Date of Award

8-2011

Level of Access Assigned by Author

Campus-Only Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Ecology and Environmental Sciences

Advisor

Eric Gallandt

Second Committee Member

William Halteman

Third Committee Member

Timothy Griffin

Abstract

While Maine boasts the highest percentage of organic dairies in the country, high feed costs are threatening the viability of these operations. Traditionally, farmers in this region have relied extensively on cereal grains imported from the Midwest and Canada. However, organic grains and grain-derived concentrates constitute the largest expense on dairies, averaging 34% of annual operating costs. While farmers in the Northeast are planting more grains on-farm to reduce their grain bills, growers indicate that weeds remain the most challenging aspect of growing cereals. Although spring-planted cereals are inherently quite competitive due to rapid establishment, weeds often reduce yield and quality. Many growers rely on spring-tine harrowing to reduce weed competition in organic small grains like wheat, barley, and rye. This cultivating implement uses flexible metal tines to uproot weeds, which then desiccate on the soil surface. Given ideal conditions of dry soil and very small weeds, harrowing can kill over 90% of weeds in the field. In Maine, frequent spring precipitation makes timely and effective spring- tine harrowing nearly impossible, leaving farmers with no alternative methods of non-chemical weed control. Research demonstrates the potential of alternative practices, which act to limit weeds through either improved crop-weed interference or more selective physical weed control. To understand how amenable these practices are to our farming systems in Maine, I compared current “standard practice” for cereal production to alternative methods that (i) facilitate better physical weed control by using wide rows in combination with inter-row hoeing, as is practiced in “row crops” like corn and soybeans or (ii) enhance crop-weed competition through narrower rows and increased seeding rate. Results from four years of field experiments have demonstrated the potential of both of these systems to provide superior control over regional standard practice. However, these results were dependent on the severity of weed competition. With low weed density, cereals are sufficiently competitive to not require changes in weed management strategy. Economic analysis combined with simulation modeling of the weed seedbank response illustrate the short and long-term tradeoffs of employing these alternative systems, and under what conditions farmers are most likely to achieve acceptable results.

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