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United States Department of Agriculture

Agricultural Research Service

Title: Nitrogen Fertility and Weed Management Critical for Continuous No-Till Wheat in the Pacific Northwest)

item Young, Francis - Frank
item Thorne, Mark
item Young, Douglas

Submitted to: Weed Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/6/2006
Publication Date: 9/6/2006
Citation: Young, F.L., Thorne, M.E., Young, D.L. 2006. Nitrogen Fertility and Weed Management Critical for Continuous No-Till Wheat in the Pacific Northwest. Weed Technology. Volume 20:658-669.

Interpretive Summary: Background: In the Palouse region of the Pacific Northwest, dryland winter wheat production is the highest in the world. Because soil erosion under conventional tillage in this region is among the highest in the United States, growers are implementing conservation tillage systems to reduce soil erosion. However, to maintain high winter wheat yields in these systems, fertility and herbicide inputs are high. Currently there is no information available to assist growers in making decisions on how to manage these two inputs. Description: A 6-yr study conducted in the Palouse evaluated all combinations of three nitrogen (N) fertility levels and two weed management levels on crop yield, weed populations, and profitability in a winter wheat - winter wheat - spring wheat rotation. N rates ranged from recommended levels to 50% of recommended levels and herbicide levels ranged from the high labeled rate to approximately 55% of labeled rate. Reduced N input severely reduced crop competition and therefore increased herbicide dependency for effective weed control. However, if N fertility was adequate, herbicide levels could be reduced, especially if broadleaf weeds were predominate. The worst-case scenario was to reduce recommended N and herbicide inputs simultaneously. Impact: This research provides growers with guidelines on balancing the reduction of effective but expensive production costs in no-till wheat. The research also illustrates the need for a diverse conservation cropping system for the Pacific Northwest.

Technical Abstract: No-till cropping is an option for growers choosing to reduce soil erosion in the Palouse annual-crop region of the Pacific Northwest where wheat production is ideal. A six-year field study was conducted to determine optimum levels of fertilizer and herbicide input in a no-till continuous wheat crop production system. Three levels of nitrogen (N) and two weed management levels (WML) were compared in a three- yr spring wheat (SW)-winter wheat (WW)-WW rotation that maximized WW production. The high WML reduced germinated weeds about 50% and likely reduced the weed seedbank in the soil. In general, herbicide treatments were more effective on broadleaf weeds and may have facilitated a shift towards grass weeds. The high WML effectively reduced grass weed biomass only at the reduced N levels while the high WML reduced broadleaf weed density at all N levels. Variable environmental conditions affected wheat yield; however, yield tended to be highest when winter wheat followed spring wheat the first time. Nitrogen had little effect on weed density but increased crop yield about 13% with each increased increment of N. Crop yield was greater with the high WML at each N level even though weed density and biomass were reduced least at the highest N level. The highest crop yield and net returns were produced with the highest N and WML, however none of the N and WML combinations were profitable.

Last Modified: 05/25/2017
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