Water And Fertilizer Response Of Forage Crops And Optimal Allocation Of Irrigation Water Under Different Planting Patterns In Desert Area Of Northern Xinjiang

The arid desert area of Northern Xinjiang is located in the pastoral area of Northwest China,which has the characteristics of drought and less rain,shortage of water resources,high pressure of grass and livestock,extensive irrigation water management and lack of research on the response of forage water and fertilizer.In this study,silage corn and alfalfa were used as the main experimental objects to carry out the insufficient irrigation and fertilizer coupling experiment,in order to solve the specific problems in the construction of irrigated forage grassland,such as unclear irrigation water law,lack of forage crop coefficient,lack of irrigation water management strategy,low utilization efficiency of water and fertilizer,incoordination of fertilization and irrigation amount in time and space experiment.Based on the analysis of water requirement law,output effect and irrigation water benefit of irrigated forage crops under the condition of intercropping,the optimal intercropping combination mode of alfalfa and silage maize was put forward,the simplified calculation method of ET₀in the area lacking data was optimized,and the forage crop coefficient K_crecommended by FAO was modified.Based on the least square method,the crop water model of sudangrass,alfalfa and silage corn was determined,and the dynamic programming method was used to optimize the allocation of irrigation water,and the decision-making scheme of irrigation water management for irrigation forage field under different water supply conditions was put forward;the mathematical model of water and fertilizer coupling yield of irrigation forage under monoculture and mixed intercropping conditions was constructed,and the optimal allocation method was put forward The research results of water and fertilizer response relationship and optimal allocation of irrigation water for forage crops in arid desert area of Northern Xinjiang have been formed.The research results can provide technical support for large-scale and efficient development and utilization of forage grassland in arid desert areas of Northern Xinjiang.The results are as follows.（1）Water requirement and drip irrigation schedule of forage crops under Different Planting PatternsTwo crops of alfalfa were harvested throughout the year,and the growth period of each crop was about 60 days.During the whole growth period,the water consumption was 607 mm under continuous drought,which was only 88%of that under full irrigation.The water consumption of Sudan grass decreased gradually with the intensification of crop drought.The water consumption under full irrigation was 431.0 mm,which was only 48.0%of that under severe drought.The minimum water consumption of silage maize was only 341.0mm during earing-flowering period without irrigation,which was60%of that under full irrigation.The irrigation quota of alfalfa,Sudangrass and silage corn were 407 m³/mu,264 m³/mu and 367 m³/mu respectively when the yield was the highest,and 367 m³/mu,172 m³/mu and 286 m³/mu when the water use efficiency was the highest.Under the condition of intercropping,more crude protein,calcium and phosphorus could be obtained by using 2 rows of silage corn and 12 rows of alfalfa,and alfalfa monoculture was the planting mode with the highest nutritional output.Intercropping 4rows of silage corn and 8 rows of Alfalfa had the highest light utilization rate,and it could cover the ground better.When the water requirement was 660.5mm,the highest yield and economic benefit could be obtained.It was suitable to promote intercropping 4rows of silage corn and 8 rows of alfalfa.（2）Optimization of ET₀ calculation method and correction of K_Cvalue based on FAO recommended methodIn most periods of the whole growth period,the calculated results of FA056 PM method were close to those of FAO Penman method and IA method.The relative errors were 9.26%and 13.51%.ET₀calculated by PT method and HS method was generally larger than that calculated by FAO56 PM,and the deviation was large.The meteorological data required by IA method are only temperature and sunshine time,and the calculation results are of high accuracy.IA method can replace FA056 PM method to complete ET₀calculation in Fuhai County,Altay region.After correction,the K_C of silage corn in the early growth stage,rapid growth stage,middle growth stage and late growth stage were 0.8,0.96,1.03 and 0.79 respectively,and the average K_Cof the whole growth stage was 0.92.The K_Cof sudangrass in early growth stage,rapid growth stage,middle growth stage and late growth stage were 0.66,0.77,0.91 and 0.84 respectively,and the average K_Cof the whole growth stage was 0.80.The K_Cof the first/second stubble of alfalfa was 0.94/0.51,1.03/1.18 and 0.86/1.09,respectively.The average K_Cof the whole growth stage was 0.93.Compared with the recommended value of FAO56,the K_Cof Sudan grass,silage corn and alfalfa increased by 10.00%,13.04%and 5.38%respectively.（3）Forage yield response and crop water model validation under inadequate irrigationThe yield of alfalfa,silage maize and Sudan grass was the highest under full irrigation,and there was a significant linear correlation between the yield of Sudan grass and the percentage of soil water content in field water capacity.The water production efficiency of alfalfa was the highest when it was affected by drought during the greening and branching stage.The water production efficiency of Sudan grass was the lowest under light drought and the highest under severe drought.The water production efficiency of silage maize reached the highest when it was subjected to light drought at heading and flowering stage,and the lowest when it was subjected to continuous drought at jointing stage and heading and flowering stage.Jensen model,Stewart model and Jensen model could be used to simulate and predict the relationship between the water demand（consumption）of alfalfa,Sudan grass and silage maize in arid desert area of northern Xinjiang.The most sensitive growth stages of alfalfa,Sudan grass and silage maize are branches of alfalfa and bud gestation stage（first crop）,grain-filling stage of Sudan grass and milking stage of silage maize.（4）Optimal allocation of limited irrigation water based on forage crop water model and DP methodOptimizing the crop irrigation system through this way,when the irrigation water supply appeared a slight shortage（alfalfa 420 mm≤M≤500 mm,Sudan grass 250mm≤M≤360 mm,silage corn 200 mm≤M≤450 mm）,alfalfa,Sudan grass and silage corn should be given priority to ensure the water supply in the extension period of vine branches,the gestation and flowering period,gestation and flowering period respectively.When the irrigation water supply is very limited（alfalfa M≤420 mm,Sudan grass M≤250mm,silage corn M≤200 mm）.The water supply of alfalfa,sultan grass and silage maize should be guaranteed at the flowering and mature,seedling and booting stage of the second crop respectively.（5）Response of forage crops to water and fertilizer couplingIn the arid desert area of northern Xinjiang,the plant height and stem diameter of corn silage under mulch drip irrigation increased with the increase of fertilizer amount at jointing stage under different soil water content.The fastest increase of maize plant height was at high fertilizer,light drought and heading stage.The leaf area index（LAI）of silage maize increased with the increase of nitrogen application rate under the conditions of no drought and mild drought.Under moderate drought and severe drought conditions,the leaf area index of medium and low fertilizers was similar.Irrigation amount is 280m³/mu,fertilizer amount is 13 kg/mu,maize yield can reach 3000 kg/mu.When the amount of irrigation and fertilizer was greater than the above optimal amount,the yield increased slightly.The highest efficiency of water utilization was the treatment with high fertilizer and severe drought,while the efficiency of chemical fertilizer utilization and the coupling efficiency of water and fertilizer were the treatment with low fertilizer and no drought.Production value is higher for the high fertilizer is not affected by drought,in the fertilizer is not affected by drought and in the fertilizer light drought treatment.When alfalfa and different forage grass are mixed intercropping,the best combination of mixed sowing was alfalfa and Elymus sibiricus,with fertilization amount of 1231 kg/mu and irrigation quota of 240 m³/mu;and the best combination of intercropping was alfalfa and Elymus sibiricus,the fertilization rate was 2248.9 kg/mu,and the irrigation quota was 180 m³/mu.Under the condition of mixed sowing,the maximum water requirement intensity of forage in the growth period was 5.73 m³/（mu·d）,and the irrigation quota of mixed sowing forage crops was 240 m³/mu,which was irrigated 8 times a year.The water requirement intensity,yield and fertilizer utilization of forage crops in mixed intercropping grassland are higher than those in monoculture grassland.