Study On The Rotation Effect Of Alfalfa And Three Gramineous Forage Grasses

The unreasonable structure of farmland forage planting in China is common.Although forages have been planted on a continuous scale in successive years.In order to alleviate a series of problems caused by continuous forage crops,to explore new models for legumesgrasses grass rotation.In this experiment,the five-year-old Alfalfa(marked as A)was used as the previous stubble,rotation Kentucky bluegrass,Smooth bromegrass(marked as S),and Tall fescue(marked as T);and Kentucky bluegrass(marked as K)were used as the previous stubble,rotation Smooth bromegrass(marked as S),and Tall fescue(marked as T),Alfalfa as a stubble.Measure the indicators of forage agronomic traits,nutrients,soil fertility and soil enzyme activity under different rotation modes,and use principal component analysis to comprehensively screen out and select a reasonable rotation mode.The main conclusions of this experiment are as follows:(1)The plant height and dry yield,crude protein of the Kentucky bluegrass-Alfalfa,Alfalfa-Kentucky bluegrass,Alfalfa-Smooth bromegrass,Alfalfa-Tall fescue models are higher than Alfalfa-Alfalfa,Kentucky bluegrass-Smooth bromegrass,Kentucky bluegrass-Tall fescue,Kentucky bluegrass-Kentucky bluegrass.But the content of neutral detergent fiber and acid detergent fiber is opposite.(2)Under different rotation years,the organic matter,total nitrogen,available nitrogen,total phosphorus,available phosphorus content of the alfalfa first crop and three grasses for the next crop in the 0~20 cm soil layer and 20~40 cm are lower than alfalfa continuous cropping;while available phosphorus and total phosphorus content are higher than alfalfa continuous cropping in two soil layers.In the second year of rotation,K2 A rotations of soil organic matter,total nitrogen,alkaline nitrogen,total phosphorus,available phosphorus,total potassium,and available potassium 16.78%?12.87%?25.69%?10.06%?2.54%?6.22%?16.21%.In the third year of rotation,0~40 cm K3 A,K3S,K3 T rotation soil nutrient indicators the highest patterns increased 9.71%?12.87%?25.82%?6.32%?8.03%?7.96%?17.18% compared to K3 K.(4)The soil enzyme activities of alfalfa continuous crop and Kentucky bluegrassAlfalfa patterns were higher than the other patterns.After alfalfa and grasses forage rotation,the soil enzyme activity decreased,while Kentucky bluegrass and other forage rotation increased soil enzyme activity.In the second year of rotation 0~40 cm layer,The K2 A rotation of the urease,invertase,alkaline phosphatase and catalase enzyme activities are higher than 27.60%,30.19%,15.70%,and 16.33% by K2 K,respectively.The K2 A rotation of four enzyme activities are higher than 14.58%,14.16%,17.33%,17.16% by K2 K,respectively.(5)Principal component analysis was used to comprehensively evaluate 16 indicators including forage agronomic traits,nutritional quality,and soil nutrients under different rotation patterns.The results show that through dimensionality reduction,a total of 3 principal components are extracted,with a contribution rate of 92.14%.The variance contribution rate of the first principal component is 60.37%,the variance contribution rate of the second principal component is 23.77%,and the variance contribution rate of the third principal component is 8%.The comprehensive scoring of each model can be obtained: the Kentucky bluegrass-alfalfa and alfalfa continuous cropping modes ranked 1 and 2,and the alfalfa-smooth bromegrass and kentucky bluegrass-kentucky bluegrass patterns ranked 7 and 8.