Effect Of Mechanized Planting Methods On Productivity Of Rice And Annual Grain Production

With the rapid development of economy and the transfer of rural labor force,speeding up the process of rice mechanization is crucial to realizing the prolific and dependable rice yield.Mechanized planting is important link in the rice mechanized production,as well as the difficulty of realizing the whole mechanization of high yield and high efficiency of rice production and the research hotspot.In the lower reaches of Yangtze River,a rice-wheat rotation system is wildly applied and the mainstream of rice mechanized planting methods here are mechanical transplanting with carpet seedlings(MC),mechanical direct seeding(MD),and mechanical transplanting with pothole seedlings(MP).Different rice mechanized planting methods have their own production characteristics and restrictions as affected by wheat growth in a rice-wheat rotation system.Thus understanding the differences in yield traits and the ecological and physiological traits of yield formation of rice among MC,MP and MD is of great importance not only to rice scientists but also rice farmers to develop a high-yield production system under mechanical conditions in a rice-wheat rotation system.These results could provide theoretical reference and data support for the rational application of mechanized planting methods,and for the research and development of high-yield and high-efficiency cultivation technology under mechanical conditions.However,such traits are yet to be studied among rice varieties of japonica-indica hybrid rice(JIHR),japonica conventional rice(JCR),and indica hybrid rice(IHR).Field experiments were conducted in 2014 and 2015,where six cultivars of the three rice types JIHR,JCR,and IHR were grown individually with MP,MC,and MD methods,under respective managements for each method to achieve maximum attainable yield.The traits and differences in yield and yield components,temperature and light utilization,photosynthetic production,plant type,lodging resistance,nitrogen absorption,rice quality and annual yield of rice among mechanized planting methods had been systematically studied.The main results were as follows:(I)The MP and MC produced 20.0%and 13.1%more rice yield than MD,respectively,and the influences of mechanized planting methods on yield of JIHR and IHR were observed bigger than JCR.The analysis of yield components showed that insignificant differences were detected in filled grains percentage and filled grain weight among mechanized planting methods,but significant differences were in total number of spikelet with tendency of MP>MC>MD.The components of total number of spikelet,panicle number per hectare and number of spikelet per panicle showed different trends among mechanized planting methods,with MP<MC<MD for panicle number per hectare and MP>MC>MD for number of spikelet per panicle,respectively.Compared to MD,MP and MC significantly reduced the panicle number per hectare by 4.4%and 2.6%and increased the number of spikelet per panicle by 22.1%and 13.3%,which resulted in 16.7%and 10.3%increase in total number of spikelet,respectively.The panicle length,grain density,grain weight per panicle,branch-number and spikelet-number of primary rachis-branches and of secondary rachis-branches,contribution ratio of total grains in secondary rachis-branches to total grains per panicle,and seed-setting rate of spikelet-number in secondary rachis-branches of rice showed a tendency of MP>MC>MD,while the ratio of number of primary rachis-branches to number of secondary rachis-branches,ratio of total grains of primary rachis-branches to total grains of secondary rachis-branches,and contribution ratio of spikelet-number in primary rachis-branches to total grains per panicle showed the opposite trend.Thus,sufficient panicles per hectare,increased spikelet number per panicle,large sink capacity,and stable filled grains percentage and filled grain weight were important features for higher rice yield under MP than MC and MD.(Ⅱ)The sowing date of MP and MC were 28 and 16 d earlier than MD,resulting in an earlier stem elongation by 7-13 and 5-9 d,earlier heading by 7-15 and 4-10 d,and earlier maturity by 5-15 and 3-11 d,respectively.Compared to MD,the rice growth durations under MP and MC were 13-23 and 5-14 d longer,respectively,mainly owing to the prolonged duration from sowing to stem elongation under MP and MC than MD.The tendency of daily production of JIHR and IHR was MP>MC>MD,while daily production of JCR under MC was bigger than MP and MD.Both the growth duration and daily production showed significant positive correlations with yield,indicating that prolonging the growth duration and increasing the daily production would be conductive to increasing the rice yield.Compared with MD,MP and MC increased the effective accumulated temperature by 14.9%-19.6%and 9.1%-11.6%,and increased cumulative solar radiation by 16.1%-24.8%and 8.3%-14.2%.The mean daily temperature of rice in the entire growth duration among mechanized planting methods were MP>MC>MD,with tendency of MP<MC<MD during vegetative phase(from sowing to stem elongation)and tendency of MP>MC>MD during reproductive(from the stem elongation to heading)and grain filling(from heading to maturity)phases,respectively.This study demonstrated that when the mean daily temperature is<25.1 ℃ in vegetative phase and>20.1 ℃ in grain filling phase,rice yield could be increased by selecting mechanized planting methods.Thus,longer growth duration,higher temperature and light utilization,relative lower mean daily temperature in vegetative phase and higher mean daily temperature in grain filling phase were important yield traits for rice under MP.(III)The traits of tiller dynamic for MP and MD were respective "slow rise and slow reduction" and "rapid rise and rapid reduction",while the trait for MC was between MP and MD.As a result the tendency of percentage of productive tillers was MP>MC>MD.The dry matter accumulation of rice under MP was larger than MC and MD,and the difference in this among mechanized planting methods was increased with the growth process moving forward.Lowering the ratio of dry matter in vegetative phase to dry matter at maturity,controlling the ratio of dry matter in reproductive phase to dry matter at maturity,and increasing the ratio of dry matter in grain filling phase to dry matter at maturity were the important way for MP to accumulate more biological yield than MC and MD.Moreover,the MP favored plant growth as well as enriched the stems plus sheaths during grain-filling phase,as compared with MC and MD.More obvious second enrichments in stems plus sheaths after milky stage were observed in rice plants under MP than MC and MD.In addition,the output ratio and translocation ratio of dry matter per stem plus sheath from heading to milk and from heading to maturity under MP were respective lower and higher than MC and MD.After heading,the tendencies for high leaf area duration,crop growth rate and net assimilation rate were MP>MC>MD,which greatly improved the photosynthetic performance of rice under MP and in turn laid the material foundation for high rice yield.(IV)The top three leaves of rice plants under MP had longer leaf length,bigger specific leaf weight,smaller leaf basal and drooping angle than those under MC and MD.Compared to MC and MD,the LAI,ratio of leaf area from flag leaf to 3rd leaf,panicle,and grain-leaf radio of rice plants under MP were bigger,with increased chlorophyll content and net photosynthetic rate in flag leaf.The rice plants were higher under MP than MC and MD,with longer stalk height,panicle length,and neck internode length,but shorter basal internodes length.The 1st,2nd and 3rd internodes of rice plants under MP had significantly increased breaking resistance and bending moment,but significantly reduced lodging index,which would benefit from their bigger culm diameter,thicker culm wall,larger biomass accumulation and larger dry weight of unit internode,as compared with those under MC and MD.Thus,this study demonstrated that the MP method could improve the rice plant type,optimize the rice population,and increase the rice lodging resistance.(V)As affected by mechanized planting methods,the tendencies of N content of rice plants at stem elongation stage were MP<MC<MD and at heading and maturity stages were MP>MC>MD.And the tendencies of N uptake of rice plants at main growth stages were the same with N content,while the differences in N uptake at stem elongation stage were not significant,but at heading and maturity stages were significant.After stem elongation,the N accumulation,ratio to total and uptake rate of rice plants among mechanized planting methods were MP>MC>MD.Moreover,the N uptake per 100 kg grain,partial factor productivity of applied N,and N harvest index of rice under MP were larger than MC and MD,but the N use efficiency of grain yield and biomass were smaller for rice under MP than MC and MD,indicating that rice under MP had lower nitrogen production efficiency.Thus the efficient utilization of nitrogen fertilizer should be attached importance to the cultivation technology research in order to realize the high-yield and high-fertilizer-utilization rice production under mechanical condition.The N content of leaf,stem plus sheath,and panicle of plants at heading and maturity among mechanized planting methods were MP>MC>MD.Moreover,the N translocation amount,apparent N translocation rate,and N translocation conversion rate of plant leaves under MP were significant higher than MC and MD,which promoted the grain accumulating more nitrogen.(VI)The head rice rate and head rice yield under MP were 1.6%and 7.8%larger than those under MC,and 4.9%and 25.9%larger than those under MD,respectively,indicating a better processing quality under MP method.Compared with MC and MD,MP decreased appearance quality with increased chalky grain rate,chalkiness size and chalkiness degree,and increased protein content and nutrition quality with the increase of 8.7%and 28.0%in protein yield,respectively.The effects on amylose content,setback and pasting temperature were MP<MC<MD,and those on gel consistency,peak viscosity,trough viscosity,final viscosity and breakdown were MP>MC>MD,which indicated that the cooking and eating quality under MT might be meliorated.The taste quality was not of significant difference among planting methods,showing a tendency of MP<MC<MD for JCR and JIHR,and of MC>MP>MD for IHR.(VII)The harvest time for rice under MP was earlier than MC and MD,thus the sowing date of succeeding crop wheat was earlier under MP than MC and MD.Then as affected by the rice mechanized planting method,the growth duration biological yield and economic yield of wheat showed a tendency of MP>MC>MD.In conclusion,the annual yield was of significant difference among rice mechanized planting methods.Compared to the rice under MD plus wheat rotation(MDR-W),rice under MP plus wheat rotation(MPR-W)and rice under MC plus wheat rotation(MCR-W)increased the annual economic yield by 19.3%and 12.2%,increased the annual biological yield by 17.5%and 11.2%,and increased the annual daily production by 9.1%and 7.2%.The crop growth duration under MPR-W was respective 32 and 16 d longer than and MCR-W and MDR-W.In addition,the crop growth duration under MPR-W was more than 366 d.In diferent rotation systems,the annual effective accumulated temperature,cumulative solar radiation,and temperature-light production efficiency showed tendency of MPR-W>MCR-W>MDR-W.The annual solar energy use efficiencies of grain and biomass under MPR-W were 15.8%and 14.0%higher and under MCR-W were 10.5%and 9.5%higher than MDR-W.The role of MP played on promoting the rice and wheat production were,(i)rice yield was increased through cultivating bigger panicle and accumulating larger dry matter;(ii)wheat yield was increased through earlier sowing and coordinating the spike number per hectare and grain number per spike;(iii)the annual crop yield was increased through regulating the growth duration of rice and wheat,prolonging the growth duration of rice and wheat,and improving the growth environment of rice and wheat.