Weed communities associated to wheat and pea crops in the Rolling Pampas

POGGIO, S.L., SATORRE, E.H., DE LA FUENTE, E.B.

Foz do Iguassu, Brasil.

Congreso; 3rd International Weed Science Congress; 2000

International Weed Science Society

Wheat (Triticum aestivum L.) is the most important winter crop grown in the Rolling Pampas while pea (Pisum sativum L.) have limited distribution. Pea is a feasible crop alternative in this region and its sown area may increase, affecting winter weed communities function and composition. In order to evaluate the extent of the differences between pea and wheat weed communities the floristic composition of field crops was described and compared. Eighteen pea and four wheat fields were surveyed during 1999. A set of 32 wheat fields surveyed in 1996 was also included in the analysis, since they did not significantly differed from the recent wheat surveys. In each field, species presence was recorded and their abundance determined by ground cover estimations. Floristic composition was studied by multivariate analysis, considering only species with constancy greater than 10%. Cluster analysis was used to define species groups, and reciprocal averaging was applied to define fields ordering. Total and mean number of species surveyed were 71 and 20, and 60 and 13 in pea and wheat fields, respectively. Species diversity and constancy were greater in pea fields. Eigenvalues obtained were 0.51, 0.37, and 0.28 for Axes 1, 2, and 3, respectively. Axis 1 clearly represented the contrast between pea and wheat fields. When abundance values were plotted against Axis 1, Cotula australis (Sieb.) Hook (constancy 5 79%) was associated to pea fields and a group of winter annuals to wheat fields [Bowlesia incana Ruiz et Pav., Stellaria media (L.) Vill., Coronopus didymus (L.) Smith, Carduus acanthoides L.], despite the fact that they were present in pea fields but with higher constancy and lower abundance. In both wheat and pea fields, Glycine max L., and Zea mays L. were present as volunteer crops; however, wheat plants were observed only in pea crops.