EFFECT OF PHOSPHORUS SOURCE AND RATE OF APPLICATION ON VAM FUNGAL INFECTION AND GROWTH OF MAIZE (ZEA-MAYS L)

The effects of two phosphorus (P) sources (triple superphosphate and Ghafsa phosphate rock), applied at rates equivalent to 44 kg ha(-1) and 22 kg ha(-1), on vesicular-arbuscular mycorrhizal (VAM) fungal infection in roots, dry matter yield and nutrient content of maize grown in an oxisol and an alfisol, were investigated in a growth cabinet. The application of 44 kg P ha(-1) resulted in root infection by VAM fungi not was significantlyresulted in root infection by VAM fungi not was significantly different (P less than or equal to 0.01) from when no P was applied. Root infection was significantly greater when P was applied as triple superphosphate at the rate of 22 kg ha(-1) the higher rate. Phosphate rock treatments at both rates of application resulted in significantly greater root infection than in controls with no P or when triple superphosphate was applied at 44 kg ha(-1). Plant P uptake increased in all soils with the different P treatments compared with the control. No direct effects of the treatments on the aluminium and zinc contents of maize plants were observed. In the gleyic alfisol, reduced Mn uptake as a result of increased infection of plants with the superphosphate treatments was observed. Higher Mn was also found in plants with the higher rate of superphosphate treatment than with the phosphate rock treatments in the haplustox, although infection rates in plants with the latter treatments were higher. With the exception of plants with the phosphate rock treatment applied at 22 kg ha(-1), dry matter yields of plants with all P sources were significantly greater than the controls.