| Huang-Huai-Hai(HHH)Plain is one of the most important grain production regions in China.Although the grain production in China doubled during the first 35 years of the Green Revolution,the increasing population is driving up food demand while arable land is decreasing.In order to maximize grain yield of winter wheat,irrigation and nitrogen fertilizer are required.Intensive use of groundwater and chemical fertilizer has led to serious negative impacts on environmental conditions.This study combined field data with model analysis using the CERES-Wheat model distributed with the Decision Support System for Agrotechnology Transfer(DSSAT v4.6)to investigate long-term winter wheat productivity and water use from irrigation management.In addition,the effects of different crop managements on grian yield and water use of winter wheat under field condition were investigated.Finally,field data with CERES-Wheat and-Miaze model were combined to determine the best long-term management production strategies for the double cropping system that increased long-term simulated yield and reduced environmental impacts.Irrigation at jointing produced the highest yield in normal and dry rainfall years,and irrigation at double ridge gave the highest simulated yield in wet years.A single simulated irrigation at jointing produced yields that were 88%compared to using a double irrigation treatment in wet years,86%of that in normal years,and 91%of that in dry years.A single irrigation at jointing or double ridge produced higher water use efficiency because it obtained higher evapotranspiration.The simulated farmer irrigation practices produced the highest yield and net income.When the cost of water was taken into account,limited irrigation was found to be more profitable based on assumptions about future water costs.In order to increase farmer income,a subsidy will likely be needed to compensate farmers for yield reduction due to water saving.These results showed that there is a cost to the farmer for water conservation,but limiting irrigation to a single irrigation at jointing would minimize impact on farmer net return in HHH Plain.The effect of different crop managements on grain yield of winter wheat was different.Irrigation amount and tillage practices significantly affect grain yield.The main reseaon limiting irrigation reduced grian yield was that the grain weight decreased.There was a bit of overlap in grain yield of limiting irrigation and water-saving irrigation.Thus,limiting irrigation can produced higher grain yield.The decrease of yield by water-saving strategies can partly be compensated by plough tillage practice.But the effect of tillage on grain yield will be undermined by irrigation.Plough tillage and subsoiling tillage can increase soil reservoir capacity to store more summer rainfall.This study showed that plough tillage practice produced higher biomass under rain fed condition,however the effect of tillage practices on grain yield differed between the two growing seasons.In 2014-2015,pre-anthesis dry matter remobilization to grain with plough tillage under rain fed condition was higher than that with rotary tillage,because more soil water consumption at early stage by plough resulted in water stress during grain filling period.In 2015-2016,plough tillage gave lower dry matter remobilization and higher dry matter accumulation after anthesis,thus resulted in higher gain yield.This was because more water with plough tillage stored in soil during the summer season.Under limiting irrigation condition,the simulated grain yield of winter wheat averaged over 22 seasons increased with increasing N rates for each plant density until N rate exceeded 180 kg ha-1,after which simulated grain yield no longer responded to N rate.Plant density had a negative effect on grain yield at populations above 225?300 plants m-2 for all N rates.Compared with N rate of 240 kg ha-1,N rate of 180 kg ha-1 increased PFP by about 33%.The 180 kg N ha-1 rate produced an AE 30.27%?33.30%(average 31.76%)higher than that of the 240 kg N ha-1 nitrogen application rate.Overall,N application rate of 180 kg ha-1 with a plant density of 300 plants m-2 improved nitrogen use,stabilized grain yield,produced the highest net return,and reduced soil residual N to minimize environment risk.Rainfall,irrigation and soil water content of winter wheat were significantly positively correlated to grain yield of winter wheat.Although irrigation amount during summer maize growing season was significantly negtively correlated to grain yield of winter wheat,the interaction of irrigation amount and rainfall of during summer maize season was significantly positively correlated to wheat yield.Thus,optimizing the irrigation time and amount for winter wheat can obtain higher grain yield and water use efficiency based on rainfall and irrigation amount during summer maize season.Because soil water content was significantly lower after wheat harvest,maize should be irrigated immediately after sowing to ensure seed germination.The positive effect of nitrogen fertilizer and irrigation on annual water footprint was mainly through its positive effect on N leaching in both wheat and maize.Irrigation and N management strategies impact the water footprints for the both crops.The water footprint of wheat increased with the increase of nitrogen rate,but the increments of total and grey water footprint of maize by increasing nitrogen fertilizer applying for maize were higher than those of wheat.The water footprint of summer maize was also significantly affected by nitrogen rate applied to winter wheat.The increase in water footprint with increasing irrigation was higher than that with increasing nitrogen for wheat.Based on the simulation results,240 mm water-saving irrigation with 360 kg ha-1 of nitrogen(180 kg N ha-1 for wheat and another 180 kg N ha-1 for maize)can maintain higher grain yield and have a lower water footprint and thus,lower impact on the environment.Overall,limting irrigatin strategy,irrigating 1-2 times for wheat during growth season based on rainfall and irrigation during summer maize season,can obtain heigher grain yield.In order to cover the loss of yield due to limiting irrigation,rotary tillage following deep tillage should be used,meanwhile,N rate 180 kg hm-2 with 300 plants m-2 was adopted to lower environment risk.This strategy significnatly reduce the irrigatin amount,and will be of great importance in achieving the trade-offs between alleviating water resource over-exploitation and food self-sufficiency. |
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