Abstract

COVACEVICH, Fernanda; SAINZ ROZAS, Hernán; BARBIERI, Pablo  and  ECHEVERRIA, Hernán. Phosphorus placement effect on growth and indigenous mycorrhizal colonization of wheat under no-tillage. Cienc. suelo [online]. 2008, vol.26, n.2, pp.169-175. ISSN 1850-2067.

Wheat (Triticum aestivum L.) yields of crops under no-tillage (NT) that have had broadcast phosphorus (P) applications do not differ from NT wheat crops that have had near-the-seed banded P applications. Although it is believed that an adequate colonization of roots by arbuscular mycorrhiza (AM) under NT could contibute to a better crop growth, the effect of P placement on the AM colonization of a wheat crop under NT is unknown. The objective of the study was to evaluate the influence of P fertilizer placement (banded or broadcast) on growth and the AM indigenous colonization of wheat under NT. The experiment was carried out in a soil with 13.9 mg kg^-1 Bray-P and the treatments were: 0 (NP0), 25 (NP25) y 50 kg ha^-1 (NP50), banded (inc) at planting or broadcast (vol) three months before planting. In addition, two treatments were included: one without fertilizer application (N0P0) and another with 150 kg of P ha^-1 broadcast (NP150 vol). Aerial plant P concentration and biomass production, percentage of AM in roots, arbuscules content (A) and soil Bray-P availability was evaluated in tillering and stem elongation at two soil depths (0-10 and 10-20 cm). Phosphorus fertilization increased the soil P content (0-10 cm) and the plant P content. At the two soil depths, fertilization with 25 and 50 kg P ha^-1 depressed AM and A as compared to the unfertilized treatments, mainly when the P was banded. Mycorrhizal colonization was negatively associated with the soil and plant P contents. We found a high (r²= 0.85, P< 0.05) relationship among AM and the soil P content (0-20 cm). The rate of AM colonization was slower in the 6-13 mg kg^-1 soil P-Bray range. In situations with similar soil P contents, treatments with P inc produced a smaller AM colonization compared to the broadcast P treatments. This could explain the lack of grain yield response between different P placements in soils under NT with low P contents.

Keywords : Phosphorus placement; Mycorrhizal colonization; No tillage; Triticum aestivum.

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