Effects Of Density And Nitrogen Application On Yield,quality And Water Utilization Of Forage Crops In Silage Maize/Lablab Bean Intercropping System In Hexi Irrigation Area

Promote silage maize planting vigorously is one of the important measures to respond to the national strategy of“converting grain to forge”and promote the structural adjustment of the planting industry.In this study,two planting patterns including silage maize/lablab bean intercropping（I）and monoculture silage maize（M）,three planting densities(D1:75,000;D2:90,000;and D3:105,000 plants hm^-2),and three nitrogen application levels(N1:0;N2:240;and N3:360 kg hm^-2),were used to explore their commulative effects on agronomic traits,yield,quality and water utilization of forage crops in Hexi irrigation area.The main research results are as follows:（1）From 2019 to 2020,the LAI of intercropping system was significantly higher than that of monoculture.The total yield of fresh grass and hay yield in 2020,total crude protein yield in two years of the intercropping system was higher than that in monoculture because of the addition of lablab bean.Compared with monoculture,the two-year average total hay yield was increased by 8.22%,and total crude protein yield by 35.20%.Under the two-year intercropping system,the contents of crude protein,crude ash,crude fat,and neutral detergent fiber（NDF）of whole maize were not significantly different from those of monoculture.The total contents of crude protein,crude ash,and relative feeding value（RFV）of the intercropping system were higher than those of monoculture,while the total starch and NDF contents were lower than those of monoculture.The two-year average total crude protein content of intercropping system was increased by 23.64%and the total RFV by 1.40%.There was no significant difference in soil water storage and evapotranspiration between the intercropping and the monoculture system,but the total water use efficiency（WUE_T）of the inercropping system was higher than the monoculture system,and was increased by 7.55%respectively.Overall,compared with monoculture,the intercropping system increased the yield of fresh hay and crude protein,improved forage quality,and improved WUE_T.（2）In 2019,the plant height of D2 treatment was significantly higher than that of D1 and D3,while the SPAD value of D1 was significantly higher than that of D3.The stem diameter,100-grain weight,and grain weight per spike of D1 and D2 treatments were significantly higher than those of D3,but LAI increased significantly with the increase of planting density.The fresh and hay yield of maize and system increased with the increase of planting density in two years.The crude protein yield of whole maize plant in D2 treatment was significantly higher than that of D1 treatments during both years,and D2 treatment was significantly higher than that of D3 in 2020.Compared with D1,the two-year average total hay yield of D3 and D2 was increased by 27.58%and 21.13%,and crude protein yield by 9.69%and 12.76%,respectively.The crude protein content of whole maize decreased significantly with the increase of planting density in two years.The total crude protein content in D1 and D2 treatments was significantly higher by 15.35%and 8.33%respectively than that in D3 treatment,respectively.During both years,the starch content of the whole maize plants in D1treatment was significantly higher than that of D3,while the content of NDF and ADF were significantly lower than that of D3.The RFV of whole maize plant and system under D1 and D2 treatment during both years were significantly higher than that of D3,and the two years averaged RFV was increased by 5.75%and 5.86%respectively compared with D3 treatment.The field evapotranspiration of D3 treatment was significantly higher than that of D1 in two years.In 2019,the water use efficiency（WUE_G）of maize grain yield,WUE_B,and WUE_T were increased significantly with the increase of planting density.In 2020,the D2 and D3 treatments showed the most promising effect compared to D1,but there was no significant difference between D2and D3.When compared with D1,the two years average WUE_T of D3 and D2treatments were increased by 9.69%and 12.76%respectively.In general,our results indicated that D2 treatment increased the fresh hay yield and WUE_T compared with D1 treatment,and increased RFV,crude protein content,and yield compared with D3treatment.Therefore,D2 treatment can be considered as the most suitable planting density for silage maize in Hexi irrigation area.（3）In 2020,N2 and N3 treatments significantly increased the stem diameter of maize compared with N1,but there was no significant difference in 2019.Compared with N1,the N2,and N3 treatments significantly increased the SPAD value,LAI,100-grain weight,and ear-grain weight thus significantly increased the fresh hay yield,starch,and crude protein yield of maize.The two-year average data indicated that the total hay yield of N3 and N2 treatments were increased by 10.75%and 11.58%respectively,and total crude protein yield was increased by 51.57%and 45.91%respectively.In 2019,with the increase of nitrogen application rate,the crude protein content of whole maize plant and system was increased significantly.When compared with N1,the N2,and N3 treatments significantly increased the crude protein,starch,and crude fat content of the whole maize plant in 2020.The average total crude protein content of N3 and N2 treatments were increased by 35.87%and 29.92%respectively compared with N1.In 2019,the NDF and ADF contents of N2 and N3treatments were significantly lower than those of N1,while there was no significant difference in ADF contents of different nitrogen treatments in 2020.The total RFV of N3 and N2 treatments were significantly higher than that of N1,and the two years averaged total RFV was increased by 7.68%and 6.17%respectively compared with that of N1.In 2019,with the increase of nitrogen application,water storage at the harvesting period was decreased significantly,while field evapotranspiration was increased.In 2020,N2 and N3 teatments significantly reduced field evapotranspiration compared with the N1 treatment.The WUE_B and WUE_T of N2treatment in two years were significantly higher than that of N1,but was not significantly different from N3 treatment.The average WUE_T of N3 and N2treatments in two years increased by 6.96%and 9.17%respectively compared with N1.Therefore,compared with N1,the N2 treatment improved the agronomic characteristic and quality of forage,increased the yield and WUE_T,but had no significant difference with that of N3.Therefore,planting density of 90,000 plants hm^-2 and nitrogen application rate of 240 kg hm^-2（I-D2-N2）under silage maize/lablab bean intercropping is an efficient management measure for high-yield and quality of silage maize in Hexi irrigation area.