A RAPID METHOD FOR MEASURING DYNAMIC CHANGES IN PH OF FERTILIZER MICROSITES

Nutrient availability from banded fertilizers will depend on the prope rties of the fertilizer band or microsite. Increased pH from urea hydr olysis may change P fertilizer reactions with the soil. A rapid method is described which allows precise measurement and visualization of dy namic changes in pH near microsites around fertilizer granules or band s. One day after application of urea and triple superphosphate fertili zers into the soil, a 0.75% agar solution containing 0.06% bromocresol purple was poured onto the soil surface. The pH was measured using a combination microelectrode placed on the agar and the pH range was est imated from agar colour 2, 4, 6 and 8 d after placement of the fertili zer mixture. Triple superphosphate reduced and retarded pH increases f rom urea hydrolysis. The results demonstrate the ability of the agar m ethod to monitor pH changes around fertilizer granules or bands.