| Maize-soybean intercropping is one of the important agriculture measures to increase yield,and regulating planting density and nitrogen application rate is an effective measure to improve the productivity of intercropping system.However,the density and nitrogen application rate of forage maize with high yield,high quality and high efficient utilization of water and nitrogen under intercropping condition in Hexi region are still uncertain.Therefore,in this study,a two-year field experiment carried out in this area,and two planting patterns of intercropping of forage maize and forage soybean（I）and monoculture of forage maize（M）were set up.Under each planting pattern,three planting densities(D1:70,000 plants hm-2;D2:85,000 plants hm-2;D3:100,000 plants hm-2)and four nitrogen application levels(N1:0 kg hm-2;N2:120 kg hm-2;N3:240 kg hm-2;N4:360 kg hm-2)were set,to explore the effects of different planting pattern,density and nitrogen application levels on yield,quality,and water and nitrogen utilization of forage maize,to clarify the suitable planting mode,planting density and nitrogen application amount of forage maize in Hexi region,it can provide theoretical and technical support for the high yield and high quality cultivation and the efficient utilization of water nitrogen in this region.The following main research results were obtained:（1）Compared with forage maize monoculture,there were no significant difference in plant height,Stem diameter and relative chlorophyll content（SPAD）of forage maize under intercropping system,but the total leaf area index were significantly higher than monoculture in the powder period and harvest period of forage maize,which is beneficial to increase the whole forage yield.The fresh grass yield and hay yield under intercropping condition was no significant difference with monoculture condition,the total crude protein yield under intercropping system was significantly increased because of the addition of forage soybean,compared with monoculture,crude protein yield in the intercropping system was increased with an average increase of 30.26%in two years.The crude protein,crude fat,crude ash and neutral washing fiber（NDF）content of forage maize under intercropping system were not significantly different from those under maize monoculture,and the average value showed that in 2020 and 2021,the total crude protein content of the intercropping system was increased by 17.08%in two years,and the total grading index was increased by 14.90%.In addition,Under the condition of intercropping,the two-year average precipitation use efficiency（PUE）,water use efficiency（WUE）and nitrogen use efficiency（NUE）of forage crops were increased by 9.64%,9.72%and 34.94%,respectively,compared with monoculture.（2）With planting density was increased,and the stem thickness of forage maize were significantly decreased,and the whole leaf area index was significantly increased.The total hay yield and total starch yield under D2 density were significantly higher than D3 density in 2021,while there was no significant difference between D2 and D3 in 2020.In two-year study,compared with D2 density,the total NDF content under intercropping system were significantly increased,while the total crude protein yield,the total crude protein content and total crude fat content,and the total RFV and RFQ under D3 density were significantly decreased.The two-year average total grading index of D3 density was significantly reduced by 17.75%compared with D2,D3 density significantly reduced PUE,WUE and Nitrogen fertilizer agriculture efficiency（AEN）of forage crops in 2021,and D3 density significantly reduced nitrogen uptake and NUE of forage crops compared with D2,with an average decrease of 9.69%and 23.97%in two years,respectively.It can be seen that,the suitable planting density（D2）can not only improve the forage yield and quality,but also promote the efficient utilization of nitrogen fertilizer.（3）Compared with no nitrogen application,nitrogen application treatment significantly increased the plant height,stem thickness,SPAD of forage maize,and the total leaf area index.Compared with N2,N3 treatment significantly increased the hay yield,crude protein yield and starch yield of the intercropping system,with an average increase of 16.17%,38.56%and 46.18%in the two years.Compared with N2,N3 treatment significantly reduced the NDF and ADF content of forage maize and its population,and significantly increased the content of crude protein,starch and crude fat,as well as RFV,relative forage quality（RFQ）and the grading index.Compared with no nitrogen application,nitrogen application significantly increased the WUE,PUE and nitrogen uptake of forage crops,but there was no significant difference between N3 and N4.Compared with N2,N3 significantly increased the WUE,PUE and total nitrogen uptake of forage crops,with an average increase of 16.10%,16.23%and 36.28%in two years,respectively.Compared with N2,N3 significantly increased the physiological use efficiency of NUE and nitrogen fertilizer of forage crops,with an average increase of 31.87%and 48.65%in two years.Compared with N3,N4 significantly reduced the NUE and AEN of forage crops,with an average decrease of 26.67%and 32.55%in two years.It can be seen that the high nitrogen application rate（N4）cannot further improve the yield and quality of forage crops compared with the medium nitrogen application rate（N3）,instead reduced the NUE.Among all treatments,I-D2-N3 treatment ranked first in the gray correlation analysis,the treatment can not only ensure forage yield,but also improve nutritional quality and increase water and nitrogen use efficiency,which is worth popularizing in Hexi region. |
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