Study On Sowing Date Effect On Development Of Rapeseed(Brassica Napus L.)

In this paper,sowing date effect on physiological and biochemical metabolic,yield, quality and quality process of rapeseed was investigated systematically.Influence of mean daily temperature and accumulated temperature on pod development and yield was studied to form simulation models between accumulated temperature and growth indicators of rapeseed with the aim of finding out key temperature indicator,and provide theoretical basis for high efficiency of rapeseed production.Impact on character and dry matter distribution of rapeseedWhole growing period of 180 to 250 days had to be experienced when rapeseed was sown in six sowing dates between Sep 1^st tO Nov 15^th.Seedling and enlongating stages witted the greatest difference with mean day gap of 32.5,30.5 respectively,flowering period followed by 7.25 days,and then maturing stage 6.25 days.Variance analysis showed that there was significant differences in seedling and enlongating stages but no differences in maturing stage and flowering stage in four-year experiments.Sowing date effect on physiological and biochemical metabolism of rapeseedChlorophyll content,soluble sugar content and glucosinolate content were negatively correlated with mean daily temperature,and correlation between soluble sugar content and mean daily temperature produced a significant level in treatments of B1 to B4.B3 and B4 had a significant positive correlation with mean daily temperature.Seed soluble sugar content showed negative relation with oil content,and they both experienced slow-quick-slow period when growing.Protein content stayed the same level from the beginning,glucosinolate content fluctuated at first and decreased later.Late sowing postponed process of pod development and high daily temperature increased pod metabolism.Sowing date effect on yield of rapeseedPostponed sowing date reduced plant height,stem diameter,branch number, available pod number,biological and economic yield of rapeseed,but increased economic index.When sowing date was postponed to Oct 15^th,a significant decrease occured in character and yield component indicators of rapeseed,and yield differences between B1 and B4,B6 got 601.09,2198.23kg/ha reapectively.Pod grain number and 1000 seed-weight were mainly influenced by environmental factors like termperature,water conditions and so on,but no direct relationship with sowing date.Inerannual climatic difference impact rapeseed yield greatly,and could cause significant difference.Yield increase effect of plant density was not significant when rapeseed was sown before Oct 15^th.When after that period,increasing density could greatly improve yield of rapeseed.Thus the plant density was increased from 4000,16000,16000 plant/667m² to 8000,24000,24000 plant/667m² in sowing date B4 to B6 respectively,yield could be increased by 45.33,58.14,70.09%respectively.Sowing date effect on quality of rapeseedDifferences of seed oil content was related with meteorological conditions esspecially mean daily temperature,therefore it was not correct to describ it as a disciplinary change along with sowing date.Protein content increased with postponed sowing date and 3%difference exsisted between early and late sowing.Seed glucosinolate content was lower than 20μmol/g when sowing before Oct 15^th and no significant difference during this period.When sowing after Oct 30^th,an extremly high glucosinolate content was witted,5-7μmol/g higher than former sowing dates.Soluble sugar content had some certain relationship with pod material metabolism, but not influenced by sowing date.Under late sowing and high density cultivation condition,glucosinolate content was extremly high,for instance,under sowing date B5 and B6 with plant density of 32000 plant/667m²,the glucosinolate content could reach 44.05,45.06μmol/g respectively.Effect of temperature indicators on growth process of rapeseedOver 110℃accumulated temperature was needed from sowing to cotyledon extension in winter and sub-winter rapeseed varieties.Half of growing stage of rapeseed was consumed by seedling stage,and 600 to 2000℃accumulated temperature was needed,which range could be great.Rapeseed enlongated stem when continuous mean daily temperature stablized above 10℃,and about 200 to 400℃accumulated temperature was reauired to complete enlongation.Relatively strict climate conditions were must by flowering stage,with over 15℃mean daily temperature and 300 to 400℃was needed to finish flowering.Flower time would be prolonged when encoutering continuous rainy weather.Accumulated temperature of 550 to 650℃was required to complete pod development,and daily temperature of 20 to 25℃,sufficent sunlight were good to pod growth.Effect of temperature on pod material metabolismAccumulated temperature of 460 to 500℃for pericap morphogical establishment. Metabolism process of pod photosynthetic product could be divided into three separate period,morphogical establishment period,synthesis and transformation peak period and function declining period,among which synthesis and transformation peak period was signed with soluble sugar content declined by over 100%per day and oil content increased by 1.50%per day.Mean daily temperature above 18℃was beneficial to accumulation of soluble sugar and sythesis of fatty acid,and 150 to 160℃accumulated temperature was needed to complete sugar transformation,160 to 230℃was needed to finish oil sythesis. Accumulation and conversion of photosynthate was basically completed at grain filling time,corresponding process began to slow down to low speed,at this period of time,mean daily temperature stablized above 19℃,another 220℃accumulated temperature was needed to lose water and mature.Establishment of simulation models related temperature indicatorssimulation results were obtained through establishing temperature-related growth and development model,the results indicated that,1363.4℃accumulated temperature was needed from emergance to enlongation,1695.8℃was needed to innitial flowering, 1819.3℃was needed to pod development and the whole growing stage required about 1922.7℃.rapeseed could produce 1.44 leaves for every 100℃accumulated temperature. Leaf growth was mainly related to termperature conditions,but no significant relationship with dry matter.Up to 400℃accumulated temperature after flowering was needed to establish pericap morphogical,meanwhile seed dry weight began to increase rapidly,and fatty acid began to synthesis greatly.Pericap held a sound function when accumulated temperature stayed up to 500℃,dry weight of pericap stop increasing,synthesis of seed dry matter, fatty acid and transformation of soluble sugar stayed at peak time for nearly 12days.At 700℃accumulated temperature,conversion of sugar was basically finished,and the content remained at 5-7%to harvest,oil content got over 40%to the end.Pod growth and development,physiological metabolism were bacically completed when accumulated temperature was 800℃,and another 100℃had to be experienced before harvest.