Mycorrhizas in hill country soils

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Abstract
Mycorrhizal fungi stimulated shoot growth of ryegrass in soils with up to 60 μg P/ml Truog phosphorus, although responses were generally greater in less fertile soils. The size of the mycorrhizal response was also influenced by soil type, the species of mycorrhizal fungus used, and the number of ryegrass crops grown in the test soil. In the first ryegrass crop grown in four hill country soils, Gigaspora margarita stimulated from 8% less to 213% more phosphorus uptake than the indigenous mycorrhizal fungi. After four successive crops, the increased phosphorus uptake by Gigaspora-infected plants ranged from 59% to 550% in the four soils. As soils became depleted of phosphorus with successive crops, non-mycorrhizal plants and those infected with inefficient mycorrhizal fungi became less able to extract phosphorus from soil.