Effects of lime and gypsum on growth of sweet potato in two strongly acid soils

There were strong relationships between exchangeable aluminium (Al) and rel ative top yield, and between soil pH and relative top yield in the Garret a nd Bisinella soils. Sweet potato plants produced maximum top yields at soil exchangeable Al <3.0 cmol (+)/kg, with a 10% yield reduction coinciding wi th a value of approximately 5.0 cmol (+)/kg. The value was lower for the Bi sinella soil than the Garret soil. In the case of pH, maximum yield in both soils was evident at a soil pH of 5.0 with 90% of maximum yield being achi eved at about pH 4.7. These results suggest that soil pH would be a good in dex for Al toxicity. The close relationships between sweet potato growth an d both exchangeable Al and soil pH need to be explored further to determine whether it will hold across a wide range of acid soil groups.