Effects Of Planting Densities And Nitrogen Application On Yield,Quality,Water-Nitrogen Utilization Of Silage Maize In Hexi Region

Silage maize planting is promoted in response to the national grain reform strategy to alleviate the feed shortage in animal husbandry.In this study,three planting densities(L:67,500 plants hm^?2;M:82,500 plants hm^?2;H:97,500 plants hm^?2)and four nitrogen（N）application levels(N0:0 kg hm^?2;N1:120 kg hm^?2;N2:240 kg hm^?2;N3:360 kg hm^?2)were used to study the effects of planting densities and nitrogen application levels on the growth,yield,quality and,water and nitrogen utilization of silage maize.The main results were as follows.（1）Effects of planting densities and nitrogen application levels on the growthcharacteristics of silage maizeUnder the same planting density,the plant height,stalk diameter,relative chlorophyll content（SPAD）,leaf area index（LAI）and aboveground dry matter（ADM）of each nitrogen application treatment had no significant difference in the early stages of maize growth（6 leaf stage and 12 leaf stage）.But,in the late growth stages（blister stage and harvest stage）,the above parameters and indices showed significantly greater values in the N2 and N3 treatments under medium and high planting densities,compared to the N0.The LAI of N1,N2 and N3 increased by 21.2,46.2 and 45.1%,and the ADM by 26.4,57.1 and 51.3%,respectively,than the N0.At the same level of nitrogen application,there was no significant difference in SPAD and ADM for each density treatment in the early growth stages.In the late growth stages,SPAD and stalk diameter under L were significantly greater than that of the H,while the LAI and ADM were significantly lower than that of the M and H treatments.The LAI of M and H treatments increased by 21.9 and 28.2%,and ADM by 28.5 and 38.3%,respectively,compared to L treatment.（2）Effects of planting densities and nitrogen application levels on ear and yield of silage maizeUnder the same planting density,the ear length,row grain number,ear grain number,ear grain weight and yield（fresh grass,hay and grain）of N2 and N3treatments were significantly higher than that of the N0.Meanwhile,the ear diameter,ear row number and 100-grain weight for each nitrogen treatment were not significantly different.The average values showed that the hay yield of N1,N2 and N3 treatments increased by 29.8,55.9 and 54.9%,and the fresh grass yield increased by 29.7,51.5 and 55.2%,respectively,compared to the N0.Under the same fertilization level,there were no significant differences for ear length,ear diameter,row grain number,ear grain number and 100-grain weight among the different densities.However,under the application of N2 and N3,the ear grain weight of L and M treatments were significantly higher than that of the H while the fresh grass and hay yield of M and H treatments were significantly higher than that of the L.The average value showed that H treatment significantly reduced the ear length,row grain number,ear grain number,ear grain weight and 100-grain weight compared with the L and M.However,the yield of M and H treatments（fresh grass,hay and grain）was significantly higher than that of the L.The hay yield of M and H treatments was 25.2and 31.3%higher and fresh grass yield 24.2 and 30.9%higher than that of the L,respectively.（3）Effects of planting densities and nitrogen application levels on the quality of silage maizeUnder the same planting density,the content of crude protein and ether extract of the whole plant in N2 and N3 was significantly higher than that of the N0.Nevertheless,the starch and neutral detergent fiber（NDF）content of each treatment were not significantly different.Compared to N0,the mean values showed significant increase in the content of crude protein,ether extract and crude ash of N2and N3 treatments,while significant decrease in the content of starch and acid detergent fiber（ADF）and,thus increased the relative feed value（RFV）.The increase in yield of crude protein was greater by 107.2 and 113.1%,and the yield of starch was greater by 46.6 and 43.3%in the N2 and N3,respectively,compared to N0.At the same fertilization level,there was no significant difference in crude protein,crude ash and ADF content among the density treatments.The average value showed that with increase of planting density,the content of crude protein,starch and ether extract decreased,while NDF and ADF increased,resulting in a significant decrease of RFV.However,the yield of crude protein,starch and crude ash in M and H treatments was significantly higher than that in the L;the yield of crude protein increased by 23.2 and25.5%and the yield of starch by 17.2 and 16.3%,respectively.（4）Effects of planting densities and nitrogen application levels on water and nitrogen utilization efficiency of silage maizeUnder the same planting density,the grain water use efficiency（WUE_G）,biomass water use efficiency（WUE_B）and nitrogen uptake（Nup）of N2 and N3 were significantly higher than that of the N0.The results showed that WUE_G,WUE_B,Nup and the physiological utilization efficiency of nitrogen（NupE）of N2 and N3treatments were significantly higher than that of the N1,while agronomic efficiency of nitrogen（AEN）and nitrogen use efficiency（NUE）of N3 treatments were significantly lower than that of the N1 and N2.Accordingly,the WUE_B of N1,N2 and N3 increased by 23.1,40.0 and 36.0%,and NupE by 34.5 and 28.1%,respectively,compared with the N0.AEN of N1 and N2 increased by 62.8 and 53.0%,and NUE by27.3 and 42.9%compared to the N3,respectively.At the same fertilization level,there was no significant difference in the soil water storage,evapotranspiration,NupE,AEN,NUE of each density treatment but the WUE_B and Nup of M and H were significantly higher than that of the L.The mean values showed that the WUE_G,WUE_B,Nup,AEN and NUE of M and H were significantly higher than that of the L,among which WUE_B was 24.7 and 25.8%higher,and NUE was 34.6 and 29.5%higher,respectively.The WUE_B(84.6 kg hm^?2 mm^?1),NUE(1.2 kg kg^?1)and NupE(24.0 kg kg^?1)of M-N2were the highest in all treatments.In conclusion,the planting density of 82,500 plants hm^?2 and nitrogen application rate of 240 kg hm^?2 are the most appropriate management strategies for silage maize productivity in Hexi region.Thus,it can promote growth of silage maize;improve grass yield and nutritional quality as well as the water and nitrogen utilization efficiency which is worth popularizing.