Intercropping corn with soybean, lupin and forages: weed control by intercrops combined with interrow cultivation

Intercropping corn with legumes is an alternative to corn monocropping and is a possible way to reduce the use of inputs, such as herbicides, while maintaining current weed control levels. Two experiments were carried out at each of two sites in both 1993 and 1994. The first experiment investigated the effects of seeding soybean or lupin alone or in combination with one of three forages (annual ryegrass, Lolium multiflorum Lam.; perennial ryegrass, Lolium perenne L.; and red clover, Trifolium pratense L.) on weed control. The second experiment examined the effects of seeding date (simultaneous with corn or 3 weeks later) and number of rows of large-seeded legumes (one or two) seeded between the corn rows, on weed control. Whenever seeding of legumes/forages was delayed, weekly interrow tillage operations were used to control weeds until legume/forage seeding. The density and biomasses of monocot weeds, either on or between the corn rows, were not affected by cultivation or intercropping. The density and biomass of dicot weeds on corn rows were reduced by some intercrop systems. For the various cropping systems tested, the dicot weed biomass and density between corn rows were most affected (in some cases reduced by 73-100% of the weedy control). A more effective dicot weed control was observed in delay seeded treatments, which allowed extra interrow cultivations. Intercrops that included soybean were also more successful at reducing weed populations than those containing lupin. Underseeded forages did not reduce weed biomass or density. (C) 1998 Elsevier Science B.V.