| The establishment of reasonable population and appropriate nitrogen application are critical for achieving high and stable yield of wheat plants grown in rice-stubble field. This study was conducted on the Experimental Farm of Key Laboratory of Crop Genetics and Physiology of Jiangsu Province during the two wheat growing seasons from 2012 to 2014. With Guangmingmai 1 as test material, a field experiment was conducted to investigate the regulation effects of sowing date, planting density, nitrogen application amount on grain yield and quality, NUR, population quality, and physiological activities of flag leaves of wheat plants grown in rice-stubble field, using a mathematical model based on a quadratic regression rotation-orthogonal combination design. This study was of practical importance for developing a suitable combination of planting density and nitrogen fertilizer under different sowing date conditions. The main results were as follows:1. Delayed sowing date significantly increased the number of day from seeding to emergence and significantly lowered the average daily temperature (ADT), accumulated temperature higher than 0℃ (AT) before winter, leaf age, tiller number, LAI, and dry biomass accumulation. With the increase in planting density and nitrogen application amount, tiller number at the initial over-wintering stage, LAI, and biomass accumulation were increased. However, there were no significant effects of planting density and nitrogen application amount on leaf age and developmental process. There was an exponential correlation between ADT and the days from seeding to seed. AT (≥0℃) before over-wintering stage was positively linearly correlated with the growing days, leaf age, tiller number, LAI, and biomass accumulation from seeding date to before-wintering stage. Considering climate warming, the optimum AT (≥0℃) and sowing date were 580-640℃ and on October 27 to October 29, with the best AT (≥0℃) of 500-670℃ and sowing date from October 23 to November 4, the suitable density and nitrogen application amount were 180×104 plants/hm2 and 240 kg/hm2.2. As a whole, planting density had the greatest effects on grain yield, followed by sowing date and nitrogen application amount. Nitrogen application amount had the greatest effects on NUR and protein content, followed by sowing date and planting density. The interaction of sowing date and planting density had the greatest effects on grain yield, NUR and protein content, followed by the interactions of sowing date and nitrogen application amount and the interactions of planting density and nitrogen application amount.3. When sowing date varied between October 31 to November 3, planting density ranged from 170 to 180×104 plants/hm2, and nitrogen application amount was maintained at 200-230 kg/hm2, grain yield was over 7000 kg/hm2, NUR was over 42.0%and protein content was over 11.5%. When seeds were sown at an appropriate early date (October 24 to October 30) and planting density and nitrogen application amount were 120～150×104 plants/hm2and 225～255 kg/hm2 and seeds were sown at an appropriate late date (November 4 to November 11) and planting density and nitrogen application amount were 210～240×104 plants/hm2and 225～240 kg/hm, grain yield was over 6600 kg/hm, protein content was over 13.0%, NUR was over 41.0%and 39.0%. When seeds were sown at an early date (October 21 to October 23) and planting density and nitrogen application amount were 100～120×104 plants/hm2 and 240～255 kg/hm2 and seeds were sown at an late date (November 12 to November 14) and planting density and nitrogen application amount were 240～260×104 plants/hm2 and 210～225 kg/hm2, grain yield was over 6200 kg/hm2, protein content was over 13.0%, NUR was over 41.0% and 39.0%.4. Along with the delay in seeding, tiller number and LAI were increased firstly and then decreased, and biomass accumulation was increased. Along with the delay in seeding and the increase in nitrogen application amount, the percentage of ear-bearing stems and tillers, LAI at booting stage, biomass accumulation after anthesis were firstly increased and then decreased. Along with the increase in planting density, the percentage of ear-bearing stems and tillers and biomass accumulation after anthesis were increased firstly and then decreased, and LAI at booting stage was increased. When the planting density, sowing date, and nitrogen application amount were 180×104 plants/hm2, November 2, and 240 kg/hm2 applied at a ratio of 5:1:2:2 (the ratio of nitrogen application at seeding, tillering, jointing, and booting), the population quality characteristics that achieved high yield, efficiency and quality in Guangmingmai 1 were: the percentage of ear-bearing stems and tillers of 48%, LAI 6.5-7.0 at booting stage, and biomass accumulation of 6000-6500 kg/hm2 after anthesis5. In all the treatments, MDA content was increased after anthesis, and the activities of SOD, POD, and CAT were increased firstly and then decreased after anthesis, with peaks appeared on 21th,14th, and 7th days after anthesis. When the planting density, sowing date, and nitrogen application amount were 180×104 plants/hm2, November 2, and 240 kg/hm2 applied at a ratio of 5:1:2:2, flag leaves after anthesis had higher activities of SOD, POD, CAT, and less MDA content, which delayed leaf senescence and enhanced the ability to remove peroxides, leaf photosynthetic capacity, and grain filling rate.6. Under the conditions of planting density at 180×104 plants/hm2, sowing date on November 2, nitrogen application amount at 240 kg/hm2, the percentage of ear-bearing stems and tillers, LAI, and biomass accumulation after anthesis were maintained at 48%,7, and 6000 kg/hm2, grain yield was at the high level of 7500 kg/hm2 when ratio of nitrogen application was 5:1:2:2. |
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