Research On Yield Formation Mechanism And High Yield Cultivation Techniques Of Machine-transplanted Early-late Season Double-cropping Rice

Great progress had been made in the mechanization of rice production in China,but the technology of machine transplanting was developed slowly,especially in double cropping rice in Yangtze River regions.In order to alleviate the contradictions of growth period mating problem of machine-transplanted double cropping rice in Yangtze River regions,the“Early-late season varieties collocation mode”was proposed(Early rice varieties were transplanted in late season).In our current study,field experiments(varieties selection experiment,comparison experiment between the early and late rice,different transplanter comparison experiment between 25 cm and 30 cm spacing,different seeding number per hole experiment,different machine densities and nitrogen fertilizer rate experiment)were conducted to determine yield formation mechanism and high yielding cultivation techniques of the machine-transplanted early-late season double cropping rice.The results were showed as following:(1)The“Early-late season varieties collocation mode”could solve the contradictions of growth period mating problem of machine-transplanted double cropping rice and get the high yield at the same time.So it could be applied in machine-transplanted double cropping rice system.(2)In the“Early-late season varieties collocation mode”,the early rice should choose the varieties with the growth period above 110 days without affecting the normal production of late rice,while the late rice could choose the early rice varieties with the low temperature sensitivity.(3)When the early rice varieties transplanted in late season,the growth duration was shortened,while the yield of late rice was not reduced with the significantly shortened growth duration.The high net assimilation rate,growth rate,leaf area index and canopy interception rate before heading become the physiological reasons for the not reduced yield.(4)25 cm row spacing transplanter had 4.5%higher yield than that of 30 cm line spacing transplanter.The high yield of 25 cm row spacing transplanter treatment was attributed to the effective number of panicles.The number of seedlings per hill had a great influence on early rice,but had little effect on late rice.This showed that the 25 cm spacing rice transplanter is suitable for the promotion of double-cropping rice transplanting technology in Hunan.In order to obtain high yield,the early rice must have high planting density and high seedlings per hill to ensure sufficient effective panicles,while the late rice could adjust the seedlings number per hill reasonably.(5)The grain yield of machine-transplanted double cropping rice was increased with the increasing of transplanting density and nitrogen fertilizer application.There was no significant difference between high nitrogen rate(176 kg/ha in early season,189 kg/ha in late season)and low nitrogen rate(110 kg/ha in early season,140 kg/ha in late season)under the condition of high density(36.4 hills/m~2).N use efficiency declined with increasing N application and improved with increasing density.The treatment of high density with low nitrogen rate reached the highest N use efficiency,and it certain advantages of dry matter accumulation and radiation use efficiency compared with the treatment of low density(19.0hills/m~2)with high nitrogen rate.As a result,adopted high planting density and low nitrogen fertilizer could not only achieve high yield,but also significantly improve RE_N in early-late season double cropping rice.The key technology provided in the study would be available for machine-transplanted double cropping rice cultivation in the Yangtze River regions.