| Silage maize is an important fodder resource for ruminants.The study of suitable cultivation measures for silage maize can not only provide high-quality forage yield,it also promotes better farming practices and grassland management.In this study,a two-year field experiment was conducted in the Hexi irrigated area,using three planting densities(D1:75,000 plants hm-2;D2:90,000 plants hm-2;D3:105,000plants 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),to investigate the effects of different planting densities and nitrogen levels on the agronomic traits,yield,quality and nitrogen utilization status of forage grass in the silage maize/forage soybean intercropping system.The following main research results were obtained:（1）The planting density did not show any significant effects on the plant height and ear thickness of silage maize during two-year study.The stem thickness of silage maize significantly decreased while the whole leaf area index（LAI）significantly increased when plant density was increased.The average value showed that the plant height,stem diameter,relative chlorophyll content（SPAD）,and LAI of N3 and N4treatments were significantly higher when compared with N1 during the two-year study,and there was no significant difference between N3 and N4.In 2019,ear length and number of grains per spike increased significantly with the increase of nitrogen application level,however,ear thickness did not change significantly.In 2020,ear grain number increased significantly with the increase of nitrogen application level,but ear length and ear thickness did not change significantly.In general,D2-N3treatments improved the agronomic traits of forage crops and increased LAI.（2）The fresh grass yield,hay yield and starch yield of silage maize,forage soybean and intercropping system under D2 and D3 treatments were significantly higher than those under D1 treatment in two-year study,and the crude protein yield of silage maize,forage soybean and intercropping system under D2 was significantly higher than that under D1 and D3 in 2020.The average value showed that in 2019 and2020,the hay yield of the intercropping system under D2 and D3 treatments increased by 17.03%,21.54%,9.71%,9.12%,respectively.The crude protein yield increased by23.36%,16.39%,13.76%,5.29%,respectively.Starch production increased by20.13%,20.92%,11.41%,12.10%,respectively.The average value showed that the fresh grass yield,hay yield,crude protein yield,and starch of silage maize,forage soybean and intercropping system under N3 and N4 treatment in two-year study were significantly higher than those under N2 and N1.Compared with N1,the hay yield of intercropping systems under N2,N3 and N4 treatment in 2019 and 2020 increased by16.37%,37.31%,33.29%and 18.48%,30.82%,29.07%respectively,and crude protein yield increased by 53.53%,100.59%,96.47%and 38.76%,90.70%,93.02%respectively,and starch production increased by 12.70%,34.65%,38.91%and24.39%,80.28%,101.43%respectively.In 2019 and 2020,the highest total hay yields were obtained under the D2-N3 treatment,which were 36.16 t hm-2 and 27.31 t hm-2respectively.（3）During the two-year silking and harvest period,with the increase in planting density,the crude protein,starch,crude fat content and relative feed value（RFV）of the silage maize,forage soybean and intercropping system showed a downward trend.Ash content,neutral detergent fiber（NDF）,acid detergent fiber content（ADF）showed an increasing trend.The crude protein,starch content and RFV of silage maize,forage soybean,and intercropping system under N2,N3 and N4 treatments were significantly higher than that under N1 at harvest period,while NDF and ADF of silage maize,forage soybean and intercropping system decreased with the increase of nitrogen application rate at silking and harvest period.The crude fat content of the intercropping system under the N2,N3 and N4 treatments in the 2019 harvest period were significantly higher than that under N1.However,there was no significant difference among N2,N3 and N1 in 2020.The crude ash content under N3 and N4treatments during two-year study was significantly lower than that under N1,but there was no significant difference between N3 and N4.In all treatments,D2-N3 obtained higher crude protein content and RFV,which improved forage quality.（4）The nitrogen content,nitrogen uptake and nitrogen use efficiency（NUE）of the intercropping system under D2 treatment were significantly higher than D3,while the physiological nitrogen use efficiency（Nup E）under D2 treatment was significantly lower than D3.In 2019 and 2020,compared with D1 treatment,the NUE under D2and D3 increased by 37.65%,25.88%and 20.34%,13.56%respectively.The nitrogen content and nitrogen uptake of the intercropping system under N2,N3 and N4treatments were significantly higher than that under N1,and the agronomic use efficiency（AEN）,Nup E,and NUE under N3 treatment were significantly higher than N4.In 2019 and 2020,compared with N4,the AEN of N2 and N3 increased by65.87%,71.10%and 44.15%,62.48%respectively,and the NUE increased by67.12%,56.16%and 24.53%,47.17%respectively.Among all treatments,D2-N3 had the highest NUE,which was 1.41 kg kg-1 and 0.86 kg kg-1 in 2019 and 2020,respectively.Therefore,the planting density of 90,000 plants hm-2 and the nitrogen application rate of 240 kg hm-2（D2-N3）were suitable management strategy for the intercropping system of silage maize/forage soybean in the Hexi irrigated area.This measure can improve forage crops agronomic traits,increase yield and improve nutritional quality and NUE,which have promotion value. |
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