Effect of Nitrogen Regimes on Grain Yield, Nitrogen Utilization, Radiation Use Efficiency, and Sheath Blight Disease Intensity in Super Hybrid Rice

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1 Journal of Integrative Agriculture 2012, 11(1): January 2012 RESEARCH ARTICLE Effect of Nitrogen Regimes on Grain Yield, Nitrogen Utilization, Radiation Use Efficiency, and Sheath Blight Disease Intensity in Super Hybrid Rice LI Di-qin 1, TANG Qi-yuan 1, ZHANG Yun-bo 1, QIN Jian-quan 1, LI Hu 1, CHEN Li-jun 1, YANG Sheng-hai 1, ZOU Ying-bin 1 and PENG Shao-bing 2 1 State Key Laboratory of Hybrid Rice, Hunan Agricultural University, Changsha, Hunan , P.R.China 2 Crop Physiology and Production Center (CPPC), Huazhong Agricultural University, Wuhan , P.R.China Abstract Poor nitrogen use efficiency in rice production is a critical issue in China. Site-specific N managements (SSNM) such as real-time N management (RTNM) and fixed-time adjustable-dose N management (FTNM) improve fertilizer-n use efficiency of irrigated rice. This study was aimed to compare the different nitrogen (N) rates and application methods (FFP, SSNM, and RTNM methods) under with- and without-fungicide application conditions on grain yield, yield components, solar radiation use efficiency (RUE), agronomic-nitrogen use efficiency (AE N ), and sheath blight disease intensity. Field experiments were carried out at Liuyang County, Hunan Province, China, during 2006 and A super hybrid rice Liangyou 293 (LY293) was used as experimental material. The results showed that RTNM and SSNM have great potential for improving agronomic-nitrogen use efficiency without sacrificing the grain yield. There were significant differences in light interception rate, sheath blight disease incidence (DI) and the disease index (ShBI), and total dry matter among the different nitrogen management methods. The radiation use efficiency was increased in a certain level of applied N. But, the harvest index (HI) decreased with the increase in applied N. There is a quadratic curve relationship between grain yield and applied N rates. With the same N fertilizer rate, different fertilizer-n application methods affected the RUE and grain yield. The fungicide application not only improved the canopy light interception rate, RUE, grain filling, and harvest index, but also reduced the degree of sheath blight disease. The treatment of RTNM under the SPAD threshold value 40 obtained the highest yield. While the treatment of SSNM led to the highest nitrogen agronomic efficiency and higher rice yield, and decreased the infestation of sheath blight disease dramatically as well. Nitrogen application regimes and diseases control in rice caused obvious effects on light interception rate, RUE, and HI. Optimal N rate is helpful to get higher light interception rate, RUE, and HI. Disease control with fungicide application decreased and delayed the negative effects of the high N on rice yield formation. SSNM and RTNM under the proper SPAD threshold value obtained highyield with high efficiency and could alleviate environmental pollution in rice production. Key words: super hybrid rice, real-time N management, fixed-time adjustable-does N management, grain yield, sheath blight, radiation use efficiency, agronomic-nitrogen use efficiency INTRODUCTION Poor nitrogen use efficiency is a critical issue in irrigated rice systems in China (Wang et al. 2001; Peng et al. 2002). Irrigated rice accounts for about 7% of global N consumption, with China being the world s largest consumer of nitrogen (N) fertilizer (Peng et al. Received 23 December, 2010 Accepted 3 June, 2011 Correspondence TANG Qi-yuan, Tel: , cntqy@yahoo.com.cn

2 Effect of Nitrogen Regimes on Grain Yield, Nitrogen Utilization, Radiation Use Efficiency, and Sheath Blight Disease ). Excessive nitrogen input and improper timing of N application lead to the poor nitrogen use efficiency in rice production in China and cause problems such as environmental pollution, increased production cost, grain yield reduction, and could even lead to global warming (Peng et al. 2010). Site-specific N managements such as real-time N management (RTNM) and fixed-time adjustable-dose N management (FTNM) have been developed to increase the N use efficiency of irrigated rice at the International Rice Research Institute, Manila, Philippines (Peng et al. 2006). In RTNM, N is applied only when the leaf content is below a critical level (Peng et al. 1996). In this approach, the timing and number of N applications vary across seasons and locations while the rate of each N application is fixed. The leaf N content can be estimated non-destructively with a chlorophyll meter (SPAD) or leaf color chart (LCC) (Tao et al. 1990; Peng et al. 1996; Balasubramanian et al. 1999; Yang et al. 2003). Average grain yield increased by 11% and RE N increased from 31% to 40% across all sites in Asia (Dobermann et al. 2002). The grain yield and NUE are both increased with the improved N management such as SSNM (Peng et al. 2010). Yield reduction is often observed under excessive N input due to greater pest incidence, disease damage, and lodging (Peng et al. 2010). Among the three major diseases of rice today, sheath blight disease (ShB) is the most harmful. N application is critical in the occurrence of the disease, since excess N promotes a dense foliar canopy which is in turn provides a more conducive environment for ShB development (Savary et al. 1995; Cu et al. 1996; Hu et al. 2004; Tang et al. 2007). Crop radiation use efficiency (RUE) is defined as the amount of biomass accumulated per unit solar radiation intercepted (Monteith 1977). Grain yield depends on three main factors: light interception, radiation use efficiency, and harvest index (Mitchell et al. 1998). To gain a high yield, solar energy should be effectively used in the production of biomass. Radiation use efficiency is influenced by N nutrient, CO 2, drought stress, and seasonal radiation environment (Sinclair et al. 1999). In rice, better nourishment raises RUE, while the shortage of N reduces its value (Sinclair et al. 1989). Previous studies on N management and sheath blight were conducted at two N rates (high and low N) mostly in a single season, with hybrid rice or inbred rice as experimental materials. The information on the interactive effect between site-specific N management and sheath blight control in super hybrid rice is relatively rare. In this study, super hybrid rice was used under two disease controls and seven N rates in two years. The objectives of this study were (1) to evaluate different N management strategies for increasing AE N and develop optimal N management for LY293 using RTNM and FTNM in China; (2) to compare radiation use efficiencies under FFP, SSNM, and RTNM nitrogen management methods; and (3) to identify ShB intensity and yield loss from ShB across different N rates of super hybrid rice. RESULTS The results showed that the grain yield was significantly (P=0.05) increased under SSNM and fungicide application (Table 1). A quadratic curve correlative relationship between grain yield and applied N rate was observed as shown in Fig. 1, and the relationship of quadratic curve correlation in 2006 was more significant than that in 2007 which may be caused by the maximum N fertilizer amount in 2006 (320 kg ha -1 ) and 2007 (270 kg ha -1 ). In addition, the highest grain yield and AE N were observed only under the treatment of SSNM without fungicide application, and the grain yield was also increased with the treatments of S40, S42, and FFP after fungicide application in Interestingly, the highest AE N was observed in both treatments of with fungicide and without fungicide application, but the grain yield of SSNM under both treatments was less than that of treatments S40, S42, and FFP in This may have resulted from better weather condition during the late growth stage in 2007, similar to the result of He et al. (2007) (Tables 1 and 2). From the view of yield components, the application of fungicide had contributed to the highest grain yield of S40 among all treatments in 2007 (Table 2). Fungicide application raised the AE N in each experiment (Table 3). The intercepted solar radiation rate was raised with

3 136 LI Di-qin et al. Fig. 1 N response on yield with and without fungicide treatments. Table 1 Grain yield and yield components under different N management methods and fungicide control in Liuyang Country, Hunan Province, China in 2006 Treatment N treatment Yield (t ha -1 ) Panicles (m 2 ) Spikelet per panicle Grain filling (%) Grain weight (g) Non-fungicide N d c b 81.2 abc 24.1 b SSNM 9.99 a b b 81.5 ab 25.0 a S c ab b 79.5 abc 24.8 a S bc b a 77.4 c 24.0 b S a ab a 80.0 abc 24.1 b S abc a b 78.9 bc 23.7 b FFP 9.70 ab a b 83.1 a 24.8 a Mean c d cd 80.7 bcd 24.0 b SSNM 9.89 a c ab 82.2 abc 24.9 a S b c bc 83.5 ab 25.0 a S a bc ab 77.6 d 24.0 b S a ab a 81.9 bc 24.0 b S a a d 84.8 ab 23.7 b FFP a ab d 86.0 a 24.7 a Mean The values denoted by different letters within the same column represent significant difference at 0.05 level as compared with the identical fungicide treatment. The same as below. Table 2 Grain yield and yield components under different N management methods and fungicide control in Liuyang Country, Hunan Province, China in 2007 Treatment N treatment Yield (t ha -1 ) Panicles (m 2 ) Spikelet per panicle Grain filling (%) Grain weight (g) Non-fungicide N e c cd 75.2 abc 22.1 e SSNM 8.83 c a ab 72.9 c 23.3 bc S d bc a 78.7 a 22.5 d S cd b ab 74.6 bc 23.5 b S a a abc 77.3 ab 23.0 c S ab a bc 73.9 bc 23.3 bc FFP 8.96 bc a d 74.4 bc 24.1 a Mean d e cd 74.0 bc 22.6 cd SSNM 8.99 b c ab 73.7 c 22.9 bc S c de a 78.9 a 22.4 d S b cd ab 75.5 abc 22.9 bc S a ab bc 79.3 a 23.0 b S a a abc 77.8 abc 23.2 b FFP 9.14 b bc d 78.1 ab 24.0 a Mean

4 Effect of Nitrogen Regimes on Grain Yield, Nitrogen Utilization, Radiation Use Efficiency, and Sheath Blight Disease 137 Table 3 Growth duration, leaf area index (LAI) at flowering, harvest index, total dry weight, and agronomic-n use efficiency (AE N ), and radiation use efficiency (RUE) under different N management methods and fungicide control in 2006 Treatment N treatment Growth duration (d) LAI at flowering Total dry weight (g m -2 ) Havest index AE n (kg kg -1 ) RUE (g MJ -1 ) Non-fungicide N e 1390 d 0.54 a 1.12 SSNM c 1867 abc 0.51 cd S d 1742 c 0.54 a S d 1748 bc 0.53 ab S c 1965 a 0.52 bc S a 1949ab 0.47 e FFP b 2011 a 0.51 d Mean e 1353 d 0.55 a 1.13 SSNM c 1797 bc 0.53 ab S d 1735 c 0.54 ab S cd 1776 c 0.53 ab S b 1985 ab 0.52 b S a 2115 a 0.49 c FFP b 1934 ab 0.53 ab Mean the increasing of N application in rice growth stages including mid-tillering, panicle initiation, flowering, and 15 d after flowering (Tables 4 and 5). Intercepted solar radiation rate showed a much more significant correlation after using fungicide with applied N rate than that of without fungicide treatment in the both year (Tables 4 and 5). No significant difference was observed for intercepted solar rate between the treatments with same amount of N applied but with different N applying regimes, for example, S40 and FFP with N 210 kg ha -1, and SSNM, S38 with N 120 kg ha -1 significant differences were observed. However, after fungicide application, the solar intercepted rate of treatments SSNM and S40 were much higher than that of S38 and FFP (Tables 4 and 5). A positive linear relationship was observed between RUE and amount of applied N with a certain N applying range. In addition, the RUE was significantly decreased in year 2006, when the amount of applied N was over 210 kg ha -1. A quadratic curve correlative relationship between RUE and solar intercepted radiation rate was formed in 2006 (Fig. 2). Further more, after using fungicide, the RUE was correspondingly increased. Under applying same amount of N but with different applied regimes, the RUE showed an obvious difference (Fig. 2). For example, both RUE under with fungicide and without fungicide application of SSNM (1.34 and 1.41) and S40 (1.43 and 1.42) were higher than that S38 (1.30 and 1.30) and FFP (1.43 and 1.42) (Fig. 2). Total above-ground dry matter increased with the Table 4 Light interception rate (%) at different growth stages under different N treatments and fungicide application in 2006 Treatment N treatment Mid tillering (%) Panicle initiation (%) Flowering (%) Days after flowering (%) Non-fungicide N b 76.8 d 72.1 f 70.1 d SSNM 27.0 b 88.6 c 91.7 c 90.3 b S b 80.2 c 80.0 e 78.1 c S b 86.5 c 88.8 d 86.9 bc S b 91.3 b 94.8 b 92.3 a S b 94.8 a 97.2 a 94.8 a FFP 47.8 a 93.5 a 96.8 a 91.8 ab Mean c 75.9 d 82.8 d 80.4 c SSNM 29.3 b 87.8 c 93.4 bc 92.0 b S b 85.8 c 92.0 c 91.2 b S b 87.0 c 92.2 c 92.0 b S a 90.9 b 96.0 ab 96.2 a S ab 95.5 a 97.7 a 97.2 a FFP 37.1 a 94.0 a 95.9 ab 95.6 a Mean

5 138 LI Di-qin et al. Table 5 Light interception rate (%) at different growth stages under different N treatments and fungicide application in 2007 Treatment N treatment Mid-tillering (%) Panicle initiation (%) Flowering (%) Days after flowering (%) Non-fungicide N a 56.9 d 69.6 c 68.2 f SSNM 31.6 a 76.2 b 94.7 a 90.8 cd S a 71.8 c 81.9 b 85.7 e S a 73.4 bc 93.1 a 89.3 d S a 84.5 a 97.8 a 94.1 ab S a 86.9 a 95.0 a 96.7 a FFP 31.5 a 87.3 a 96.1 a 93.1 bc Mean c 59.8 d 72.4 d 77.6 e SSNM 27.0 b 77.6 b 96.1 a 92.7 b S ab 68.6 c 82.3 c 86.0 d S b 75.5 b 91.8 b 88.8 c S a 85.0 a 97.9 a 95.2 a S ab 85.8 a 98.2 a 95.9 a FFP 29.1 ab 86.6 a 97.2 a 92.8 b Mean Fig. 2 N response in rice radiation use efficiency (RUE) with and without fungicide treatments. increase in applied N rate. In contrast, harvest index was decreased correspondingly to the applied N rate. Although, no obvious correlation was observed among the total dry weight, harvest index and different N applying strategy with same N-rate, harvest index was raised with the fungicide application (Tables 3 and 6). The results indicate that the sheath blight disease incidence (DI) and the disease index (ShBI) showed a significant difference in different production years of 2006 and DI was lower in 2006 than that in Therefore, ShBI in 2006 showed a higher value than that in 2007 (Table 7). The nitrogen application regime plays a significant role in the variation of sheath blight disease. The results show that both DI and ShBI increased with increasing of applied N rate. As shown in Table 7, treatment N 0 showed the lowest DI. The DI of the treatments with high N rate as S40, S42 were significantly higher than that of lower N rate including S36 and S38. The ShBI of S40, S42, and FFP in 2006 were more than 46%, which led to a significant loss of rice yield without fungicide treatment (Table 1). The ShBI of plots with low N rate was less than 25% and caused less loss on grain yield. Therefore, the results suggest that the high N rate leads to a larger ShBI, which further affect the grain yield of rice (Tables 1 and 2, Fig. 3). DISCUSSION Both FTNM and RTNM have great potential for improving agronomic-nitrogen use efficiency without sac-

6 Effect of Nitrogen Regimes on Grain Yield, Nitrogen Utilization, Radiation Use Efficiency, and Sheath Blight Disease 139 Table 6 Growth duration, leaf area index (LAI) at flowering, harvest index, total dry weight, and agronomic-n use efficiency (AE N ), and radiation use efficiency (RUE) under different N treatments and fungicide control in 2007 Treatment N treatment Growth duration (d) LAI at flowering Total dry weight (g m -2 ) Havest index AE n (kg kg -1 ) RUE (g MJ -1 ) Non-fungicide N f e 0.54 a 1.24 SSNM c b 0.51 cd S e d 0.54 a S d 1792 c 0.53 ab S a ab 0.52 bc S a a 0.47 e FFP b 1 957b 0.51 d Mean e d 0.55 a 1.24 SSNM c b 0.53 ab S d 1572 c 0.54 ab S d 1765 b 0.53 ab S ab a 0.52 b S a a 0.49 c FFP bc b 0.53 ab Mean Table 7 Effects of N and fungicide treatment on disease intensity of rice sheath blight Treatment N treatment DI (%) ShBI (%) DI (%) ShBI (%) 1.4 c 3.3 d 28.3 c 10.3 b SSNM 9.7 bc 26.4 cd 40.3 c 11.1 b S c 12.5 d 32.6 c 10.6 b S c 10.4 d 48.4 bc 14.0 b S a 53.7 ab 68.5 ab 22.4 a S a 74.5 a 78.2 a 25.2 a FFP 25.0 ab 46.2 bc 32.2 c 8.5 b Mean Non-fungicide N c 3.2 c 10.5 c 3.5 c SSNM 5.7 ab 20.5 ab 19.2 bc 5.5 bc S bc 8.5 bc 21.7 bc 7.4 abc S bc 9.2 bc 23.2 bc 7.4 abc S a 30.9 a 32.4 ab 9.3 ab S a 33.3 a 42.2 a 12.2 a FFP 6.3 ab 20.8 ab 18.3 bc 5.1 bc Mean Fig. 3 Relationship between rice sheath blight disease index (ShBI) and N fertilizer rate under fungicide treatments. rificing the grain yield. Super hybrid rice Liangyou 293 may obtain the highest grain yield and high AE N of 12.4 to 16.9 kg kg -1 if RTNM is applied with SPAD threshold value of 40, but high application N rate must be inte-

7 140 LI Di-qin et al. grated with pest and diseases control in order to reduce the risk of sheath blight diseases. SSNM obtained the highest AE N (ranging from 14.2 to 24.3 kg kg -1 ), substantially reduced the risk of sheath blight disease, obtained the highest grain yield amid unfavorable weather conditions (as experienced in 2006), and produced better grain yield under improved weather (in 2007). Earlier application of high N rate of FFP led to low AE N. Total dry weight and harvest index are two critical standards for rice grain yield. The related studies indicate that increasing the dry matter weight and harvest index can substantially increase grain yield, especially in super hybrid rice (Xie et al. 2003; Peng et al. 2004, 2008; Cheng et al. 2005). Photosynthesis is the foundation of crop yield formation, as more than 90% of crop dry matter weight come from photosynthesis (Wang et al. 1994). The difference among grain yield of crops may be caused by the difference of their photosynthetically active radiation and/or their radiation use efficiency (Tollenaar et al. 1992). In super hybrid rice, optimal N application is an important factor to obtain more photo-synthetically active radiation rate and high RUE. RUE, HI, and grain yield decreased with excessive N application. The study showed that nitrogen application regimes and disease control have different effects on super hybrid rice grain yield. Disease control can reduce and postpone the positive risk of high application N rate to grain yield. Sheath blight disease is a multi-spectrum which is caused by Rhizoctonia solani Kühn and an effective multi-spectrum antigen can not be found from germplasm resources (Savary et al. 1995; Hu et al. 2004). The disease is greatly influenced by fertilizer, water, and other environmental factors. Yield reduction is about 10 to 30%, even can reach more than 50% if seriously affected (Ahn et al. 1986). The reduction is from 20 to 42% in inoculated treatments with high N rate (Cu et al. 1996). Ahn and Mew (1986) reported that grain yield had a significant reduction when the comparative height of sheath blight disease symptoms was more than 30%, while no reduction was observed when the comparative height was less than 20%. It showed that rice grain yield slipped minimum by controlling ShBI appropriately during rice growth and development. Many experiments showed that high N rate favors sheath blight infestation (Zhang et al. 2006; Tang et al. 2007). Three factors influencing its prevalence are amount of sclerotia, applied N rate, and irrigation method; and applied N rate is the most important impact factors which influences its prevalence (Zhong et al. 2006). This study showed that the nitrogen application regime has a significant effect on sheath blight disease. DI and ShBI increased upon increased N application rate, and DI and ShBI of treatments S40, S42, and FFP were higher than that of S36 and S38. In 2006, ShBI of treatments S40, S42, and FFP were from 46 to 75% under without fungicide condition which caused significant yield loss. When ShBI was controlled below 33%, grain yield under high N rate treatments was higher than that of low N rate treatments. In 2007, grain yield of treatments with high N rate reduced a little under ShBI below 25%. The fungicide application significantly reduced ShBI of the high N rate treatments, and had a little influence on grain yield. In conclusion, both FTNM and RTNM were effective in achieving high grain yield and AE N in LY293 during the 2-yr period of the study. Significant differences were observed in term of light interception rate, DI, ShBI, and total dry weight among the nitrogen management methods of RTNM, SSNM, and FFD. Fungicide application not only improved the light interception rate, RUE, grain filling rate, and harvest index, but also reduced the degree of sheath blight disease. SSNM and RTNM under the proper SPAD threshold value obtained high yield with high efficiency and alleviate environmental pollution in rice production. MATERIALS AND METHODS The field experiments were conducted during 2006 and 2007 at Liuyang (28 09 N, E, 43 m asl), Hunan Province, China. The soil was clay with the following properties: ph 5.5, 31.1 g kg -1 organic matter, 127 mg kg -1 alkali hydrolyzable nitrogen, 19.2 mg kg -1 available P, and mg kg -1 available K. The soil test was based on samples taken from the upper 20 cm of the soil. Super hybrid rice Liangyou 293 was used in each experiment. Plots were laid out in a split-plot design with fungicide application as main plot and seven N rates as subplot with 4 replications. Subplots were treated as zero-n control, and S36, S38, S38, S40, as well as S42 were supplied with N rate of 80, 85, 170, and 320 kg ha -1 in 2006; 110, 120, 210, and 275 kg ha - 1 in 2007 with RTNM (real-time N management) pattern,

8 Effect of Nitrogen Regimes on Grain Yield, Nitrogen Utilization, Radiation Use Efficiency, and Sheath Blight Disease 141 respectively. Total N amount of 210 and 120 kg ha -1 were used in treatment FFP (farm practice fertilizer) and SSNM (site specific N management) during 2006 and 2007, respectively (Table 8). The rate and time of nitrogen application after transplanting was based on plant leaf s SPAD values. A chlorophyll meter (SPAD-502, Soil-plant Analysis Development Section, Minolta Camera Co., Osaka, Japan) was used to obtain SPAD values on five uppermost fully expanded leaves in each plot. Three SPAD readings were taken around the midpoint of each leaf blade, 30 mm apart, on one side of the midrib. SPAD was weekly monitored and started the measurement on d 14 after transplanting until heading. A more detailed information is given in Table 9. Pre-germinated seeds were sown in seedbed. Twentyday-old seedlings were manually transplanted on 12 June 2006 and 2007, respectively. Two seedlings per hill were transplanted at a hill spacing of 0.23 m 0.23 m. Phosphorus (50 kg P ha -1, calcium superphosphate) and zinc (5 kg Zn ha -1, zinc sulfate heptahydrate) were applied and incorporated in all plots 1 d before transplanting. Potassium (100 kg K ha -1, potassium chloride) was split equally and used at basal and panicle initiation stage. Crop management was done according to the standard cultural practices. The experimental field was kept flooded from transplanting to 10 d before maturity. Insects were intensively controlled by chemicals to avoid biomass and yield loss. Plants were sampled from a m 2 area (10 hills) to determine LAI (leaf area index) with a leaf area meter (LI- 3000A, LICOR, Lincoln, NE, USA) at MT (mid-tiller stage), PI (panicle initiation stage), FL (flowering stage), FL15 d (15 d after flowering stage), and maturity stages. Ten hills were sampled diagonally from a 5 m 2 harvest area at MA (maturity stage) to determine total dry weight, harvest index, and yield components. Panicles of each hill were counted to determine the panicle number per m 2. Plants were separated into straw and panicles. The dry weight of straw was determined after oven-drying at 70 C to constant weight. Panicles were hand-threshed and the filled spikelets were separated from unfilled spikelets by submerging them in tap water. Three subsamples of 30 g of filled spikelet and 3 g of unfilled spikelet were taken to count the number of spikelet. Dry weights of rachis, and filled and unfilled spikelets were determined after ovendrying at 70 C to constant weight. Total dry weight was the sum of the weight of straw, rachis, and filled and unfilled spikelets. Spikelets per panicle, grain-filling percentage (100 filled spikelet number/total spikelet number), and harvest index (100 filled spikelet weight/aboveground total dry weight) were calculated. Grain yield was determined from a 5 m 2 area in each plot and adjusted to the standard moisture content of 0.14 g H 2 O g -1. Canopy light interception was measured between 11:00 and 13:00 at mid-tillering, panicle initiation, flowering, 15 d after flowering, and maturity stages using Sunscan Canopy Analysis System (Delta-T Devices Ltd., Burwell, Cambridge, UK). In each plot, light intensity inside the canopy was measured by placing the light bar in the middle of two rows and slightly above the water surface. Three readings were taken within rows and another three between rows. Incoming light intensity was recorded simultaneously, when canopy light intensity was measured. Canopy light interception was calculated as the percentage of incoming light intensity that was intercepted by the canopy (100 (incoming light intensity-light intensity inside canopy)/ Table 8 The rate and time of nitrogen application after transplanting under N 0, FFD, and SSNM treatments N treatment Basal MT mid-tillering PI panicle initiation HD heading Total N amount N FFP SSNM * 40 ** 0 *** 120 The N fertilizer application amount after transplanting was based on the site-specific N management as follows: *, if SPAD>38, then 20 kg N ha -1 was applied; if SPAD value between 36 and 38, then 30 kg N ha -1 was applied; if SPAD<36, then 40 kg N ha -1 was applied. **, if SPAD>38, then 30 kg N ha -1 was applied; if SPAD value between 36 and 38, then 40 kg N ha -1 was applied; if SPAD<36, then 50 kg N ha -1 was applied. *** if SPAD<38, then 20 kg N ha -1 was applied; otherwise, if SPAD 38, no N was applied. Table 9 The rate and time of nitrogen application after transplanting at different SPAD fertilizer threshold values 1) Year N treatment 2) Basal 1 d Time and rate after transplanting (d) Total N (kg ha -1 ) 2006 S36 * S38 ** S40 *** S42 **** S S S S ) SPAD was weekly monitored and the measurement was started on d 14 after transplanting until heading. 2) * if SPAD<36, 30 kg N ha -1 was applied; ** if SPAD<38, 35 kg N ha -1 was applied; *** if SPAD<40, 40 kg N ha -1 was applied; **** if SPAD<42, 45 kg N ha -1 was applied; otherwise, N was not applied.

9 142 LI Di-qin et al. incoming light intensity). Intercepted radiation during each growth period was calculated by using the average canopy light interception and accumulated incoming solar radiation during this growth period (1/2 (canopy light interception at the beginning of the growth period+canopy light interception at the end of the growth period) accumulated incoming radiation during the growth period). Intercepted radiation during the entire growing season was the summation of intercepted radiation during each growth period. Radiation use efficiency (RUE) was calculated as the ratio of aboveground total dry weight to intercepted radiation during the entire growing season. Solar radiation, and minimum and maximum temperatures were recorded daily using a Vantage Pro2 weather station (Davis Instruments Corp., Hayward, CA, USA). On 14th d after flowering, 50 hills from a 2.5 m 2 area were investigated for sheath blight disease. Using a reference table, each plant was evaluated according to the degree of lesions (Sha 1998). The formulaes used were: DI (%)=100 (n 1 +n 2 +n 3 +n 4 +n 5 )/N, ShBI (%)=100 (5 n 1 +4 n 2 +3 n 3 +2 n 4 +1 n 5 )/5 N and N=n 1 +n 2 +n 3 +n 4 +n 5 +n 6. The detail information is given in Table 10. Data were analyzed according to the analysis of variance (Statistix 8) and means of varieties were compared based on the least significant difference test (LSD) at the 0.05 probability level for each year. Table 10 Criteria to score sheath blight disease lesion Degree Content Degree Content 0 Has any lesion in plant of all hills n 1 Total lesion plants of the 1st degree 1 Lesion on the 4th leaf from the top or its sheath or beneath of them n 2 Total lesion plants of the 2nd degree 2 Most significant position lesion on the 3rd leaf from the top or on its sheath n 3 Total lesion plants of the 3rd degree 3 Most significant position lesion on the 2nd leaf from the top or on its sheath n 4 Total lesion plants of the 4th degree 4 Most significant position lesion on the flag leaf from the top or on its sheath n 5 Total lesion plants of the 5th degree 5 Lesion on panicle or plant death n 6 Total lesion plants of the 6th degree Acknowledgements The study was conducted under the support of the National Natural Science Foundation of China ( ), the Ministry of Science and Technology of China (2009CB ). References Ahn R C, Mew T W Relationship between rice sheath blight and yield. International Rice Research Newsletter, 11, Balasubramanian V, Morales A C, Cruz R T, Abdulrachman S On-farm adaptation of knowledge-intensive nitrogen management technologies for rice systems. Nutrient Cycling in Agroecosystems, 53, Cheng S H, Cao L Y, Chen S G, Zhu D F, Wang X, Min S K, Zhai H Q Conception of late-stage vigor super hybrid rice and it s biological significance. Chinese Journal of Rice Science, 19, (in Chinese) Cu R M, Mew T W, Cassman K G, Teng P S Effect of sheath blight on yield in tropical, intensive rice production system. Plant Disease, 80, (in Chinese) Dobermann A, Witt C, Dawe D, Abdulrachman S, Gines H C, Nagarajan R, Satawathananont S, Son T T, Tan P S, Wang G H, et al Site-specific nutrient management for intensive rice cropping systems in Asia. Field Crops Research, 74, He F, Huang J L, Cui K H, Zen J M, Xu B, Peng S B, Boland B J Effect of real-time and site-specific nitrogen management on rice yield and quality. Scientia Agricultura Sinica, 40, (in Chinese) Hu C J, Li Y R, Huang S L New progress in research of rice resistance to rice sheath blight. Chinese Agricultural Science Bulletin, 20, (in Chinese) Hussain F, Bronson KF, Singh Y, Singh B, Peng S B Use of chlorophyll meter sufficiency indices for nitrogen management of irrigated rice in Asia. Agronomy Journal, 92, Mitchell L P, Sheehy J E, Woodward F I Potential yields and the efficiency of radiation use in rice. International Rice Research Notes Discussion Paper Series, 32, Monteith J L Climate and efficiency of crop production in Britain. Philosophical Transactions of the Royal Society (London), B281, Peng S, Buresh R J, Huang J, Yang J, Zou Y B, Zhong X H, Wang G H, Zhang F S Strategies for overcoming low agronomic nitrogen use efficiency in irrigated rice systems in China. Field Crops Research, 96, Peng S B, Garcia F V, Laza R C, Sanico A L, Visperas R M, Cassman K G Increased N-use efficiency using a chlorophyll meter on high yielding irrigated rice. Field Crops Research, 47, Peng S B, Huang J L, Zhong X H, Yang J C, Wang G H, Zou Y B, Zhang F S, Zhu Q S, Buresh R, Witt C Research strategy in improving fertilizer-nitrogen use efficiency of irrigated rice. Scientia Agricultura Sinica, 35, (in Chinese) Peng S B, Khush G S, Virk P, Tang Q Y, Zou Y B Progress in ideotype breeding to increase rice yield potential. Field Crops Research, 108, Peng S B, Laza R C, Visperas R M, Khush G S Rice: progress in breaking the yield ceiling. In: Proceedings

10 Effect of Nitrogen Regimes on Grain Yield, Nitrogen Utilization, Radiation Use Efficiency, and Sheath Blight Disease 143 of the 4th International Crop Science Congress. Brisbane, Australia. Peng S B, Buresh R J, Huang J L, Zhong X H, Zou Y B, Yang J C, Wang G H, Liu Y Y, Tang Q Y, Cui K H, Zhang F S, Dobermann A Improving notrigen fertilization in rice by site-specific N management. A review. Agronomy for Sustainable Development, 30, Peng X L, Liu Y Y, Luo S G, Fan L C, Song T X, Guo Y W Effects of the site-specific nitrogen management on yield and dry matter accumulation of rice in cold areas of northeastern. China Scientia Agricultura Sinica, 39, (in Chinese) Savary S, Castilla N P, Elazegui F A Direct and indirect effects of nitrogen supply and disease source structure on rice sheath blight spread. Phytopathology, 85, Sha X Measurement and inheritance of resistance to sheath blight caused by RHIZOCTONIA SOLANI KUHN in rice. Ph D thesis, Philippines University. Sinclair T R, Horie T Leaf N, photosynthesis, and crop radiation use efficiency: A review. Crop Science, 29, Sinclair T R, Muchow R C Radiation use efficiency. Advances in Agronomy, 65, Tang Q Y Canopy eco-physiological properties and the influence factors in irrigated rice. Ph D thesis, Hunan Agricultural University. (in Chinese) Tang Q Y, Peng S B, Buresh R J, Zou Y, Castilla N P, Mewc T W, Zhong X H Rice varietal difference in sheath blight development and its association with yield loss at different levels of N fertilization. Field Crops Research, 102, Tao Q N, Fang P, Wu L H, Zhou W Study of leaf color diagnosis of nitrogen nutrition in rice plants. Soils, 22, (in Chinese) Tollenaar M, Aguilera A Radiation use efficiency of an old and a new maize hybrid. Agronomy Journal, 84, Wang G H, Dobermann A, Witt C, Sun Q Z, Fu R X Performance of site-specific nutrient management for irrigated rice in southeast China. Agronomy Journal, 93, Wang Q C, Wang S Z Progress of crop photosynthesis research. In: Zou Q, Wang X C, eds., Progress in Physiological Research of Crop High Yield and High Efficiency. Science Press, Beijing, China. pp (in Chinese) Xie H A, Wang W Q, Yang H J,Yang G Q, Li Y Z The characteristics of super high yield hybrid rice. Fujian Journal of Agricultural Science, 18, (in Chinese) Yang W H, Peng S, Huang J, Sanico A L, Buresh R J, Witt C Using leaf color charts to estimate leaf nitrogen status of rice. Agronomy Journal, 95, Zhong X H, Peng S B, Buresh R J, Huang N R, Zheng H B Some canopy indices influencing sheath blight development in hybrid rice. Chinese Journal of Rice Science, 20, (in Chinese) (Managing editor WENG Ling-yun)