The quality of a protein for animal growth is partially determined by the relative abundance of essential amino acids. Those essential amino acids supplied in the lowest quantity relative to the animal’s requirement limit growth. Examination of soybean protein across genetic sources and environments has indicated that the abundance of potentially limiting amino acids within soybean protein may be influenced by the seed protein concentration. Our objective was to evaluate the effects of seed protein concentration on relative amino acid abundance under controlled environments in order to better understand the biological basis of this apparent relationship. This was accomplished through the use of source-sink treatments that altered seed protein concentration within environments. Increasing the source-to-sink ratio through partial pod removal and open environment treatments significantly increased seed protein; however, the resulting protein was disproportionately enriched in the amino acids glutamic acid and arginine at the expense of the limiting amino acids lysine, cysteine, methionine, threonine, and tryptophan. Defoliation treatments gave the opposite response to pod removal, resulting in a more favorable amino acid balance but with a lower seed protein concentration. Alternatively, the shade treatment increased protein concentration, but the relative concentration of the limiting amino acids was not reduced. This indicates that limiting amino acid abundance is not solely dependent on seed protein percentage and that limiting amino acids may be supplied by the vegetative tissue under C-limited conditions. The ultimate goal of soybean seed improvement is to increase yield while also increasing or maintaining seed protein concentration and the balance of the limiting amino acids. Meeting two of these goals was achieved through the current source-sink treatments as the open environment treatment increased seed yield and protein concentration while shade increased protein concentration and maintained limiting amino acid balance. Meeting all three goals concurrently for soybean improvement was not achieved in the current experiment and may be difficult.