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Fertilizer application method affects nitrogen uptake in weeds and wheat

Blackshaw, Robert E., Semach, Gregory, Janzen, H. Henry
Weed science 2002 v.50 no.5 pp. 634-641
Setaria viridis, Sinapis arvensis subsp. arvensis, Triticum aestivum, ammonium nitrate, application methods, biomass, crop-weed competition, cropping systems, fertilizer application, grain yield, growing season, integrated weed management, nitrogen, nitrogen fertilizers, soil, soil nutrient dynamics, spring, spring wheat, weeds
Managing fertilizer in cropping systems may be an important component of integrated weed management programs. A field study was conducted to determine the effect of various application methods of the ¹⁵N-enriched nitrogen (N) fertilizer on N uptake in green foxtail, wild mustard, and spring wheat and on crop––weed competition. N application methods consisted of ammonium nitrate in solution applied broadcast on the soil surface, applied in pools on the soil surface at 20-cm intervals between every second wheat row, and point injected 10 cm deep at intervals similar to those of the surface pools. An unfertilized control treatment was also included. N uptake by green foxtail throughout the growing season was often greater from surface broadcast than from surface pools or point-injected N and was sometimes greater from surface pools than from point-injected N. In contrast, N uptake by wild mustard was rarely affected by the fertilizer placement method. In the presence of weeds, the ranking of N uptake by wheat usually was point injected > surface pools > surface broadcast. Weed biomass was often greater with surface broadcast than with either surface pools or point-injected N. In the absence of weeds, wheat yields were similar across the three N application methods. However, in the presence of green foxtail, wheat yields were greater with point-injected N than with surface broadcast N in two of the 3 yr and with surface pools of N in one of the 3 yr. In the presence of wild mustard, wheat yields were greater with surface pools and point-injected N compared with the unfertilized control in two of the 3 yr, whereas yields with broadcast N were never greater than the unfertilized control. Study findings suggest that point-injected N results in suppressed weed growth, not by reduced N uptake by weeds but instead by greater N uptake by wheat that increases its competitiveness with weeds. Information gained in this study will be utilized to develop a more integrated program for weed management in spring wheat.Nomenclature: Green foxtail, Setaria viridis (L.) Beauv. SETVI; wild mustard, Brassica kaber (DC.) L. C. Wheeler SINAR; spring wheat, Triticum aestivum L. ‘‘Katepwa’’.