It has been established that plant leaves and other above-ground parts are capable of absorbing chemicals and nutrients. However, there is scarce information regarding translocation and recovery rate of ion uptake via leaves during different growing stages. Urea has generally been found to be the least toxic and most effective form of N for foliar application becasuse of its nonpolar and undisociated characteristics. ¹⁵N-labelled urea combined with KCl or KH₂PO₄ was both applied on selected leaves of com and wheat at different middle-latter growing periods. The top dressing of ¹⁵N-labelled urea in sand culture of corn at silking stage was also investigated to compare the effects of different foliar and root top dressing on plant growth. The N input in leaves of both crops was remobilized rapidly to other organs. For summer corn, the transferred percentages into roots of ¹⁵N input in lower (the fifth leaf) and middle (the eighth leaf) leaf were 9.0% and 2.4%, respectively, at jointing stage. Recovery rate of leaf-input urea-¹⁵N in whole corn plant ranged in 59.9%-75.3%, while the rate in above-ground part of winter wheat was in 54.5%-68.9%. There was very similar tendency for the two crops that the ¹⁵N recovery rate taken up via leaves was apparently increased as delay of application period. Compared with urea feeding alone, combined foliar application of urea with KCI or KH₂PO₄ increased the recovery rate and improved the N nutritional status of whole plants, in which the optimum treatment for com was foliar feeding of urea plus KH₂PO₄ to middle leaf. Therefore foliar fertilization should also focus on balance supply, suitable application stage and leaf position. Foliar feeding of N or P and K fertilizer not only improved the corresponding nutrient status in plants, but also stimulated root uptake of the other two nutrients and increased translocation ratio of N and P to grain. The finally accumulated ratios of labelled urea-¹⁵N in grains top-dressed via the roots and leaves at Bilking period were 56% and 70%, respectively.