Forage Production And Water And Nitrogen Use Efficiency Of Several Annual Forage Crops On The Tableland Of Longdong

The Longdong Loess Plateau（also referred to as Dongzhiyuan）was the largest tableland region in the Loess Plateau,which was the important grain production area in Gansu Province.However,the traditional simple grain planting structure in the local area has gradually failed to meet the needs of the food structure diversification,and it was difficult to further improve the agricultural production efficiency.Optimizing the planting structure,implementing forage-grain crop rotation,and integrating the forage-grain crop-livstock systems were important ways to improve the agricultural systems economic and ecological.However,rainfall was uneven distribution and insufficient,and the effect of planting forage on the soil water/nutrient balance is still uncertain in the Longdong Loess Plateau region.Therefore,this study was conducted to evaluated the biomass yield,soil water/nitrogen distributions,and water/nitrogen use efficiency of four annual forage crops（forage maize,millet,oat,and common vetch）.Field experiment was conducted in 2019 and 2020 at the Qingyang experimental station of Lanzhou University,including five treatments:maize,millet,oat,common vetch,oat/common vetch mixture.We mainly measured dry matter yield,crude protein yield,soil water content,soil nitrogen,water use efficiency,and nitrogen use efficiency of forage crops among two growing seasons.The main results are as follows:（1）This experiment showed that the dry matter yield and crude protein yield of C4crops（forage maize and millet）were significantly higher than C3 crops（oats,common vetch,and oat/common vetch mixture）（P<0.05）.The dry matter yields of forage maize in 2019 and 2020 were 28.6 and 24.5 t hm^-2,and the crude protein yields were 2.3 and1.8 t hm^-2,respectively.The dry matter yields and the crude protein yields of forage maize were the highest among all treatments.In 2019,the dry matter yield of oat was the highest among the C3 crops,which was 3.5 and 2.9 t hm^-2 higher than common vetch and oat/common vetch mixture,respectively.The crude protein yield of oats,common vetch and oat/common vetch mixture were no significant difference.The dry matter yield of oat/common vetch mixture in 2020 was the highest 1.7 and 1.9 t hm^-2higher than oats and common vetch,and the crude protein yield of common vetch was the highest in C3 crops.（2）In 2019,at the forage crops harvested stage,the 0-200 cm soil layer average soil water content of oat/common vetch treatment had the highest,which was 5.9%,4.7%,1.2%and 0.6%higher than forage maize,millet,oats and common vetch,respectively.The soil moisture content of forage maize in 2020 is still the lowest,which is 30.0%,25.9%,22.5%and 28.9%lower than millet,oats,common vetch,and oat/common vetch mixture.In 2019,the water use and dry matter water use efficiency of forage maize were the highest,469.6 mm and 61.1 kg hm^-2 mm^-1;respectively.The oat had the highest crude protein water use efficiency(6.9 kg hm^-2 mm^-1).The water use of oat/common vetch was 18.4%and 20.0%lower than oats and common vetch,respectively,and the water use efficiency was between in oat and common vetch.In2020,the water use and dry matter water use efficiency of forage maize are still the highest,334.1 mm and 74.7 kg hm^-2 mm^-1,respectively;the crude protein yield of millet has the highest water use efficiency(8.1 kg hm^-2 mm^-1).The dry matter water use efficiency and crude protein water use efficiency of oat/common vetch mixture were increased by 19.4%and 35.1%,respectively,and 3.9%and 21.9%higher than the sole oat and common vetch.（3）The oat had the highest partial productivity factor of nitrogen(242.2 kg kg^-1)in 2019,which was 27.1%,120.6%,61.1%,and 45.6%higher than forage maize,millet,common vetch,and oat/common vetch mixture,respectively.In 2020,the oat/common vetch mixture had the highest partial productivity factor of nitrogen,which was 200.6kg kg^-1,and millet was the lowest(88.8 kg kg^-1)and was significantly lower than other crops（P<0.05）.In 2019,the oats/common vetch mixture had the highest nitrogen use efficiency,which was 96.8 kg kg^-1,followed by millet(83.5 kg kg^-1),and common vetch the lowest(33.5 kg kg^-1).The oat/common vetch mixture nitrogen use efficiency was significantly higher than the sole oat and common vetch（P<0.05）.In 2020,oat/common vetch mixture also had the highest nitrogen use efficiency(87.0 kg kg^-1),followed by forage maize(84.4 kg kg^-1),and the common vetch is the lowest.The oat/common vetch mixture nitrogen use efficiency was higher than 34.5 and 52.4 kg kg^-1 in sole oat and vetch,respectively.In summary,these several annual forage crops have advantages in forage production,water utilization,and nitrogen utilization,which could be used for construction grain-forage rotation systems and adjustment of cropping systems structure in Longdong Loess Plateau.Forage maize has the highest dry matter yield and water use efficiency,but it depleted amount of water and nitrogen fertilizer,which could be adversely affected subsequent crops growth.Compared to sole oat and vetch,Oat/vetch mixture can increase system yield and enhance water,nitrogen use efficiency.In practical applications,selecting suitable forage crops should be considering to the water and fertilizer consumption characteristics in different grain crops.The diversity grain-forage rotation patterns in different agricultural systems scales and the rotations systems optimization need more experiments and modeling work to further investigation.