Canopy Structure Characteristics, Solar Radiation Use Efficiency And Their Effects On Grain Yield In Super Hybrid Rice

Food grain has attracted great attention of all the countries' governments and the scientific institutions, with the rapid increase of the world's population.The Ministry of Agriculture of the PRC started to implement the Super Hybrid Rice Breeding Plan in 1996, and the Specific Project for Super Hybrid Rice Varieties Breeding, Demonstration and Extension in 2005. Some 69 new varieties or combinations over the country up to June of 2009 had been certificated by the Ministry through the super hybrid rice variety appraisement . The super hybrid rice grown areas had annually reached 5.56 million hectare in the country by the end of 2008, accounting for 19.2% of the country's total rice grown areas.From the view of solar energy utilization, crop yield is decided by three factors such as canopy intercepted solar radiation quantity, radiation use efficiency (RUE) and harvest index (HI). It is of great importance to determine solar radiation interception quantity and its use efficiency, its relationship with canopy structure characteristics, and their effects on yield in super hybrid rice for rice production practice. This study was conducted to analyze the effects of N application and sowing date on yield of super hybrid rice, and to compare the differences in yield and yield formation between super hybrid rice, and ordinary hybrid rice and inbred varieties. The results were shown as follows:1. Yield of super hybrid rice. It was 21.7% and 15.8% higher significantly than that of ordinary hybrid rice and inbred varieties, respectively. In yield components, the spikelets number of super hybird rice was 20.6% and 18.0% higher significantly and its glumous number was 21.7% and 15.2% higher significantly; and in dry weight (DW), the total dry weight (TDW) of super hybrid rice was 1.6% and 5.7% higher, and its harvest index (HI) was 11.5% and 7.7% higher significantly, than that of ordinary hybrid rice and inbred varieties, respectively. In solar energy utilization, the radiation use efficiency (RUE) of super hybrid rice was 6.1% higher than that of ordinary hybrid rice, and its intercepted photosynthetically active radiation (IPAR) was 6.8 to 14.7% higher significantly than that of inbred varieties from Mid-tillering stage (MT) to Maturity stage (MA); and in canopy characteristics at the mid- and late stage of growth and development, the leaf area index (LAI) of super hybrid rice was 2.4 to 12.1% higher than that of inbred varieties, and its specific leaf weight (SLW) was 13.4 to 18.5% and 6.1 to 8.9% higher than that of ordinary hybrid rice and inbred varieties, respectively, and its population's photosynthetic rate was significantly higher than that of ordinary hybrid rice and inbred varieties.2. Effects of the sowing date on super hybrid rice yield. The effects were apparent, the postponement of the sowing date decreased the yield by 2.4%. In the yield components, the spikelets number decreased by 26.6% and the total glumous flower number reduced by 6.1%. In the total dry weight (TDW), the total dry weight (TDW) increased 4.7%, but the harvest index(HI) decreased 7.7% so that the yield declined. In the interceped photosynthetically active radiation (IPAR) and the radiation use efficiency (RUE), from the Booting stage (BT) on, the population's interceped photosynthetically active radiation (IPAR) increased by 4.2 to 21.4% and the radiation use efficiency (RUE) decreased only 1.4%, so the total dry weight (TDW) increased, but the harvest index (HI) declined, finally the yield decreased. In the canopy's leaf area index(LAI) and specific leaf weight (SLW), with the increased by 1.1 to 33.2% and the population's specific leaf weight (SLW) decreased by 1.8 to 14.4%, the population's total dry weight (TDW) showed an up trend, but the harvest index (HI) declined, finally the yield decreased.3. Effects of N application treatments on super hybrid rice yield. The effects were obvious. At the different N application rates, the yield of NO treatment was the lowest, 7609.0kg/hm~2 and that of N5 treatment was the highest, 10604.0 kg/hm~2; and the quadratic correlation was obviously found between N application rate and yield. At the same N application rate, the yield of the Site-specific nutrient management (SSNM) was 1.61% higher than that of the Real-time nutrient management (RTNM), the latter was 5.14% higher than that of the Farm fertilizer practice (FFP). The yield improvement mainly resulted from the increase in effective panicles and glumous flower number.4. Effects of N application treatments on the total dry weight (DW), hervest index (HI) and total crops growth rate (TCGR). The effects were apparent, the total dry weight (TDW) of NO treatment was the lowest, 1183.9kg/hm~2 and that of N6 treatment was the highest, 1813.2 kg/hm~2; and the higher the N application rate, the higher the total dry weight (TDW), but the lower the hervest index (HI). At the N application rate range from 0 to 210 kg/hm~2 , the total crops growth rate (TCGR) of NO treatment was the lowest, 11.2g/m~2 .d and that of N5 treament was the highest, 16.4 g/m~2.d %; and the higher the N application rate, the higher the total crops growth rate (TCGR), but the lower the population's the total crops growth rate (TCGR) beyond the above range. At the same N application rate, the Site-specific nutrient management (SSNM) could more significantly increase the total dry weight(TDW) and the total crops growth rate (TCGR) than the Real-time nutrient management (RTNM) could, and the Real-time nutrient management (RTNM) could more significantly do them than the Farm fertilizer practice (FFP) could; and the Site-specific nutrient management (SSNM) could help to enhance the harvest index (HI).5. Effects of N application treatments on the population's canopy height (CH), leaf area index (LAI) and specific leaf weight (SLW) of super hybrid rice. The effects were obvious. At the different N application rates, the higher the N application rate, the higher the canopy height (CH) and the leaf area index (LAI), but the lower the specific weight (SLW). At the same N application rate and in different N management patterns, there was no significant difference in the population's the canopy height (CH) and specific leaf weight (SLW) between the different N application treatments.6. Effects of N application treatments on the interceped photosynthetically active radiation (IPAR) and the radiation use efficiency (RUE) of super hybrid rice . The effects were significant. At the different N application rate, the higher the N application rate, the higher the interceped photosynthetically active radiation (IPAR). At the same N application rate, the Site-specific nutrient management (SSNM) could do it more significantly than the Real-time nutrient management(RTNM)could, the Real-time nutrient management (RTNM) could do it more significantly than the Farm fertilizer practice (FFP) could; and the Site-specific nutrient management (SSNM) could be helpful to increase the radiation use efficiency (RUE).