Effects of combined controlled released nitrogen fertilization on yield and nitrogen use efficiency of mid-season rice-ratoon rice in early-maturing indica hybrid rice

【Objective】This field experiment was conducted to investigate the effects of different types of slow and controlled release fertilizers and combinations with urea on the mid-season indica hybrid rice-ratoon rice yield，nitrogen use efficiency. The study aimed to screen suitable slow and controlled release fertilizers and fertilization methods，and to provide theoretical and practical basis for high yield and high efficiency production of ratoon rice in the upper reaches of the Yangtze River.【Method】With indica rice Guang 8 Youyuehesimiao（G8YYHSM）as material，an experiment was conducted with six fertilization treatmentsin the mid-season of indica hybrid rice，included no nitrogen application in mid-season and ratoon season（CK），conventional split fertilization（CF），4 months single fertilization of polymer-coated urea （B-PCU），single fertilization of slow-release fertilizer blend（B-SRFB），4 months base-tiller N fertilizer of polymercoated urea（BT-PCU），base-tiller N fertilizer of slow-release fertilizer blend（BT-SRFB）. The differences of yield and yield components，dry matter accumulation，leaf SPAD value and nitrogen use efficiency of different treatments were compared and analyzed.【Result】The yield of mid-season rice was ranged from 6.8 to 8.9 t/ha，with the order of BT-SRFB> B-SRFB>CF>BT-PCU>B-PCU>CK. The yield of mid-season rice in B-SRFB and BT-SRFB treatments was significantly higher than that in CK（P<0.05，the same below），but there was no significant difference between slow and controlled release fertilizer treatment and CF treatment（P>0.05，the same below）. The yield of ratoon rice was ranged from 1.5 to 2.6 t/ha，with the order of BT-SRFB>B-SRFB>BT-PCU>B-PCU>CF>CK. The results showed that the yield of fertilizer treatment was significantly increased compared with CK，and the yield of BT-SRFB and B-SRFB was significantly higher than that of CF. In terms of fertilization methods，the yield of medium and ratoon rice of base-tiller nitrogen fertilizer treatments were higher than that ofsingle fertilization. There was no significant difference indry matter weight at jointing and heading stage between slow and controlled release fertilizer treatment and CF. But dry matter weight at maturing stage of base-tiller nitrogen fertilizer treatment was significant higher than that of single fertilization and conventional split fertilization. There was no significant difference in dry matter weight between different nitrogen treatments at heading and maturing stages of ratoon rice. Compared with CF treatment，the slow and controlled release fertilizer treatments increased nitrogen partial factor productivity（PFP），agronomic efficiency（AE）and recovery efficiency（RE）in mid-season and ratoon rice，and the BT-SRFB showed the highest increase range. Compared with CF treatment，the BT-SRFB treatment increased the PFP，AE，physiological efficiency（PE）and RE by 5.5 kg/kg，5.5 kg/kg，0.6 kg/kg and 24.4%， respectively.【Conclusion】In conclusion，base-tiller nirogen fertilizer of combined slow-release fertilizer application can improve grain yield and fertilizer-nitrogen use efficiency of the early-maturing indica hybrid rice G8YYHSM across midseason and ratoon season in the upper Yangtze River.