“…Studies aiming to increase the use efficiency of N are mainly focused on the following aspects: (1) breeding crop varieties with high N use efficiency (Shi et al, 2002), (2) improving the formulation of N fertilizers such as manufacturing of slow-release fertilizers (Huang and Dal, 2002), (3) supplementing nitrification inhibitor or using urease inhibitor (Chen and Lu, 1997), and (4) ameliorating of application methods, such as the split application (Kawashima, 1984), deep placement of N fertilizer (Bautista et al, 1999) and flooding the rice field after top-dressed fertilization (Chen et al, 1987). Some report that totally basal dressing to the cultivated layer could significantly increase the N use efficiency and thus increase rice yield (Imori, 1993;Shuai and Yang, 1998).…”