| Groundwater shortage has been a seriously threate to agricultural sustainability in the North China Plain(NCP).The spring maize mono-cropping system has been considered as a promising replacement of winter wheat-summer maize double rotation system to meet the goal of conserving water and maintaining a high yield farming system at the same time.However,the larger yield gap between spring maize and winter wheat-summer maize is a main obstacle to expand spring maize planting area.In the current study,we focused on three maize management practices-sowing date adjustment,spring maize varieties selection,and nitrogen management,to indentify its effect on increasing spring maize yield and relevant mechanism.The main results are listed as follows:1.We identify the appropriate sowing date for spring maize and its relevant mechanism in the NCP.Accumulate solar radiation and precipitation in the early sowing spring maize were better than that of late sowing spring maize,however,maize was affected by high-temperature stress around silking period,especially for maize that sown during mid-April to early-May.High temperature stress reduced effective kernel numbers.Maize sown after late-May was the least affected by high temperature stress,which resulted a higher kernel number and kernel weight compared with other sowing dates.Averaged yield of maize sown on late-May was 10274.3kg ha-1 during 3 experimental years,which was increased by 3.8%-12.2%compared to other sowing dates.2.We select four high yield spring maize varieties and analyze the characteristics of high-yielding varieties.Two semi-compact hybrid varieties Jinhai5,Funong821 and two compact hybrid varieties stranded out from 25 involved maize varieties in the NCP.The averaged yield of the above-mentioned 4 maize varieties was 12845kg ha-1,which was 31.4%higher than the average yield of the 25 involved maize varieties.Semi-compact hybrid variety Jihai5 had a high yield potential at plant level,the floret number of Jinhai5 is 26%higher compared to compact hybrid variety Ludan9066.However,compared with Ludan9066,anthesis silking interval of Jinhai5 is averaged 1.5 days longer,which resulted in an average 17.3%higher grain loss rate due to the failure of flowering.Moreover,the time required to reach to the maximum grain-filling rate of apical kernel of Jinhai5 is 0.5 day longer than Ludan9066,but the average kernel weight at the maximum grain-filling rate and the active grain filling period were 6.7 mg kernel-1 and 10.2 days,respectively,less than that of Ludan9066.Therefore,the semi-compact hybrid variety Jinhai5 is less resistant than the compact hybrid variety Ludan9066,especially for planting density tolerance.3.We preliminary discuss proper nitrogen management model for spring maize and its mechanism in the NCP.Compared to the control treatment,which applied nitrogen one time before planting,nitrogen regimes significantly increased spring maize yield ranged from 6.6%to 13.5%during the experimental years in the NCP.Nitrogen regimes increased nitrogen supply during middle to late growth stage of spring maize,LAI and SPAD value increased by 6.7%-10.7%and 14.5%-22.6%,respectively,during the grain-filling stage.Moreover,leaf relative electric and MDA content were 7.5%and 10.3%lower in average than that of the control,and the photosynthetic rate increased by 9.7%-17.5%.4.We preliminary discuss the direction of spring maize varieties selection and nutrient management model.In the U.S Corn Belt,higher tolerance to low nitrogen stress,higher nitrogen utilization capacity had higher and stable yield performance and strong tolerance of planting density are the most important three indexes for evaluating the quality of hybrid varieties.These quality should be the preferred selection direction for spring maize in the NCP in the future.Average yield of 83 involved maize varieties was 44.9%higher than the average yield of maize varieties tested in NCP.Mainly because of average planting density of 83 maize varieties in the U.S Corn Belt was 65.4%higher than that of the NCP.In the U.S ultra-high yield experiment,even though nitrogen application exceeded 700kg ha-1 under intensive management treatment,however,maize tissue nitrogen content still lower than sufficient nitrogen content by about 6.4 g kg-1 in average during the most of growing stages.These results indicated that increasing nitrogen application failed to solve the problem of nitrogen deficiency during most growth periods.Correlations analysis results showed maize tissue nitrogen content was significant correlate with other nutrient content such as phosphorus,magnesium,sulfur,zinc,manganese and copper. |
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