Weed spatial distribution as a function of soil properties in two distinct environments of the Brazilian semi-arid region.

The present study aimed was to evaluate the spatial variability of weed species by means of phytosociological parameters and their correlations with the physical-chemical soil properties, under semiarid climate conditions. Weed phytosociology and soil characterization were carried out in two areas one newly deforested area covering 8.86 ha, and one experimental agricultural area covering 24.7 ha; both in the semi-arid region of Brazil. Weed and soil were sampled by following georeferenced grids in each area. Biomass and the total number of weed individuals, as well as soil properties, were mapped by the ordinary Kriging method. The predominant herbaceous plants in the newly deforested area were Hexasepalum teres and Digitaria insularis. The weed species that predominated in the agricultural area were Cyperus rotundus L., Euphorbia heterophylla L. and Herissantia Crispa (L.) Brizicky; the latter species outstanding for dry biomass (873.5g). Spatial dependence was observed for the predominant species, except for Digitaria insularis. The spatial distribution of these weeds was conditioned by soil K+ contents in both areas, and by sand content for the experimental agricultural area. Therefore, these two soil attributes resulted key factors for weed infestation in this semi-arid region.