Effects Of Water Regulation Under Subsurface Drip Irrigation On Yield, Quality And Soil Environment Of Alfalfa In Desert Irrigation District

In view of the lack of water resources and water use efficiency（WUE）in desert irrigated areas,such as the low yield and poor quality of the alfalfa and the desertification is becoming more and more serious.This article studied different degrees of water regulation as 35%⁴5%（W₀:severe water regulation）,45%⁵5%（W₁:moderate water regulation）,55%⁶5%（W₂:light water regulation）,65%⁷5%（W₃:full irrigation）of field capacity in the alfalfa branching,bud period and full growth period at Gansu Hexi Desert irrigation area with typical desert climate characteristics.The changes of alfalfa plant height,stem diameter and soil moisture as well as nutrients were analyzed under different water control stages at different growth stages.The response of rehydration to drought stress and hay yield as well as quality of the alfalfa to water control during the period of drought stress was explained.The quality,yield,economic benefit,the effect of water regulation,etc.on the performance of alfalfa,based on the multi objective index of water,was analyzed by the grey correlation analysis method.And the key growth period of water control and the gradient of soil moisture control was selected at the same time.The main results show that:（1）The water consumption of alfalfa increased with the increase of irrigation amount,and the soil moisture of alfalfa field tended to decrease with the increase of water regulation.As the depth of soil deepened,it decreased first and then increased,and the soil moisture changes in different soil layers under light water regulation during the whole growth period was not significant.And the soil moisture could be kept within the normal growth range of alfalfa,which was beneficial to the growth of alfalfa and reduced the loss of water ineffective.Soil organic matter,alkali hydrolyzable nitrogen,available P and K decreased with soil depth,and pH had no significant difference.Water content regulation has significant influence on the content of pH,organic matter,alkali hydrolysable nitrogen,available P and K in 0⁴0cm soil layers.The content of organic matter and alkali hydrolysable nitrogen is increasing with the reduction of the degree of water regulation,and the content of pH,available P and K is decreasing.（2）The average plant height,stem diameter and hay yield in the growth period decreased with the increase of the cutting times,which showed the second cuttings than the third cuttings higher and increased with the decrease of water control degree.Water stress of different degrees in the branching period showed a certain compensation effect on plant height and stem growth after re-watering in the budding period.The yield of two stubble alfalfa hay was 4589.59 kg·hm^-2 and3781.96 kg·hm^-2 respectively under the treatment of mild water control at branching stage,and there was no significant difference from CK treatment（P>0.05）.The water control at the branching stage was more favorable to the growth and yield of alfalfa than in the budding stage.Light water regulation during the budding stage and the whole growth period will not cause a significant decrease in the alfalfa plant height.The WUE of hay yield decreased with the water control degree,and the maximum WUE of hay yield under the A9 treatment of the both stubble alfalfa was 3.47 kg·hm^-2 and 2.96 kg·hm^-2 respectively.（3）With the increase of the cutting times,the stem/leaf ratio was the second stubble more than the third stubble,the crude protein content was the second stubble less than the third stubble,the stem/leaf ratio and the crude protein content increased and then decreased with the reduction of water control degree.The reasonable water treatment in the branching stage was better than the budding stage in reducing the stem/leaf ratio and accumulation of crude protein content.The minimum of stem/leaf ratio of the both stubble alfalfa,under the light water regulation of the whole growth period,was 1.29 and 0.88 respectively,and the highest content of crude protein was21.08%and 23.26%respectively.The yield of crude protein was the same trend as the yield of hay.The yield of crude protein declined from the second cutting to the third cutting,and the yield of crude protein increased with the degree of water regulation to reduce.The highest yield of crude protein under the control of A3 treatment in the two cuttings alfalfa was 902.90 kg·hm^-2 and825.26 kg·hm^-2 respectively,but there was no significant difference from the light water regulation in the whole growth period,and light water regulation in the branching period and the whole growth period was more beneficial to the increase of crude protein yield.The WUE of quality decreased with the degree of water regulation to reduce,and water regulation in the branching period was more beneficial to improve the WUE of quality than the budding stage.The WUE obtained from the hay yield was basically the same.The reasonable water control during the whole growth period was beneficial to improve the quality of WUE.And the highest WUE of the second and third stubble alfalfa were 0.64 kg·m^-3 and 0.55 kg·m^-3 respectively under the treatment of severe water regulation and light water regulation during the whole growth period.（4）With the increase of the cutting times,the content of crude fat（CF）and crude ash（CA）increased,and the contents of acid detergent fiber（ADF）and neutral detergent fiber（NDF）decreased.With the reduction of the degree of water regulation,the content of crude fat and ash increased,and the content of ADF and NDF decreased first and then increased,and the relative feed value（RFV）increased first and then decreased.Water regulation in the budding stage was more beneficial to increase the content of CF and CA.Water control in branching period was more beneficial to reduce the content of ADF and NDF in alfalfa and increase the RFV value.The content of ADF and NDF was the lowest under the light water regulation treatment of the whole growth period（A7）,and the maximum RFV value was 169.32 and 223.48,respectively.（5）The grey correlation analysis method based on hay yield and quality of WUE,crude protein yield and RFV,etc.the effects of each index on the performance of alfalfa,in turn,were:protein yield,hay yield,protein water use efficiency,RFV and hay yield water use efficiency.The weighted correlation degree under A7 is 0.8052,followed by A2,A3,CK,A9,A8,A6,A1,A4,A5.The moisture control in the branching period was beneficial to the improvement of the performance of alfalfa,and the best comprehensive character under the light water regulation treatment of the whole growth period was the best suitable for the water control of the local alfalfa.It was beneficial to achieve high yield&quality in a ideal water saving model.