Crop Rotation and Intercropping Strategies for Weed Management

Abstract

Results of a literature survey indicate that weed population density and biomass production may be markedly reduced using crop rotation (temporal diversification) and intercropping (spatial diversification) strategies. Crop rotation resulted in emerged weed densities in test crops that were lower in 21 cases, higher in 1 case, and equivalent in 5 cases in comparison to monoculture systems. In 12 cases where weed seed density was reported, seed density in crop rotation was lower in 9 cases and equivalent in 3 cases when compared to monocultures of the component crops. In intercropping systems where a main crop was intersown with a "smother" crop species, weed biomass in the intercrop was lower in 47 cases and higher in 4 cases than in the main crop grown alone (as a sole crop); a variable response was observed in 3 cases. When intercrops were composed of two or more main crops, weed biomass in the intercrop was lower than in all of the component sole crops in 12 cases, intermediate between component sole crops in 10 cases, and higher than all sole crops in 2 cases. It is unclear why crop rotation studies have focused on weed density, whereas intercropping studies have focused on weed biomass. The success of rotation systems for weed suppression appears to be based on the use of crop sequences that create varying patterns of resource competition, allelopathic interference, soil disturbance, and mechanical damage to provide an unstable and frequently inhospitable environment that prevents the proliferation of a particular weed species. The relative importance and most effective combinations of these weed control tactics have not been adequately assessed. In addition, the weed-suppressive effects of other related factors, such as manipulation of soil fertility dynamics in rotation sequences, need to be examined. Intercrops may demonstrate weed control advantages over sole crops in two ways. First, greater crop yield and less weed growth may be achieved if intercrops are more effective than sole crops in usurping resources from weeds or suppressing weed growth through allelopathy. Alternatively, intercrops may provide yield advantages without suppressing weed growth below levels observed in component sole crops if intercrops use resources that are not exploitable by weeds or convert resources to harvestable material more efficiently than sole crops. Because of the difficulty of monitoring the use of multiple resources by intercrop/weed mixtures throughout the growing season, identification of specific mechanisms of weed suppression and yield enhancement in intercrop systems has so far proven elusive. Significant advances in the design and improvement of weed-suppressive crop rotation and intercropping systems are most likely to occur if three important areas of research are addressed. First, there must be continued attention to the study of weed population dynamics and crop-weed interference in crop rotation and intercropping systems. More information is needed concerning the effects of diversification of cropping sys...

Ecological principles underlying the increase of productivity achieved by cereal-grain legume intercrops in organic farming. A review

“…Intercrops can potentially reduce weeds, diseases and pests (Trenbath 1993;Altieri 1999) often regarded as determinant factors influencing crop production (Liebman 1988;White and Scott 1991;Liebman and Dyck 1993;Midmore 1993;Bulson et al 1997;Liebman and Davis 2000;HauggaardNielsen et al 2001b). In particular, grain legumes, such as peas (P. sativum L.), are known to be weak competitors against weeds when grown as the sole crop (Wall et al 1991;Townley-Smith and Wright 1994;Mcdonald 2003), and weed infestations have been shown to severely limit the N nutrition and grain yield of organically grown grain legumes (Corre-Hellou and Crozat 2005).…”

Eliminating soil disturbance reduces post-alfalfa summer annual weed populations

“…To maximize the weed suppressing ability of alfalfa, information regarding the impact of alfalfa stand termination on weed populations is required (Liebman and Dyck 1993).…”

Competition between corn and a living mulch

“…other hand, weed control is more challenging with reduced tillage (Liebman and Dyck 1993) and crop yields are commonly maintained by herbicide use (Weersink et al 1992). An alternative strategy is the use of living mulches.…”