[Effects of postponing nitrogen application on photosynthetic characteristics and grain yield of winter wheat subjected to water stress after heading stage].

A pot culture experiment was conducted to study the effects of postponing nitrogen (N) application on photosynthetic characteristics and grain yield of winter wheat subjected to water stress after heading stage. Equal in the total N rate in winter wheat growth season, N application was split before sowing, and/or at jointing and /or at anthesis at the ratio of 10:0:0 (N1), 6:4:0 (N2) and 4:3:3 (N3), combined with unfavorable water condition (either waterlogged or drought) with the sufficient water condition as control. The results showed that, under each of the water condition, both N2 and N3 treatments significantly improved the leaf photosynthetic rate and the SPAD value of flag leaf compared with N1 treatment during grain filling stage, and also the crop ear number, grain number per spike and above-ground biomass were increased. Although postponing nitrogen application increased water consumption, both grain yield and water use efficiency were increased. Compared with sufficient water supply, drought stress and waterlogging stress significantly reduced the photosynthetic rate of flag leaves at anthesis and grain filling stages, ear number, 1000-grain mass and yield under all of the N application patterns. The decline of photosynthetic rate under either drought stress or waterlogging stress was much less in N2 and N3 than in N1 treatments, just the same as the grain yield. The results indicated that postponing nitrogen application could regulate winter wheat yield as well as its components to alleviate the damages, caused by unfavorable water stress by increasing flag leaf SPAD and maintaining flag leaf photosynthetic rate after anthesis, and promoting above-ground dry matter accumulation.

[Shoot type morphology and growth characteristics of winter wheat sown at different dates].

Aiming at the delayed sowing of winter wheat induced by the drought and water logging often occurred in Huanghuai Plains of China, six sowing dates (15 October, normal sowing; 30 October, moderate delay; 15 November, delay; 30 November, seriously delay; 15 February, early spring sowing; and 1 March, spring sowing) were designed to investigate the effects of different sowing dates on the shoot type morphology and growth characteristics of winter wheat. With the delay of sowing date, the winter wheat grew and developed faster, and the growing period of the wheat sown in early spring and spring was 115-130 days shorter than that with normal sowing. As compared with those of the wheat with normal sowing, the shoot height, spike number per unit area, and productive spikelets per unit ear of the wheat sown delayed had a decrease, leaf position and canopy moved down, and leaf area reduced. When the sowing was delayed from the date 15 October (normal sowing) to 1 March (spring sowing), the harvest index increased from 0.46 to 0.53. Delaying sowing date also resulted in the significant reduction of grain yield, with the maximum decrement as high as 43. 6%. The spring-sown winter wheat not going through vernalization could still form yield.