Effects Of Nitrogen Application On Alfalfa Production Performance And Soil Nitrogen Content

A greenhouse pot experiment and a field experiment were conducted in Beijing and Qingdao,respectively, to examine the response of alfalfa (Medicago sativa L.) to nitrogen fertilization. Both thepot and filed experiments were a completely random design. The pot experiment consisted of fournitrogen rates(urea,46.6%N), namely0,30,60and90kgN/hm2,code named as N0, N30, N60and N90,respectively, with four replicates. The field experiment included all the same four nitrogen rate, but anadditional treatment,120kgN/hm2(N120), was added and three replicates were used. The results weresummarized as follows:1.Alfalfa plant height, stem diameter, number of branches increased significantly (P<0.05) with N rate,while the SPAD values were not significantly different among treatments (P>0.05). The total rootsurface area, total root volume, crown diameter and number of root crossings increased with N rate,while the total root length, average root diameter and and root branches increased with N rate, butdecreased when N rate was greater than N60.2.The accumulated above ground biomass and total underground biomass of alfalfa plant increasedsignificantly with N fertilizer rate (P<0.05), with the accumulated above ground biomass of N30, N60and N90increased by2.51%,13.37%and22.00%compared to the conrol. The total undergroundbiomass of N60and N90increased by17.46%and21.95%compared to the control.3.Nitrogen fertilizer could not only increase the crude protein content, but also reduced the crude fiber,indicating that nitrogen fertilizer could improve the alfalfa nutrition quality.4.The number of effective nodules per alfalfa plant increased with N rate and decreased when N ratereached a high level, with N60had the highest nodule number (68/plant) while N0for the lowest(46/plant). The nodule number of N30, N60and N90was28.54%,46.04%,18.71%more than thecontrol, respectively.5. The soil total nitrogen content tested after each cut was not significantly different among treatments,while soil nitrate-N and ammonium-N levels were lower than those at pre-planting indicating thatsymbiotic nitrogen fixation of alfalfa could not fully meet the need of its growth.6. In conclusion, alfalfa might need nitrogen fertilizer at establishment, and a better N response could beobtained when applied at sowing and the beginning of the last growth circle in the growing season.