CHAPTER 4. COVER CROPS AND WEED MANAGEMENT

Authors: Teasdale, John; BRANDSAETER, LARS - THE NORWEGIAN CROP RES IN; CALEGARI, ADEMIR - INST AGRONOMICO DO PARANA; NETO, FRANCISCO - INST AGRONOMICO DO PARANA

Submitted to: Book Chapter
Publication Type: Book / Chapter
Publication Acceptance Date: 5/25/2006
Publication Date: 10/1/2007
Citation: Teasdale, J.R., Brandsaeter, L.O., Calegari, A., Neto, F.S. 2007. Chapter 4. cover crops and weed management. In: Upadhyaya, M.K., Blackshaw, R.E., editors. Non Chemical Weed Management Principles, Concepts and Technology. Wallingford, UK: CABI. p. 49-64.

Interpretive Summary: The term "cover crops" encompasses a wide range of plants that are grown for various ecological benefits other than as a cash crop. They may be grown in rotations during periods when cash crops are not grown or they may grow simultaneously during part or all of a cash cropping season. This chapter reviews the contribution that cover crops can make to weed management and the tradeoffs that may be required between achieving weed management, crop production, and environmental benefits. These benefits are reviewed in a range of representative climate areas including northern temperate agriculture in northern Europe, southern temperate agriculture in the United States, and subtropical and tropical agriculture in Brazil. Cover crops suppress weeds most reliably during the vegetative growth phase of the cover crop. The maintenance of a vigorous groundcover during fallow periods in crop rotations represents an application of cover crops where the goals for weed management coincide well with other important environmental goals for improving soil quality and fertility and for reducing erosion. Residue remaining after cover crop death is less reliable for suppressing weeds, particularly for the duration of a cash-cropping season. The biggest tradeoffs between optimizing weed control and enhancing environmental protection occur during the cash-cropping period that follows cover cropping. In this case, since the cover crop cannot be expected to adequately control weeds without interfering with the cash crop, management of cover crops for growing the cash crop should focus on enhancing their environmental benefits to the agroecosystem rather than their contribution to weed management. This review will help farm advisors and researchers worldwide to identify optimum strategies for using cover crops and to focus future cover crop research programs.

Technical Abstract: Cover crops have been shown to have multiple influences on the agroecosystem. The introduction of cover crops into the agroecosystem offers opportunities for managing many aspects of the system simultaneously. But it also adds a higher level of complexity and potential interactions that may be more difficult to predict and manage. This chapter reviews the contribution that cover crops can make to weed management and the tradeoffs that may be required between achieving weed management, crop production, and environmental benefits. Cover crops can be used most reliably to suppress weeds during the vegetative growth phase of the cover crop. The maintenance of a vigorous groundcover during fallow periods in crop rotations represents an application of cover crops where the goals for weed management coincide well with other important environmental goals for improving soil quality and fertility and for reducing erosion. However, cover crops must be managed carefully to optimize environmental benefits and minimize potential liabilities for crop production. Cover crops that have been grown during any period unavailable for cash crops, whether a fallow period or an off-season winter period in temperate production systems, will need to be managed before planting the next cash crop. The cover crop essentially becomes a weed that needs to be managed properly or it will become a liability rather than a benefit. Residue remaining after cover crop death is less reliable for suppressing weeds, particularly for the duration of a cash-cropping season. This has led to many lines of research to enhance the inconsistent weed control achieved by cover crop residue. Attempts to increase residue biomass can enhance weed suppression but also can enhance the probability of crop suppression. Another strategy has been use of the more effective weed-suppressive capabilities of live cover crops by developing intercropping systems, however, research has shown that most live cover crops effective enough to suppress weeds will also suppress crops. Thus, the biggest tradeoffs between optimizing weed control and enhancing environmental protection occur during the cash-cropping period that follows cover cropping. In this case, since the cover crop cannot be expected to adequately control weeds without interfering with the cash crop, management of cover crops for growing the cash crop should focus on enhancing their environmental benefits to the agroecosystem rather than their contribution to weed management. Cover crops may ultimately contribute most to weed management within subsequent cash crops by reducing weed populations during fallow periods. The agronomic goal would be to replace unmanageable weed populations with a more manageable cover crop population. Live cover crops can significantly suppress weed biomass, seed production, and growth of perennial structures. In addition, research has suggested that live vegetation may be important for enhancing activity of seed predators and reduction of seed populations. More research is needed to understand effects of cover crops on weed seed production and predation and on seed mortality in soil. More research also is needed on perennial weed responses to cover crops. Regulation of weed population dynamics and community structure could become an important objective for future weed management programs using cover crops. Long-term cover cropping strategies need to be developed which will integrate both weed population management and enhanced environmental services.