SUMMARY
One crop of clover followed by three crops of ryegrass were infected with several mycorrhizal fungi and grown in sterilized soil which had received soluble phosphate or Nauru rock phosphate. Plant growth responses to mycorrhizal infection were larger in later crops. Glomus tenuis was successfully introduced into soil already infested with the indigenous mycorrhizal fungi, and was the most efficient fungus used at stimulating phosphate uptake. In all four crops, Nauru rock phosphate was available to mycorrhizal plants but unavailable to non‐mycorrhizal plants. Plants infected with G. tenuis and the indigenous mycorrhizal fungi recovered 10‐27% of the phosphate fertilizer applied to the soil while non‐mycorrhizal plants recovered only 0.4‐13%.
Clover seedlings were inoculated with the indigenous or one of three introduced mycorrhizal fungi and transplanted into undisturbed cores of eight hill country soils. After several harvests, at least one of the introduced fungi had increased shoot growth in each soil from between 16 to 117%. In most soils, the growth benefit from inoculating with an introduced mycorrhizal fungus tended to decrease after the initial shoot harvest, and was then maintained at a lower level over subsequent harvests. In a Taihape silt loam, however. the growth benefit from Glomus tenuis inoculation increased steadily over six harvests. In four out of five soils. previous application of phosphate fertiliser (50 kg P fha/year) did not reduce mycorrhizal growth responses.
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