Variable Rate Irrigation Management Method For Winter Wheat And Summer Maize In The North China Plain

Suitable water management method is the key for variable rate irrigation system(VRI)to apply water appropriately in real-time and specific site and improve water use efficiency(WUE).Based on the different rainfall during the growth period of winter wheat and summer maize in the North China Plain,the different soil water management methods were established and evaluated,the buried location of soil water content sensor network under VRI system was studied.Field experiments were conducted from 2015 to 2018 at the Dongchengfang Town,Zhuozhou City,Hebei Province.One 1.64 ha quadrant of the center pivot was selected as the experimental plot.Four management zones were delineated by their available soil water holding capacity(AWC),and the AWC range was 152 to 161 mm,161 to 171 mm,171 to 185 mm,and 185 to 205 mm within the 1 m soil profile.Varied soil profiles were found in the four management zones.For the winter wheat where the semi-arid climate prevailed,the rainfed treatment and three irrigation treatments representing different water stress levels were arranged for each management zone.The responses of plant height,leaf area index(LAI),leave relative chlorophyll content,dry biomass of leaf and stem as well as grain,plant nitrogen uptake,yield,yield components,and WUE to deficit irrigation were studied.For the summer maize where the semi-humid climate prevailed,three irrigation management methods of soil water balance modeling(SWB),measured soil water content(SWC),and a combination of SWB and the rain forecast for the next three days(RF)were evalued.The responses of plant height,LAI,dry biomass of leaf and stem as well as grain,plant nitrogen uptake,yield,yield components,WUE,and deep percolation(DP)to variable water management methods were studied.The dynamic variation of soil water content of winter wheat and summer maize under VRI management were monitored regularly.The effects of soil profile characteristics and water management methods on the positioning of soil water content sensors along the depth and the spatial direction were studied.Based on the suitable VRI management methods for winter wheat and summer maize metioned above,the potential of VRI on irrigation water,yield,and WUE was studied and verified.The main conclusions of this study are as follows:(1)During the growing season of winter wheat,the plant height,LAI,dry biomass,yield,and WUE basically increased as the water applied increased.Although no significant differences in LAI,dry biomass,plant nitrogen uptake,yield,and WUE were observed,the different water production functions were gained in different management zones.The cumulative seasonal irrigation amount in zone 2 where a more uniform soil profile detected was 6%and 12%less than that in zones 1 and 3,and the WUE were 18%and 25%higher,respectively.Taking the optimal application rate of maximizing WUE in zone 1 as a basis,89%,94%,and 68%of the rate in zone 1 was recommended for zones 2,3 and 4,respectively.(2)During the growing season of summer maize,compared with the rainfed treatment,the application of irrigation did not significantly increase the plant height,the dry biomass and plant nitrogen uptake,however,the areal-weighted mean yield for the two seasons was 27%higher in the irrigation treatments.The growth parameters,yield and WUE for zone 4 were lower than those for the other management zones.The areal-weighted mean amounts of irrigation in the SWC treatments for the two seasons were 23%and 21%less than that applied in the SWB and RF treatments,and the WUE was 17%and 14%higher,respectively.For the semi-humid climatic conditions taking the maximum WUE as the obj ective for VRI management,the SWC method was recommended.(3)The DP was induced by precipitation mainly,and an obvious delay and superposition phenomenon of deep percolation rate was observed.The average cumulative DP in zone 2 was 88%and 66%less than in zones 1 and 3,respectively.The two-year cumulative DP amount in the RF treatment considering precipitation forecast information was reduced by 85%and 19%than in SWC and SWB treatments,respectively.For the semi-humid climatic conditions taking the minimum DP as the objective for VRI management,the RF method was recommended.(4)In order to improve the applicability of the SWB method in VRI,the crop coefficient(Kc)were calculated before and after the deep percolation,respectively.After considering the DP amount,the average K,was reduced by 11%.The three Kc recommendations for four stages for zones 1 to 3 were 0.48,1.04,0.27;0.49,0.89,0.54,and 0.64,1.15,0.36.The site-specific Kc values for different management zones can effectively improve the management accuracy of the SWB method.The crop water requirement considering the different Kc reduced 37 mm than the treatments using the single Kc,especially the maximum decrease in zone 2 was 75 mm.(5)The variation of the percentage of sand content along the depth hindered the movement of soil water content.The soil water content in zones 1 and 3 decreased sharply along the soil depths.The soil water content in zone 2 changed little along the depth.The sensors should be placed above the interface where the layered soils exist.In the spatial direction,the time stability of soil water content existed for the different soil water stress treatments,significant linear regressions(P<0.05)between the mean clay percentile and the clay percentile representing the mean soil water content sites were found.The fitted equation coefficients ranged from 0.66 to 1.03 in the two seasons,demonstrating a clearly increasing trend as the severity of water stress increased.When the mean clay percentile was used for a priori identification for positioning soil water content sensors in the management zones under variable rate irrigation system in a field with sandy loam soil,the strategies of water stress management should be considered in determining a fitted equation coefficient.(6)Field experiments of the benefit of VRI showed that by comparing with the conventional sprinkler irrigation management method based on the soil water content in the minimum AWC management zone and the average soil water content of the field,the irrigation water was reduced by 19%and 16%and the WUE was increased by 23%and 21%,respectively,for the VRI method using different application ratios in different management zones for winter wheat.While the irrigation water was reduce by-9%and 40%and the WUE was increased by 5%and 27%,respectively,for the VRI method combining with the weather forecast and the real-time supplement of soil water depletion for summer maize.