Physiological And Ecological Characteristics Of No-Till Direct Seeded Super Hybrid Rice In Rice-Oilseed Rape Cropping System

Good progress has been made in the super hybrid rice breeding in China. However, rice yield not only depends on the genetic characteristics but also on the agronomic practices. Simplified cultivation technologies for rice have become increasingly attractive in recent years in China because of their social, economical and environmental benefits. No-till direct seeding is a simplified cultivation technology that greatly simplifies both land preparation and crop establishment. Currently, limited information is available on the no-till direct seeded super hybrid rice in rice-oilseed rape cropping system. In our current study, field experiments (cultivar performance trial for super hybrid rice in Changsha, Guidong and Nanxian, Hunan Province in 2007～2009; fixed experiment for comparing cultivation technologies for super hybrid rice in rice-oilseed rape cropping system in Changsha, Hunan Province in 2004～2010; cultivar performance trial for no-till direct seeded super hybrid rice in Nanxian, Hunan Provinve in 2009 and 2010) and rice production surveys (super hybrid rice production survey in Guidong, Nanxian and Ningxiang, Hunan Province in 2009; no-till direct seeded super hybrid rice production survey in rice-oilseed rape cropping system in Anxiang, Taoyuan and Loudi, Hunan Province in 2010) were conducted to determine yield characteristics of super hybrid rice and physiological and ecological characteristics of no-till direct seeded super hybrid rice in rice-oilseed rape cropping system. The results were showed as following:1. Relationship between grain yield and yield components in super hybrid riceYield potential has been increased by 11% in super hybrid rice cultivars (Liangyoupeijiu, Y-liangyou 1, Zhunliangyou 527, D-you 527,Ⅱ-you 084,Ⅱ-youhang 1, Neiliangyou 6 and Zhongzheyou 1) compared with common hybrid (Shanyou 6) and inbred (Shengtai 1) cultivars. The higher yield of super hybrid cultivars was attributed to improvement in panicle size. However, when analysis was made in the super hybrid rice cultivars, panicles per m2 had the highest positive contribution to grain yield with the exception under yield level of 10.0 to 12.0 t ha-1, and was positively related to grain yield in farmer’s field at all of the high- (Guidong), moderate- (Nanxian) and low-yielding (Ningxiang) regions.2. Yield formation characteristics of no-till direct seeded super hybrid rice in rice-oilseed rape cropping systemGrain yield of no-till direct seeded and conventional-till transplanted super hybrid rice were equal. Compared with conventional-till transplanted super hybrid rice, no-till direct seeded super hybrid rice was characterized by more panicle number per m2 but less spikelet number per panicle, and lower aboveground biomass production before heading but higher aboveground biomass accumulated during heading to maturity. In super hybrid rice, panicle number per m2 was positively related to maximum tiller number per m2, but negatively to panicle-bearing tiller rate; there was a tight positive linear relationship between spikelet number per panicle and spikelet production efficiency; grain yield was not closely associated with aboveground biomass at heading, but with aboveground biomass at maturity. Grain yield differed with cultivar and year for no-till direct seeded super hybrid rice (Liangyoupeijiu and Y-liangyou 1). Y-liangyou 1 produced 4% higher grain yield than Liangyoupeijiu in 2009, whereas in 2010 both cultivars yielded similar. Grain yields of both cultivars were higher in 2009 than in 2010. Higher grain yield in Y-liangyou 1 in 2009 was associated with higher spikelet filling (spikelet filling percentage and grain weight), which resulted from higher biomass production. Crop growth rate after heading was critical to the biomass production by the super hybrid rice.3. Physiological factors for no-till direct seeding effects on yield components of super hybrid rice in rice-oilseed rape cropping systemThe large number of panicles per m2 in no-till direct seeded super hybrid rice was derived from the increased number of tillers per m2 rather than increased rate of panicle-bearing tillers, and the number of tillers per m2 was mainly determined by the number of hills per m2 because the number of tillers per hill was small in no-till direct seeded super hybrid rice. Tillering rate, tillering duration as well as carbohydrate and nitrogen metabolism (soluble protein content, net photosynthetic rate, soluble sugar content, glutamine synthetase activity and nitrogen content in leaves) were critical to the reduced number of tillers per hill in no-till direct seeded super hybrid rice. In no-till direct seeded super hybrid rice with fewer spikelets per panicle, the numbers of primary branches and secondary branches per panicle, spikelets per primary and secondary branches, and also panicle length and spikelets per unit panicle length were smaller. These differences were attributed to the smaller source leaf size as well as lower root activity (bleeding sap flowing rate, and soluble sugar and amino acid concentration in bleeding sap) and the nutritional status at panicle initiation.4. Physiological factors for no-till direct seeding effects on biomass production of super hybrid rice in rice-oilseed rape cropping systemThe lower aboveground biomass accumulation before heading in no-till direct seeded super hybrid rice was attribute to the less number of tillers, which was determined by the capacity of photosynthetic carbon metabolism (leaf area index, and chlorophyll content, net photosynthetic rate and soluble sugar content in leaves) at early growth stage. However, no reductions were observed in total aboveground biomass in no-till direct seeded super hybrid rice, because the negative effects of no-till direct seeding on aboveground biomass production before heading were compensated for by its positive effects on aboveground biomass accumulation after heading. The reduction in growth before heading of no-till direct seeded super hybrid rice made its population density lower but more suitable during heading to 20 days after heading, resulting in a more appropriate leaf area index, a lower leaf senescence and a consequent increase in net assimilation rate.5. Physiological nitrogen efficiency of no-till direct seeded super hybrid rice in rice-oilseed rape cropping systemThe differences in physiological N efficiency of super hybrid rice were insignificant among cultivation technologies (conventional-till transplanting, no-till transplanting, conventional-till direct seeding and no-till direct seeding) but were significant among years. In super hybrid rice, grain yield was closely related with physiological N efficiency but not with total N accumulation in aboveground biomass; there was a tight positive correlation between physiological N efficiency and N distribution in straw.6. Effects of rice establishment method and tillage on soil properties in a super hybrid rice-oilseed rape cropping systemThere were no main effects of rice establishment method (transplanting and direct seeding) and no significant interactive effects between rice establishment method and tillage (conventional-till and no-till) on the measured soil properties (soil bulk density, pH, contents of active organic carbon, NaOH hydrolysable nitrogen, double acid phosphorus and NH4OAc extractable potassium, and activities of invertase, urease and acid phosphatase), however, tillage had significant effects on the soil properties except pH. Averaged across two rice establishment methods, bulk density was 18% higher in the 5～10 cm soil layer, contents of active organic carbon, NaOH hydrolysable nitrogen and NH4OAc extractable potassium were 16%～31% higher in the 0-5 cm soil layer but 10%～24% lower in the 5～10 cm soil layer, activities of invertase, urease and acid phosphatase were 12%-35% higher in the 0-5 cm soil layer but 26%～33% lower in the 5～10 cm soil layer, and double acid phosphorus content was 9% and 13% higher in the 5～10 cm and 10～20 cm soil layers, respectively, under no-tillage compared to conventional tillage.7. Effects of no-till direct seeding on energy use in super hybrid rice production in rice-oilseed rape cropping systemNo-till direct seeded super hybrid rice had a total energy use of 15.28 GJ ha-1, which was 21% less than conventional-till transplanted super hybrid rice. The reduced total energy use in no-till direct seeded super hybrid rice production was attributed to less energy use in both field operations and producing external inputs. For field operations, no-till direct seeded super hybrid rice had less energy use by both labor and machinery, which contributed 44% of the reduced total energy use. For producing external inputs, the less energy use in no-till direct seeded super hybrid rice was mainly driven by reduced N fertilizer application.