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Daniel C. Brainard and D. Corey Noyes

Management practices that build soil organic matter—including reduced tillage, cover cropping, and compost applications—may be useful for protecting vulnerable crops from extreme weather events, reducing energy costs, and suppressing pests in carrot (Daucus carota subsp. sativa) production systems. The primary objective of this research was to assess the effects of strip tillage, compost, and carrot cultivar on carrot quality, yield, and profitability. An important secondary objective was to evaluate the impact of tillage and compost on establishment of important weeds in carrot systems—including two species that have developed resistance to linuron: Powell amaranth (Amaranthus powellii) and common purslane (Portulaca oleracea). Field experiments were conducted in 2009 and 2010 comparing conventional tillage (CT) to strip tillage (ST) under two rates of mature compost addition (0 or 3 dry t·ha−1) for three processing carrot varieties (‘Canada’, ‘Finley’, and ‘Recoleta’). In the ST system, a pre-established barley cover crop was left to grow as a windbreak between crop rows until carrots were established. Partial budget analysis was used to estimate net returns associated with all treatments. Compared with CT, the ST system resulted in 1) either equivalent or greater (2010, Finley cultivar) total carrot yields and net returns; and 2) either equivalent or lower summer annual weed densities. Addition of compost resulted in equivalent (2010) or higher (2009) carrot yields and gross returns but did not affect net returns as a result of the increased costs associated with compost application. Compost reduced the density of common purslane in 2009 but resulted in a threefold increase in the density of Powell amaranth in 2010. Our results demonstrate that both ST and compost applications are potentially valuable tools for improving the profitability of carrot production systems. Future research examining the mechanistic basis for compost and tillage effects on carrots and weeds as well as the long-term effects of these practices on profitability of rotational crops would be helpful for optimizing their use in vegetable production systems.

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Daniel C. Brainard, John Bakker, D. Corey Noyes and Norm Myers

Living mulches growing below asparagus (Asparagus officinales) fern can improve soil health and suppress weeds but may also suppress asparagus through competition for water or nutrients. The central objective of this research was to test whether cereal rye (Secale cereale) living mulch, in combination with overhead irrigation, could provide comparable weed suppression to standard residual herbicides without reducing asparagus yields. A field experiment was conducted from 2008 to 2010 in a mature asparagus planting on sandy soils in western Michigan to evaluate the effects of irrigation (none vs. overhead) and weed management systems (standard herbicides vs. rye living mulch) on weed suppression, soil moisture content, and asparagus yield. Rye living mulch and herbicide treatments were established immediately after asparagus harvest in late June of each year. Rye living mulch reduced soil-available water in early August by 26% to 52% compared with herbicide treatments but had no detectable effect on asparagus yields. Compared with herbicide treatments, rye living mulch reduced fall-germinating weed emergence and resulted in lower densities of horseweed (Conyza canadensis) during asparagus harvest. However, in 2 of 3 years, the living mulch system resulted in higher densities of summer annual weeds—including Powell amaranth (Amaranthus powellii) and longspine sandbur (Cenchrus longispinus)—during the fern growth period compared with herbicide treatments. After 3 years, the density of summer annual weeds was more than 10-fold greater in rye living mulch treatments compared with standard residual herbicides treatments. Our results suggest that 1) soil-improving rye cover crops can partially suppress weeds but may also compete with asparagus for soil moisture in dry years unless irrigation is used; and 2) successful use of rye living mulches for weed management will depend on identification of complementary weed management practices to avoid build-up of the summer annual weed seedbank.