Effects Of N Management On Photosynthetic Character And Fertilizer-N Use Efficiency Of Rice In Cold Area Of China

Heilongjiang is the main high-quality japonica rice producer in China. The average amount of fertilizer-N applied in Heilongjiang is 150 kg·hm-2, which is 50% higher than needed. Most of the fertilizer-N is applied as basal and tillering fertilizer. This fertilization pattern resulted low yield and low N use efficiency (NUE). To overcome these problems, our research group put forward a technologe called integrated nitrogen management (INM), which can increase rice yield by 15%, increase NUE by 30% as well.This study was conducted on the basis of previous research to investigate the mechanisms of N management improving rice yield and NUE. Two field experiments were included:(1) field experiment with two N application rates (105 kg·hm-2 and 135 kg·hm-2) and two application patterns (INM and farmers' fertilization practice, FFP) in order to study the effects of INM on photosynthetic character and NUE. (2) A plot experiment with two transplanting densities and two nutrient management methods to clarify the effect of INM on yield and NUE, and to explain the key process of achiving high yield and high NUE through N absorption and dry matter accumulation regulation. The main results obtained are as follows:1. INM increased the net photosynthetic rate (Pn) of rice after heading. There was a significant positive correlation between Pn 10 d after heading and yield (P<0.05). The difference of photosynthetic N use efficiency (PNUE) between INM and FFP was significant. The PNUE 10d after heading was positively correlated with NUE. INM also increased SPAD value, net assimilation rate and soluble sugar content of rice leaves.2. INM significantly improved population quality of rice. This population had a properiate LAI at heading stage, and kept relative higher effective leaf area after heading stage. The leaves had a high productivity. Under the condition of low N rate, INM reduced LAI declining rate by 9.8%, and the LAI declining rate of high N rate was higher than that of low N rate. INM treatments under different densities reduced LAI declining rate by 20.9-53.9(P<0.05), and significantly increased SLW, grain/leaf area and culm-sheath dry weight as well.3. INM significantly increased dry matter accumulation after heading stage, and there was a significant positive correlation (P<0.01) between dry matter accumulation and yield. Compared with FFP treatments, INM treatments reduced translocation ratio of stem and leaf, increased contribution ratio of net assimilation after heading(P<0.05).4. INM significantly increased N accumulation at later stages. N accumulation at panicle initiation stage was negatively correlated with yield, whereas N accumulation afer heading was positively correlated with yield. The translocation ratios and translocation contribution ratios of INM after heading were significantly lower than that of FFP, and the contribution ratios of N assimilation were higher than that of FFP treatments.5. INM increased rice yield by 11.6%～23.5%(P<0.05), increased NUE by 6.7～30.2 percentage points, increased AE by 8.12～16.12 kg·kg-1, and increased PFP by 8.12～38.46 kg·kg-1.