Effect of the incubation of the phosphorus with the soil on growth and vesicular arbuscular micorrhizal infection in Lotus glaber and L. corniculatus.

The effect of the incubation of different concentrations of phosphorus (P), incubated in a Typic Natraquol soil, on plant growth and P uptake, and their relationship with VA-micorrhizal (VAM) infection in Lotus glaber (syn. L. tenuis Waldst. et Kit.) and Lotus corniculatus L. was investigated.

A group of soil samples were fertilized with KH2PO4 (0-400 µg P/g soil) and then incubated at 30   oC during 34 days. Another group of soil samples (control) were incubated under the same conditions, but they received the levels of P after the incubation and before sowing. Plants of L. glaber and L. corniculatus were grown separately in glasshouse conditions during 47 days. The yield of tops and P content as well as the root length infected by VAM were determined.

The yield of tops increased with the level of added P in both species. P previously incubated in the soil decreased plant growth, but the yield of tops per unit of P uptake did not differ between incubated soil-P and non-incubated soil-P treatments. Thus, differences in growth between treatments were due to differences in P uptake rather than its utilization within the plant.

Micorrhizal infection was maximum at lower levels of added P. This value was lower for the treatment at wich the P was incubated with the soil. This effect suggests that the incubation of the P with the soil may depress the infectivity of the inoculum of VAM present in the soil.

Key words: Lotus spp., soil P, P uptake, micorrhizas, plant growth.