| Alfalfa is a high quality forage for the development of agricultural economy in China.However,due to unreasonable fertilization,the yield and quality of alfalfa are not high,soil hardening,nutrient imbalance,fertility decline and soil microbial community is destroyed.In order to propose a reasonable alfalfa fertilization system and explore the influence mechanism of fertilization on soil microbial driven soil nutrient cycling process,this paper took alfalfa as the research object,adopted a randomized block experiment design,and set five fertilization gradients(N-P2O5-K2O).The effects of different fertilization treatments on alfalfa growth traits,nutrient quality and soil microbial nutrient utilization characteristics were studied.The main research results are as follows:1.Fertilization had significant effects on plant height,stems/leaves ratio,hay yield and crude protein content of alfalfa,but had no significant effects on branch number,acid detergent fiber,neutral detergent fiber and relative feeding value.When the application rate(N-P2O5-K2O)was 135(30-45-60)kg·hm-2,the yield of alfalfa hay was as high as 19.01 t·hm-2,with a higher crude protein content(17.74%),which was the optimal application rate for alfalfa planting in this study area.2.Fertilization had significant effects on soil nutrients,microbial nutrients and extracellular enzyme activities.With the increase of fertilizer application rate,the contents of soil organic carbon,inorganic nitrogen and available phosphorus increased first and then decreased,while the contents of total nitrogen and total phosphorus increased.The contents of dissolved organic carbon(DOC)decreased,the contents of dissolved organic nitrogen(DON)and dissolved organic phosphorus(DOP)decreased first and then increased,the soil DOC:DON decreased significantly,and the contents of DOC:DOP and DON:DOP increased first and then decreased.Soil microbial biomass C,N,P(MBC,MBN,MBP)increased first and then decreased with the increase of fertilizer application rate.Fertilization had no significant effect on soil MBC:MBN,while MBC:MBP and MBN:MBP decreased significantly.Fertilization significantly decreased the activities of N-source enzyme(NAG+LAP)and P-source enzyme(AKP)in soil,while the activities of C-source enzyme(BG)in soil showed a trend of first increasing and then decreasing with the increase of fertilizer application rate.Soil In BG:In(NAG+LAP),In BG:In AKP and In(NAG+LAP):In AKP all increased first and then decreased with the increase of fertilizer application rate,and the change of soil resource measurement ratio led to the enhancement of soil microorganisms' carbon limitation.3.Fertilization significantly changed the stoichiometric imbalance between soil microorganisms and their resources,and the C:N imbalance decreased with the increase of fertilizer application,which strengthened the degree of carbon restriction on soil microbial growth.The relationship between soil resource measurement ratio and element ratio threshold indicated that the soil microbial element utilization efficiency changed from high nitrogen and phosphorus utilization efficiency to high carbon utilization efficiency with the increase of fertilizer application rate.There was a significant correlation between soil microbial carbon use efficiency and element ratio threshold under fertilization treatment,which indicated that soil microorganisms adjusted their own stoichiometric homeostasis by comparing extracellular enzymes and soil nutrient metabolism threshold to soil environment during their self-regulation process.4.Fertilization had little effect on soil microbial abundance and diversity,soil p-source enzyme and microbial biomass carbon had the largest effect on bacterial community structure,and dissolved organophosphorus and inorganic nitrogen had the largest effect on fungal community structure.Fertilization affects alfalfa productivity by changing soil nutrients and microbial characteristics,and soil organic carbon is considered to be the main soil factor affecting alfalfa productivity. |
PDF Full Text Request