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1 May 2009 Phosphorus Fertilizer Application Method Affects Weed Growth and Competition with Wheat
Robert E. Blackshaw, Louis J. Molnar
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Strategic fertilizer management is an important component of integrated weed management systems. A field study was conducted to determine the effect of various application methods of phosphorus (P) fertilizer on weed growth and wheat yield. Weed species were chosen to represent species that varied in their growth responsiveness to P: redroot pigweed (medium), wild mustard (medium), wild oat (medium), green foxtail (high), redstem filaree (high), and round-leaved mallow (high). P fertilizer application methods were seed placed at a 5-cm depth, midrow banded at a 10-cm depth, surface broadcast immediately before seeding, and surface broadcast immediately after seeding of wheat. An unfertilized control was included. P treatments were applied to the same plot in four consecutive years to determine annual and cumulative effects over years. Shoot P concentration and biomass of weeds were often lower with seed-placed or subsurface-banded P fertilizer compared with either surface-broadcast application method. This result occurred more frequently with the highly P-responsive weeds and was more evident in the latter study years. P application method had little effect on weed-free wheat yield but often had a large effect on weed-infested wheat yield. Seed-placed or midrow-banded P compared with surface-broadcast P fertilizer often resulted in higher yields when wheat was in the presence of competitive weeds. Seedbank determinations at the conclusion of the study indicated that the seed density of five of six weed species was reduced with seed-placed or subsurface-banded P compared with surface-broadcast P. Information gained in this study will aid development of more effective weed management systems in wheat.

Nomenclature: Green foxtail, Setaria viridis (L.) Beauv. SETVI; redroot pigweed, Amaranthus retroflexus L. AMARE; redstem filaree, Erodium cicutarium (L.) L'Her. ex Ait. EROCI; round-leaved mallow, Malva pusilla Sm. MALPU; wild mustard, Sinapis arvensis L. SINAR; wild oat, Avena fatua L. AVEFA; wheat, Triticum aestivum L. ‘AC Abbey’.

Robert E. Blackshaw and Louis J. Molnar "Phosphorus Fertilizer Application Method Affects Weed Growth and Competition with Wheat," Weed Science 57(3), 311-318, (1 May 2009).
Received: 21 November 2008; Accepted: 1 January 2009; Published: 1 May 2009
Banded fertilizer
fertilizer placement
phosphorus concentration
phosphorus fertilizer
weed biomass
weed seedbank
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