Growth response to organic nitrogen application was observed among various crops. We used rice bran mixed with rice straw as organic nitrogen source with a C/N ratio of 20. Nitrogen was not readily released from the organic matter because of the high C/N ratio. Organic nitrogen was applied with chemical fertilizers in an upland field to various crops such as upland rice, maize, potato, sugar beet and soybean. Inorganic nitrogen level in fallow soil was lower until the middle of the growth stage when organic nitrogen and chemical N-P-K fertilizers were applied, compared to the application of chemical fertilizers, only. In contrast to the inorganic nitrogen level in soil, upland rice grew better with organic nitrogen than chemical fertilizer, and took up more nitrogen than other crops during the first 100 days after amendment with organic nitrogen. These results can be attributed to 2 factors. (1) Higher mineralization rate in the rhizosphere of upland rice compared with other crops. Upland rice may enhance nitrogen mineralization in soil by the secretion of some enzymes such as protease and/or materials promoting microorganism activity. (2) Upland rice has a greater ability to take up organic nitrogen directly. If a crop is capable of taking up organic nitrogen in the form of amino acids, peptides and protein, the crop could absorb nitrogen with less competition for nitrogen with microorganisms compared with a crop which absorbs nitrogen mainly as nitrate. The protease activity in the soil planted with maize and sugar beet was higher than that in the soil planted with upland rice and in fallow soil. These results show that the enhancement of nitrogen mineralization is not essential for upland rice. In relation to hypothesis (2), upland rice took up more amino acids than maize in a solution culture containing some kinds of amino acids. The amino acid and protein contents in the soils from the rhizosphere and non-rhizosphere zones of upland rice (hereafter referred to as “rhizosphere and non-rhizosphere soils”) were lower than those in the case of maize, soybean and fallow soil. We also observed that upland rice took up nitrogen before mineralization based on a ¹⁵N-labelled rice bran application test. These results suggest that upland rice may take up organic nitrogen preferentially compared with other crops. We examined the nitrogen uptake mechanism of upland rice and maize. Upland rice takes up nitrogen preferentially in the organic form rather than as nitrate which is the favorite form for maize. Endocytosis is one of the mechanisms for organic nitrogen uptake by upland rice.