The preferential form of nitrogen absorption (15NH4+ or 15NO3-) by soy beans, beans, rice and corn crops

In annual crops, the nitrogen fertilizer application practice can supply the nitrogen needed for maximum yield. However, taking into account the damaging effects on the environment of improperly planned fertilizer use, it is necessary to adjust the amount and the forms of N to be applied according to crop requirement. Viewing to determine the N form which is preferentially absorbed by the plants at their initial growth stage, an experiment was carried out under green house conditions in a Hapludox soil. Ammonium nitrate (AN) in which 2% of the N was labelled N (15N) either as NH4+ or as NO3- was used. The AN solution was then applied onto the soil surface of each vase at the rate of 100 mg of N either at sowing or 10 days later. The results showed that the soybean plants, when fertilization was made at sowing, had no preferred form of N. But, if fertilization took place 10 days after sowing, the NH4+ form was the preferred one. Common bean plants showed no preferred form. Rice plants preferred the NH4+ form irrespective of fertilization time. Corn plants preferred the ammoniacal form when fertilization was made at sowing. (author)