Crop-livestock integration benefits grain and animal production simultaneously. However, the weed species that mainly competes with the annual crop is forage. This study aimed at the quantification of Brachiaria brizantha emergence periods on soybean. The trial carried out under greenhouse conditions evaluated 7 emergence periods of B. brizantha (-21, -14, -7, 0, 7, 14, and 21 days after soybean emergence) and soybean monocrop. When soybean was in full flower (stage R2), the leaf area and dry biomass partitioning in both species, the number of trifoliolate leaves and nodes per soybean plant, as well as the stem number of B. brizantha were evaluated. At soybean harvest (stage R8) the aerial dry biomass and stem number of B. brizantha were determined as well as the grain yield per plant, number of pods per plant, and number of seeds per pod. The B. brizantha emergence period in relation to soybean was determinant for both species’ growth. A grain yield reduction for intercropped soybean compared to soybean monocrop of 97, 96, 91, 80, 34, 27, and 15% was observed, approximately, when B. brizantha emerged within -21, -14, -7, 0, 7, 14, and 21 days, respectively. The forage accumulated an aerial dry biomass of 275, 279, 267, 202, 79, 46, and 23 g per pot in these treatments, respectively. Listed in decreasing order, the morphological traits expressing soybean susceptibility to B. brizantha interference were: trifoliolate leaf numbers and leaf area > dry biomass of leaves, stem, roots and nodules > node number. The number of pods per soybean plant was not affected by B. brizantha interference when its emergence occurred 21 days after soybean emergence and the number of seeds per pod was only negatively affected when the forage emergence occurred -21 and -14 days after soybean’s.
Glycine max; Brachiaria; competition; interference; biomass partitioning
