27. Poblaciones, biomasa y banco de semillas de arvenses en cultivos de maiz zea mays l. Y frijol phaseolus vulgaris l. Efecto de m+todos de control y rotaciones. (Weed population, biomass, and seed bank in maize and bean crops. Effects of control methods and crop rotations).

Tesis Maestria, Chapingo, Mexico, Colegio de Postgraduados, 1987, 192 pp.

The changes in weed population and groups in maize, beans, and maize/beans in rotation were assessed for the 4th consecutive yr, using 3 weed control measures:

- chemical control (linuron plus alachlor) in beans and atrazione plus metolachlor in maize;
- mechanical control (hoeing), and
- unweeded check.

In 1982 and 1983, Amaranthus hybridus was the dominant species as to population and DM, but in 1984 and 1985 Simsia amplexicaulis dominated.

In 1985 (the 4th yr), S. amplexicaulis and the group of Gramineae were the most abundant under chemical control and Simsia and Chenopodium album in the unweeded check. Total DM of these species at crop harvest accounted for approx. 87 percent of total weed DM. Under mechanical control, the most abundant species were Galinsoga parviflora and the group of Gramineae, represented by Eleusine multiflora, Eragrostis mexicana spp. mexicana, and Cynodon dactylon; the DM of the group accounted for approx. 35 percent of total weed DM. Parameters used to evaluate the structure of the group of Gramineae were species diversity and equity. Forty-four species (7 more than in previous yr) were recorded. Results of diversity and equity indicated that the structure of the group was unaltered by weed control methods, since greater diversity occured under mechanical control and less diversity in the unweeded check. The highest bean seed yield was registered under mechanical control. The highest maize yield was obtained in the rotational scheme, yield increase being attributed to the increased soil fertility resulting from soil-N fixation by beans planted in the previous cycle. The highest density and wt. of weeds was registered in beans; competition therefore affected this crop more than it affected maize. Amaranthus and Chenopodium were the most abundant species found in the soil of the seed bank. The correlation between the no. of seeds in the soil with the no. of seedlings that emerged indicated a correlation between Eleusine seeds in bean and maize plantings (P less than 0.01); a correlation was also found between Simsia seeds in bean crops (P less than 0.05), indicating that it is possible to predict the presence of weeds in these crops.

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Plant protection

Africa, Nigeria, study, weed control, cassava, maize, cowpea, melon, groundnut, intercropping

ZUOFA, K. et al.