| The impact of drought on crop yield has become the core problem of comprehensive disaster prevention and reduction,which is the main cause of crop failure.Therefore,to assess the effect of drought on agricultural production in a correct way will help individuals and society adjust agricultural structures in time to improve crop yield,the evolution of the reasonable assessment of drought characteristics,to understand the status of the agricultural drought and its effect on maize yield fluctuation,so as to minimize production losses related to drought and reduce food security threat is of great significance.This study was based on the meteorological data of 12 meteorological stations and maize yield data of corresponding counties of Ningxia from 1988 to 2017,discusses the various agricultural regions suitable for maize yield separation method,and based on SPEI drought index to quantify the evolution characteristics of meteorological drought the maize growth period and the influence rule of meteorological drought on maize yield.The main conclusions are as follows:(1)A reasonable and reliable maize yield separation method suitable for each agricultural area in Ningxia was exploredDifferent methods could fit trend yield of maize well,and there was no significant difference in trend yield fitting between the four methods.However,the trend yield of maize in the Yellow River irrigation area fitted by quadratic exponential smoothing method and five-point quadratic smoothing method can better reflect the actual situation,while all the four methods can better reflect the actual yield changes of maize in the Middle arid zone.Except the polynomial fitting method,the trend yield of maize in the Southern mountains fitted by other methods can better reflect the actual social development situation.And most of the consistency correlation coefficients with average trend yield of each agricultural region reached good or excellent grade,only a few areas in the Southern mountains have very poor consistency.When the basic phase of regional meteorological change characteristics at the same time,the relative meteorological yield of the Yellow River irrigation area and the Southern mountains separated by the five-point quadratic smoothing method is more obvious in phase change characteristics,and the results of the quadratic exponential smoothing method in the Middle arid zone can better reflect the impact of meteorological factors on the annual change of the yield.The relative meteorological yield model established by five-point quadratic smoothing method in the Yellow River irrigation area and the Southern mountains,and the meteorological yield model established by quadratic exponential smoothing method in the Middle arid zone can reasonably explain the relationship between meteorological factors and yield and accord with the characteristics of maize growth and development.Comprehensive analysis shows that the five-point quadratic smoothing method is more universal in the Yellow River irrigation area and the southern mountains,while the quadratic exponential smoothing method is more universal in the Middle arid zone,which can reflect the yield changes caused by meteorological factors.(2)The evolution characteristics of meteorological drought during maize growth period in Ningxia were analyzed Yellow River irrigation area and the southern mountains of maize growth period continuous drought event more,meteorological drought occurrence frequency and severity is greater than the Middle arid zone.At different time scales,the variation trend of SPEI in maize growth period gradually increased from southwest to northeast,the trend rate of SPEI index at most stations in central and northern of Ningxia was greater than 0,and the drought trend was not obvious in the southern mountains.In addition,the maize growth period in Ningxia is mainly characterized by slight and moderate drought,and the spatial distribution and frequency drought are different among different grades.Among them,the drought was very serious in the whole growth period of maize in the northern and southern regions,and the frequent period of drought in the Middle arid zone was from sowing period to tasseling period.The average frequency of drought was in the Yellow River irrigation area > the Southern mountains > Middle arid zone.The spatial distribution of extreme drought frequency firstly increased and then decreased from north to south,the drought was the mainly concentrated in the central and northern regions,while there was almost no extreme drought in the Southern mountains.And with the increase of maize growth period,the trend of extreme drought in all agricultural regions showed a decreasing trend.The spatial distribution of moderate drought frequency firstly decreased and then increased from northwest to southeast,mainly concentrated in the northern and southern regions.With the increase of maize growth period,the trend of moderate drought frequency decreased in the northern and southern regions,but increased in the central region.The spatial distribution of slight drought frequency increased from northeast to southwest,and the drought frequency was higher in central and southern regions.With the increase of maize growth period,the trend of slight drought frequency increased in northern and southern regions,while decreased in central regions.(3)The effects of meteorological drought on maize yield at different time scales during maize growth period were revealedIn general,the drought condition in the southern mountains had the greatest effect on maize yield during the growth period,and the Yellow River irrigation area had the least effect on maize yield.The whole maize growth period in the middle and south of Ningxia is faced the risk of drought,and the decrease of maize yield in Huinong and Zhongning county may be related to the continuous drought.The critical value and sensitivity of maize affected by drought were different in different areas of southern mountains.The dry and wet changes in June and July had a greater impact on maize yield in Guyuan,the maize yield in Xiji County was the most sensitive to dry and wet conditions in April,and SPEI in Longde County had a greater impact on maize yield in all months except April.In addition,the relative meteorological yield series Yr and SPEI of maize in the southern mountains showed a linear positive correlation growth relationship,and the significance of the equations reached the level of 0.05.The relative meteorological yield series of maize in Guyuan increased with the increase of SPEI at the jointing and heading stage,and the threshold of influencing Yr was-0.004 and-0.111,respectively.When SPEI1-4 in Xiji County is greater than 0.027,maize yield will increase on the basis of trend yield.The maize relative meteorological yield increased with the increase of SPEI from June to September in Longde County,the decrease of SPEI from June to September led to the decrease of Yr by5.892-8.372%.Therefore,the decrease of maize yield caused by SPEI in August and September was the most serious.In other words,drought in August and September in Longde County will make maize seriously short of water,weaken photosynthesis and obstruct organic matter transportation,which is not conducive to the improvement of its yield. |
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