Fertilizer-Nitrogen Use Efficiency and Its Physiological Mechanism under Site- Specific Nitrogen Management in Rice

Abstract

Nitrogen (N) fertilizer is one of the most important factors affecting grain yield in rice. High N inputs and low use efficiency is a main problem in rice production in China. Site-specific N management (SSNM) has been considered as a new technique, which could increase N use efficiency in rice. However, its underlying mechanism is not understood. In this study, one indica hybrid Shanyou 63 and two japonica cultivars Wuyujing 3 and Yangjing 9538 were field-grown, and two treatments, SSNM and farmers' fertilizer practice (FFP), were conducted. The results showed that SSNM reduced N rate by 48.1-63.0% and increased grain yield by 0.1-9.3% when compared with FFP. The recovery efficiency and agronomic efficiency of fertilizer-N under SSNM were increased by 31.4-56.8% and 143.6-166.0%, resp., as compared with those under FFP. The peak of N uptake appeared during the period from panicle initiation to heading. The N uptake during this period and its ratio to total N uptake during the whole growth stage were significantly higher under SSNM than under FFP. The amount of N uptake after heading under SSNM was also much higher than that under FFP. From panicle initiation, root weight and activity (especially root activity per stem) under SSNM were higher than those under FFP. SSNM also significantly increased the activities of glutamine synthetase, nitrate reductase and Fd-glutamate synthase in leaves at the panicle initiation and heading stages. Photosynthetic rate of the flag leaves was also obviously greater under SSNM than under FFP. These results indicated that SSNM could promote root growth, increase matter production and nutrient uptake during the mid and late growth periods, leading to higher fertilizer-N use efficiency in rice.