2 Seedlings of bok choy and tomato were grown in soils with different nitrogen (N) sources [no N (−N), ammonium sulfate (AS), and cattle farmyard manure (CM)]. Comparison between soils treated with −N and CM indicated that the growth and N accumulation in bok choy were significantly enhanced by CM treatment, whereas no difference was found in tomato. In the rhizosphere soils, the highest protease activity was detected in CM treatment irrespective of species. Correlation analysis between rhizospheric protease activity and total N accumulation of plant treated with {N and CM showed a significant positive correlation only for bok choy. The determination of amino acid absorption rate in excised roots indicated that glycine was taken up at a significantly higher rate in bok choy than tomato. This study suggested that at least two possible factors affected the acquisition of organic N: rhizospheric protease activity and ability to absorb amino acids in roots.