Cultivation Practices For Enhancing The Growth And Yield Of Rapeseed And Mitigating The Lodging-related Losses

Rapeseed(Brassica napus L.)is one of the major oilseed crops in China.Many climatic and agronomic factors affect the growth,yield and seed quality of rapeseed;including lodging,plant density and fertilizers rates.Lodging is a most common problem in rapeseed occurs before or at the beginning of grain filling which cause yield loss,deterioration in seed quality and difficult to harvest.Integrated agronomic practices,including optimum planting date,balanced fertilizer management and variety selection,are important strategies for improving crop productivity,lodging resistance and resource use efficiency.Plant density affects yield and the extent of lodging by altering the crop canopy.This study aimed to examine how agronomic practices and artificial lodging angles affected the yield,plant growth,photosynthesis,light interception and lodging resistance in rapeseed under different Planting density and nitrogen rates.Experiment 1 was conducted to investigate the influence of plant density(D)and nitrogen(N)rates on morphological and physiological traits related to yield,nitrogen use efficiency and lodging resistance in rapeseed.We evaluated rapeseed cultivar ‘Huayouza9’ for two consecutive growing seasons(2014–2016)under three plant densities(LD,10 plants m-2;MD,30 plants m-2;HD,60 plants m-2)and four N rates(0,60,120 and 180 kg ha-1).Experiment was laid out in split plot design using density as a main factor and N as sub-plot factor with three replications each.Plants were harvested at the wintering and maturity stages to record morphological and yield related traits.Experiment II was conducted to investigate the effects of induced lodging angles on yield losses and oil quality in rapeseed cultivar ‘Huayouza 62’at different pod filling stages,nitrogen(N)rates,and plant densities(D).In the first trial,we identified the critical pod filling stage and in second trial using that stage different lodging angles were induced.In the 2014/15 growing season,a single lodging angle(30°)was manually induced at three pod filling stages(10 d post flowering,S10;20 d post flowering,S20;and30 d post flowering,S30)of plants sown at different densities(D15,15 plants m-2;D30,30 plants m-2;and D45,45 plants m-2)and fertilized with different N rates(N180,180 kg N ha-1;N270,270 kg N ha-1;and N360,360 kg N ha-1)to identify the critical pod filling stage.In the 2015/16 and 2016/17 growing seasons,four lodging angles(0°,30°,60°,and 90°)were manually induced at the critical pod filling stage(S10)of plants sown and fertilized in the same manner as in 2014/15.Results from these trials indicated that(I)Seed yield was increased by increasing density and N rate,reaching a peak at HD with 180 kg N ha-1.The effect of N rate was consistently positive in increasing the plant height,pod area index,1,000 seed weight,shoot and root dry weights and root neck diameter,reaching a peak at 180 kg N ha-1.Plant height was decreased by increasing D at both wintering and maturity stages.The maximum radiation interception(approximately80 %)and net photosynthetic rate were recorded at MD at highest N.Lodging resistance and nitrogen use efficiency significantly increased with increasing D from 10 to 30 plants m-2,and N rate up to 120 kg ha-1,further increase of D and N decreased lodging resistance and NUE.Hence,planting density 30 plants m-2 can improve yield,nitrogen use efficiency and enhance lodging resistance by improving crop canopy.(II)Timing and angle of lodging had significant effects on yield.Lodging induced at S10 caused the highest decrease in yield,biomass,and silique photosynthesis.Root biomass and root neck diameter were not affected by lodging,in contrast to the yield and aboveground biomass,which were reduced.Lodging at 90° induced at S10 caused the maximum yield reduction of 14–32% compared with th0 e control(0°).Furthermore,lodging caused a higher reduction in yield at higher N rates with maximum yield loss at N360D45.Lodging decreased seed oil content,altered the fatty acid composition of the seed oil by increasing stearic and palmitic acids and decreasing linoleic and linolenic acids,and also reduced oil quality by increasing erucic acid and glucosinolates.This study showed that lodging at an early pod filling stage critically affected yield loss and reduced seed quality in rapeseed,especially at high N rates.Furthermore,a fertilization/density combination of N270D45 produced the maximum observed yield and seed quality.Therefore lodging induced yield loss and reduction in oil content might be lessened by selecting optimum N and density rate.