Two greenhouse trials were carried out under greenhouse conditionsat the Department of Agricultural Biology at FCAV-UNESP in Jaboticabal, SP, Brazil to study tbiomass accumulation as well as macronutrient distribution and accumulation during the life cycle of the soybean cultivar BR 16 from October 2000 to February 2001, and Richardia brasiliensis (Brazilian pusley), from October 1998 to February 1999. Brazilian pusley is one of the most important weeds in the mid western soybean growing area, mainly under no tillage system. The studies were conducted in a randomized complete design with four replications. Four plants were grown in seven liter pots filled with sandy substrate irrigated daily with a nutritive solution. The treatments were represented by timing of sampling, performed at 14 day intervals, 22, 36, 50, 64, 78, 92, 106, 120, 134, 148, 162 and 176 days after emergence (DAE) of R. brasiliensis plants; and 21, 35, 49, 63, 77, 91, 105 and 119 DAE of the soybean plants BR-16 (early maturity) For both plants, the leaves had the highest biomass partition during seven weeks. For these data, partition was higher in reproductive structures in soybean and in the stems for Brazilian pusley. The maximumcritical biomass accumulation was estimated at 104 days for soybean (36.6 g plant-1) and at 146 days for R. brasiliensis (16.4 g planta-1). From emergence up to 50 DAE, the leaves presented higher participation in biomass accumulation, in both species. After 50 DAE, it was observed in both species an inversion in leaf representativity per shoots, for the weed species and per shoots and later per reproductive structures, for thecrop. The maximumdaily macronutrient uptake ratewas achieved between 69 and 87 days in soybean and 106 and 111 DAE in R. brasiliensis. Considering of the inflexion point average observed for the soybean culture, it is possible to estimate that, at 78 DAE, this plant theoretically accumulates 25.9 g of dry weight ; 615.6 mg oN; 77.2 mg P; 538.6 mg K; 535.0 mg Ca; 171.5 mg Mg and 39,5 mg S. In the same period, one razilian pusley plant accumulates 3.7 g dry weight; 50.8 mg N; 3.2 mg P; 104.4 mg K; 127.8 mg Ca; 18.8 mg Mg and 3. 7 mg oS.
Soybean; Brazilian pusley; weeds; plant nutrition; ecophysiology
