Crop and stubble effects on seedling emergence of sourgrass, palmer amaranth, wild radish and fleabane

Abstract

Abstract. Crop diversity, crop structures and crop residue can modify the seed-bank environment, influencing the seedling emergence of some weeds. The objectives of this work were to analyse (1) the effect of winter crop canopies of canola and wheat and soybean stubble on seedling emergence of Conyza sumatrensis and Raphanus sativus and (2) the effect of different soybean crop structures and soybean stubble on Digitaria insularis and Amaranthus palmeri seedling emergence. Two different field experiments were conducted at Buenos Aires University in a completely randomised factorial design with five replicates. The two winter species showed differences in the emergence timing whereas the two summer species emerged at the same time but with differences between years. Seedling emergence of A. palmeri was reduced by the presence of crop residue while the effect on C. sumatrensis and R. sativus emergence were more variable between years and D. insularis was not affected. Crops did not affect seedling emergence of winter species or that of A. palmeri. However, D. insularis emergence was favoured by soybean presence, mainly with closer canopy structures. Management decisions that promote the presence of crop residues favour the reduction of seedling emergence of palmer amaranth. In contrast, evaluated crop plant densities and planting dates were not able to reduce the seedling emergence of C. sumatrensis, R. sativus and D. insularis. Planting soybean in more competitive crop structures with closer canopies is not a good option due to the improvement of seedling emergence of D. insularis. Crop management decisions that inhibit seedling emergence in some species could stimulate it in others.