Influences Of Different Drip Irrigation Amount And Nitrogen Topdressing Period On Spatial Distribution Of Roots And Yields Of Winter Wheat

To realize the high yield and scientific managements of water and nitrogen are the main challenges future agricultural development in northern China.In order to clarify the response characteristics of winter wheat root spatial distribution,yield,water and nitrogen use efficiency to different irrigation amounts and nitrogen topdressing periods under sub-surface drip irrigation system,a field experiment with 3 irrigation amounts(D1:irrigated to 80%of the field water capacity when soil water content is lower than 65%of field capacity;D2:irrigated to 75%of the field water capacity when soil water content is lower than 60%of field capacit;D3:irrigated to 70%of the field water capacity when soil water content is lower than 55%of field capacit)and 2 top-dressing managements(N1:topdressed at jointing and booting stages;N2:topdressed at jointing,booting and early filling three topdressing)were conducted in Gaoyang County,Hebei Province from October 2020 to June 2021.The main results are as follows:1.The yield was significantly affected by irrigation amount and nitrogen topdressing period,and was positively correlated with the root mass density which was closed to the drip lines.Under the same fertilization treatments,the wheat yield ranged from 8850.6 to 10691.3 kg·hm-2,and the highest yield(10691.3 kg·hm-2)was found in D1N1 which was 6.5%～12.6%higher(P<0.05)than that of other treatments.Under the same irrigation treatments,the wheat yield of N1 treatment was significantly higher than that of N2.Additionally,different irrigation amounts and nitrogen topdressing periods had significant effects on panicle numbers and 1000-grain weight,but had no significant effect on grain number per spike.2.The drip irrigation amount,nitrogen topdressing period and their interactions had significantly effects on the root spatial distribution,root length density,root surface area density,root mass density,root projection area density and root volume density(P<0.05).Under N1 fertilization treatment,the root mass density of D1N1 was significantly higher than that of D2N1 and D3N1.D2N1 had higher root length density and root surface area density,and was significantly higher than D1N1,and there was no significant difference between D2N1 and D3N1.Under N2 fertilization treatment,the root length density,root surface area density and root mass density of D1N2 treatment were significantly higher than those of D2N2 and D3N2.With the increase of drip irrigation amount,the distribution of soil surface roots increased,and the closer to the drip irrigation belt,the more the distribution of soil surface roots.D1 drip irrigation treatment could promote the growth of surface roots.For example,compared with D2 and D3,it significantly increased the root length density and root mass density of surface soil.When the irrigation amount decreased,the root length density and root surface area density of the lower soil increased.Under the same irrigation level,N1 fertilization treatment had more root distribution in the surface soil,and N2 fertilization treatment had more root distribution in the deep soil.When the amount of drip irrigation was constant,the root length density,root surface area density,root mass density,root projection area density and root volume density of wheat roots increased,and the increase of irrigation amount also promoted the increase of root auxin(IAA),zeatin riboside(ZR)and gibberellin(GA)content,and the content of abscisic acid(ABA)decreased.3.The water use efficiency was mainly affected by drip irrigation amount and the interaction between drip irrigation amount and nitrogen topdressing period.The root length density was significantly positively correlated with water use efficiency(N1).The increase of root length was beneficial to the absorption of water by wheat,and it was mainly the contribution of the increase of root length density and root surface area density to the absorption of water in the second row of wheat from drip irrigation belt.The water use efficiency of D3N1 treatment was the highest,which was 21.67 kg·hm-2·mm-1,which was significantly increased by 8.7%～16%compared with other treatments.The partial factor productivity of nitrogen fertilizer was mainly affected by irrigation,nitrogen topdressing period and their interaction.D1N1 had the highest partial factor productivity of nitrogen fertilizer,which was 50.91kg·kg-1 significantly increased by 6.5%～12.6%compared with other treatments.4.The yield per unit root length density,dry matter accumulation,leaf area index and nitrogen uptake and accumulation were significantly affected by drip irrigation amount and nitrogen topdressing period,and were closely related to root hormone content.The unit root length yield,dry matter accumulation,leaf area load and nitrogen absorption accumulation of D1N1 treatment were the highest.Considering the yield,water and nitrogen use efficiency,D1 combined with N1 could achieve the higher yield and nitrogen production efficiency,yield per unit root length density,dry biomass and leaf area index,and accumulation uptake,which would be recommended and of great significance to alleviate water shortage and reduce yield loss in this region.