Effects Of Cultivated Grassland Types And Management Measures On Grass Yield,quality,water And Nitrogen Utilization In The Loess Plateau

Cultivated grassland is an important measure to improve degraded land,ecological environment and to develop grass and animal husbandry in the Loess Plateau of China.It is of application value to explore its cultivation techniques of high yield,high quality and efficient utilization of water and fertilizer.We conducted a two-year field experiment in the Loess Plateau of China during 2019 and 2020.Three type of cultivated grassland were set up i.e.,alfalfa（Medicago sativa L.,A）,tall fescue（Festuca arundinacea L.,T）unicast and alfalfa and tall fescue mixed（AT）.There were six field management measures under each grassland type:no nitrogen+cutting every 25 days（F1）,no nitrogen+cutting every 50 days（F2）,no nitrogen+alfalfa flowering period（tall fescue heading period）cutting（F3）,nitrogen+cutting every 25 days（F4）,nitrogen+cutting every 50 days（F5）,and nitrogen+alfalfa flowering period（tall fescue heading period）cutting（F6）.The effects of different cultivated grassland types and management measures on forage yield,quality and water and nitrogen utilization were studied.The main findings of our experimental study are as follows;（1）In 2019,the plant height accumulation of alfalfa of AT treatment was significantly higher than that of A,but there was no significant difference in 2020.The relative chlorophyll content（SPAD）of alfalfa of AT treatment was significantly higher than that of T,but there was no significant difference with A in both years.In2019,the fresh hay yield,crude protein yield,precipitation use efficiency（PUE）,water use efficiency（WUE）and nitrogen uptake of AT were significantly higher compared with the A and T,and the crude fat and ash content of AT treatment was significantly higher compared with the T.In 2020,the fresh hay yield,crude protein yield,crude fat content,crude ash content,PUE and WUE of AT treatment was significantly higher compared with the T,but there was no significant difference with A.The crude protein content,relative feeding value（RFV）and nitrogen utilization efficiency（NUE）of AT and A treatments were significantly higher compared with the T,and the acid detergent fiber（ADF）and neutral detergent fiber（NDF）content was significantly lower compared with the T.Mean based on two years results showed that compared with the T treatment,the hay yield,crude protein yield,WUE and NUE of AT and A treatments increased by 60.7%and 51.4%,122.1%and 112.6%,50.3%and43.4%,180.1%and 179.3%.The effect of AT treatment on improving yield and water and nitrogen use efficiency was significantly higher than that of A treatment.（2）The plant height,chlorophyll content,fresh hay yield and crude protein yield of F4,F5 and F6 treatments were significantly higher compared with the F3 in both years.Mean based on two years data showed that the plant height of F4,F5 and F6treatments were increased by 45.7%,28.5%and 18.1%and the hay yield was increased by 33.1%,29.9%and 25.5%compared with the F3.During 2019,only the crude protein,crude fat and crude ash content of F4 treatment were significantly higher compared with the F3,while the crude protein content of F4,F5 and F6treatment were significantly higher compared with the F3 in 2020,and the ADF and NDF contents of F4 and F5 treatment were significantly lower compared with the F3in both years,thus significantly improved the RFV.Mean based on two years data showed that the crude protein content of F4,F5 and F6 treatments were increased by12.1%,6.9%and 4.5%compared with the F3,and RFV was increased by 21.4%,12.9%and 6.5%compared with the F3.The soil water storage capacity of F4,F5 and F6treatments were significantly lower compared with the F3,but there were no significant differences in soil evapotranspiration.Compared with the F3,the PUE and WUE of F4,F5 and F6 treatments were significantly increased in two years,and the WUE of F4,F5 and F6 treatments were increased by 27.4%,22.4%and 18.2%.The nitrogen content and nitrogen uptake of F4,F5 and F6 treatments were significantly higher compared with the F3,and the nitrogen uptake of F4 treatment was significantly higher compared with the F5 and F6.The two-year average results showed that the nitrogen uptake of F4,F5 and F6 treatments were increased by 49.6%,39.2%and 31.4%compared with the F3.In 2020,the NUE of F4 treatment was significantly higher compared with the F5 and F6,but there was no significant difference among nitrogen treatments during 2019.The two-year average showed that F4 treatment obtained the highest NUE(0.38 kgkg^-1)compared with the other treatments.Therefore,the alfalfa-tall fescue mixed grassland combined with nitrogen application of 160 kghm^-2 and cutting every 25 days（AT-F4）can improve forage yield,water and nitrogen use efficiency,and improve forage nutrition quality,which is a suitable field management measure for cultivated grassland in the Loess Plateau.