| The material and energy exchanged between soil system and the external environment,while the water and salt migrated complicatedly in the system.In order to reveal the effect of the combination of water and nitrogen on the soil water,temperature and nitrate nitrogen migration during seasonal freezing and thawing,7 kind of test combinations with two irrigation levels(375,750 m3 / hm2)and three fertilization levels(100,300 and 500 kg / hm2),combined with bare land(N0W0),the 7 kinds of test combinations were set up.Based on field monitoring data,the temporal and spatial changes of soil water,temperature and nitrate nitrogen were studied by one-way ANOVA,LSD and gray correlation.The results were as follows:(1)The level of water and nitrogen had a significant effect on the temporal and spatial changes of soil temperature during freezing and thawing(p <0.05): The temperature of 0-150 cm was higher than that of bare land in unstable freezing and rapid freezing stage.the greater the amount of irrigation,the better the warming effect;In the later of stable freezing stage,the recovery of soil temperature of Irrigation treatment was lower than that of 0-40 cm,and the higher the amount of irrigation,the slower the warming.The negative temperature of water and nitrogen treatment plots was extended to about 60 cm,and the negative temperature of N0W0 extended to 70 cm.In the thawing period,the temperature of 0-40 cm soil water was lower than that of N0W0,and increased with the increase of nitrogen level.(2)The level of water and nitrogen had an effect on soil moisture: In the unstable freezing stage,water and nitrogen treatment increased soil moisture content.With the increase of water and nitrogen,the water content of 0-110 cm soil layer increased.In the rapid freezing phase,with the increase of water and nitrogen content,the amount of water migration to soil moisture accumulation area increased,and the soil moisture content increased at 20-40 cm.In stable freezing stage,the water content of 20-40 cm increased with the increase of water and nitrogen.40-60 cm soil appeared weak moisture effect,water and nitrogen treatment of soil moisture effect was lower than that of N0W0.In view of the whole freeze-thaw period,the soil water content difference between treatment plots and N0W0 above 40 cm increased with the increase of water and nitrogen,and the mean difference of W750 was higher than that of W375 at 50-60 cm.During the freezing and thawing period,the similarity of water content between treatment plots and N0W0 was increased at 0-60 cm.(3)The level of water and nitrogen had significant effect on the profile distribution of nitrate nitrogen in soil during freezing and thawing.Before freezing,the soil nitrate nitrogen content increased with the increase of nitrogen level in 0-110 cm.During the rapid freezing period,the soil nitrate nitrogen content at 0-20 cm increased with the increase of nitrogen,and the nitrate content of W375 was higher than that of W750 under the same nitrogen level.20-40 cm nitrate nitrogen content increased with the increase of water and nitrogen,And the time increment of soil nitrate nitrogen at 0-40 cm increased with the increase of nitrogen level.In stable freezing stage,nitrate nitrogen was reintroduced into the soil system with the infusion of snow water,with the increase of water and nitrogen,the time increment of soil nitrate of 0-20 cm increased.And the soil nitrate content at 0-60 cm increased with the increase of water and nitrogen.The accumulation of nitrate nitrogen in soil profile was more obvious at 60-80 cm,and the cumulative effect was more obvious under high irrigation(W750).In view of the whole freezing-thawing period,the difference of 0-40 cm soil nitrate nitrogen content between treatment plots and N0W0 increased with the increase of water and nitrogen.and the mean difference of W750 was higher than that of W375 at 50 cm and 60 cm.(4)When water was transferring during soil freezing,the level of water and nitrogen had an effect on soil water content and nitrate nitrogen peak.The peak water content of 10-40 cm was higher than that of N0W0 and increased with the increase of water and nitrogen level.The peak time of water content at 10 cm and 20 cm for treatment plots was consistent with N0W0,30 cm and 40 cm peak appeared on January 28,compared with N0W0 lag 11 d.Besides,The peak time of soil nitrate content at 10 cm and 20 cm for treatment plots was the same as that of N0W0,on January 17,and 30 cm peak time appeared on January 28,more than N0W0 lag 11 d,40cm at January 17,compared with N0W0 ahead of 11 d.The peak increased with the increase of nitrogen level.(5)Water and nitrogen significantly increased the accumulation effect of soil nitrate,the accumulation soil nitrate at 0-110 cm increased with the increase of water and nitrogen.Before freezing and rapid freezing period,the soil nitrate relative accumulation of W750 at 0-60 cm was lower than that of W375,and 60-110 cm was opposite.In the stable freezing stage and thawing period the relative accumulation of 0-60 cm nitrate increased with the increase of nitrogen content,while the 60-110 cm soil layer decreased.(6)The SEN of NO3-N in the same soil layer under different combinations of water and nitrogen was significantly different,The SEN of N100W750 and N100W375 were significantly higher than other treatments.Under the same irrigation amount,the SEN of soil profile decreased with the increase of nitrogen content.The SEN of W750 was higher than W375. |
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