Study On Water And Nitrogen Utilization Under Drought Stress In Soybean And Irrigation Schemes In Different Hydrological Years

Harbin is located in a semi-arid area with shortage of water resources.The development of water-saving irrigation has significantly improved the efficiency of local agricultural water use,ensuring food production and alleviating the contradiction between water supply and demand.The authors conducted a potted soybean experiment in the shelter of the College of Water Conservancy of Northeast Agricultural University,and systematically analyzed the water requirement,growth and crop yield of soybean under different drought stress levels.The stable isotope mass spectrometry technique was used to study the changes of water use efficiency and nitrogen use efficiency in soybean leaves,and the effects of drought stress on water and nitrogen use efficiency of soybean were further explored.Using meteorological data of Harbin from 1956 to 2015,soil data,crop parameters and the Mann-Kendall trend test method,temporal change of meteorological factors was analyzed,the water requirement,effective rainfall and irrigation water requirement at different growth stages of soybean,simulated by the CROPWAT model,were analyzed.At the same time,the coupling degree of soybean water requirement and effective rainfall with different annual rainfalls were compared.Finally,the irrigation schedules of soybean with different annual rainfalls of Harbin were formulated.The main findings of the pilot study are as follows:(1)Through drought stress treatment of soybeans in different growth stages,it was found that the soybean yield varied significantly with the change of crop growth period and irrigation water volume,maintaining water use efficiency and reducing irrigation water requirements by maintaining mild drought stress during seedling and flowering.For the branching and pod-forming period,the effect of drought stress on yield is relatively large;from the perspective of making full use of water and maintaining yield,the amount of irrigation water should be appropriately reduced in the seedling stage,flowering stage and drum maturity stage.The branching and pod-forming periods should meet the water supply needs of soybeans with sufficient water.(2)Results showed that water stress affected the water use efficiency(WUE)of soybean to a certain extent,the WUE increased most significantly under the condition of mild water stress at flowering stage.The C/N ratios of soybean leaves at different growth stages under water stress were as follows: severe stress > moderate stress > mild stress.During each growth period,the ?13C of soybean leaves was negatively correlated with WUEi,WUEn and NUE.The correlations between ?13C and WUEi,WUEn and NUE at flowering stage were more significant than those at seedling stage.Moreover,?13C of leaves was more indicative of WUEn than WUEi in each treatment.Water stress could significantly improve WUE and NUE,and ?13C had significant correlation with WUEi,WUEn and NUE.This study revealed the carbon and nitrogen metabolism of soybean leaves under different water management patterns at different growth stages,and provided a theoretical basis for improving WUE of soybean through water control method.(3)During the growing season of soybean,the maximum and minimum monthly-average temperature increased significantly,while the monthly-average wind speed decreased significantly.The water requirement of soybean decreased with the rate of 9.24 mm/10 a,and its variation range was 331.5~495.6 mm.In the extremely dry year,dry year,normal year and wet year,the water requirement of soybean was 440.6,407.9,377.5 and 366.6 mm,respectively.The net irrigation amount in extremely dry year,dry year and normal year was 122.5,105.8 and 65.8 mm,respectively.With climate change,the water requirement,effective rainfall and irrigation water requirement of soybean during growing season showed a decreasing trend.The effective rainfall was unable to meet the demand of the soybean except in wet years.In agricultural production,appropriate irrigation should be carried out at different growth stages according to different hydrological years to ensure stable and high yield of soybeans.