Summer 1993 (v5n4)
	Crop rotation and intercropping strategies for weed management. Liebman, Matt and Elizabeth Dyck Ecological Applications 3(1) :92-122.1993 Abstract reprinted with permission of publisher and authors. "Results of a literature survey [234 references] 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 [see Table 1]. 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 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 systems on weed seed longevity, weed seedling emergence, weed seed production and dormancy, agents of weed mortality, differential resource consumption by crops and weeds, and allelopathic interactions. Second, there needs to by systematic manipulation of specific components of rotation and intercropping systems to isolate and improve those elements (e.g., interrow cultivation, choice of crop genotype) or combinations of elements that may be especially important for weed control. Finally, the weed-related impacts of combining crop rotation and intercropping strategies should be assessed through careful study of extant, complex farming systems and the design and testing of new integrated approaches. "Many aspects of crop rotation and intercropping are compatible with current farming practices and could become more accessible to farmers if government policies are restructured to reflect the true environmental costs of agricultural production." For more information write to: Matt Liebman, Sustainable Agriculture Program, Deering Hall, University of Maine, Orono, Maine 04469. (RTN. 154) Contributed by David Chaney Table 1. Summary of research papers comparing weed control in crop rotations vs. Monocultures. Summarized in Liebman, M. and E. Dyck. 1993. Crop rotation and intercropping strategies for weed management. Ecological Applications 3(1):92-122. Study Rotation Test Crop Emerged Weed Density in Rotation1 Test Crop Yield in Rotation Stewart and Pittman (1931)2 wheat/sugar beet wheat lower higher potato/potato/pea/sugar beet/sugar beet/wheat wheat lower higher wheat/red clover/potato/sugar beet/ field bean wheat lower higher alfalfa (5 yrs)/potato/sugar beet/ pea/sugar beet/wheat wheat lower higher potato/oats/maize/field bean oats lower higher alfalfa (3 yrs)/oats/sugar beet/sugar beet/oats oats lower higher Dospekhov (1967) fallow/winter rye/potato/oats+clover/clover/flax winter rye lower unavailable potato equal unavailable oats lower unavailable clover lower unavailable flax lower unavailable Austenson et al. (1970) summer fallow/wheat wheat lower higher3 summer fallow/wheat/ wheat wheat lower higher3 MacHoughton (1973) maize/maize/soybean maize -l higher maize/soybean/wheat soybean -l higher Dowler et al. (1974) maize/peanut/cotton/soybean maize lower equal peanut equal equal cotton equal equal soybean lower higher Zawisiak (1980)4 sugar beet/field bean/spring barley sugar beet higher-e unavailable winter rye/winter rape/winter wheat field bean lower-1 unavailable spring barley lower-e unavailable winter rye lower-1 unavailable winter rape lower-e unavailable wheat lower-1 unavailable Covarelli and Tei winter wheat/maize maize lower-1 unavailable (1988) maize/winter wheat/maize maize equal-1 unavailable winter wheat/maize/maize maize equal-1 unavailable winter wheat/winter wheat/maize maize lower-1 unavailable 1 Where data were available, comparison of weed seed numbers are given as: -1 (lower), -e (equal) 2 Actual weed numbers were not reported in this study. Comparisons between rotation and monoculture treatments were based on qualitative observations. 3 Mean yield on cropped land area. 4 Weed density data represent means of combined herbicide and nonherbicide treatments. However, no interactive effects between cropping system (monoculture vs. rotation) and weed control regime (herbicide vs. nonherbicide) were reported. References for table 1: Austenson, H.M., A. Wenhardt, and W.J. White. 1970. Effect of summer-fallowing and rotation on yield of wheat, barley, and flax. Canadian J. Plant Science 50:659-666. Covarelli, G. and F. Tel. 1988. Effet de la rotation culturale sur la flore adventice du mais. In VIIeme colloque infemafional sur la biologie, l'ecologie ef la sysfemarique des mauvaises herbes. volume 2, pp.477-484. Comite Francais de Lutte Contre les Mauvaises Herbes, Paris, France. Dospekhov, B.A. 1967. The effect of long term fertilizer application and crop rotation on the infestation of fields by weeds. weed Abstracts 17:132. Dowler, C.C., E.W. Hauser and A.W. Johnson. 1974. Crop-herbicide sequences on a southeastern coastal plain soil. weed Science 22:500-505. MacHoughton J. 1973. Ecological changes in weed populations as a result of crop rotations and herbicides Dissertation Abstracts 34:4160B-4161B. Stewart, G. and D.W. Pittman. 1931. Twenty years of rotation and manuring experiments at Logan, Utah. Utah Agricultural Experiment Station Bulletin 228. Zawislak, K. 1980. Stopien specjalizacji zmianowan a aktualne I potencjalne zachwaszczenie stanowisk. zeszyty Naukowe Akademil Rolniczo-Technicznel w Olsztynie, Rolniciwo 29:283-293 [ Back | Search | Feedback ]