium oxide, fertilization results were invariably poor.
