Effects Of Fertilizer Application Rate On Soil Respiration And Growth Of Winter Wheat In Semi-arid Area

Fertilizer input has always been one of the key measures to improve crop yield in China.As the main grain producing area in the Loess Plateau region,the unreasonable fertilizer input has made the grain yield in this region low and unstable.In order to further understand the effects of different fertilization rates on the farmland ecological environment and crop yields,this experiment was conducted in a semi-arid area（Pengyang County,Guyuan City,Ningxia Hui Autonomous Region）.Four types of fertilization rates were used in the flat cropping mode:no fertilizer(N:0 kg N ha^-1;0 kg P₂O₅ ha^-1),low fertilizer(L:90 kg N ha^-1;60 kg P₂O₅ ha^-1),medium fertilizer(M:180 kg N ha^-1;120 kg P₂O₅ ha^-1)and high fertilizer(H:270 kg N ha^-1;180 kg P₂O₅ ha^-1)to analyze the effects of different fertilization rates on soil temperature,moisture,and respiration in winter wheat fields,as well as the growth and yield of winter wheat.This study can provide a theoretical basis for the semi-arid area to increase and stabilize the production of winter wheat while taking into account the development of the ecological environment.The main research results were shown below:（1）Different fertilizer rates had significant effects on soil respiration rate in winter wheat fields.The pattern of 2018-2019 was consistent with that of 2019-2020,showing a seasonal trend of decreasing（seedling stage-greenback stage）,increasing（greenback stage-jointing stage）,and decreasing（jointing stage-grain filling stage）,increasing（grain filling stage-mature stage）.The average soil respiration rate under four treatments from 2018 to2019 was significantly higher under L(2.66μmol m^-2S^-1)than that under M(2.44μmol m^-2S^-1)and H(2.23μmol m^-2S^-1),both of which were significantly higher than that under N(1.96μmol m^-2S^-1).Compared with N,soil respiration rate of L,M and H increased by35.7%,24.5%and 13.8%,respectively.From 2019 to 2020,the average soil respiration rate under different treatments was 2.61μmol m^-2S^-1,2.29μmol m^-2S^-1,2.08μmol m^-2S^-1,and1.80μmol m^-2S^-1,and compared with N,L,M and H increased by 45.0%,27.2%and 15.6%,respectively.（2）The relationship between soil respiration and soil temperature（0-25 cm）and soil water content（0-60 cm）showed that soil respiration gradually increased with increasing of soil temperature in all soil layers.The fitting coefficient of soil temperature and soil respiration in 10 cm soil layer was significantly higher than that in other soil layers.When soil temperature rose,the effect of soil respiration in the 10 cm soil layer was higher than that in other soil layers.In the 10 cm soil layer,soil respiration increased gradually with the increase of soil moisture content,and the fitting coefficient between soil temperature and soil respiration in the 10 cm soil layer was significantly higher than that in other soil layers.Through the path analysis of soil respiration factors,it was found that fertilization mainly caused the change of soil respiration by regulating soil temperature.（3）Fertilization promoted the cumulative CO₂ emission during the growth period of winter wheat.With the increase of fertilizer rates,the cumulative CO₂ emission showed a trend of L>M>H,which was consistent with the change of soil respiration rate in each growth period.In 2018-2019,compared with N,L,M and H increased by 25.9%,18.9%and9.5%,respectively,while the cumulative CO₂ emission of L,M and H from 2019 to 2020increased by 32.3%,20.9%and 12.0%,respectively.（4）Fertilization promoted the plant height of winter wheat.With the increase of fertilizer application,the plant height of winter wheat showed a changing trend of L>M>H.In 2018-2019,compared with N,fertilization significantly increased the plant height by11.4%（L）,7.5%（M）and 1.2%（H）,respectively.From 2019 to 2020,it showed the same pattern with an increase of 14.2%（L）,7.4%（M）and 5.0%（H）,respectively.Besides,fertilization promoted the effective leaf area of winter wheat.With increasing fertilizer rates,the effective leaf area showed a trend of M>H>L,and the leaf area of winter wheat all peaked at the flowering stage.Compared with N in 2018-2019,the leaf area increased by5.4%（L）,3.6%（M）and 2.7%（H）,respectively.From 2019 to 2020,the leaf area increased by 12.8%（L）,7.2%（M）and 4.4%（H）respectively compared with N.Fertilization promoted the accumulation of above-ground biomass of winter wheat.With the increase of fertilization,it showed a trend of M>H>L,and the above-ground biomass peaked in the late stage of grouting.Compared with N in 2018-2019,the accumulation of above-ground biomass of winter wheat increased by 41.0%（L）,25.5%（M）,and 2.0%（H）,respectively,while increased by 31.0%（L）,22.6%（M）and 19.3%（H）from 2019 to 2020.（5）Fertilization significantly increased the yield of winter wheat and showed a change rule of M>H>L with the increase of fertilizer rates.Compared with N,the grain yield of M,H and L in 2018-2019 increased by 53.5%,49.2%and 30.0%respectively,and compared with N,M,H and L increased by 75.4%,54.4%and 30.7%respectively in 2019-2020.According to the analysis of the yield components of winter wheat by the application rate,the spike number and grain number per ear increased most significantly compared with the M,H and L.From 2018 to 2019,L,M and H had significant differences compared with N,and the spike number increased by 18.2%,13.4%and 10.0%,respectively.From 2019 to2020,the spike number of L,M and H increased by 14.3%,13.3%and 11.3%,respectively.The grain number per spike of winter wheat under four treatments in two years showed the same change rule,showing as M>H>L>N.Compared with N from 2018 to 2019,M,H and L increased by 22.8%,15.9%and 2.8%,respectively,and from 2019 to 2020,M,H and L increased by 35.4%,21.0%and 8.4%,respectively.The 1000-grain weight of winter wheat under four treatments showed the same rule,showing a changing trend of H>M>L>N.From 2018 to 2019,H,M and L increased by 16.9%,10.1%and 6.9%,respectively.Compared with N in 2019-2020,H,M and L increased by 14.6%,12.9%and 5.4%,respectively.（6）Fertilization significantly improved the water use efficiency of winter wheat,with the trend of M>H>L with the increase of fertilization.From 2018 to 2019,M,H,and L increased by 51.2%,50.0%,and 34.3%,respectively,while there was no significant difference between M and H.From 2019 to 2020,there were significant differences among the four treatments,with M,H,and L increasing by 28.5%,22.2%and 9.5%,respectively.Besides,the fertilizer yield contribution rate and fertilizer agronomic efficiency showed the trend of M>H>L.In conclusion,fertilization promoted the increase of winter wheat yield（M>H>L）,use efficiency of water and fertilizer,and the cumulative CO₂ emission during the growth period（L>H>M）in semi-arid region.Therefore,it was recommended to increase the yield of winter wheat in the semi-arid region,while minimizing the CO₂ emission from the field,and to use a medium fertilizer rate(N 180 kg hm^-2:P₂O₅ 120 kg hm^-2)in production.