01999naa a2200181 a 450000100080000000500110000800800410001910000190006024501010007926000090018050001330018952013190032265000220164165300230166365300200168670000210170677300900172711010332019-07-09       1999    bl uuuu     u00u1 u    #d1 aMARENCO, R. A.  aCrop rotation reduces weed competition and increases chlorophyl concentration and yield of rice.  c1999  aTítulo em português: A rotação de cultura reduz a matocompetição e aumenta o teor de clorofila e a produtividade do arroz.  aCrop rotation is an essential in sustainable agricultural systems, because its effects on soil fertility and other benefits including reduction on weed competition. A field experiment was carried out at the UEMA experimental station, Sao Luis, Maranhao State, Brazil, to evaluate the effect of crop rotation on weed population, leaf chlorophyll concentration and yield of rice (Oryza sativa L. cv. Guarani). The rice was cultivated with and withourt N application, and in rotation with cowpea (Vigna unguiculata (L.) Walp.), hyacinthbean (Crotalaria paulina Schrank) and velvetbean (Mucuna aterrima Piper & Tracy). First crop legume residues were highest in hyacinthbean, less in velvetbean and least in cowpea. They were left at soil surface as mulch for the second crop, which was cultivated in a minimum tilage system without using herbicides. At the second crop, weed biomass, weed cover, and weed density were lower in the hyacinthbean and velvetbean rotation than in continuos rice. Leaf chlorophyll concentration was greater in the hyacinthbean-rice sequence than in control plots. Rice yield was greater when rotated with hyacinthbean or velvetbean than in continuous crop with or without N application. It was concluded that legume in rice rotation reduces weed competition and improves the yield of rice.  aVigna Unguiculata  aCrotalaria paulina  aMucuna aterrima1 aSANTOS, A. M. B.  tPesquisa Agropecuária Brasileira, Brasília, DFgv. 34, n. 10, p. 1881-87, out. 1999