| With the implementation of rapeseed's mechanized and simplified cultivation light mode,high-density cultivation will be widely used in the production.Nitrogen fertilizer was an indispensable source of nitrogen for crop growth and development.When it was insufficient,the yield potential of the variety will be affected;if it was applied too much,there would be a negative impact on the yield,maturity and lodging.Meantime,nitrogen fertilizer would be wasted and the soil would be polluted.Therefore,it was important to study the suitable nitrogen fertilizer application under the condition of high planting density of rapeseed hybrids.In this study,three rapeseed(Brassica napus L.)were selected and five treatments were applied at a density of 25,000 plants per mu(0,112.5kg/hm~2,187.5kg/hm~2,262.5 kg/hm~2,337.5kg/hm~2,)to study the agronomic traits,yield,lodging related traits and N absorption under different nitrogen application amount.The main results are as follows:(1)Effects of different nitrogen application amount on growth period and agronomic traitsField observations and records show that W25 was more precocious than Shaanyou16and Shaanyou0913 for 4 days.The time of bolting stage,flowering stage,final flowering stage and other growth period under high nitrogen treatment are later than low nitrogen treatment for 3-4 days,and the ripe stage was more serotinous for 2-3 days.The plant height(PH)and the effective branch height(EBH)of rapeseed are increased with the increasement of nitrogen application rate.EBH of Shaanyou16 and Shaanyou0913was increased with the increasement of nitrogen application rate,W25 showes the rise-fall-up-down trend.The main inflorescence length(MIL)was increased first and then decreased,and was up to the maximum when the amount of nitrogen was 187.5kg/hm~2,which are 66.50cm(Shaanyou16),58.75cm(Shaanyou0913)and 55.25cm(W25).(2)Effects of different nitrogen application amount on yield and yield related traitsWith the increasement of nitrogen application rate,the yield of rapeseed increases first and then decreases.The yield of Shaanyou16 and Shaanyou0913 reaches the maximum when the amount of nitrogen fertilizer was 187.5kg/hm~2,which are 4068.59kg/hm~2 and3988.59kg/hm~2 respectively.W25's highest yield was 4091.45kg/hm~2 when the amount of nitrogen fertilizer was 262.5kg/hm~2.The correlation analysis shows that the effect of agronomic traits on rapeseed grain yield was:MIL>EBH>PH>effective branch number(EBN).The effect of yield components on rapeseed yield was:the number of pods per plant>1000 grain weight>the number of seed per pod.(3)Effects of different nitrogen application amount on rapeseed lodging and lodging-related traitsThe effect of nitrogen fertilizer on the lodging index of rape stalk it was significant:the lodging index of the three cultivaries was increased with the increasement of nitrogen application rate.When the amount of nitrogen fertilizer was 337.5kg/hm~2,the lodging index was the highest(average value was 16.5)but the lodging resistance was the weakest.When the amount of nitrogen fertilizer was 262.5kg/hm~2,the lodging index was the smallest(average value was 10.8)but the lodging resistance was the strongest.The effects of different nitrogen application levels on the stem soluble sugar content of the three cultivars are significant at the flowering stage,the final flowering stage and the mature stage.In the high flowering stage,the soluble sugar content of the stem in the high nitrogen level was higher than low nitrogen level.But in the final flowering stage and the mature stage,that was higher in the low nitrogen level.The effects of different nitrogen application levels on the stem cellulose content of the three cultivaries are significant at the flowering stage,the final flowering stage and the mature stage.The stem cellulose content of the final flowering stage was significantly higher than that of the flowering stage and mature stage.The effects of different nitrogen application levels on the stem lignin content of the three cultivars are significant at the final flowering stage.But there was not obvious change of the content of stem lignin with the increasement of nitrogen application.The stem lignin content of the final flowering stage was significantly lower than that of the flowering stage and mature stage.The effects of different nitrogen application levels on the total area of stem vascular bundle(AVB),stem large vascular bundle area(ALVB)and small vascular bundle area(ASVB)of the three cultivaries are significant at the flowering stage,the final flowering stage and the mature stage.But with the increase of nitrogen application level,there was not obvious change.The correlation degree of the rupture resistance index of the rape stalk was as follows:ALVB>AVB>VBS>the cortical number>the cortical layers>the content of lignin>the content of cellulose>the thickness of tissue layers>the pith ray(negative correlation).the soluble sugar content>ASVB(positive correlation).When the amount of nitrogen fertilizer was 187.5-262.5kg/hm~2,the lodging resistance of stalk was stronger.The lodging resistance strength of three varieties(combination)shows:Shaanyou16>Shaanyou0913>W25.As for lodging-resistant varieties,the content of cellulose and lignin was higher,the content of soluble sugar was lower,the vascular bundles are larger and neatly arranged,the number of vascular bundles was moderate,the formation of layers of cells arranges closely,the interval between the vascular bundles was smaller.(4)Effects of different nitrogen application amount on total nitrogen content in rape leavesFrom the bud stage to the mature stage,the total nitrogen content of the leaves of different nitrogen treatment was decreased with the growth process.There was significant difference of Shaanyou16 during each nitrogen application,which was higher in the bud stage and flowing stage under high-N(more than 187.5 kg/hm~2)treatment,and was higher in the final flowering stage and the mature stage under low-N(less than 187.5 kg/hm~2)treatment.There was non-significant difference of Shaanyou0913 and W25 during each nitrogen application.However,The total nitrogen content of leaves in Shaanypu16 was significantly lower than that in Shaanyou0913 and W25.The results show that the translocation rate of nitrogen in Shaanyou16 might be higher than that of Shaanyou0913 and W25.Taking into account,in the high-density cultivation,the three varieties of nitrogen application amount recommended 262.5kg/hm~2. |
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