Influence of rice paddy cultivation on V.A. mycorrhizal status of soil and on crop zinc uptake
A set of pot experiments and a field experiment were conducted to investigate the possible rate of vesicular-arbuscular mycorrhizal infection in alleviation of zinc deficiency in flooded rice cultivation. One of the main goals of these experiments was to infect rice seedlings with VAM fungi at the nursery stage under non-flooded conditions and, thereafter, to transplant them to flooded field conditions. In addition, other aspects such as the effect of duration and intensity of anaerobiosis on VAM fungal inoculum potential of soil comparison of the performances of different VAM fungal strains under different redox conditions, and the effect of VAM on uptake of fertilizer 65Zn, were studied. These studies revealed that short term flooding had no significant effect on VAM inoculum potential of soils. Anaerobic conditions caused by flooding and application of electron acceptors with glucose also had no marked effect on VAM inoculum potential. However, infection in rice was significantly lower than in maize and tomato, even under non-flooded conditions. A clear decrease in percentage VAM infection was observed after transplanting infected rice seedlings to flooded conditions. However, even with a low percentage infection, rice showed enhanced growth and nutrition of zinc and other nutrients due to the VAM association. In these experiments, Glomus caledonium and two tropical flood-adapted strains did not perform well. However, experiments conducted in Sri Lanka revealed that there are indiginous VAM strains in flooded soils that are well adapted to flooded conditions. Therefore, future research should be conducted to isolate and bulk these strains to use for inoculation of rice seedlings and further evaluation.