Effects Of Water-saving Irrigation On Soil Water,Salinity Dynamics And Water Use Efficiency Of Alfalfa Grassland In An Inland Arid Region

There is a shortage of water resources in the inland arid regions of Hexi,China,and the traditional flood irrigation method has led to a large area of secondary salinization in the region.It is an important issues in local agricultural production that how to efficiently utilize limited water resources,reasonably use large areas of salined land,and improve agricultural output value.Alfalfa(Medicago sativa)with the characteristics of salinity tolerance,high yield performance is suitable for planting in arid and semi-arid areas.Planting alfalfa is beneficial for economic and ecological benefits in the region.Meanwhile,water-salt dynamics,dry matter accumulation efficiency,and water use efficiency of alfalfa grassland under water-saving irrigation conditions are still unclear.This study was conducted from May to October 2017 at the Dayu Water-saving Company Experimental Base in Qian tan Village,Minghua Town,Su nan Yugu Autonomous County,Zhangye City,Gansu Province.The irrigation methods were flood irrigation and drip irrigation,six water control treatments for both irrigation methods were set,treatment 1:full irrigation during the whole growth season;treatment 2:light water deficit during the whole growth season,irrigation volume was 70%of the full irrigation volume;treatment 3:heavy water deficit during the whole growth period,irrigation amount was 50%of full irrigation;treatment 4:water deficit at branching and heading;treatment 5:water deficit at branching;treatment 6:water deficit at heading.Dynamics on soil water and soluble total salt content,alfalfa production and quality were measured,The main results were as follows:1.Drip irrigation was lower than flood irrigation in the water amount.Due to the deep dripper buried drip irrigation was conducive to infiltrate of water to down profile.The soil moisture content in surface layer under drip irrigation was lower than that under flood irrigation in the same measurement period,there was no significant difference in deep layer soil moisture content between two irrigation methods,the highest average soil moisture content in 0-100 cm soil layer was found under treatment 1,the lowest was found under treatment 3 and treatment 4.2.With the growth development,the soil electronic conductivity in all treatments showed a trend of decrease gradually,especially occurred in 0-50 cm soil layer.After the last irrigation in autumn,under the condition of flood irrigation,the soil electronic conductivity decreased of each soil layer under treatment 1 was not significant,and the rest of the treatments decreased by 1.72-2.34 mS/cm compared with the beginning of growth period.The treatment 5 was the best in salt reduction with drop as high as 38.4%.Under the drip irrigation condition,the soil electronic conductivity of each treatment was significantly lower than that at the beginning of the growth period,which decreased by 1.51-2.16 mS/cm,and treatment 1 had the largest decrease of 36.4%.3.The yield of alfalfa under flood irrigation was higher than that of drip irrigation,but the quality of alfalfa under drip irrigation was superior to flood irrigation's.The lower limit of irrigation reduced the alfalfa protein content,but the crude protein yield of alfalfa was not significantly different between under drip irrigation and water limited treatment difference(P>0.05).Compared with adequate irrigation,the yield and quality of alfalfa dry matter obtained under treatment 6 were optimal,in which the dry matter yield during the whole growth period reached 5716.67 kg/m~2 and5292.33 kg/hm~2,crude protein yields were 1296.09 kg/hm~2 and 1055.04 kg/hm~2.The yield of alfalfa under the treatment 3 and treatment 5 conditions reduced in the both two irrigation methods,respectively,which indicated that severe deficient water and deficient water during the branching period had a greater impact on yield,while the heading period had less effect.The water use efficiency of alfalfa under high-water at the heading stage was higher in both irrigation methods.In summary,under both irrigation conditions,light water deficit during the whole growth season and water deficit at heading have little effect on the growth of alfalfa,what is more,these conditions can save irrigation.Drip irrigation not only improves water use efficiency better,but also maintain the degree of soil salinization,and it is recommended to promote the method in irrigation.The study can provide guidance for the practice of alfalfa grassland irrigation in inland arid and semi-arid regions.