Effects Of Gramineae/Legume Intercropping And Nitrogen Application On Yield,Quality,Water And Nitrogen Utilization Of Forage Crops In Hexi Region

Intercropping of gramineous and leguminous crops has been widely used in many developing countries.However,the effects of intercropping of gramineous and leguminous crops on crop yield,quality,water use efficiency（WUE）and nitrogen use efficiency（NUE）are different for different crop varieties and with different fertilizer application rates.In this study,field experiments were carried out in Hexi region from2019 to 2020,with three planting patterns（LM:Lablab bean/silage maize intercropping;FM:Forage soybean/silage maize intercropping;M:Silage maize monoculture）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).The main results are described as follows:（1）Comparied with N1,treatments of N2,N3 and N4 significantly increased the fresh hay yield,total yield of silage maize and legume crops,across the two years,total hay yield on average increased by 27.21%,60.38%and 56.45%respectively.In addition,comparied with N1,N3 and N4 had higher crude protein and starch yields.Across the two years,crude protein and starch yields of N3 and N4 on average were106.71%and 100.00%higher than that of N1,respectively,and 73.31%and 65.00%higher than that of N1,respectively.There was no significant difference in silage maize yield between LM and FM across the two years,but the total fresh hay yield and crude protein yield of intercropping were significantly higher than those of M due to the existence of legumes.Compared with M,the two-year average total hay yield of LM and FM increased by 3.70%and 1.72%respectively,and the two-year average crude protein yield of LM and FM increased by 32.05%and 22.82%respectively.LM-N3 had the highest two-year average total hay yield(33.10 t hm^-2),total crude protein yield(3.31 t hm^-2)and total starch yield(10.19 t hm^-2).（2）Compared with N1,treatments of N3 and N4 significantly increased the contents of crude protein,starch,ether extract content and crude Ash,decreased the contents of neutral detergent fiber（NDF）and acid detergent fiber（ADF）,and significantly increased the relative feed value（RFV）.Compared with N1,the crude protein content of N2,N3 and N4 increased by 16.55%,30.94%and 31.65%respectively,and the RFV increased by 5.75%,14.85%and 20.96%respectively.Compared with M,treatments of LM and FM increased the contents of crude protein,crude Ash and RFV,and decreased the contents of NDF and ADF.The two-year average crude protein content of LM and FM increased by 20.81%and 15.44%respectively,and RFV increased by 6.12%and 3.50%respectively,which improved the nutritional quality of silage crops,and the silage quality of LM was better than that of FM.（3）Across the two years,there was no significant difference in the field evapotranspiration of different nitrogen treatments.The two-year average biomass water use efficiency（WUE_B）of N2,N3 and N4 treatments were 24.38%,55.80%and49.80%higher than that of N1,respectively,and the WUE_B of N3 was significantly higher than that of other treatments.Compared with monoculture（M）,the WUE_B of intercropping system increased by 10.49%and 6.02%respectively.Compared with N1,treatments of N2,N3 and N4 significantly increased the nitrogen content and absorption of silage maize and legumes,and N2,N3 significantly increased the nitrogen use efficiency（NUE）of silage maize,legumes and the population.The two-year average NUE of N2 and N3 increased by 37.30%and 59.52%compared with N4,respectively.LM-N3 had the highest two-year average nitrogen uptake(529.72 kg hm^-2)and NUE(1.16 kg hm^-1)among all treatments.In conclusion,240 kg hm^-2（LM-N3）nitrogen application under silage maize/lablab bean intercropping is the appropriate management measure for silage crops in Hexi region.This management measure can improve forage yield,nutritional quality,water and nitrogen use efficiency,which has a potential promotion value.