Analysis On Yield Gaps And Its Water And Nitrogen Use Efficiency Of Winter Wheat In Loess Plateau

The Loess Plateau is one of the major winter wheat producing areas in China.We focused on the spatial distribution characteristics and temporal variation trends of yield gaps in four agricultural climatic zones of the Loess Plateau,including yield gap between actual yield and potential yield,yield gap between water limited yield and potential yield,and yield gap between nitrogen limited yield and potential yield.This will help to estimate quantitatively the improvement space of winter wheat yield in the study area,reveal the factors that limit the yield increase,and identify the significant regions to increase winter wheat yield in the future,as well as practical measures to increase yield.In this study,we based on the climate region of the GYGA-ED（Global Yield Gap Atlas Extrapolation Domain）method in the global yield difference assessment system,according to the growing degree days（GDD）,the annual aridity index（the mean annual precipitation/the mean annual potential evapotranspiration）,DEM and topographical factors,under the premise that maintained the integrity of the county line,the loess plateau winter wheat planting area can be divided into four agricultural climate zones（Ⅰ,Ⅱ,ⅢandⅣ）.Based on the climate conditions,soil data,crop management data and statistical data,we used the APSIM–Wheat model and ArcGIS to analyze the temporal and spatial distribution characteristics of the winter wheat yield gaps in the study area,analyze the main limiting factors that cause the yield gaps,and quantify the degree of restriction.We have clarified the irrigation water use efficiency（IWUE）and agronomic efficiency of applied nitrogen（AE_N）under different category years,and explored the improvement space of winter wheat yield in each agricultural climatic zones of the Loess Plateau.Main results were as follows:（1）From 1961 to 2016,the weighted average planting area of the potential yield and nitrogen limited yield of winter wheat on the Loess Plateau are 8868.62kgha^-1 and5415.61kgha^-1,respectively.In the past 55 years,the potential yield and water limited yield decreased by 9.6 kgha^-1,21.17kgha^-1 and nitrogen limited yield increased by0.92 kgha^-1.The coefficient of variation of water limited yield is 14.3%,respectively.It can be seen that the water limited yield in the Loess Plateau is low and the stability is poor.Among the climatic zones,the potential yield of zoneⅠis the highest,and that of nitrogen limited yield is the lowest.ZoneⅢhas the lowest potential yield,while its nitrogen limited yield the highest.ZoneⅡhas the highest water limited yield and ZoneⅣhas the lowest water limited yield.（2）Under the background of climate change,the solar radiation,precipitation and the maximum temperature in the growing season of winter wheat are the main factors affecting the potential yield,water restricted yield and nitrogen limited yield of winter wheat in the whole Loess Plateau,all of which are positive effects（P<0.01）,and the correlation coefficients are 0.64,0.83 and 0.63,respectively.（3）The spatial difference of actual yield of winter wheat in the Loess Plateau is obvious,and overall spatial distribution is high in the northwest and low in the southeast.The average yield of the whole region is 3382kg ha^-1.In the past decade,the average actual yield has significantly increased with a rate of 64.99 kg ha^-11 per year.Increase fertilizer application in ZoneⅠ,agricultural machinery inputs in ZonesⅡandⅢ,and irrigation in ZoneⅣcan increase yield of winter wheat to the greatest extent.（4）The winter wheat yield on the Loess Plateau still has a lot of room for improvement,and the main limiting factors affecting the yield increase in each climate zone are different.The average yield gap between the potential yield and the actual yield of winter wheat on the Loess Plateau is 5,416.58 kg ha^-1,according for 57%of potential yield,which has a large scope for improvement.The yield gap has decreased with a rate of 174.62 kg ha^-1 yr^-1in the past 11 years.The average yield gap between winter wheat potential yield and water limited yield is 2353 kg ha^-1,according for 27%of potential yield.In the past 55 years,the yield gap has increased with a rate of 11.57 kg ha^-1 yr^-1.The yield gap caused by nitrogen limitation of winter wheat on the Loess Plateau is 3430 kgha^-1.The ratio of nitrogen limited yield to potential yield is 61%,and the scope for improvement is large.The yield gap has decreased with a rate of 11.57 kg ha^-1 per year during the past 55 years.It can be seen from the above analysis that nitrogen has the greatest impact on winter wheat yield in Loess Plateau,followed by water,but the degree of impact on each agricultural climatic zone is different.Nitrogen has the greatest impact on Zone I,and water input has the greatest impact on ZoneⅣ.（5）The IWUE of winter wheat in Loess Plateau was the highest in the dry years,which was 52.31%.In this precipitation year type,the yield can be improved by supplementary irrigation with the highest space of 39.9%.Under different climatic zones,the irrigation input of ZoneⅠis increased,and the return on income is greater.The AE_N of the wet years loess plateau was the highest,which was 50.11%.In this precipitation year type,application of nitrogen fertilizer production has the highest room for improvement,at 40.3%.Increasing the efficiency of nitrogen use in ZoneⅢis the key to reducing the yield difference caused by nitrogen fertilizer restrictions in this area.