Effects Of Nitrogen Reduction And Compound Microbial Fertilizer On The Regenerative Grass Yield、Quality And Photosynthetic Characteristics Of Hybrid Pennisetum ’Zhongkai No.1’

The high quality forage of Pennisetum americanum×P.Purpuerum’Zhongkai No.1’can fill the gap of green forage in southern summer.Excessive application of chemical nitrogen fertilizer results in waste of resources and soil compaction and environmental pollution.A field experiment was conducted to study the effects of pure nitrogen（7 g/m²,14g/m²,21 g/m²）on the yield and quality of’Zhongkai No.1’by no nitrogen application as the control（CK1）,based on the calculation and analysis of comprehensive membership function and single factor fertilizer effect function,the optimum nitrogen application range was selected,and then the optimum nitrogen application rate of 16 g/m²was used as control（CK2）to reduce nitrogen（30%,50%,100%）by applying 179 g/m²compound microbial fertilizer,the effects of different treatments on the yield,quality,photosynthetic characteristics,economic benefit and soil condition of the’Zhongkai No.1’were studied by comparing with 21 g/m²high nitrogen fertilizer.The results showed that:1.The natural height,absolute height,leaf area per cluster,crown width,number of tillers and yield of the’Zhongkai No.1’were all increased in the range of 0～14 gm²topdressing,but the increasing range of each index was slowed down when 21 g/m²topdressing;The fresh grass yield of 14g/m²was 79.66 kg/hm²,which was 156.80%and1.90%higher than CK1 and 21 g/m²,respectively,the crude protein content increased with the increase of nitrogen amount,with 21 g/m²as the highest,reaching 12.16%,but the crude fiber content of 14 g/m²was 11.80%lower than that of 21 g/m².The optimum nitrogen application rate of the’Zhongkai No.1’is 14 g/m²～17.72 g/m²by comprehensive calculation and analysis of the subordinate function and single factor fertilizer effect function.2.The agronomic traits of the’Zhongkai No.1’were the best when nitrogen was reduced by 30%under nitrogen reduction combined with the application of the same amount of composite microorganisms,and the total yield of regenerated fresh grass was increased by 16.59%and 27.80%（P<0.05）compared with CK2 and high nitrogen（21g/m²）;the total yield of regenerated hay was increased by 12.69%and 29.89%（P<0.05）compared with CK2 and high n（P<0.05）,and the maximum economic benefit was54,633.12 yuan/hm²,which was 9.17%higher than CK2.There was no significant difference between the total yield of fresh hay and CK2 when nitrogen was reduced by 50%（P>0.05）,but it was significantly higher than that of high nitrogen treatment（P<0.05）,and the soil bulk density was reduced by 14.7～25.81%than that of CK2 in the range of30%～100%nitrogen reduction.But applying compound microbial fertilizer（100%nitrogen reduction）was the worst,and the grass yield was the lowest.3.The average crude protein content of the’Zhongkai No.1’decreased with the decrease of nitrogen fertilizer.When nitrogen fertilizer was reduced by 30%,the average crude protein content decreased by 13.45%and 25.07%respectively compared with CK2and high nitrogen treatment,but the three treatments of the annual average crude protein yield are close,nitrogen reduction 30%was 0.90%and 2.50%lower than CK2、higher nitrogen;the contents of acid washing lignin decreased by 16.06%and 45.58%respectively compared with those of CK2 and high nitrogen,the content of acid detergent fiber decreased by 1.11%and 1.90%.When the nitrogen content was reduced by 50%,the content of crude protein decreased by 5.99%、18.66%、29.55%respectively compared with nitrogen reduction 30%、CK2、high nitrogen,the average acid detergent fiber increased by0.82%compared with nitrogen reduction 30%.And the average feed value of 30%～50%nitrogen reduction was higher than 100,but the quality of the’Zhongkai No.1’the worst when the compound microbial fertilizer（100%nitrogen reduction）was applied alone.4.The daily mean value of net photosynthetic rate（Pn）and stomatal conductance（Gsw）of the’Zhongkai No.1’first increased and then decreased with the decrease of nitrogen application amount.The daily mean value of Gsw was the highest(0.126mol·m^-2·s^-1)when nitrogen was reduced by 30%,the intercellular CO₂concentration was the lowest(125.19 umol·mol^-1);the average daily Pn increased by 0.56%and 13.76%compared with CK2 and high nitrogen treatment,respectively,and the average leaf area index increased by 28.31%and 22.77%（p<0.05）;the peak Pn was 32.44 umol·m^-2·s^-1,in the afternoon of the day,which decreased the photosynthetic"midday rest",and the fitted initial carboxylation efficiency（CE）,initial quantum efficiency（α）and maximum net photosynthetic rate（Pnmax）were the highest,while the photoabsorption rate（Rp）was lower,which indicated that the photosynthetic capacity of the’Zhongkai No.1’was improved.The effect of nitrogen reduction by 50%was weaker than that nitrogen reduction by 30%.But the photosynthetic performance of the’Zhongkai No.1’of compound microbial fertilizer（100%nitrogen reduction）was the worst.