N And P Ecological Stoichiometry Of Soil-alfalfa-weed In Alfalfa Fields At Different Ages

Alfalfa is a kind of high quality legume forages,and have good palatability,high nutritional value,was called "the king of the grass".Previous studies have found that the ages and cuts of the alfalfa all could affect the production performance and soil physical and chemical properties,and weed coverage increased,the grassland degradation with age increase.Predecessor already had used ecological stoichiometry study grassland ecological problems,and there were little reports to solve the problem of weed through ecological stoichiometry.This study measured(2,3,4,5)alfalfa soil physical and chemical properties,production performance,and explore the contents of N,P and N:P of soil,alfalfa and weeds through chemical element measurement in alfalfa artificial field,research the relation of soil and alfalfa stoichiometric characteristics with weeds,so as to provide theoretical basis for alfalfa planting and weeds control.1.The physical and chemical properties of soil and production performance of alfalfa at different agesThe soil organic matter,total nitrogen(total N),total phosphorus(total P),available phosphorus(available P),total potassium(total K)contents,fresh grass yield,hay yield and plant height of alfalfa at different ages(2,3,4,5 ages)and five cuts were measured.The results showed that,soil organic matter,total N,available P contents,fresh grass yield,hay yield of 3 age were higher than other ages;soil organic matter,total N contents of first increased after decreased along with the ages;total P contents continuously reduce along with ages;total K contents in a steady state along with ages;soil organic matter,total N,total P,total K contents did not change significantly along with cuts,and in the smooth state all the year;available P contents had large change extent along with cuts of 3 and 5 ages alfalfa grassland;fresh grass yield,hay yield and plant height continuously reduce along with cuts.2.The N,P ecological stoichiometry characteristics of alfalfa at different agesMeasured and analyzed leaf and stem of N,P contents and stoichiometric ratio in alfalfa with different ages(2,3,4,5 age).The results showed that:N,P contents of 3 age alfalfa leaf and stem was higher than other ages on the whole.N:P of 4 age alfalfa leaf and stem were significantly higher than other ages(P<0.05),and N:P of 3 age alfalfa leaf and stem were significantly lower than other ages each cuts(P<0.05).N,P contents of alfalfa leaf and stem first increased after decreased along with the cuts of four ages,and reach maximum on the third cut(except N content of 3 age alfalfa stem).N:P of 2 and 4 age alfalfa leaf first increased after decreased along with the cuts;and N:P of alfalfa stem first increased after decreased along with the cuts(except 5 age),and reach maximum on the fourth cut.N,P contents and N:P of alfalfa leaf and stem were affected significantly by stand age and cut change;N contents of alfalfa leaf and stem were basically positicely correlated with N:P;P contents of alfalfa leaf and stem were basically negatively correlated with N:P.3.The correlation of contents N,P and N:P between the soil,alfalfa and weeds of alfalfa fields at different ages2,4,and 5 ages alfalfa fields appeared more weeds since 3 cut,and different kinds of weeds maybe were mainly restricted by N elements in surface layer;N:P of 3 alfalfa soil N:P was higher than other ages,may can use nitrogen fertilizer in 10-20cm and 20-30cm soil layer to improve soil N:P,and then achieve the weed control effect.The correlation of soil the contents of N,P and N:P of alfalfa with the contents of N,P and N:P of weeds influenced by age and cut in different soil layer.