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Little attention has been paid to the effect of arbuscular mycorrhizal (AM) fungi on the uptake of nutrients that move mainly by mass flow. The objective of this study was to assess the possible contribution of indigenous AM fungi to the K, Ca and Mg nutrition of maize (Zea mays L.) as influenced by soil P levels and its impact on plant dry mass. The field experiment had a split plot design with four replicates. Treatments included soil fumigation status (fumigation and non-fumigation) and three levels of P fertilization (0, 60 and 120 kg P2O5 ha-1) in a loamy sand soil in 1997 and a fine sandy loam soil in 1998. Soil fumigati on with Basamid® was used to suppress indigenous AM fungi. Plants were sampled at four different growth stages (6-leaf stage, 10-leaf stage, tasseling and silking). Soil fumigation decreased shoot dry weight, but P fertilization increased shoot dry weight at most sampling times. When no P fertilizer was added, fumigation in the loamy sand soil reduced shoot K and Ca concentrations while, in contrast, in the fine sandy loam soil only Mg concentration was reduced by soil fumigation. The concentration of K in maize shoots was positively correlated (P < 0.05) with extraradicular hyphal length in both soils. The correlation between the abundance of extraradicular hyphae and the concentrations of Ca and Mg in maize shoots was significant only for soils where available Ca or Mg was relatively low. Arbuscular mycorrhizal fungi could increase corn biomass production and K, Ca and Mg uptake in soil low in these elements and low in P. These results indicate that the contribution of mycorrhizae to maize K, Ca and Mg nutrition can be significant in a field situation and that the extent of this contribution depends on the availability of these nutrients and of P in soils. Key words: Arbuscular mycorrhizal fungi, soil fumigation, extraradicular hyphae, uptake of K, Ca, and Mg, soil P levels, maize

ABSTRACTing the USEPA and Canadian health standards limit of 10 mg NO